Author name code: ayres ADS astronomy entries on 2022-09-14 author:"Ayres, Thomas R." OR author:"Ayres, Tom" ------------------------------------------------------------------------ Title: The Beat Goes On Authors: Ayres, Thomas Bibcode: 2022cxo..prop.6408A Altcode: Chandra has been following magnetic heartbeats of late-type stars via high-contrast coronal X-rays. Goal is to provide fundamental observational constraints for contemporary and future studies of the underlying magnetic dynamo, whose internal workings remain elusive. The Sun's high-energy modulations play an important space weather role in our heliosphere, as do stellar counterparts for their exoplanets. A 3-year continuation (joint with HST) is proposed for current cycles targets Xi Boo (G8V+K4) and 70 Oph (K0V+K5V). Key questions: (1) origin of diverging branches in rotational period vs. cycle duration, where Sun sits isolated in the middle, possibly in a transitional state; (2) extent of high-energy variability bias, which can affect interpretations of large surveys. Title: HST STIS Observations of ζ Aurigae A's Irradiated Atmosphere Authors: Harper, Graham M.; Bennett, Philip D.; Brown, Alexander; Ayres, Thomas R.; Ohnaka, Keiichi; Griffin, Elizabeth Bibcode: 2022AJ....164...16H Altcode: The details of the processes responsible for heating the chromospheres of evolved cool stars remain uncertain. While most spectroscopic diagnostics measure spatially-integrated emission, here we examine diagnostics sensitive to localized atmospheric regions that are specific to cool evolved stars in binary systems with hot main-sequence companions: emission from Si I and C I resulting from the ultraviolet irradiation of the evolved star's atmosphere. HST Space Telescope Imaging Spectrograph (STIS) high-spectral-resolution near-ultraviolet observations of ζ Aurigae A+B (K4 Ib + B5 V) were obtained at three orbital phases, including total eclipse, to search for Si I and the corresponding C I line emission. Si I 2987.645 Å emission was detected at phases ϕ = .101 and .448 (from periastron) in-line with predictions from a previous study of optical Si I 3905 Å and Si I 4102 Å emission lines. No other Si I line emission is apparent, and the analogous C I lines at 2478.561 Å and 2582.901 Å also are not detected. High-spectral-resolution HST STIS and Goddard High Resolution Spectrograph spectra confirm the results of a previous study that showed that the intrinsic chromospheric fluxes on the visible hemisphere of ζ Aur A, observed during total eclipse, are representative of the single K supergiant λ Vel (K4 Ib). Furthermore, the HST spectra show that the chromospheric turbulent velocities are very close to those in this spectral-type proxy. These combined results highlight the importance of detailed spatially-resolved chromospheric models of ζ Aur systems, based on sequences of atmospheric eclipse spectra, to help constrain the poorly understood mechanisms that heat the atmospheres and drive stellar winds in cool evolved stars. Title: The Origin of Weakened Magnetic Braking in Old Solar Analogs Authors: Metcalfe, Travis S.; Finley, Adam J.; Kochukhov, Oleg; See, Victor; Ayres, Thomas R.; Stassun, Keivan G.; van Saders, Jennifer L.; Clark, Catherine A.; Godoy-Rivera, Diego; Ilyin, Ilya V.; Pinsonneault, Marc H.; Strassmeier, Klaus G.; Petit, Pascal Bibcode: 2022ApJ...933L..17M Altcode: 2022arXiv220608540M The rotation rates of main-sequence stars slow over time as they gradually lose angular momentum to their magnetized stellar winds. The rate of angular momentum loss depends on the strength and morphology of the magnetic field, the mass-loss rate, and the stellar rotation period, mass, and radius. Previous observations suggested a shift in magnetic morphology between two F-type stars with similar rotation rates but very different ages (88 Leo and ρ CrB). In this Letter, we identify a comparable transition in an evolutionary sequence of solar analogs with ages between 2-7 Gyr. We present new spectropolarimetry of 18 Sco and 16 Cyg A and B from the Large Binocular Telescope, and we reanalyze previously published Zeeman Doppler images of HD 76151 and 18 Sco, providing additional constraints on the nature and timing of this transition. We combine archival X-ray observations with updated distances from Gaia to estimate mass-loss rates, and we adopt precise stellar properties from asteroseismology and other sources. We then calculate the wind braking torque for each star in the evolutionary sequence, demonstrating that the rate of angular momentum loss drops by more than an order of magnitude between the ages of HD 76151 and 18 Sco (2.6-3.7 Gyr) and continues to decrease modestly to the age of 16 Cyg A and B (7 Gyr). We suggest that this magnetic transition may represent a disruption of the global dynamo arising from weaker differential rotation, and we outline plans to probe this phenomenon in additional stars spanning a wide range of spectral types. Title: The Wind Temperature and Mass-loss Rate of Arcturus (K1.5 III) Authors: Harper, Graham M.; Ayres, Thomas R.; O'Gorman, Eamon Bibcode: 2022ApJ...932...57H Altcode: In this paper we aim to constrain the wind temperature, outflow and turbulent velocities, ionization state, and mass-loss rate of the single red giant Arcturus (α Boo K1.5 III) using high spectral resolution Hubble Space Telescope Space Telescope Imaging Spectrograph profiles of Si III 1206.5 Å , O I 1304 Å and 1306 Å, C II 1334 Å and 1335 Å, and Mg II h 2802 Å. The use of the E140-H setting for α Boo allows the Si III 1206.5 Å line to be cleanly extracted from the echelle format for the first time. The ratios of the wind optical depths of lines from different species constrain the temperature at the base of the wind to T wind ~ 15,400 K. The mass-loss rate derived is 2.5 × 10-11 $\,{{M}_{\odot }\,{\rm{yr}}}^{-1}$ for Epoch 2018-2019, smaller than previous semiempirical estimates. These results can be reconciled with multiwavelength Very Large Array radio continuum fluxes for Epoch 2011-2012 by increasing the temperature to T wind ~ 18,000 K, or increasing the mass-loss rate to 4.0 × 10-11 $\,{{M}_{\odot }\,{\rm{yr}}}^{-1}$ . Interpreting the wind acceleration and turbulence in terms of a steady WKB Alfvén wave-driven wind reveals that the wave energy damping length increases with increasing radius, opposite to the trend expected for ion-neutral damping of monochromatic waves, confirming a previous result by Kuin and Ahmad derived for ζ Aur binaries. This implies that a spectrum of waves is required in this framework with wave periods in the range of hours to days, consistent with the photospheric granulation timescale. Constraints on a radial magnetic field (B) at 1.2 R * are an upper limit of B ≤ 2 G from the implied wave heating, and B ≥ 0.3 G to avoid excessive wave amplitudes. Title: Intrinsic Lyman alpha Profiles of High-Velocity G, K, and M Dwarfs Authors: Youngblood, Allison; Pineda, J. Sebastian; Ayres, Thomas; France, Kevin; Linsky, Jeffrey; Wood, Brian; Redfield, Seth; Schlieder, Joshua Bibcode: 2022AAS...24011801Y Altcode: Observations of H I Lyman alpha, the brightest UV emission line of late-type stars, are critical for understanding stellar chromospheres and transition regions, modeling photochemistry in exoplanet atmospheres, and measuring the abundances of neutral hydrogen and deuterium in the interstellar medium. Yet, Lyman alpha observations are notoriously challenging due to severe attenuation from interstellar gas, hindering our understanding of this important emission line's basic morphology. We present high-resolution far- and near-UV spectroscopy of five G, K, and M dwarfs with radial velocities large enough to Doppler shift the stellar Lyman alpha emission line away from much of the interstellar attenuation, allowing the line core to be directly observed. We detect self-reversal in the Lyman alpha emission line core for all targets, and we show that the self-reversal depth decreases with increasing surface gravity. Mg II self-reversed emission line profiles provide some useful information to constrain the Lyman alpha line core, but the differences are significant enough that Mg II cannot be used directly as an intrinsic Lyman alpha template during reconstructions. We show that reconstructions that neglect self-reversal could overestimate intrinsic Lyman alpha fluxes by 60-100% for G and K dwarfs and 40-170% for M dwarfs. Title: Wilson-Bappu 2022 Authors: Ayres, T. Bibcode: 2022fysr.confE..26A Altcode: The Wilson-Bappu Effect (WBE) has long fascinated astronomers (well, at least a few of us) and the general public (see Season 3, Episode 21 of the "Big Bang Theory" [viewer discretion advised]). O.C. Wilson and M.K.V. Bappu made the original discovery in the mid-1950's: a striking systematic correlation between the absolute visual magnitudes of late-type stars and the widths of their 395 nm Ca II H \& K chromospheric emission cores as measured on photographic plates. The Ca II width-luminosity relation tracks seamlessly from intrinsically faint red dwarfs to the most luminous yellow supergiants. Initially attributed to chromospheric kinematics, the WBE is now seen as a consequence of an intricate interplay between outer-atmosphere heating, hydrogen ionization and surface gravity. This is a progress report on a new effort to analyze the existing vast collection of HST NUV spectra of the analogous 280 nm Mg II h \& k resonance lines, to re-script the Wilson-Bappu story for the modern era. Title: X-Ray Chronicles of Alpha Centauri: The Swooning of α Cen B Authors: Ayres, Tom Bibcode: 2022RNAAS...6...24A Altcode: The central AB binary of Alpha Centauri has been visited regularly by Chandra X-ray Observatory since late 2005. Up to mid-2020, the B component, an early K dwarf, had traced out a relatively smooth 8 yr coronal (T ~ 2 MK) activity cycle. Recently, however, B's X-ray count rate suddenly dipped, from cycle maximum levels to near minimum in just 16 months. Previous cycle decays were 3-4 yr. The significance of the swoon remains to be seen. Title: Intrinsic Lyα Profiles of High-velocity G, K, and M Dwarfs Authors: Youngblood, Allison; Pineda, J. Sebastian; Ayres, Thomas; France, Kevin; Linsky, Jeffrey L.; Wood, Brian E.; Redfield, Seth; Schlieder, Joshua E. Bibcode: 2022ApJ...926..129Y Altcode: 2022arXiv220101315Y Observations of H I Lyman α, the brightest UV emission line of late-type stars, are critical for understanding stellar chromospheres and transition regions, modeling photochemistry in exoplanet atmospheres, and measuring the abundances of neutral hydrogen and deuterium in the interstellar medium. Yet Lyα observations are notoriously challenging owing to severe attenuation from interstellar gas, hindering our understanding of this important emission line's basic morphology. We present high-resolution far- and near-UV spectroscopy of five G, K, and M dwarfs with radial velocities large enough to Doppler-shift the stellar Lyα emission line away from much of the interstellar attenuation, allowing the line core to be directly observed. We detect self-reversal in the Lyα emission-line core for all targets, and we show that the self-reversal depth decreases with increasing surface gravity. Mg II self-reversed emission-line profiles provide some useful information to constrain the Lyα line core, but the differences are significant enough that Mg II cannot be used directly as an intrinsic Lyα template during reconstructions. We show that reconstructions that neglect self-reversal could overestimate intrinsic Lyα fluxes by as much as 60%-100% for G and K dwarfs and 40%-170% for M dwarfs. The five stars of our sample have low magnetic activity and subsolar metallicity; a larger sample size is needed to determine how sensitive these results are to these factors. Title: On the Same Wavelength as the Space Telescope Imaging Spectrograph Authors: Ayres, Thomas R. Bibcode: 2022AJ....163...78A Altcode: The Hubble Space Telescope Imaging Spectrograph (STIS) is a powerful tool for high spectral resolution ultraviolet (UV; 1150-3200 Å) studies of bright cosmic sources. However, achieving the superb wavelength precision inherent in its UV echelle channels is hampered by subtle camera distortions that are not fully compensated for by the CALSTIS pipeline. The systematics arise from the low-order (n = 2) bivariate polynomial dispersion model employed in the echellegram processing. The formulation does remarkably well given its simplicity (only seven terms in the current implementation), but cannot account for apparent higher frequency undulations in the STIS spectral images. Previous correction schemes have built elaborate distortion maps, with up to thirty-six terms, operating on the individual echelle orders in the pipeline "x1d" file, prior to merging the orders. There is, however, a more straightforward, although partial, solution: a polynomial formula in the wavelength domain applied to the order-merged spectrum; just n = 3 for most of the STIS settings, although up to n = 5 for a few of the more recalcitrant ones. Title: In the Trenches of the Solar-stellar Connection. V. High-resolution Ultraviolet and X-Ray Observations of Sun-like Stars: The Curious Case of Procyon Authors: Ayres, Thomas R. Bibcode: 2021ApJ...923..192A Altcode: A joint X-ray (0.2-2 keV) and ultraviolet (1150-3000 Å) time-domain study has been carried out on three nearby bright late-type stars, bracketing the Sun in properties. Alpha Cen A (HD 128620: G2 V) is a near twin to the Sun, although slightly more massive and luminous, slightly metal-rich, but older. Alpha Cen B (HD 128621: K1 V) is cooler than the Sun, somewhat less massive and lower in luminosity. Procyon (HD 61421: F5 IV-V) is hotter, more massive and more luminous than the Sun, half the age, but more evolved. Stellar observations were from Chandra X-ray Observatory and Hubble Space Telescope (HST). The Sun provided a benchmark through high-energy spectral scans from solar irradiance satellites and novel high-dispersion full-disk profiles of key UV species-Mg II, C II, and Si IV-from the Interface Region Imaging Spectrograph. Procyon's flux history was strikingly constant at all wavelengths, in contrast to the other three cycling-dynamo stars. Procyon also displays a strong subcoronal (T ~ 1 × 105 K) emission excess, relative to chromospheric Mg II (T ≲ 104 K), although its X-rays (T ~ 2 MK) appear to be more normal. At the same time, the odd sub-Gaussian shapes, and redshifts, of the subgiant's "hot lines" (such as Si IV and C IV) are remarkably similar to the solar counterparts (and α Cen AB). This suggests a Sun-like origin, namely a supergranulation network supplied by magnetic flux from a noncycling "local dynamo." Title: HD 41004: A Photometric Sheep in Wolf's Clothing? Authors: Ayres, Tom; Buzasi, Derek Bibcode: 2021RNAAS...5..243A Altcode: HD 41004 is an unusual multiple star/planet system. Recent TESS photometry revealed a striking 31 hr period, far too short for the slowly rotating K dwarf primary. Instead, the modulation likely is from the diminutive dM secondary, spun-up to synchronous rotation by its close-in brown dwarf companion, and suffering intense magnetic activity as a result. If so, the red dwarf is perhaps destined to someday return the favor by cannibalizing its substellar partner. Title: Alpha Centauri and Environs Authors: Ayres, Thomas Bibcode: 2021cxo..prop.6169A Altcode: Chandra has been tracking coronal activity cycles of late-type stars via high-contrast soft X-rays, jointly with HST to capture UV tracers. Objective is to provide fundamental observational constraints for contemporary and future studies of the underlying magnetic dynamo, whose inner workings remain elusive. The Sun's high-energy modulations play an important "Space Weather" role in our heliosphere, as do stellar counterparts for their exoplanets. 3-year time-domain campaign (joint with HST) is proposed for iconic Alpha Centauri, already followed by HRC-I since 2006. The Alpha Cen field also is rich in serendipitous sources, including flaring red dwarfs and several possibly cycling F-K stars. Title: Alpha Centauri and Environs Authors: Ayres, Thomas R. Bibcode: 2021hst..prop16834A Altcode: (Note: this is the HST part of a joint Chandra/HST project: the original Chandra proposal abstract follows.)

Chandra has been tracking coronal activity cycles of late-type stars via high-contrast soft X-rays, jointly with HST to capture UV tracers. Objective is to provide fundamental observational constraints for contemporary and future studies of the underlying magnetic Dynamo, whose inner workings remain elusive. The Sun's high-energy modulations play an important "Space Weather" role in our heliosphere, as do stellar counterparts for their exoplanets. 3-year time-domain campaign (jointly with HST) is proposed for iconic Alpha Centauri, already followed by HRC-I since 2006. The Alpha Cen field also is rich in serendipitous sources, including flaring red dwarfs and several possibly cycling F-K stars. Title: In the Trenches of the Solar-stellar Connection. IV. Solar Full-disk Scans of C II, Si IV, and Mg II by the Interface Region Imaging Spectrograph Authors: Ayres, Thomas; De Pontieu, Bart; Testa, Paola Bibcode: 2021ApJ...916...36A Altcode: About once a month, the Interface Region Imaging Spectrograph conducts day-long raster scans of the full Sun in three ultraviolet spectral channels. These full-disk mosaics are valuable in the solar context, but provide a unique connection to the distant, unresolved stars. Here, 10 deep-exposure scans (4-8 s per slit step), collected during the peak and decline of sunspot Cycle 24, were analyzed. Spatial spectra (2″ pixels) of resonance lines of C II (T ~ 104 K), Si IV (8 × 104 K), and Mg II (8 × 103 K) were fitted with a pseudo-Gaussian model to track the emission strengths, widths, and shifts in the various surface features that comprise the quiet Sun and active regions. The full-disk mosaic spectra compare well to tracings of solar-twin α Centauri A (HD 128620; G2 V). The contrast between disk-average spectra from cycles MIN and MAX is relatively modest (~50% in Si IV), but, remarkably, the brightest solar pixels in active regions, at 2″ resolution, exceed the global-average intensities of the most active Sun-like stars, suggesting a deeper solar-stellar connection. Si IV shows a conspicuous bright ring at the limb, whereas optically thicker C II and Mg II are suppressed (more so for the latter). The Si IV emission favors the bright knots of the large-scale supergranulation network, while the cooler Mg II emission is more ubiquitous and C II intermediate. The non-Gaussian profile of full-disk C IV, similar in formation temperature to Si IV, was previously interpreted as a combination of narrow and broad dynamical components, but the prevalence of the characteristic line shape in the finest resolution spatial pixels of Si IV here provides support for alternative formation scenarios, for example, invoking κ-distributions. Title: Cycles and the Seven Dwarfs Authors: Ayres, Thomas R. Bibcode: 2021hst..prop16787A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are relevant for understanding the Sun's analogous high-energy modulations, in turn crucial to Earth-impacting "Space Weather" (SW). Similarly, stellar SW counterparts can have equivalent, or more severe, adverse effects on their exoplanets. The solar decadal oscillations are symptomatic of a deep-seated magnetic pump -- the Dynamo -- whose internal workings remain elusive. Key question: is Sun's 11-year cycle normal, or instead a transition state? A 3-year addition to earlier long-term joint Chandra/HST programs (previously involving Alpha Cen [G2V+K1V] and Procyon [F5IV]), will be carried out for two new targets, the nearby binaries Xi Bootis (G8V+K4) and 70 Ophiuchi (K0V+K5V).

The HST part of the program will measure FUV subcoronal (T~100,000 K) emission lines, like Si IV 140 nm, C IV 155 nm, and density-sensitive O IV 140 nm, as well as important chromospheric (T~10,000 K) features, like O I 130 nm, C II 133 nm, and C I 165 nm, in both pairs of stars, with one COS visit per system each year. Analyses of these emissions, including dynamical information encoded in Doppler shifts and distortions of the line shapes, can provide insight concerning the thermal/pressure structure of the anomalously hot outer layers of these stars; and how these structural properties change with the ebb and flow of a magnetic activity cycle. Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: In the Trenches of the Solar-Stellar Connection. III. The HST/COS Ecliptic-poles Stellar Survey (EclipSS) Authors: Ayres, Thomas R. Bibcode: 2021ApJ...910...71A Altcode: The Ecliptic-poles Stellar Survey (EclipSS) collected far-ultraviolet (FUV: 1160-1420 Å) spectra of 49 nearby (d ≲ 100 pc) F3-K3 main-sequence stars, located at high ecliptic latitudes (north and south), using the Cosmic Origins Spectrograph of the Hubble Space Telescope. The ecliptic poles receive higher exposures from scanning missions like the Transiting Exoplanet Survey Satellite (high-precision optical photometry) and Extended Roentgen Survey with an Imaging Telescope Array (X-ray monitoring), which can deliver crucial contextual information, not otherwise easily secured. The objective was to support theoretical studies of stellar hot outer atmospheres—chromospheres (∼104 K) and coronae (≳1 MK)—which, among other things, can adversely impact exoplanets via host-star "space weather." Flux-flux diagrams (e.g., C II 1335 Å versus O I 1306 Å) were constructed for the EclipSS stars, solar Cycle 23/24 irradiances, and long-term FUV records of α Cen A (G2 V) and B (K1 V). The EclipSS cohort displays similar minimum ("basal") fluxes to the Sun and solar twin α Cen A, in chromospheric O I 1306 Å. In hotter C II 1335 Å, a downward slump of the basal fluxes—noted in previous, less controlled surveys—can now be explained as an effect of subsolar abundances. The consistent basal minima in chromospheric and higher temperature species at solar metallicity favor the idea that stellar analogs of the solar supergranulation network provide a baseline of high-energy emissions. The magnetic network is replenished by a "local dynamo" independently of the stellar spin. It can operate even when the starspot-spawning internal dynamo has ceased cycling, as during the Sun's 17th century Maunder Minimum. Title: A Multiwavelength Look at the GJ 9827 System: No Evidence of Extended Atmospheres in GJ 9827b and d from HST and CARMENES Data Authors: Carleo, Ilaria; Youngblood, Allison; Redfield, Seth; Casasayas Barris, Nuria; Ayres, Thomas R.; Vannier, Hunter; Fossati, Luca; Palle, Enric; Livingston, John H.; Lanza, Antonino F.; Niraula, Prajwal; Alvarado-Gómez, Julián D.; Chen, Guo; Gandolfi, Davide; Guenther, Eike W.; Linsky, Jeffrey L.; Nagel, Evangelos; Narita, Norio; Nortmann, Lisa; Shkolnik, Evgenya L.; Stangret, Monika Bibcode: 2021AJ....161..136C Altcode: 2021arXiv210106277C GJ 9827 is a bright star hosting a planetary system with three transiting planets. As a multiplanet system with planets that sprawl within the boundaries of the radius gap between terrestrial and gaseous planets, GJ 9827 is an optimal target to study the evolution of the atmospheres of close-in planets with a common evolutionary history and their dependence from stellar irradiation. Here we report on the Hubble Space Telescope (HST) and CARMENES transit observations of GJ 9827 planets b and d. We performed a stellar and ISM characterization from the ultraviolet HST spectra, obtaining fluxes for Lyα and Mg II of F(Lyα) = (5.42 ${}_{-0.75}^{+0.96}$ ) × 10-13 erg cm-2 s-1 and F(MgII) = (5.64 ± 0.24) × 10-14 erg cm-2 s-1. We also investigated a possible absorption signature in Lyα in the atmosphere of GJ 9827b during a transit event from HST spectra, as well as Hα and He I signature for the atmosphere of GJ 9827b and d from CARMENES spectra. We found no evidence of an extended atmosphere in either of the planets. This result is also supported by our analytical estimations of mass loss based on the measured radiation fields for all three planets of this system, which led to a mass-loss rate of 0.4, 0.3, and 0.1 planetary masses per Gyr for GJ 9827b, c, and d, respectively. These values indicate that the planets could have lost their volatiles quickly in their evolution and probably do not retain an atmosphere at the current stage. Title: In the Trenches of the Solar-Stellar Connection. II. Extreme Ultraviolet Flux-Flux Correlations across Solar Cycle 24 Authors: Ayres, Thomas R. Bibcode: 2021ApJ...908..205A Altcode: Solar extreme-ultraviolet (EUV: 100-1100 Å) radiation rises in the 104 K upper chromosphere and hotter layers extending into the million-degree corona. Much of the EUV normally is not visible in other stars owing to interstellar H I absorption. The present study derived power-law scaling relations for EUV species based on irradiance spectra from the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory, over the rise and fall of recent sunspot Cycle 24. These relations not only can test solar models, but also allow "invisible" stellar EUV emissions to be reconstructed from more accessible ultraviolet (UV: 1100-3000 Å) proxies, with implications for heating, ionization, and erosion of exoplanet atmospheres by Sun-like hosts. Hot EUV coronal tracers like Si XII 520 Å (8 MK) show strongly curved power laws relative to chromospheric H I 1025 Å Lyβ, as was seen in Paper I for 0.2-2 keV soft X-rays versus Mg II 2800 Å. The brightest EUV feature, He II 303 Å, exhibits a nearly 1:1 correlation with Lyβ (and H I 1215 Lyα, but slightly steeper than 1:1 relative to Mg II). The second brightest, C III 977 Å, has a shallower power-law slope of ∼0.5. Correlations for low first ionization potential species, such as Mg, Si, and Fe, might be affected by cycle-dependent chemical fractionation. Parameterized flux-flux relations are presented for most of the strong EUV (and selected UV) features, together with fluxes of individual lines and broad EUV wavelength bands at the highs and lows of Cycle 24. Title: Measuring the fine-structure constant on a white dwarf surface; a detailed analysis of Fe V absorption in G191-B2B Authors: Hu, J.; Webb, J. K.; Ayres, T. R.; Bainbridge, M. B.; Barrow, J. D.; Barstow, M. A.; Berengut, J. C.; Carswell, R. F.; Dumont, V.; Dzuba, V.; Flambaum, V. V.; Lee, C. C.; Reindl, N.; Preval, S. P.; Tchang-Brillet, W. -Ü. L. Bibcode: 2021MNRAS.500.1466H Altcode: 2020MNRAS.tmp.3074H; 2020MNRAS.500.1466H; 2020arXiv200710905H The gravitational potential ϕ = GM/Rc2 at the surface of the white dwarf G191-B2B is 10 000 times stronger than that at the Earth's surface. Numerous photospheric absorption features are detected, making this a suitable environment to test theories in which the fundamental constants depend on gravity. We have measured the fine-structure constant, α, at the white dwarf surface, used a newly calibrated Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph spectrum of G191-B2B, two new independent sets of laboratory Fe V wavelengths, and new atomic calculations of the sensitivity parameters that quantify Fe V wavelength dependency on α. The two results obtained are: Δα/α0 = (6.36 ± 0.35stat ± 1.84sys) × 10-5 and Δα/α0 = (4.21 ± 0.48stat ± 2.25sys) × 10-5. The measurements hint that the fine-structure constant increases slightly in the presence of strong gravitational fields. A comprehensive search for systematic errors is summarized, including possible effects from line misidentifications, line blending, stratification of the white dwarf atmosphere, the quadratic Zeeman effect and electric field effects, photospheric velocity flows, long-range wavelength distortions in the HST spectrum, and variations in the relative Fe isotopic abundances. None fully account for the observed deviation but the systematic uncertainties are heavily dominated by laboratory wavelength measurement precision. Title: CYRA: the cryogenic infrared spectrograph for the Goode Solar Telescope in Big Bear Authors: Yang, Xu; Cao, Wenda; Gorceix, Nicolas; Plymate, Claude; Shumoko, Sergey; Bai, XianYong; Penn, Matt; Ayres, Thomas; Coulter, Roy; Goode, Philip R. Bibcode: 2020SPIE11447E..AGY Altcode: 2020arXiv200811320Y CYRA (CrYogenic solar spectrogRAph) is a facility instrument of the 1.6-meter Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). CYRA focuses on the study of the near-infrared solar spectrum between 1 and 5 microns, an under-explored region which is not only fertile ground for photospheric magnetic diagnostics but also allows a unique window into the chromosphere lying atop the photosphere. CYRA is the first-ever fully cryogenic spectrograph in any solar observatory with its two predecessors, on the McMath-Pierce and Mees Telescopes, being based on warm optics except for the detectors and order sorting filters. CYRA is used to probe magnetic fields in various solar features and the quiet photosphere. CYRA measurements will allow new and better 3D extrapolations of the solar magnetic field and will provide more accurate boundary conditions for solar activity models. The superior spectral resolution of 150,000 and better allows enhanced observations of the chromosphere in the carbon monoxide (CO) spectral bands and will yield a better understanding of energy transport in the solar atmosphere. CYRA is divided into two optical sub-systems: The Fore-Optics Module and the Spectrograph. The Spectrograph is the heart of the instrument and contains the IR detector, grating, slits, filters, and imaging optics all in a cryogenically cooled Dewar (cryostat). The sensor is a 2048 by 2048 pixel HAWAII 2 array produced by Teledyne Scientific and Imaging, LLC. The cryostat interior and the readout electronics are maintained at 90 Kelvin by helium refrigerant-based cryo-coolers, while the IR array is cooled to 30 Kelvin. The Fore-Optics Module de-rotates and stabilizes the solar image, provides scanning capabilities and transfers the GST image to the Spectrograph. CYRA has been installed and is undergoing its commissioning phase. This paper reports on the design, implementation, and operation of CYRA in detail. The preliminary scientific results have been highlighted as well. Title: In the Trenches of the Solar-Stellar Connection. I. Ultraviolet and X-Ray Flux-Flux Correlations across the Activity Cycles of the Sun and Alpha Centauri AB Authors: Ayres, Thomas R. Bibcode: 2020ApJS..250...16A Altcode: This study focuses on high-energy proxies of stellar magnetic activity over long-term starspot cycles of three low-activity Sun-like stars: α Centauri A (HD 128620: G2 V), α Cen B (HD 128621: K1 V), and the Sun itself. Data sets include: daily solar ultraviolet irradiance spectra and X-ray fluxes from the Solar Radiation and Climate Experiment, during recent sunspot Cycles 23 and 24; Interface Region Imaging Spectrograph long-slit stigmatic imaging of solar Mg II h (2803 Å) and k (2796 Å) in quiet and active regions; and Hubble Space Telescope Imaging Spectrograph ultraviolet, and Chandra X-ray, campaigns on α Cen AB. Established stellar "flux-flux" relations, for example X-rays (T ∼ 1 MK) versus Mg II (T ∼ 8000 K), showed increasing power-law slopes with increasing formation temperature, but these give way on the Sun to bent power laws, and surprising inversions in the activity hierarchy: Si III is more "active" (steeper power laws) than N V, despite the latter's four times higher formation temperature. The Sun's flux-flux behavior, nevertheless, remarkably parallels its low-activity solar twin α Cen A. In contrast, the cooler, somewhat more active, K dwarf companion displays correlations more in line with the previous stellar paradigm. The new flux-flux relations offer a way to vet numerical spectral simulations and proxy-based irradiance models, and extrapolate solar global activity indices into regimes below or above the grasp of contemporary records, or to exoplanet hosts at the low end of the Sun-like activity ladder. Title: The Bad Attitude Project Authors: Ayres, Thomas Bibcode: 2020cxo..prop.5812A Altcode: Spacecraft heating causes parts of Chandra's sky -- especially the Ecliptic poles (EP) -- to be undesirable for scheduling. Normally, the EP are a celestial sweet spot: always 90 degrees from Sun (good for satellites and ground-based) and high-exposure for scanning missions like TESS and eROSITA. HST's recent Ecliptic poles Stellar Survey (EclipSS) identified 10 FUV-extreme stars among 49 late-type dwarfs of the sample. Objective is to obtain short exposures of these objects with HRC-I (best soft response), to link coronal X-rays to existing FUV material. Jointly, HST/COS will cover key parts of the spectrum (C IV and Mg II) reluctantly sacrificed in original survey. While the EP target attitudes are bad, the exploration science is great, and well worth the extra scheduling effort. Title: The (Chandra) Bad Attitude Project Authors: Ayres, Thomas R. Bibcode: 2020hst..prop16376A Altcode: Spacecraft heating causes parts of Chandra X-ray Observatory's sky -- especially the Ecliptic poles (EP) -- to be undesirable for scheduling. Normally, the EPs are celestial sweet spots. Always 90 degrees from the Sun, they are good for observations by satellites and from the ground, and receive high exposurse by scanning missions like TESS and eROSITA. HST's recent "Ecliptic poles Stellar Survey" (EclipSS) identified 10 FUV-extreme stars among 49 late-type dwarfs of the original target sample. Objective is to obtain short exposures of these objects with Chandra's HRC-I camera (best soft response of the available sensors), to link coronal X-rays to the existing FUV material. Jointly, HST/COS will cover key parts of the spectrum (especially C IV 155 nm) reluctantly sacrificed in the original fast survey (single orbit per target). While the EP target attitudes are "bad" (for Chandra heating), the exploration science is great, and well worth the extra scheduling effort. Title: Stellar X-ray Cycles: the Shape of Things to Come Authors: Ayres, Thomas R. Bibcode: 2020hst..prop16254A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are relevant for understanding the Sun's analogous high-energy modulations, in turn crucial to Earth-impacting "Space Weather" (SW). Similarly, stellar SW counterparts can have eqivalent, or more severe, adverse effects on their exoplanets. The solar decadal oscillations are symptomatic of a deep-seated magnetic pump -- the Dynamo -- whose internal workings remain elusive. Key question: is Sun's 11-year cycle normal, or instead a transition state? A 3-year continuation of previous long-term Chandra/HST programs will be carried out for Alpha Cen AB (G2V+K1V) and Procyon (F5IV), nearby bright stars that bracket the Sun in their fundamental stellar properties.

HST part of the program will measure FUV subcoronal (T~100,000 K) emission lines, like Si IV 140 nm and C IV 155 nm, as well as the important NUV chromospheric (T~10,000 K) emission doublet of Mg II at 280 nm, in all three stars, with one visit of STIS echelle spectroscopy per system each year. Non-standard wavecals provide better wavelength calibrations, so that subtle Doppler shifts of the high-excitation emissions can be assessed. Dynamical information also is encoded in distortions of the line shapes, captured using combinations of FUV medium- and high-resolution echelle settings. Title: Cycles and the Seven Dwarfs Authors: Ayres, Thomas R. Bibcode: 2020hst..prop16253A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are relevant for understanding the Sun's analogous high-energy modulations, in turn crucial to Earth-impacting "Space Weather" (SW). Similarly, stellar SW counterparts can have equivalent, or more severe, adverse effects on their exoplanets. The solar decadal oscillations are symptomatic of a deep-seated magnetic pump -- the Dynamo -- whose internal workings remain elusive. Key question: is Sun's 11-year cycle normal, or instead a transition state? A 3-year addition to earlier long-term joint Chandra/HST programs (previously involving Alpha Cen [G2V+K1V] and Procyon [F5IV]), will be carried out for two new targets, the nearby binaries Xi Bootis (G8V+K4) and 70 Ophiuchi (K0V+K5V).

The HST part of the program will measure FUV subcoronal (T~100,000 K) emission lines, like Si IV 140 nm, C IV 155 nm, and density-sensitive O IV 140 nm, as well as important chromospheric (T~10,000 K) features, like O I 130 nm, C II 133 nm, and C I 165 nm, in both pairs of stars, with one COS visit per system each year. Analyses of these emissions, including dynamical information encoded in Doppler shifts and distortions of the line shapes, can provide insight concerning the thermal/pressure structure of the anomalously hot outer layers of these stars; and how these structural properties change with the ebb and flow of a magnetic activity cycle. Title: A Sensitive Test for Far Ultraviolet CO absorption in the Outflow of our Nearest Supernova Progenitor - Antares Authors: Harper, Graham M.; Ayres, Thomas R.; Guinan, Edward F.; Ohnaka, Keiichi Bibcode: 2020hst..prop16256H Altcode: The massive red supergiant Antares (alpha Sco A: M1 Iab) is an excellent star to test theoretical models of mass loss because its distance, age, stellar parameters, mass-loss rate, and interstellar reddening are well established. The early-M supergiants pose a particular challenge for models of mass loss driven by radiation pressure on molecules and/or dust: The circumstellar molecular abundances and dust-to-gas mass ratios are lower than for later-M spectral-types, but they still manage to drive massive winds.

We request deep FUV and NUV observations to perform an extremely sensitive test for the most robust circumstellar molecule, CO, by observing its Fourth-Positive electronic bands against the FUV continuum of the M supergiant Antares. These observations will enable us measure any CO present in the outflow, and to place upper-limits on the effective radiation acceleration it can provide. The proposed observations will also provide an invaluable dataset for Antares, the oft neglected southern twin of Betelgeuse, and our nearest Type II supernova progenitor. Title: What can ISM and non-photospheric highly ionised lines in white dwarf spectra reveal about the β CMa tunnel? Authors: Finch, Nicolle L.; Preval, S. P.; Barstow, M. A.; Casewell, S. L.; Ayres, T.; Welsh, B.; Bainbridge, M.; Reindl, N. Bibcode: 2020IAUS..357..220F Altcode: White dwarfs are useful objects with which to study the local interstellar medium (ISM). High ionisation state absorption features that cannot be attributed to the photosphere or the ISM have been observed along the line-of-sight to a number of white dwarf stars. Suggested origins of these lines include ionisation from past supernovae, stellar winds, circumstellar disks, photoionisation from nearby hot stars or also from the white dwarf itself. In this study we consider the origin of these non-photospheric highly ionised lines in two stars towards a rarefied region of the galaxy known as the extended β CMa Tunnel. We present preliminary results from our analysis of the first of these two stars. Title: VizieR Online Data Catalog: ASTRAL: reference spectra for evolved M stars (Carpenter+, 2018) Authors: Carpenter, K. G.; Nielsen, K. E.; Kober, G. V.; Ayres, T. R.; Wahlgren, G. M.; Rau, G. Bibcode: 2019yCat..18690157C Altcode: This paper focuses on the evolved cool stars γCru and αOri and compares their spectral characteristics to the well-studied K1.5III star αBoo (Hinkle+ 2005uaas.book.....H). The observational strategy for α Ori and γ Cru, as for the other objects in the ASTRAL Cool Star Program, was crafted to find the optimal combination of spectral resolution and signal-to-noise over the complete FUV and NUV spectra (1150-3159Å).

All of the HST Space Telescope Imaging Spectrograph (STIS) spectra for the two objects are splined in a top-level data set covering the entire wavelength region. An overview of the data used in this paper is presented in Table 1, and a more detailed description of the data, including the observing strategy, data reduction, coaddition, and splicing, can be found on the Advances Spectral Library (ASTRAL) website (http://casa.colorado.edu/~ayres/ASTRAL/) and at the Mikulski Archive for Space Telescopes (MAST) (http://archive.stsci.edu/prepds/astral/).

(4 data files). Title: STROBE-X: X-ray Timing and Spectroscopy on Dynamical Timescales from Microseconds to Years Authors: Ray, Paul; Arzoumanian, Zaven; Ballantyne, David; Bozzo, Enrico; Brandt, Soren; Brenneman, Laura; Chakrabarty, Deepto; Christophersen, Marc; DeRosa, Alessandra; Feroci, Marco; Gendreau, Keith; Goldstein, Adam; Hartmann, Dieter; Hernanz, Margarita; Jenke, Peter; Kara, Erin; Maccarone, Tom; McDonald, Michael; Martindale, Adrian; Nowak, Michael; Phlips, Bernard; Remillard, Ron; Schanne, Stephane; Stevens, Abigail; Tomsick, John; Watts, Anna; Wilson-Hodge, Colleen; Wolff, Michael; Wood, Kent; Zane, Silvia; Ajello, Marco; Alston, Will; Altamirano, Diego; Antoniou, Vallia; Arur, Kavitha; Ashton, Dominic; Auchettl, Katie; Ayres, Tom; Bachetti, Matteo; Balokovic, Mislav; Baring, Matthew; Baykal, Altan; Begelman, Mitch; Bhat, Narayana; Bogdanov, Slavko; Briggs, Michael; Bulbul, Esra; Bult, Petrus; Burns, Eric; Cackett, Ed; Campana, Riccardo; Caspi, Amir; Cavecchi, Yuri; Chenevez, Jerome; Cherry, Mike; Corbet, Robin; Corcoran, Michael; Corsi, Alessandra; Degenaar, Nathalie; Drake, Jeremy; Eikenberry, Steve; Enoto, Teruaki; Fragile, Chris; Fuerst, Felix; Gandhi, Poshak; Garcia, Javier; Goldstein, Adam; Gonzalez, Anthony; Grefenstette, Brian; Grinberg, Victoria; Grossan, Bruce; Guillot, Sebastien; Guver, Tolga; Haggard, Daryl; Heinke, Craig; Heinz, Sebastian; Hemphill, Paul; Homan, Jeroen; Hui, Michelle; Huppenkothen, Daniela; Ingram, Adam; Irwin, Jimmy; Jaisawal, Gaurava; Jaodand, Amruta; Kalemci, Emrah; Kaplan, David; Keek, Laurens; Kennea, Jamie; Kerr, Matthew; van der Klis, Michiel; Kocevski, Daniel; Koss, Mike; Kowalski, Adam; Lai, Dong; Lamb, Fred; Laycock, Silas; Lazio, Joseph; Lazzati, Davide; Longcope, Dana; Loewenstein, Michael; Maitra, Dipankair; Majid, Walid; Maksym, W. Peter; Malacaria, Christian; Margutti, Raffaella; Martindale, Adrian; McHardy, Ian; Meyer, Manuel; Middleton, Matt; Miller, Jon; Miller, Cole; Motta, Sara; Neilsen, Joey; Nelson, Tommy; Noble, Scott; O'Brien, Paul; Osborne, Julian; Osten, Rachel; Ozel, Feryal; Palliyaguru, Nipuni; Pasham, Dheeraj; Patruno, Alessandro; Pelassa, Vero; Petropoulou, Maria; Pilia, Maura; Pohl, Martin; Pooley, David; Prescod-Weinstein, Chanda; Psaltis, Dimitrios; Raaijmakers, Geert; Reynolds, Chris; Riley, Thomas E.; Salvesen, Greg; Santangelo, Andrea; Scaringi, Simone; Schanne, Stephane; Schnittman, Jeremy; Smith, David; Smith, Krista Lynne; Snios, Bradford; Steiner, Andrew; Steiner, Jack; Stella, Luigi; Strohmayer, Tod; Sun, Ming; Tauris, Thomas; Taylor, Corbin; Tohuvavohu, Aaron; Vacchi, Andrea; Vasilopoulos, Georgios; Veledina, Alexandra; Walsh, Jonelle; Weinberg, Nevin; Wilkins, Dan; Willingale, Richard; Wilms, Joern; Winter, Lisa; Wolff, Michael; in 't Zand, Jean; Zezas, Andreas; Zhang, Bing; Zoghbi, Abdu Bibcode: 2019BAAS...51g.231R Altcode: 2019astro2020U.231R STROBE-X is a probe-class mission concept, selected for study by NASA, for X-ray spectral timing of compact objects across the mass scale. It combines huge collecting area, high throughput, broad energy coverage, and excellent spectral and temporal resolution in a single facility, enabling a broad portfolio of high-priority astrophysics. Title: Cycles and the Seven Dwarfs Authors: Ayres, Thomas Bibcode: 2019cxo..prop.5712A Altcode: Chandra has been following magnetic heartbeats of late-type stars via high-contrast coronal X-rays. Goal is to provide fundamental observational constraints for contemporary and future studies of underlying magnetic Dynamo, whose internal workings remain elusive. The Sun's high-energy modulations play important "Space Weather" role in our heliosphere, as do stellar counterparts for their exoplanets. 3-year time series (joint with HST) is proposed for promising new candidates Xi Boo (G8V+K4) and 70 Oph (K0V+K5V), adding four more dwarfs to the three in current "Cycles." Key question involves origin of diverging branches in rotational period vs. cycle duration, where Sun's iconic 11-yr example sits in the middle, possibly in a transitional state. Title: Cycles and the Seven Dwarfs Authors: Ayres, Thomas R. Bibcode: 2019hst..prop16003A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are relevant for understanding the Sun's analogous high-energy modulations, in turn crucial to Earth-impacting "Space Weather" (SW). Similarly, stellar SW counterparts can have equivalent, or more severe, adverse effects on their exoplanets. The solar decadal oscillations are symptomatic of a deep-seated magnetic pump - the Dynamo - whose internal workings remain elusive. Key question: is Sun's 11-year cycle normal, or instead a transition state? A 3-year addition to earlier long-term joint Chandra/HST programs (previously involving Alpha Cen [G2V+K1V] and Procyon [F5IV]), will be carried out for two new targets, the nearby binaries Xi Bootis (G8V+K4) and 70 Ophiuchi (K0V+K5V).

The HST part of the program will measure FUV subcoronal (T 100,000 K) emission lines, like Si IV 140 nm, C IV 155 nm, and density-sensitive O IV 140 nm, as well as important chromospheric (T 10,000 K) features, like O I 130 nm, C II 133 nm, and C I 165 nm, in both pairs of stars, with one COS visit per system each year. Analyses of these emissions, including dynamical information encoded in Doppler shifts and distortions of the line shapes, can provide insight concerning the thermal/pressure structure of the anomalously hot outer layers of these stars; and how these structural properties change with the ebb and flow of a magnetic activity cycle. Title: A far-UV survey of three hot, metal-polluted white dwarf stars: WD0455-282, WD0621-376, and WD2211-495 Authors: Preval, Simon P.; Barstow, Martin A.; Bainbridge, Matthew; Reindl, Nicole; Ayres, Thomas; Holberg, Jay B.; Barrow, John D.; Lee, Chung-Chi; Webb, John K.; Hu, Jiting Bibcode: 2019MNRAS.487.3470P Altcode: 2019MNRAS.tmp.1440P; 2019arXiv190512350P Using newly obtained high-resolution data (R ∼ 1 × 105) from the Hubble Space Telescope, and archival UV data from the Far Ultraviolet Spectroscopic Explorer, we have conducted a detailed UV survey of the three hot, metal-polluted white dwarfs WD0455-282, WD0621-376, and WD2211-495. Using bespoke model atmospheres, we measured Teff, log g, and photospheric abundances for these stars. In conjunction with data from Gaia, we measured masses, radii, and gravitational redshift velocities for our sample of objects. We compared the measured photospheric abundances with those predicted by radiative levitation theory, and found that the observed Si abundances in all three white dwarfs, and the observed Fe abundances in WD0621-376 and WD2211-495, were larger than those predicted by an order of magnitude. These findings imply not only an external origin for the metals, but also ongoing accretion, as the metals not supported by radiative levitation would sink on extremely short time-scales. We measured the radial velocities of several absorption features along the line of sight to the three objects in our sample, allowing us to determine the velocities of the photospheric and interstellar components along the line of sight for each star. Interestingly, we made detections of circumstellar absorption along the line of sight to WD0455-282 with three velocity components. To our knowledge, this is the first such detection of multicomponent circumstellar absorption along the line of sight to a white dwarf. Title: Make STIS Great Again! Authors: Ayres, Thomas R.; Proffitt, Charles R.; Welty, Daniel E. Bibcode: 2019hst..prop15948A Altcode: STIS is the premier high-resolution UV spectrograph in space, carrying out state-of-the-art investigations of a dizzying array of cosmic phenomena. While the instrument performance is superb, the CALSTIS pipeline wavelength scales can be improved in two significant ways: (1) collect new wavecal lamp exposures for echelle settings currently lacking adequate calibration coverage in the modern (post-SM4) era; and (2) build easy-to-apply corrections to compensate for small wavelength distortions introduced by the low-order polynomial dispersion model currently incorporated in the pipeline. In fact, success of the second improvement depends on availability of "missing" calibrations delivered by the first part. A modest expenditure of calibration time can enhance the extensive legacy of STIS, now and into the future. Title: Constraining the magnetic field on white dwarf surfaces; Zeeman effects and fine structure constant variation Authors: Hu, J.; Webb, J. K.; Ayres, T. R.; Bainbridge, M. B.; Barrow, J. D.; Barstow, M. A.; Berengut, J. C.; Carswell, R. F.; Dzuba, V. A.; Flambaum, V. V.; Holberg, J. B.; Lee, C. C.; Preval, S. P.; Reindl, N.; Tchang-Brillet, W. -Ü. L. Bibcode: 2019MNRAS.485.5050H Altcode: 2019MNRAS.tmp..796H; 2018arXiv181211480H White dwarf (WD) atmospheres are subjected to gravitational potentials around 105 times larger than occur on Earth. They provide a unique environment in which to search for any possible variation in fundamental physics in the presence of strong gravitational fields. However, a sufficiently strong magnetic field will alter absorption line profiles and introduce additional uncertainties in measurements of the fine structure constant. Estimating the magnetic field strength is thus essential in this context. Here, we model the absorption profiles of a large number of atomic transitions in the WD photosphere, including first-order Zeeman effects in the line profiles, varying the magnetic field as a free parameter. We apply the method to a high signal-to-noise, high-resolution, far-ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum of the WD G191-B2B. The method yields a sensitive upper limit on its magnetic field of B < 2300 G at the 3σ level. Using this upper limit, we find that the potential impact of quadratic Zeeman shifts on measurements of the fine structure constant in G191-B2B is 4 orders of magnitude below laboratory wavelength uncertainties. Title: Stellar X-ray Cycles: the Shape of Things to Come Authors: Ayres, Thomas R. Bibcode: 2019hst..prop15963A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are relevant for understanding the Sun's analogous high-energy modulations, in turn crucial to Earth-impacting "Space Weather" (SW). Similarly, stellar SW counterparts can have eqivalent, or more severe, adverse effects on their exoplanets. The solar decadal oscillations are symptomatic of a deep-seated magnetic pump - the Dynamo - whose internal workings remain elusive. Key question: is Sun's 11-year cycle normal, or instead a transition state? A 3-year continuation of previous long-term Chandra/HST programs will be carried out for Alpha Cen AB (G2V+K1V) and Procyon (F5IV), nearby bright stars that bracket the Sun in their fundamental stellar properties.

HST part of the program will measure FUV subcoronal (T 100,000 K) emission lines, like Si IV 140 nm and C IV 155 nm, as well as the important NUV chromospheric (T 10,000 K) emission doublet of Mg II at 280 nm, in all three stars, with one visit of STIS echelle spectroscopy per system each year. Non-standard wavecals provide better wavelength calibrations, so that subtle Doppler shifts of the high-excitation emissions can be assessed. Dynamical information also is encoded in distortions of the line shapes, captured using combinations of FUV medium- and high-resolution echelle settings. Title: Cool, evolved stars: results, challenges, and promises for the next decade Authors: Rau, Gioia; Montez, Rodolfo, Jr.; Carpenter, Kenneth; Wittkowski, Markus; Bladh, Sara; Karovska, Margarita; Airapetian, Vladimir; Ayres, Tom; Boyer, Martha; Chiavassa, Andrea; Clayton, Geoffrey; Danchi, William; De Marco, Orsola; Dupree, Andrea K.; Kaminski, Tomasz; Kastner, Joel H.; Kerschbaum, Franz; Linsky, Jeffrey; Lopez, Bruno; Monnier, John; Montargès, Miguel; Nielsen, Krister; Ohnaka, Keiichi; Ramstedt, Sofia; Roettenbacher, Rachael; ten Brummelaar, Theo; Paladini, Claudia; Sarangi, Arkaprabha; van Belle, Gerard; Ventura, Paolo Bibcode: 2019BAAS...51c.241R Altcode: 2019arXiv190304585R; 2019astro2020T.241R This White Paper identifies compelling scientific opportunities in the field of Cool, Evolved Stars, describing the observational and theoretical challenges to our understanding, and the key advancements made. We portray the pathway towards understanding, and identify, through recommendations, which advancements are necessary in 2020-2030 & beyond. Title: STROBE-X: X-ray Timing and Spectroscopy on Dynamical Timescales from Microseconds to Years Authors: Ray, Paul S.; Arzoumanian, Zaven; Ballantyne, David; Bozzo, Enrico; Brandt, Soren; Brenneman, Laura; Chakrabarty, Deepto; Christophersen, Marc; DeRosa, Alessandra; Feroci, Marco; Gendreau, Keith; Goldstein, Adam; Hartmann, Dieter; Hernanz, Margarita; Jenke, Peter; Kara, Erin; Maccarone, Tom; McDonald, Michael; Nowak, Michael; Phlips, Bernard; Remillard, Ron; Stevens, Abigail; Tomsick, John; Watts, Anna; Wilson-Hodge, Colleen; Wood, Kent; Zane, Silvia; Ajello, Marco; Alston, Will; Altamirano, Diego; Antoniou, Vallia; Arur, Kavitha; Ashton, Dominic; Auchettl, Katie; Ayres, Tom; Bachetti, Matteo; Balokovic, Mislav; Baring, Matthew; Baykal, Altan; Begelman, Mitch; Bhat, Narayana; Bogdanov, Slavko; Briggs, Michael; Bulbul, Esra; Bult, Petrus; Burns, Eric; Cackett, Ed; Campana, Riccardo; Caspi, Amir; Cavecchi, Yuri; Chenevez, Jerome; Cherry, Mike; Corbet, Robin; Corcoran, Michael; Corsi, Alessandra; Degenaar, Nathalie; Drake, Jeremy; Eikenberry, Steve; Enoto, Teruaki; Fragile, Chris; Fuerst, Felix; Gandhi, Poshak; Garcia, Javier; Goldstein, Adam; Gonzalez, Anthony; Grefenstette, Brian; Grinberg, Victoria; Grossan, Bruce; Guillot, Sebastien; Guver, Tolga; Haggard, Daryl; Heinke, Craig; Heinz, Sebastian; Hemphill, Paul; Homan, Jeroen; Hui, Michelle; Huppenkothen, Daniela; Ingram, Adam; Irwin, Jimmy; Jaisawal, Gaurava; Jaodand, Amruta; Kalemci, Emrah; Kaplan, David; Keek, Laurens; Kennea, Jamie; Kerr, Matthew; van der Klis, Michiel; Kocevski, Daniel; Koss, Mike; Kowalski, Adam; Lai, Dong; Lamb, Fred; Laycock, Silas; Lazio, Joseph; Lazzati, Davide; Longcope, Dana; Loewenstein, Michael; Maitra, Dipankair; Majid, Walid; Maksym, W. Peter; Malacaria, Christian; Margutti, Raffaella; Martindale, Adrian; McHardy, Ian; Meyer, Manuel; Middleton, Matt; Miller, Jon; Miller, Cole; Motta, Sara; Neilsen, Joey; Nelson, Tommy; Noble, Scott; O'Brien, Paul; Osborne, Julian; Osten, Rachel; Ozel, Feryal; Palliyaguru, Nipuni; Pasham, Dheeraj; Patruno, Alessandro; Pelassa, Vero; Petropoulou, Maria; Pilia, Maura; Pohl, Martin; Pooley, David; Prescod-Weinstein, Chanda; Psaltis, Dimitrios; Raaijmakers, Geert; Reynolds, Chris; Riley, Thomas E.; Salvesen, Greg; Santangelo, Andrea; Scaringi, Simone; Schanne, Stephane; Schnittman, Jeremy; Smith, David; Smith, Krista Lynne; Snios, Bradford; Steiner, Andrew; Steiner, Jack; Stella, Luigi; Strohmayer, Tod; Sun, Ming; Tauris, Thomas; Taylor, Corbin; Tohuvavohu, Aaron; Vacchi, Andrea; Vasilopoulos, Georgios; Veledina, Alexandra; Walsh, Jonelle; Weinberg, Nevin; Wilkins, Dan; Willingale, Richard; Wilms, Joern; Winter, Lisa; Wolff, Michael; in 't Zand, Jean; Zezas, Andreas; Zhang, Bing; Zoghbi, Abdu Bibcode: 2019arXiv190303035R Altcode: We present the Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays (STROBE-X), a probe-class mission concept selected for study by NASA. It combines huge collecting area, high throughput, broad energy coverage, and excellent spectral and temporal resolution in a single facility. STROBE-X offers an enormous increase in sensitivity for X-ray spectral timing, extending these techniques to extragalactic targets for the first time. It is also an agile mission capable of rapid response to transient events, making it an essential X-ray partner facility in the era of time-domain, multi-wavelength, and multi-messenger astronomy. Optimized for study of the most extreme conditions found in the Universe, its key science objectives include: (1) Robustly measuring mass and spin and mapping inner accretion flows across the black hole mass spectrum, from compact stars to intermediate-mass objects to active galactic nuclei. (2) Mapping out the full mass-radius relation of neutron stars using an ensemble of nearly two dozen rotation-powered pulsars and accreting neutron stars, and hence measuring the equation of state for ultradense matter over a much wider range of densities than explored by NICER. (3) Identifying and studying X-ray counterparts (in the post-Swift era) for multiwavelength and multi-messenger transients in the dynamic sky through cross-correlation with gravitational wave interferometers, neutrino observatories, and high-cadence time-domain surveys in other electromagnetic bands. (4) Continuously surveying the dynamic X-ray sky with a large duty cycle and high time resolution to characterize the behavior of X-ray sources over an unprecedentedly vast range of time scales. STROBE-X's formidable capabilities will also enable a broad portfolio of additional science. Title: Chandra’s Stars Authors: Ayres, Thomas Bibcode: 2019HEAD...1710502A Altcode: Stars are the powerhouses and chemical factories of galaxies; hosts of exoplanets that in some cases might harbor life. It is not surprising, then, that stars are principal objects of interest to astronomers. What is surprising: normal stars are frequent targets of kilo-volt X-ray observatories, given that stellar surfaces have temperatures no more than 0.01 keV (extreme O-type stars, at that). Nevertheless, hydrodynamic and magnetic phenomena on stars conspire to create conditions hundreds of times hotter than the tepid photospheres, to drive copious X-ray emissions in many cases. Examples include: radiative instability shocks in the warm, fast winds of early-type supergiants; accretion splash-down spots on protostars; magnetic coronae of Main-sequence cool stars; and high-energy flares from a wide variety of objects. Chandra has played a key role in stellar X-ray studies over the past two decades because, among many examples, the high spatial resolution can associate X-ray sources with optical and IR counterparts in crowded star-forming regions; the low-resolution CCD spectra can characterize faint point sources, such as planet-hosts and young embedded protostars; and the transmission gratings can diagnose plasma conditions in shocked stellar winds, T-Tauri accretion columns, and hyperactive stellar coronae. In addition to a general overview of Chandra’s impact on stellar astronomy, the presentation will mention long-term coronal activity cycles of the two sunlike stars of the nearby Alpha Centauri triple system, with relevance to planetary habitability; and the temporal behavior of serendipitous sources in the Chandra HRC-I field around Alpha Cen, as a guide to what might be anticipated in large-area X-ray surveys of the future. Title: The extreme O-type spectroscopic binary HD 93129A. A quantitative, multiwavelength analysis Authors: Gruner, D.; Hainich, R.; Sander, A. A. C.; Shenar, T.; Todt, H.; Oskinova, L. M.; Ramachandran, V.; Ayres, T.; Hamann, W. -R. Bibcode: 2019A&A...621A..63G Altcode: 2018arXiv181107820G Context. HD 93129A was classified as the earliest O-type star in the Galaxy (O2 If*) and is considered as the prototype of its spectral class. However, interferometry shows that this object is a binary system, while recent observations even suggest a triple configuration. None of the previous spectral analyses of this object accounted for its multiplicity. With new high-resolution UV and optical spectra, we have the possibility to reanalyze this key object, taking its binary nature into account for the first time.
Aims: We aim to derive the fundamental parameters and the evolutionary status of HD 93129A, identifying the contributions of both components to the composite spectrum
Methods: We analyzed UV and optical observations acquired with the Hubble Space Telescope and ESO's Very Large Telescope. A multiwavelength analysis of the system was performed using the latest version of the Potsdam Wolf-Rayet model atmosphere code.
Results: Despite the similar spectral types of the two components, we are able to find signatures from each of the components in the combined spectrum, which allows us to estimate the parameters of both stars. We derive log(L/L⊙) = 6.15, Teff = 52 kK, and log Ṁ = -4.7 [M⊙ yr-1] for the primary Aa, and log(L/L⊙) = 5.58, Teff = 45 kK, and log Ṁ = -5.8 [M⊙yr-1] for the secondary Ab.
Conclusions: Even when accounting for the binary nature, the primary of HD 93129A is found to be one of the hottest and most luminous O stars in our Galaxy. Based on the theoretical decomposition of the spectra, we assign spectral types O2 If* and O3 III(f*) to components Aa and Ab, respectively. While we achieve a good fit for a wide spectral range, specific spectral features are not fully reproduced. The data are not sufficient to identify contributions from a hypothetical third component in the system.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained (from the Data Archive) at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-13346.Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 095.D-0234(A). Title: Chapter 2 - Stellar and Solar Chromospheres and Attendant Phenomena Authors: Ayres, Thomas R. Bibcode: 2019sgsp.book...27A Altcode: This chapter describes several aspects of stars that inform us about the Sun, especially characteristics that might have changed significantly on our star's journey to its present evolutionary state. The focus is on stellar "chromospheres," an important byproduct of magnetic "activity," because this is a key area in solar physics today and one in which the stars can be most informative. The main topic is why chromospheres exist: the warm, extensive outer atmospheres of cool stars, a consequence of nonradiative heating mainly devolving from magnetic effects. Ancillary topics consider two different aspects of the underlying magnetic activity: the rotation-age-activity connection, primary signature of magnetic evolution over time; and activity cycles, outward manifestations of an enigmatic, poorly understood, and perhaps equally poorly synchronized magnetic clock deep in the stellar interior. Title: HST/COS Ecliptic-poles Stellar Survey (EclipSS) Authors: Ayres, Thomas R. Bibcode: 2019AAS...23336303A Altcode: Ecliptic-poles Stellar Survey (EclipSS) currently is collecting far-ultraviolet spectra (115-143 nm), using HST's ultra-sensitive Cosmic Origins Spectrograph (COS), of a sample of 49 F2-K2 dwarf stars in the North and South ecliptic polar regions, to further advance studies of magnetic activity among cool Main sequence stars similar to the Sun. The ecliptic poles are favored places for current and up-coming astronomical survey satellites, including TESS (exoplanets and asteroseismology) and eROSITA (coronal X-rays). These instruments scan along lines of ecliptic longitude, and thus accumulate their deepest exposures close to the ecliptic poles. EclipSS targets were selected to be bright enough for eROSITA, not too bright for TESS, and just right for COS. The combined photometric (starspots), asteroseismic, FUV, and X-ray measurements will provide synergistic information concerning rotation periods, radii, masses, metallicities, ages, activity levels, and coronal properties to inform community-wide efforts to explore stellar activity and its underlying magnetic engine, the Dynamo. As of September 2018, about half of the EclipSS sample has been successfully observed by COS. Title: Serendipitous X-Ray Sources in the Chandra HRC Field around Alpha Centauri Authors: Ayres, Thomas R. Bibcode: 2018AJ....156..274A Altcode: 2018arXiv181011674A For more than a decade, Alpha Centauri AB (G2 V+K1 V) has been observed by Chandra, in a long-term program to follow coronal (T ∼ 106 K) activity cycles of the two sunlike stars. Over 2008.4-2017.8, 19 HRC-I exposures were taken, each about 10 ks in duration, and spaced about six months apart. Beyond monitoring the AB X-ray luminosities, the HRC-I sequence represents a unique decadal record of the dozen, or so, serendipitous X-ray sources in the α Cen field, which is at low Galactic latitude and thus dominated by nearby stars. For the present study, the 10 brightest candidates were considered. Only a handful of these were persistent; most were variable, some highly so, flaring in a few epochs, weak or absent in the others. All 10 X-ray sources have Gaia objects within about 2″ mostly late-type dwarfs, but a few giants. However, two of the proposed optical counterparts have statistically significant offsets, and possible conflicts between the X-ray and optical properties. Another of the candidates brightened by a factor of 100 in X-rays during a single exposure, briefly attaining super-flare status. The Gaia counterpart is anomalously blue for its absolute G-magnitude and likely is a WD+dM pair. To the extent that the low Galactic latitude field is representative, the Chandra time-domain view emphasizes that the high-energy stellar sky is biased toward transient sources, so any snapshot survey surely will miss many of the most interesting objects. Title: The Advanced Spectral Library (ASTRAL): Reference Spectra for Evolved M Stars Authors: Carpenter, Kenneth G.; Nielsen, Krister E.; Kober, Gladys V.; Ayres, Thomas R.; Wahlgren, Glenn M.; Rau, Gioia Bibcode: 2018ApJ...869..157C Altcode: 2018arXiv181111865C The HST Treasury Program Advanced Spectral Library Project: Cool Stars was designed to collect representative, high-quality UV spectra of eight evolved F-M type cool stars. The Space Telescope Imaging Spectrograph (STIS) echelle spectra of these objects enable investigations of a broad range of topics, including stellar and interstellar astrophysics. This paper provides a guide to the spectra of the two evolved M stars, the M2 Iab supergiant α Ori and the M3.4 giant γ Cru, with comparisons to the prototypical K1.5 giant α Boo. It includes identifications of the significant atomic and molecular emission and absorption features and discusses the character of the photospheric and chromospheric continua and line spectra. The fluorescent processes responsible for a large portion of the emission-line spectrum, the characteristics of the stellar winds, and the available diagnostics for hot and cool plasmas are also summarized. This analysis will facilitate the future study of the spectra, outer atmospheres, and winds, not only of these objects but of numerous other cool, low-gravity stars, for years to come.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Title: First high-resolution look at the quiet Sun with ALMA at 3mm Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos, S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu, T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V. Bibcode: 2018A&A...619L...6N Altcode: 2018arXiv181005223N We present an overview of high-resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun regions were observed at a resolution of up to 2.5″ by 4.5″. We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full-disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by ∼305 K while the intranetwork is less bright by ∼280 K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 Å images, with somewhat larger size. We detect, for the first time, spicular structures, rising up to 15″ above the limb with a width down to the image resolution and brightness temperature of ∼1800 K above the local background. No trace of spicules, either in emission or absorption, is found on the disk. Our results highlight the potential of ALMA for the study of the quiet chromosphere. Title: Stellar X-ray Cycles: the Shape of Things to Come Authors: Ayres, Thomas R. Bibcode: 2018hst..prop15618A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are followed with highest sensitivity in coronal X-rays. Sun's high-energy modulations are crucial to Earth-impacting Space Weather, as stellar counterparts are for their exoplanets. The decadal oscillations are symptomatic of a deep-seated magnetic pump - the Dynamo - whose internal workings remain elusive. Key question: is solar 11-year cycle normal, or instead a transition state? 3-year continuation of previous CXO/HST program is proposed for Alpha Cen AB (G2V+K1V) and Procyon (F5IV). Alpha Cen cycles bracket solar behavior, although true period of sunlike A is uncertain. So far, Procyon is a flat-liner. Shape of rise and fall of cycle is a key diagnostic, most clearly traced at high energies.\n\nHST part of the program will measure FUV subcoronal (T 100,000 K) emission lines, like Si IV 140 nm and C IV 155 nm, as well as the important NUV chromospheric (T 10,000 K) emission doublet of Mg II at 280 nm, in all three stars, with one visit of STIS echelle spectroscopy per system each year. Non-standard wavecals are used to provide better wavelength calibrations, so that subtle Doppler shifts of the high-excitation transitions can be assessed. Dynamical information also is incoded in distortions of the emission lineshapes, which are captured using a combination of FUV medium- and high-resolution echelle settings. This program builds on previous long-term Chandra/HST time series on both systems. Title: Beyond the Coronal Graveyard Authors: Ayres, Thomas R. Bibcode: 2018AJ....156..163A Altcode: 2018arXiv180806092A New Chandra High Resolution Camera pointings on the “non-coronal” red giant Arcturus (HD 124897; α Boo: K1.5 III) corroborate a tentative soft X-ray detection in a shorter exploratory exposure 16 years earlier. The apparent source followed the (large) proper motion of the nearby bright star over the intervening years, and there were null detections at the previous location in the current epoch, as well as at the future location in the earlier epoch, reducing the possibility of chance coincidences with unrelated high-energy objects. The apparent X-ray brightness at Earth, averaged over the 98 ks of total exposure and accounting for absorption in the red giant’s wind, is ∼2 × 10-15 erg cm-2 s-1 (0.2-2 keV). Systematic errors in the energy conversion factor, devolving from the unknown spectrum, amount to only about 10%, smaller than the ∼30% statistical uncertainties in the count rates. The X-ray luminosity is only 3 × 1025 erg s-1, confirming Arcturus as one of Chandra’s darkest bright stars. Title: Stellar X-ray Cycles: the Shape of Things to Come Authors: Ayres, Thomas Bibcode: 2018cxo..prop.5446A Altcode: Somewhat erratic, unpredictable long-term starspot cycles of late-type stars are followed with highest sensitivity in coronal X-rays. Sun's high-energy modulations are crucial to Earth-impacting "Space Weather," as stellar counterparts are for their exoplanets. The decadal oscillations are symptomatic of a deep-seated magnetic pump -- the Dynamo -- whose internal workings remain elusive. Key question: is solar 11-year cycle normal, or instead a transition state? 3-year continuation of previous CXO/HST program is proposed for Alpha Cen AB (G2V+K1V) and Procyon (F5IV). Alpha Cen cycles bracket solar behavior, although true period of sunlike A is uncertain. So far, Procyon is a flat-liner. Shape of rise and fall of cycle is a key diagnostic, most clearly traced at high energies. Title: An Accurate Mass of the 31 Cygni Red Supergiant Authors: Bennett, Philip, D.; Brown, Alexander; Ayres, Thomas R. Bibcode: 2018csss.confE..46B Altcode: Red supergiants are massive, evolved stars that are among the brightest stars in the near infrared. But the uncertain physics of mass loss limits the ability of evolutionary models to accurately represent these stars in detail. Lacking a fundamental, predictive theory of mass loss, this process is normally incorporated into stellar models using simple parametric formulas such as Reimer’s Law. In this situation, it is important to constrain theoretical models evolved using such mass loss parametrizations by observation.
A key stellar parameter is mass. In combination with a star’s position in the H-R diagram, a well-determined mass provides a strong constraint on stellar evolution models. Unfortunately, there are very few red supergiants with masses known to even 5% accuracy. In response, the objective of Hubble Space Telescope GO program 14070 (PI: Bennett) was to determine the mass of the red supergiant K star in the long-period eclipsing binary 31 Cygni (K4 Ib + B3 V) accurate to 1%. To obtain this accuracy requires the incorporation of new optical radial velocity observations of the supergiant; that work is in progress. But the observational program of GO-14070 is now complete, and these new HST/STIS observations of the 31 Cyg binary in the ultraviolet have provided an immediate determination of the secondary orbit radial velocity amplitude, K2, accurate to 1%. This result suffices to determine the masses of both 31 Cyg stars to an accuracy of about 2%, and provides a useful constraint on the evolution of the intermediate-mass red supergiant in this well-separated binary system. Title: Chandra X-ray Time-Domain Study of Alpha Centauri AB, Procyon, and their Environs Authors: Ayres, Thomas R. Bibcode: 2018AAS...23231714A Altcode: For more than a decade, Chandra X-ray Observatory has been monitoring the central AB binary (G2V+K1V) of the α Centauri triple system with semi-annual pointings, using the High-Resolution Camera. This study has been extended in recent years to the mid-F subgiant, Procyon. The main objective is to follow the coronal (T~1MK) activity variations of the three stars, analogous to the Sun's 11-year sunspot cycle. Tentative periods of 20 yr and 8 yr have been deduced for α Cen A and B, respectively; but so far Procyon has shown only a slow, very modest decline in count rate, which could well reflect a slight instrumental degradation rather than intrinsic behavior. The negligible high-energy variability of Procyon sits in stark contrast to the dramatic factor of several to ten changes in the X-ray luminosities of α Cen AB and the Sun over their respective cycles. Further, although sunlike α Cen A has been observed by successive generations of X-ray observatories for nearly four decades, albeit sporadically, there are key gaps in the coverage that affect the determination of the cycle period. In fact, the most recent pointings suggest a downturn in A's count rate that might be signaling a shorter, more solar-like cycle following a delayed minimum in the 2005--2010 time frame (perhaps an exaggerated version of the extended solar minimum between recent Cycles 23 and 24). Beyond the coronal cycles of the three stars, the sequence of periodic X-ray images represents a unique time-domain history concerning steady as well as variable sources in the two 30'x30' fields. The most conspicuous of the variable objects -- in the α Cen field -- will be described here. Title: The Carbon Isotope Ratio of the Sun and Implications for the Solar Nebula Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R. Bibcode: 2018LPI....49.2907L Altcode: The solar C isotope ratio is -45 permil PDB. The 13C enrichment of the terrestrial planets may be due to CO self-shielding in the nebula or parent cloud. Title: Cracking the Conundrum of F-supergiant Coronae Authors: Ayres, Thomas R. Bibcode: 2018ApJ...854...95A Altcode: 2018arXiv180202552A Chandra X-ray and HST far-ultraviolet (FUV) observations of three early-F supergiants have shed new light on a previous puzzle involving a prominent member of the class: α Persei (HD 20902: F5 Ib). The warm supergiant is a moderately strong, hard coronal (T∼ {10}7 K) X-ray source, but has 10 times weaker “subcoronal” Si IV 1393 Å (T∼ 8× {10}4 K) emissions than early-G supergiants of similar high-energy properties. The α Per X-ray excess was speculatively ascribed to a close-in hyperactive G-dwarf companion, which could have escaped previous notice, lost in the glare of the bright star. However, a subsequent dedicated multi-wavelength imaging campaign failed to find any evidence for a resolved secondary. The origin of the α Per high-energy dichotomy then devolved to (1) an unresolved companion or (2) intrinsic coronal behavior. Exploring the second possibility, the present program has found that early-F supergiants do appear to belong to a distinct coronal class, characterized by elevated X-ray/FUV ratios, although sharing some similarities with Cepheid variables in their transitory X-ray “high states.” Remarkably, the early-F supergiants now are seen to align with the low-activity end of the X-ray/FUV sequence defined by late-type dwarfs, suggesting that the disjoint behavior relative to the G supergiants might be attributed to thinner outer atmospheres on the F types, as in dwarfs, but in this case perhaps caused by a weakened “ionization valve” effect due to overly warm photospheres. Title: Alpha Centauri Beyond the Crossroads Authors: Ayres, T. R. Bibcode: 2018RNAAS...2...17A Altcode: 2018RNAAS...2a..17A No abstract at ADS Title: Procyon: New Candidate for the Dynamo Clinical Trial Authors: Ayres, Thomas Bibcode: 2017hst..prop15327A Altcode: This is the third year of a joint Chandra/HST program to follow the evolution of the high-energy (X-ray and UV) activity cycles of the nearby mid-F subgiant Procyon. This bright star has high-energy attributes that are similar to the Sun, yet it is a hotter star, at the edge of the region in the H-R diagram where surface convection occurs (the power source for stellar magnetic activity). The HST part is to record STIS UV spectra of the bright star on a semiannual basis at high echelle resolution and high S/N, especially to capture the FUV Fe XII 124,134 nm coronal forbidden lines, which can tie together the non-simultaneous Chandra X-ray and HST pointings; as well as to record other key high-energy species like Si IV, C IV, and N V. The latter display Doppler-shifted, bimodal distorted emission profiles that signify high-powered dynamics in the interface regions of the stellar atmosphere between the super-hot corona (>1 MK) and the cold photosphere (<6000 K). The associated flows are a hot topic in contemporary solar physics, and one focus of a new space-based solar imaging spectrometer called IRIS. The solar and stellar FUV views are strongly complementary. The HST part of the program has two general objectives: (1) follow changes in the FUV spectra associated with any slowly evolving X-ray activity cycle of Procyon; and (2) combine the multiple epochs of echelle spectra to provide the highest possible S/N for identifying weak, but diagnostically important, emission lines (absorption, in some cases), and for decomposing the high-temperature line profiles (e.g., Si IV, C IV) into multiple dynamical components (which are though to be symptomatic of coronal heating and cooling processes). Title: Ecliptic-poles Stellar Survey (EclipSS) Authors: Ayres, Thomas Bibcode: 2017hst..prop15300A Altcode: BACKGROUND: Now and in coming years, a number of orbiting observatories will be scanning the skies for astrometry (Gaia), transiting exoplanets (TESS), and high-energy sources (eROSITA). A key characteristic of these surveys is their high degree of exposure in the ecliptic polar regions, north and south; a natural consequence of their preferred scanning orientation. Further, JWST, although not a scanning instrument, also holds the ecliptic poles in special regard because they are accessible at all times (continuous viewing zones), a key advantage for exo-planet studies.THIS PROPOSAL: Record FUV spectra, with COS G130M, of a well-defined sample of sunlike dwarfs (F2V-K2V) at the ecliptic poles to take advantage of the enhanced, wholistic information concerning rotation periods, sizes, masses, metallicities, ages, activity levels, and coronal properties that will be available for bright e-polar stars over the next few years. There is a sweet spot at about 8th magnitude where sunlike stars are not too bright for TESS, bright enough for eROSITA, and just right for COS. The G130M channel captures a wide range of ionization states, especially of Si, N, O, and C; the hydrogen Lyman-alpha emission; and also coronal forbidden transitions of Fe XII (124 nm) and Fe XXI (135 nm); altogether reflecting gas temperatures from 10,000 K to 10 MK in the magnetically disturbed stellar outer atmospheres. The combined photometric (starspots), asteroseismic, FUV, and X-ray measurements will inform community-wide efforts to explore stellar activity and its underlying magnetic machine, the Dynamo. This is a unique opportunity, and one - like a solar eclipse - too good to pass up. Title: The Initial C Isotope Ratio for the Solar System Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R. Bibcode: 2017LPICo1967.4186L Altcode: Using spectroscopic observations of CO in the solar photosphere, we have determined the 13C/12C ratio for the Sun, and therefore for the bulk initial solar system. The Sun is light in 13C by 50 permil compared to bulk Earth and marine carbonates. Title: The Carbon Isotope Composition of the Sun: Implications for Solar System Formation Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R. Bibcode: 2017LPICo1987.6370L Altcode: Following a new analysis of CO spectral lines in the solar photosphere, we have obtained a C isotope ratio of d13C = -48 ± 7‰ VPDB. Enrichment of terrestrial planets in 13C may have occurred due to CO self-shielding in the parent cloud. Title: VizieR Online Data Catalog: New FeI level energies from stellar spectra. II. (Peterson+, 2017) Authors: Peterson, R. C.; Kurucz, R. L.; Ayres, T. R. Bibcode: 2017yCat..22290023P Altcode: All of the new space-based UV spectra were obtained at a two-pixel resolution of 110000 with the E230H echelle grating of the Space Telescope Imaging Spectrograph (STIS) on HST, under program GO-14161 (R. Peterson, PI). See section 2 for further explanations.

(2 data files). Title: An abundance analysis from the STIS-HST UV spectrum of the non-magnetic Bp star HR 6000 Authors: Castelli, F.; Cowley, C. R.; Ayres, T. R.; Catanzaro, G.; Leone, F. Bibcode: 2017A&A...601A.119C Altcode: 2017arXiv170109172C Context. The sharp-line spectrum of the non-magnetic, main-sequence Bp star HR 6000 has peculiarities that distinguish it from those of the HgMn stars with which it is sometimes associated. The position of the star close to the center of the Lupus 3 molecular cloud, whose estimated age is on the order of 9.1 ± 2.1 Myr, has lead to the hypothesis that the anomalous peculiarities of HR 6000 can be explained by the young age of the star.
Aims: Observational material from the Hubble Space Telescope (HST) provides the opportunity to extend the abundance analysis previously performed for the optical region and clarify the properties of this remarkable peculiar star. Our aim was to obtain the atmospheric abundances for all the elements observed in a broad region from 1250 to 10 000 Å.
Methods: An LTE synthetic spectrum was compared with a high-resolution spectrum observed with the Space Telescope Imaging Spectrograph (STIS) equipment in the 1250-3040 Å interval. Abundances were changed until the synthetic spectrum fit the observed spectrum. The assumed model is an LTE, plane-parallel, line-blanketed ATLAS12 model already used for the abundance analysis of a high-resolution optical spectrum observed at ESO with the Ultraviolet and Visual Echelle Spectrograph (UVES). The stellar parameters are Teff = 13450 K, log g = 4.3, and zero microturbulent velocity.
Results: Abundances for 28 elements and 7 upper limits were derived from the ultraviolet spectrum. Adding results from previous work, we have now quantitative results for 37 elements, some of which show striking contrasts with those of a broad sample of HgMn stars. The analysis has pointed out numerous abundance anomalies, such as ionization anomalies and line-to-line variation in the derived abundances, in particular for silicon. The inferred discrepancies could be explained by non-LTE effects and with the occurrence of diffusion and vertical abundance stratification. In the framework of the last hypothesis, we obtained, by means of trial and error, empirical step functions of abundance versus optical depth log (τ5000) for carbon, nitrogen, silicon, manganese, and gold, while we failed to find such a function for phosphorous. The poor results for carbon, and mostly for phosphorus, suggest the possible importance in this star of NLTE effects to be investigated in future works. Title: New Fe I Level Energies and Line Identifications from Stellar Spectra. II. Initial Results from New Ultraviolet Spectra of Metal-poor Stars Authors: Peterson, Ruth C.; Kurucz, Robert L.; Ayres, Thomas R. Bibcode: 2017ApJS..229...23P Altcode: The Fe I spectrum is critical to many areas of astrophysics, yet many of the high-lying levels remain uncharacterized. To remedy this deficiency, Peterson & Kurucz identified Fe I lines in archival ultraviolet and optical spectra of metal-poor stars, whose warm temperatures favor moderate Fe I excitation. Sixty-five new levels were recovered, with 1500 detectable lines, including several bound levels in the ionization continuum of Fe I. Here, we extend the previous work by identifying 59 additional levels, with 1400 detectable lines, by incorporating new high-resolution UV spectra of warm metal-poor stars recently obtained by the Hubble Space Telescope Imaging Spectrograph. We provide gf values for these transitions, both computed as well as adjusted to fit the stellar spectra. We also expand our spectral calculations to the infrared, confirming three levels by matching high-quality spectra of the Sun and two cool stars in the H-band. The predicted gf values suggest that an additional 3700 Fe I lines should be detectable in existing solar infrared spectra. Extending the empirical line identification work to the infrared would help confirm additional Fe I levels, as would new high-resolution UV spectra of metal-poor turnoff stars below 1900 Å. Title: The Hubble Spectroscopic Legacy Archive Authors: Peeples, M.; Tumlinson, J.; Fox, A.; Aloisi, A.; Fleming, S.; Jedrzejewski, R.; Oliveira, C.; Ayres, T.; Danforth, C.; Keeney, B.; Jenkins, E. Bibcode: 2017cos..rept....4P Altcode: With no future space ultraviolet instruments currently planned, the data from the UV spectrographs aboard the Hubble Space Telescope have a legacy value beyond their initial science goals. The goal of the Hubble Spectroscopic Legacy Archive(HSLA) is to provide to the community new science-grade combined spectra for all publicly available data obtained by the Cosmic Origins Spectrograph (COS)and the Space Telescope Imaging Spectrograph (STIS). These data are packaged into "smart archives" according to target type and scientific themes to facilitate the construction of archival samples for common science uses. A new "quick look" capability makes the data easy for users to quickly access, assess the quality of,and download for archival science. The first generation of these products for the far-ultraviolet (FUV) modes of COS was made available online via the Mikulski Archive for Space Telescopes (MAST) in early 2016 and updated in early 2017; future releases will include COS/NUV and STIS/UV data. Title: Fundamental Physics from Observations of White Dwarf Stars Authors: Bainbridge, M. B.; Barstow, M. A.; Reindl, N.; Barrow, J. D.; Webb, J. K.; Hu, J.; Preval, S. P.; Holberg, J. B.; Nave, G.; Tchang-Brillet, L.; Ayres, T. R. Bibcode: 2017ASPC..509..375B Altcode: Variation in fundamental constants provide an important test of theories of grand unification. Potentially, white dwarf spectra allow us to directly observe variation in fundamental constants at locations of high gravitational potential. We study hot, metal polluted white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling and fundamental physics, in the search for variation in the fine structure constant. This registers as small

but measurable shifts in the observed wavelengths of highly ionized Fe and Ni lines when compared to laboratory wavelengths. Measurements of these shifts were

performed by Berengut et al (2013) using high-resolution STIS spectra of G191-B2B, demonstrating the validity of the method. We have extended this work by; (a)

using new (high precision) laboratory wavelengths, (b) refining the analysis methodology (incorporating robust techniques from previous studies towards

quasars), and (c) enlarging the sample of white dwarf spectra. A successful detection would be the first direct measurement of a gravitational field effect on

a bare constant of nature. We describe our approach and present preliminary results. Title: Probing the Gravitational Dependence of the Fine-Structure Constant from Observations of White Dwarf Stars Authors: Bainbridge, Matthew; Barstow, Martin; Reindl, Nicole; Tchang-Brillet, W. -Ü.; Ayres, Thomas; Webb, John; Barrow, John; Hu, Jiting; Holberg, Jay; Preval, Simon; Ubachs, Wim; Dzuba, Vladimir; Flambaum, Victor; Dumont, Vincent; Berengut, Julian Bibcode: 2017Univ....3...32B Altcode: 2017arXiv170201757B Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling and fundamental physics, in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths, (b) analysing a sample of objects, and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV. Title: A Closer Look at the Alpha Persei Coronal Conundrum Authors: Ayres, Thomas R. Bibcode: 2017ApJ...837...14A Altcode: 2017arXiv170201310A A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, the mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV) coronal-proxy Si IV unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multifaceted program tested that premise. Ground-based optical coronography and near-UV imaging with Hubble Space Telescope (HST) Wide-Field Camera 3 searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si IV emissions of α Per, in a deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as part of the joint program, are aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution—a well-separated companion—has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants. Title: The Carbon Isotope Composition of the Sun Authors: Lyons, J. R.; Gharib-Nezhad, E.; Ayres, T. R. Bibcode: 2017LPI....48.2309L Altcode: Analysis of CO spectral data for the solar photosphere shows that the Sun has d13C = -48 permil VPDB. The inner solar system is highly enriched in 13C. Title: Beyond the Coronal Graveyard Authors: Ayres, Thomas Bibcode: 2017cxo..prop.5283A Altcode: Iconic Arcturus is member of a populous class of low-mass red giants whose warm winds are a life-blood of Galactic ecology. How their mass outflows are powered has remained elusive. A solar-like coronal wind seemed unlikely, because the red giants have a very low incidence of high-energy detections. In fact, Arcturus, itself, is one of the weakest X-ray sources known among the bright cool stars. An intriguing possibility is that red giants do have significant magnetic activity and coronae, but mostly hidden beneath their puffy chromospheres. Unfortunately, the X-ray spectra that could test the "buried corona" conjecture are beyond reach of contemporary facilities. However, a new, robust X-ray detection of Arcturus would inform the next generation of high-energy observatories, whether such advanced measurements in fact would be feasible. Title: Alpha Centauri: Mind the Gap! Authors: Ayres, Thomas Bibcode: 2017cxo..prop.5281A Altcode: Cycle 19 proposal to continue long-term monitoring of coronal X-ray activity cycles of sunlike Alpha Centauri A (G2V) and B (K1V) was not approved. New Cycle 20 request will address panel's concerns. Even if Cycle 20 proposal is approved, still will be unpleasant gap in the semi-annual coverage, ongoing since 2005. Long-term HRC X-ray series on AlpCen is unique, fundamentally important: key contribution of Chandra to understanding cycling "Dynamos" of late-type stars, high scientific priority in solar-stellar physics. Although stellar cycles are known from CaII monitoring, X-rays contribute uniquely owing to 50X larger contrast at high-energies. A 5 ks pointing in mid-2018 would fill the gap. In fact, most recent AlpCen-A L_X (Ayres: 2018, RNAAS) shows a possible, unusual, rapid downturn, in the declining phase of its cycle (previous decline 2001-05 missed by lack of observations). Only Chandra can resolve AB at present. Title: HST/STIS Observations of the Local Interstellar Medium toward Very Nearby Stars: A Detailed Analysis of the a Centuari Sight Line Authors: Dann, Julian; Redfield, Seth; Ayres, Thomas R. Bibcode: 2017AAS...22934004D Altcode: The Local Interstellar Medium (LISM), a region extending about 100 parsecs and in which the Sun is currently immersed, can only be studied using UV/optical absorption features against bright background stars. Perhaps in the future in-situ measurements will be possible (e.g., the Voyager spacecraft or Breakthrough Starshot-style missions). Using high-resolution observations with the Space Telescope Imaging Spectrograph (STIS) on-board the Hubble Space Telescope (HST), we have analyzed several very nearby sight lines to measure physical properties of the LISM. The data used in this study is a part of the Advanced Spectral Library (ASTRAL) Project, an HST Large Treasury Project, in which we have analyzed the spectra of fourteen nearby stars. LISM absorption features in these stellar spectra reveal key information about the abundances, temperature, and turbulence in the intervening gas. We have fit ion transitions in the near-UV for MgII, FeII, CII, DI, SiII, and OII. These absorption features provide direct measurements of the radial velocity, Doppler broadening parameter, and the column density along the line of sight. The presence of multiple local minima in the deep and narrow ISM profile is evidence of multiple clouds moving at different radial velocities.Included in our data set is the a Centauri sight line. We provide a detailed analysis of these new observations and a comparison with previous HST observations that were observed more than 20 years ago. A discussion of the physical properties along this line of sight is provided within the context of a Breakthrough Starshot mission. These high resolution and high signal-to-noise spectra will be important for making accurate estimations of the interstellar environment to help inform such an interstellar mission.We would like to acknowledge NASA HST Grant GO-12278 and GO-13346 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555, and a student fellowship from the Connecticut Space Grant Consortium for their support of this research. Title: Alpha Centauri at a Crossroads Authors: Ayres, Tom Bibcode: 2017ChNew..24....1A Altcode: No abstract at ADS Title: A Multi-Observatory View of the Alpha Persei Coronal Conundrum Authors: Ayres, Thomas R. Bibcode: 2017AAS...22923902A Altcode: A ROSAT pointed survey of the Alpha Per open cluster in the 1990's detected its brightest star, mid-F supergiant α Persei, with an X-ray luminosity and spectral hardness similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot observation of α Per found far-ultraviolet (FUV) coronal-proxy emissions (specifically Si IV 1393 Å) unexpectedly weak. Together with a slight, but suspicious, offset of the ROSAT source, these anomalies raised the possibility that an unrecognized late-type companion might be responsible for the coronal X-rays. Recently, a multi-observatory program was carried out to test that premise; on the one hand to directly detect the putative companion, but on the other to better characterize the FUV spectrum of α Per in case it also was captured in X-rays. Initially, ground-based optical coronography from the Apache Point 3.5m, and later near-UV imaging with HST Wide Field Camera 3, searched for any close-in faint objects that plausibly could be significant X-ray emitters, but without success. Then, a Chandra pointing showed that the X-ray source is single and coincident with the bright star. In tandem, HST COS collected a much deeper FUV spectrum of α Per than the earlier brief SNAP. In hindsight, F supergiant Canopus (α Car: F0 Ib) also has a high X-ray luminosity and the same type of low Si IV/X-ray index as α Per. Significantly, the FUV Si IV emissions of both α Per and Canopus align well with the chromospheric atomic oxygen emissions (which must be intrinsic to the luminous stars), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. Ironically, the over-luminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an equally viable alternative is that both F supergiants are members of a novel class of X-ray emitters. Resolving the first possibility now has become more difficult, because the easy solution -- a well separated hyperactive companion -- has been eliminated; while testing the second will require a broader high-energy census of the early-F supergiant class. Title: The Fe Group Abundances in the B3 IV Standard ι Herculis Determined from ASTRAL II Observations Authors: Peters, Geraldine J.; Proffitt, Charles R.; Adelman, Saul J.; Ayres, Thomas R. Bibcode: 2017AAS...22915105P Altcode: Iota Herculis is an ultrasharp-lined B3 IV star that historically has been considered as an abundance standard for the early B stars. This star was one of the targets in the HST Treasury Program Advanced Spectral Library II: Hot Stars (ASTRAL II) that produced uninterrupted spectra of high to medium resolution in the region 1150-3100 Å. The abundances for the Fe group elements (Ti, V, Cr, Mn, Fe, Co, & Ni) in ι Her were determined mostly from STIS E140H and E230H (resolving power of 114,000) observations. Measurable lines from the Fe group, except for a very few multiplets of Fe II, III are not found in optical spectra. Whereas the light elements are delivered to the ISM by core-collapse supernovae (CCSNe), the Fe group elements are believed to come mostly from low/intermediate mass binaries containing white dwarfs that undergo SNe Ia explosions. A single SNe Ia can deliver 0.5 solar masses of pure Fe (and maybe Mn) to the ISM compared with about 0.07 solar masses from a CCSNe. The HST/STIS data were supplemented with optical spectra obtained at the Dominion Astrophysical Observatory (resolving power about 60,000). The abundance analysis was carried through with the NLTE code TLUSTY/SYNSPEC (Hubeny & Lanz, ApJ, 439,875,1995). The model parameters adopted for the ι Her are Teff = 17750 ± 250 K, log g = 3.75 ± 0.05 dex, Vturb = 0 km s-1, and v sin i = 5 km s-1. Solar abundances appear to prevail for the lighter elements but the abundances of Fe group elements are 0.3 - 0.7 dex below solar values determined by Grevesse et al. (2010, Ap&SpSci, 328, 179). It appears that ι Her was formed in a region our Galaxy mostly enriched by CCSNe.The authors appreciate support from STScI grants HST-GO-09848 and HST-GO-13346. SJA was a guest observer at DAO. Title: CO isotopologue ratios in the solar photosphere Authors: Lyons, James R.; Gharib-Nezhad, Ehsan; Ayres, Thomas R. Bibcode: 2016IAUFM..29A.307L Altcode: We re-evaluate the CO dipole moment function in order to obtain more accurate isotope ratios for the solar photosphere using previous infrared observations. We used a new set of dipole moments from HITEMP which were accurately determined by both semi-empirical and ab initio methods. Preliminary values of isotope ratios using the new dipole moments are in better agreement with the inferred photosphere values from Genesis, showing that the solar photosphere is isotopically similar to primitive inclusions in meteorites. Title: Cracking the Conundrum of F Supergiant Coronae Authors: Ayres, Thomas Bibcode: 2016cxo..prop.4856A Altcode: Mid-F supergiant Alpha Persei, of the eponymous young cluster, is a strong X-ray source given its minimal FUV emission, with a narrow-line FUV spectrum unlike other yellow supergiants. A slight positional offset in a ROSAT image suggested that a hyperactive companion might be responsible for the X-ray anomaly. However, a recent Chandra pointing found that the source in fact is coincident with Alpha Per. Further, the related supergiant Canopus also exhibits the same X-ray and FUV peculiarities, with a surprising connection to Cepheids in their FUV low states. New X-ray and FUV observations of additional F supergiants could help decide whether the coronal anomalies are due to unseen companions, or instead are a normal attribute of this exotic class, at the extreme edge of convection. Title: Cracking the Conundrum of F Supergiant Coronae Authors: Ayres, Thomas R. Bibcode: 2016hst..prop14848A Altcode: This is the HST part of a joint Chandra/HST program.

BACKGROUND: Mid-F supergiant Alpha Persei, of the eponymous young cluster, is a strong X-ray source, given its minimal FUV emission, with a narrow-line FUV spectrum unlike other yellow supergiants. A slight positional offset in a 1990's ROSAT image suggested that a hyperactive companion might be responsible for the X-ray anomaly. However, a recent Chandra pointing found that the source seen by ROSAT in fact is coincident with Alpha Per. Further, the related supergiant Canopus also exhibits the same X-ray and FUV peculiarities, with a surprising possible connection to Cepheid variables in their FUV low states.

THIS PROPOSAL: New X-ray and FUV observations of additional F supergiants could help decide whether the coronal anomalies of Alpha Per and Canopus are due to unseen (unresolved) hyperactive dwarf companions, or instead are a normal attribute of this exotic class, at the extreme edge of convection. This is a key missing piece in the unfolding narrative of hot (1-10 MK) stellar coronae. Title: Alpha Centauri at a Crossroads Authors: Ayres, Thomas R. Bibcode: 2016hst..prop14341A Altcode: Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized solar-like dwarf stars, which also have the best studied multi-MK coronal X-ray activity cycles, extending back to the 1970's. Objective is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual X-ray pointings in Chandra Cycles 16-18, as the system reaches a coronal crossroads: solar twin A rising toward starspot cycle maximum, K-type companion B sinking into a minimum. HST/STIS UV spectra will support and leverage the X-ray measurements by probing chromospheric and subcoronal dynamics, with connection to the corona through the FUV Fe XII 1242 forbidden line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen orbit also reaches a crossroads in 2016 (only 4" separation), and only HST/STIS can measure the bright Alpha Cen stars with sufficient UV spectral resultion and wavelength coherence. What's more, the recent validation of the STIS NDA,B,C long slits for echelle use now make feasible NUV E230H measurements (e.g., of key chromospheric tracers Mg II 2800 and Mg I 2852) which heretofore were not practical in a long-term program of this nature. Title: A Study of the Elements Copper through Uranium in Sirius A: Contributions from STIS and Ground-Based Spectra Authors: Cowley, C. R.; Ayres, T. R.; Castelli, F.; Gulliver, A. F.; Monier, R.; Wahlgren, G. M. Bibcode: 2016ApJ...826..158C Altcode: 2016arXiv160508399C We determine abundances or upper limits for all of the 55 stable elements from copper to uranium for the A1 Vm star Sirius. The purpose of the study is to assemble the most complete picture of elemental abundances with the hope of revealing the chemical history of the brightest star in the sky, apart from the Sun. We also explore the relationship of this hot metallic-line (Am) star to its cooler congeners, as well as the hotter, weakly- or non-magnetic Mercury-manganese (HgMn) stars. Our primary observational material consists of Hubble Space Telescope (HST) spectra taken with the Space Telescope Imaging Spectrograph in the ASTRAL project. We have also used archival material from the COPERNICUS satellite, and from the HST Goddard High-Resolution Spectrograph, as well as ground-based spectra from Furenlid, Westin, Kurucz, Wahlgren, and their coworkers, ESO spectra from the UVESPOP project, and NARVAL spectra retrieved from PolarBase. Our analysis has been primarily by spectral synthesis, and in this work we have had the great advantage of extensive atomic data unavailable to earlier workers. We find most abundances as well as upper limits range from 10 to 100 times above solar values. We see no indication of the huge abundance excesses of 1000 or more that occur among many chemically peculiar stars of the upper main sequence. The picture of Sirius as a hot Am star is reinforced. Title: The Carbon Isotope Composition of the Solar Photosphere Authors: Lyons, J. R.; Gharib Nezhad, E.; Ayres, T. R. Bibcode: 2016LPICo1921.6544L Altcode: We have reanalyzed infrared CO absorption line data of the solar photosphere. We obtain d18O = -51 ± 11‰l VSMOW, consistent with the inferred Genesis value. For carbon we find d13C = -48 ± 7‰l VPDB, lighter than previously reported. Title: The Cold Heart Of The Solar Chromosphere Authors: Ayres, Thomas Bibcode: 2016csss.confE..92A Altcode: A power-point presentation describing potential impact of ALMA on probing cold gas in the solar chromosphere. Title: The Dynamo Clinical Trial Authors: Ayres, Thomas Bibcode: 2016csss.confE..93A Altcode: Poster concerning the coronal activity cycles of Alpha Centauri A and B, the nearest sun-like stars, as observed by several generations of X-ray observatories including ROSAT, XMM-Newton, and most recently Chandra. Title: Assessing the dependency of the fine structure constant on gravity using hot DA white dwarfs Authors: Barstow, Martin; Ayres, Thomas R.; Bainbridge, Matthew; Barrow, John; Berengut, Julian Carlo; Burleigh, Matthew; Casewell, Sarah; Dapra, Mario; Dougan, Darren; Dumont, Vincent; Dzuba, Vladimir; Flambaum, Victor; HU, Jiting; Holberg, Jay B.; Joyce, Simon; Nave, Gillian; Preval, Simon Paul; Reindl, Nicole; Salumbides, Edcel; Ubachs, Wim; Webb, John K. Bibcode: 2016hst..prop14791B Altcode: Variation of fundamental constants is a common theme of many theories of quantum gravity and Grand Unification. Using spectra obtained with the Hubble Space Telescope, it has been shown by Berengut et al. (2013), and Bagdonaite et al. (2014), that it is possible to place strong constraints on gravitational variations of the fine structure constant (alpha), and the proton to electron mass ratio (mu) in white dwarf stars.

As part of the UV initiative, we propose to observe four hot DA white dwarf stars using STIS with the E140H grating, totalling 12 orbits. These four stars have been chosen so as to have a wide range of masses, allowing a full exploration of the compactness parameter space (M/R). We will measure several absorption features of Fe V and Ni V, and extract any potential variation in alpha in a manner similar to Berengut et al. (2013).

This proposal will be a significant advance in the effort to detect gravitational variations in alpha. A confirmed detection of alpha variation would have extensive consequences for fundamental physics, cosmology, and would also signal the breakdown of Einstein's Equivalence principle, and hence, general relativity. Furthermore, a null detection would also allow strong limits to be placed on any potential alpha variation in a strong gravitational field. Title: Procyon: New Candidate for the Dynamo Clinical Trial Authors: Ayres, Thomas R. Bibcode: 2016hst..prop14789A Altcode: This is the second year of a joint Chandra/HST program to follow the evolution of the high-energy (X-ray and UV) activity cycles of the nearby mid-F subgiant Procyon. This bright star has high-energy attributes that are similar to the Sun, yet it is a hotter star, at the edge of the region in the H-R diagram where surface convection occurs (the power source for stellar magnetic activity). The HST part is to record STIS UV spectra of the bright star on a semi-annual basis at high echelle resolution and high S/N, especially to capture the FUV Fe XII 124,134 nm coronal forbidden lines, which can tie together the non-simultaneous Chandra X-ray and HST pointings; as well as to record other key high-energy species like Si IV, C IV, and N V. The latter display Doppler-shifted, bimodal distorted emission profiles that signify high-powered dynamics in the interface regions of the stellar atmosphere between the super-hot corona (>1 MK) and the cold photosphere (<6000 K). The associated flows are a hot topic in contemporary solar physics, and one focus of a new space-based solar imaging spectrometer called IRIS. The solar and stellar FUV views are strongly complementary. The HST part of the program has two general objectives: (1) follow changes in the FUV spectra associated with any slowly evolving X-ray activity cycle of Procyon; and (2) combine the multiple epochs of echelle spectra to provide the highest possible S/N for identifying weak, but diagnostically important, emission lines (absorption, in some cases), and for decomposing the high-temperature line profiles (e.g., Si IV, C IV) into multiple dynamical components (which are though to be symptomatic of coronal heating and cooling processes). Title: Alpha Centauri at a Crossroads Authors: Ayres, Thomas R. Bibcode: 2016hst..prop14788A Altcode: Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized solar-like dwarf stars, which also have the best studied multi-MK coronal X-ray activity cycles, extending back to the 1970's. Objective is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual X-ray pointings in Chandra Cycles 16-18, as the system reaches a coronal crossroads: solar twin A rising toward starspot cycle maximum, K-type companion B sinking into a minimum. HST/STIS UV spectra will support and leverage the X-ray measurements by probing chromospheric and subcoronal dynamics, with connection to the corona through the FUV Fe XII 1242 forbidden line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen orbit also reaches a crossroads in 2016 (only 4" separation), and only HST/STIS can measure the bright Alpha Cen stars with sufficient UV spectral resolution and wavelength coherence. What's more, the recent validation of the STIS NDA,B,C long slits for echelle use now make feasible NUV E230H measurements (e.g., of key chromospheric tracers Mg II 2800 and Mg I 2852) which heretofore were not practical in a long-term program of this nature. Title: Solar Science with the Atacama Large Millimeter/Submillimeter Array—A New View of Our Sun Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu, B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin, P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz, A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.; Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary, D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.; Selhorst, C. L.; Barta, M. Bibcode: 2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases. Title: The Dynamo Clinical Trial Authors: Ayres, Thomas R. Bibcode: 2016HEAD...1511703A Altcode: The Dynamo Clinical Trial evaluates long-term stellar magnetic health through periodic X-ray examinations (by the Chandra Observatory). So far, there are only three subjects enrolled in the DTC: Alpha Centauri A (a solar-like G dwarf), Alpha Cen B (an early K dwarf, more active than the Sun), and Alpha Canis Majoris A (Procyon, a mid-F subgiant similar in activity to the Sun). Of these, Procyon is a new candidate, so it is too early to judge how it will fare. Of the other two, Alpha Cen B has responded well, with a steady magnetic heartbeat of about 8 years duration. The sickest of the bunch, Alpha Cen A, was in magnetic cardiac arrest during 2005-2010, but has begun responding to treatment in recent years, and seems to be successfully cycling again, perhaps achieving a new peak of magnetic health in the 2016 time frame. If this is the case, it has been 20 years since A's last healthful peak, significantly longer than the middle-aged Sun's 11-year magnetic heartbeat, but perhaps in line with Alpha Cen A's more senescent state (in terms of "relative evolutionary age," apparently an important driver of activity). (By the way, don't miss the exciting movie of the Alpha Cen stars' 20-year X-ray dance.) Title: Division G Commission 36: Theory of Stellar Atmospheres Authors: Puls, Joachim; Hubeny, Ivan; Asplund, Martin; Allard, France; Allende Prieto, Carlos; Ayres, Thomas R.; Carlsson, Mats; Gustafsson, Bengt; Kudritzki, Rolf-Peter; Ryabchikova, Tatiana A. Bibcode: 2016IAUTA..29..453P Altcode: Different from previous triennial reports, this report covers the activities of IAU Commission 36 `Theory of Stellar Atmospheres' over the past six years†, and will be the last report from the `old' Commission 36. After the General Assembly in Honolulu (August 2015), a new Commission `Stellar and Planetary Atmospheres' (C.G5, under Division G, `Stars and Stellar Physics') has come into life, and will continue our work devoted to the outer envelopes of stars, as well as extend it to the atmospheres of planets (see Sect. 4). Title: The Oxygen Isotope Composition of the Solar Photosphere Determined from CO Observations Authors: Lyons, J. R.; Gharib Nezhad, E.; Ayres, T. R. Bibcode: 2016LPI....47.2509L Altcode: A new analysis of observations of CO in the solar photosphere yields delta18O = -50±11‰, consistent with the Genesis inferred value from solar wind. Title: The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) Sounding Rocket Investigation Authors: Laurent, Glenn T.; Hassler, Donald M.; Deforest, Craig; Slater, David D.; Thomas, Roger J.; Ayres, Thomas; Davis, Michael; de Pontieu, Bart; Diller, Jed; Graham, Roy; Michaelis, Harald; Schuele, Udo; Warren, Harry Bibcode: 2016JAI.....540006L Altcode: We present a summary of the solar observing Rapid Acquisition Imaging Spectrograph Experiment (RAISE) sounding rocket program including an overview of the design and calibration of the instrument, flight performance, and preliminary chromospheric results from the successful November 2014 launch of the RAISE instrument. The RAISE sounding rocket payload is the fastest scanning-slit solar ultraviolet imaging spectrograph flown to date. RAISE is designed to observe the dynamics and heating of the solar chromosphere and corona on time scales as short as 100-200ms, with arcsecond spatial resolution and a velocity sensitivity of 1-2km/s. Two full spectral passbands over the same one-dimensional spatial field are recorded simultaneously with no scanning of the detectors or grating. The two different spectral bands (first-order 1205-1251Å and 1524-1569Å) are imaged onto two intensified Active Pixel Sensor (APS) detectors whose focal planes are individually adjusted for optimized performance. RAISE reads out the full field of both detectors at 5-10Hz, recording up to 1800 complete spectra (per detector) in a single 6-min rocket flight. This opens up a new domain of high time resolution spectral imaging and spectroscopy. RAISE is designed to observe small-scale multithermal dynamics in Active Region (AR) and quiet Sun loops, identify the strength, spectrum and location of high frequency waves in the solar atmosphere, and determine the nature of energy release in the chromospheric network. Title: FK Comae Berenices, King of Spin: The COCOA-PUFS Project Authors: Ayres, Thomas R.; Kashyap, V.; Saar, S.; Huenemoerder, D.; Korhonen, H.; Drake, J. J.; Testa, P.; Cohen, O.; Garraffo, C.; Granzer, T.; Strassmeier, K. Bibcode: 2016ApJS..223....5A Altcode: 2016arXiv160103305A COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast spinning, heavily spotted, yellow giant FK Comae Berenices (FK Com: HD117555; G4 III). This single star is thought to be a recent binary merger, and is exceptionally active by measure of its intense ultraviolet (UV) and X-ray emissions, and proclivity to flare. COCOA-PUFS was carried out with the Hubble Space Telescope in the UV (1200-3000 Å), using mainly its high-performance Cosmic Origins Spectrograph, but also high precision Space Telescope Imaging Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy Transmission Grating Spectrometer; together with supporting photometry and spectropolarimetry in the visible from the ground. This is an introductory report on the project. FK Com displayed variability on a wide range of timescales over all wavelengths during the week-long main campaign, including a large X-ray flare; “super-rotational broadening” of the far-ultraviolet “hot lines” (e.g., Si IV 1393 Å 8 × 104 K) together with chromospheric Mg II 2800 Å and C II 1335 Å (1-3 × 104 K); large Doppler swings suggestive of bright regions alternately on advancing and retreating limbs of the star; and substantial redshifts of the epoch-average emission profiles. These behaviors paint a picture of a highly extended, dynamic, hot (∼10 MK) coronal magnetosphere around the star, threaded by cooler structures perhaps analogous to solar prominences and replenished continually by surface activity and flares. Suppression of angular momentum loss by the confining magnetosphere could temporarily postpone the inevitable stellar spindown, thereby lengthening this highly volatile stage of coronal evolution.

COordinated Campaign of Observations and Analysis, Photosphere to Upper Atmosphere, of a Fast-rotating Star. Title: The High-Energy Environs of the Anomalous Coronal Source Alpha Persei Authors: Ayres, Thomas R. Bibcode: 2016hst..prop14349A Altcode: This is a joint Chandra/HST program to investigate the F-type supergiant Alpha Persei, brightest star in the young (50 Myr) open cluster that bears its name. The central question is whether the bright ROSAT X-ray source identified as Alpha Per truly is associated with the supergiant (which would make it quite an anomalous object in its class), or instead is due to a low-mass coronally active cluster member in the immediate vicinity of Alpha Per, but which has escaped detection owing to the glare of the very bright star nearby. In fact, the ROSAT LX is similar to that of active G dwarfs in the young cluster, and the X-ray source appears to be shifted slightly from the optical position of the bright star. Furthermore, a brief COS SNAPshot FUV spectrum of Alpha Per appeared to lack significant high-energy features (e.g., Si IV 140 nm) expected from a powerful X-ray source, although the bright FUV photospheric continuum of the warm supergiant was a major source of interference. The observational objectives of the HST part of the program are: (1) image the field with WFC3 to pin down positions of any faint, low-mass stars in the immediate vicinity of the supergiant (chromospherically active dwarfs have a large contrast advantage, for example, at Mg II 280 nm); and (2) take a deeper COS FUV spectrum than was possible in the Cycle 17 SNAPshot program, including the important Lyman Alpha region, which was forbidden in the SNAP program owing to safety issues. We now know that the Lyman Alpha observation would be safe, and access to the G130M side-B spectrum would capture key "hot lines" like N V 124 nm, where the FUV continuum is weaker, to help characterize the activity levels of the iconic supergiant. Title: Ultraviolet emission lines of Si II in cool star and solar spectra Authors: Laha, Sibasish; Keenan, Francis P.; Ferland, Gary J.; Ramsbottom, Catherine A.; Aggarwal, Kanti M.; Ayres, Thomas R.; Chatzikos, Marios; van Hoof, Peter A. M.; Williams, Robin J. R. Bibcode: 2016MNRAS.455.3405L Altcode: 2015arXiv151008755L Recent atomic physics calculations for Si II are employed within the CLOUDY modelling code to analyse Hubble Space Telescope (HST) STIS ultraviolet spectra of three cool stars, β Geminorum, α Centauri A and B, as well as previously published HST/GHRS observations of α Tau, plus solar quiet Sun data from the High Resolution Telescope and Spectrograph. Discrepancies found previously between theory and observation for line intensity ratios involving the 3s23p 2PJ-3s3p2 4P_{J^' }} intercombination multiplet of Si II at ∼ 2335 Å are significantly reduced, as are those for ratios containing the 3s23p 2PJ-3s3p2 2D_{J^' }} transitions at ∼1816 Å. This is primarily due to the effect of the new Si II transition probabilities. However, these atomic data are not only very different from previous calculations, but also show large disagreements with measurements, specifically those of Calamai et al. for the intercombination lines. New measurements of transition probabilities for Si II are hence urgently required to confirm (or otherwise) the accuracy of the recently calculated values. If the new calculations are confirmed, then a long-standing discrepancy between theory and observation will have finally been resolved. However, if the older measurements are found to be correct, then the agreement between theory and observation is simply a coincidence and the existing discrepancies remain. Title: ALMA Observations of the Sun in Cycle 4 and Beyond Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.; Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.; Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson, M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.; Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov, V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões, P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig, A.; White, S.; Yagoubov, P.; Zaqarashvili, T. Bibcode: 2016arXiv160100587W Altcode: This document was created by the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) in preparation of the first regular observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The science cases presented here demonstrate that a large number of scientifically highly interesting observations could be made already with the still limited solar observing modes foreseen for Cycle 4 and that ALMA has the potential to make important contributions to answering long-standing scientific questions in solar physics. With the proposal deadline for ALMA Cycle 4 in April 2016 and the Commissioning and Science Verification campaign in December 2015 in sight, several of the SSALMON Expert Teams composed strategic documents in which they outlined potential solar observations that could be feasible given the anticipated technical capabilities in Cycle 4. These documents have been combined and supplemented with an analysis, resulting in recommendations for solar observing with ALMA in Cycle 4. In addition, the detailed science cases also demonstrate the scientific priorities of the solar physics community and which capabilities are wanted for the next observing cycles. The work on this White Paper effort was coordinated in close cooperation with the two international solar ALMA development studies led by T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be further updated until the beginning of Cycle 4 in October 2016. In particular, we plan to adjust the technical capabilities of the solar observing modes once finally decided and to further demonstrate the feasibility and scientific potential of the included science cases by means of numerical simulations of the solar atmosphere and corresponding simulated ALMA observations. Title: The Hubble Spectroscopic Legacy Archive Authors: Peeples, Molly S.; Tumlinson, Jason; Fox, Andrew; Aloisi, Alessandra; Ayres, Thomas R.; Danforth, Charles; Fleming, Scott W.; Jenkins, Edward B.; Jedrzejewski, Robert I.; Keeney, Brian A.; Oliveira, Cristina M. Bibcode: 2016AAS...22744401P Altcode: With no future space ultraviolet instruments currently planned, the data from the UV spectrographs aboard the Hubble Space Telescope have a legacy value beyond their initial science goals. The Hubble Spectroscopic Legacy Archive will provide to the community new science-grade combined spectra for all publicly available data obtained by the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS). These data will be packaged into "smart archives" according to target type and scientific themes to facilitate the construction of archival samples for common science uses. A new "quick look" capability will make the data easy for users to quickly access, assess the quality of, and download for archival science starting in Cycle 24, with the first generation of these products for the FUV modes of COS available online via MAST in early 2016. Title: The Ultraviolet Spectroscopic Legacy of HST Authors: Ayres, Thomas R. Bibcode: 2016AAS...22722206A Altcode: Hubble Space Telescope has been a spectacularly successful platform for spectroscopy in the diagnostic-rich far-ultraviolet (FUV: 120-170 nm) and near-ultraviolet (NUV: 170-310 nm) regions. HST has hosted four generations of UV instruments, beginning with Faint Object Spectrograph (FOS) and Goddard High-Resolution Spectrograph (GHRS) in the original 1990 payload, followed by Space Telescope Imaging Spectrograph (STIS) in 1997, and more recently Cosmic Origins Spectrograph (COS) as part of Servicing Mission 4 in 2009. The latter two instruments have contributed by far the lion's share of HST's spectroscopic archive: STIS, because of its longevity (thirteen years in operation so far, although with a hiatus between 2004-2009); and COS because of its high sensitivity, which allows efficient observations, and thus many more targets in a typical GO program. STIS benefits from a compact echelle design, and the sharp stable imaging of HST, to provide high-resolution (3-7 km s-1) spectra of bright objects, including stars, nebulae, quasars, novae, and so forth. COS achieves astounding sensitivity in the FUV by a sophisticated design that compensates for the spherical abberation of HST's primary mirror, disperses the target's light, and focuses the spectral image all with just a single optical element. While the spectral resolution of COS (about 18 km s-1) is not as high as that of STIS, it is adequate for diverse investigations, including faint broad-lined AGN at the edge of the Universe, hot stars in nearby galaxies, and magnetically active planet-hosting red dwarfs in the solar neighborhood. Thanks in part to the "UV Initiative" in recent HST proposal cycles, there have been several large efforts involving both STIS and COS, to assemble important spectral collections, including full UV atlases of representative hot and cool stars at high resolution with STIS; long time series of archetype AGN ("reverberation mapping") with COS; and hundreds of sightlines to distant quasars to probe the Cosmic Web, also with COS. Altogether, these diverse spectral observations constitute one of the key legacies of HST, and hopefully one that will continue to be built upon in the coming years. Title: Scientific problems addressed by the Spektr-UV space project (world space Observatory—Ultraviolet) Authors: Boyarchuk, A. A.; Shustov, B. M.; Savanov, I. S.; Sachkov, M. E.; Bisikalo, D. V.; Mashonkina, L. I.; Wiebe, D. Z.; Shematovich, V. I.; Shchekinov, Yu. A.; Ryabchikova, T. A.; Chugai, N. N.; Ivanov, P. B.; Voshchinnikov, N. V.; Gomez de Castro, A. I.; Lamzin, S. A.; Piskunov, N.; Ayres, T.; Strassmeier, K. G.; Jeffrey, S.; Zwintz, S. K.; Shulyak, D.; Gérard, J. -C.; Hubert, B.; Fossati, L.; Lammer, H.; Werner, K.; Zhilkin, A. G.; Kaigorodov, P. V.; Sichevskii, S. G.; Ustamuich, S.; Kanev, E. N.; Kil'pio, E. Yu. Bibcode: 2016ARep...60....1B Altcode: The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory—Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115-310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems. Title: SSALMON - The Solar Simulations for the Atacama Large Millimeter Observatory Network Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Barta, M.; Hudson, H.; Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E.; De Pontieu, B.; Tiwari, S.; Kato, Y.; Soler, R.; Yagoubov, P.; Black, J. H.; Antolin, P.; Gunár, S.; Labrosse, N.; Benz, A. O.; Nindos, A.; Steffen, M.; Scullion, E.; Doyle, J. G.; Zaqarashvili, T.; Hanslmeier, A.; Nakariakov, V. M.; Heinzel, P.; Ayres, T.; Karlicky, M. Bibcode: 2015AdSpR..56.2679W Altcode: 2015arXiv150205601W The Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) was initiated in 2014 in connection with two ALMA development studies. The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful new tool, which can also observe the Sun at high spatial, temporal, and spectral resolution. The international SSALMONetwork aims at co-ordinating the further development of solar observing modes for ALMA and at promoting scientific opportunities for solar physics with particular focus on numerical simulations, which can provide important constraints for the observing modes and can aid the interpretation of future observations. The radiation detected by ALMA originates mostly in the solar chromosphere - a complex and dynamic layer between the photosphere and corona, which plays an important role in the transport of energy and matter and the heating of the outer layers of the solar atmosphere. Potential targets include active regions, prominences, quiet Sun regions, flares. Here, we give a brief overview over the network and potential science cases for future solar observations with ALMA. Title: The Intersection of Atomic Physics and Astrophysics: Identifying UV Fe I Lines from Metal-Poor Turnoff Stars Authors: Peterson, Ruth C.; Ayres, Thomas R.; Kurucz, Robert L. Bibcode: 2015hst..prop14161P Altcode: Observational surveys are expanding, recording ever-fainter sources from the ultraviolet to the infrared. Needed to characterize them are observational ultraviolet templates at high spectral resolution and low metallicity for the oldest populations, and the laboratory astrophysics data essential to model objects such as stars and nebulae at all ages, metallicities, and redshifts.

We address this by proposing to complete the high-resolution UV spectral coverage of four key metal-poor turnoff stars. These are ideal as metal-poor templates of old stars and as the "laboratory source" for the identification of the thousands of lines of neutral iron that appear in stellar spectra, but are absent from or not identified in laboratory spectra. By matching existing stellar spectra to calculations of energy levels, line wavelengths, and gf-values, Peterson & Kurucz (2015) identified 66 Fe I levels with energies up to 8.4eV, yielding 2000 new lines from 1600 Angstroms to 5.4 microns, and empirical gf-values for 640 of these. The proposed work should yield ~500 new levels and ~10,000 new Fe I lines.

The new energy levels and line parameters also will be posted on the Kurucz website. The new spectra, and supporting theoretical calculations, will be integrated into the publicly available HST Advanced Spectral Library (ASTRAL) Treasury Project. This will leverage the utility of these archival spectral templates and atlases in such diverse areas as nucleosynthesis at early epochs, infrared analysis of dust-obscured giants, reconstructing the populations of nearby globular clusters and dwarf galaxies from their integrated light, and deriving age and metallicity for old, distant galaxies. Title: Procyon: New Candidate for the Dynamo Clinical Trial Authors: Ayres, Thomas R. Bibcode: 2015hst..prop14350A Altcode: This is the first year of a joint Chandra/HST program to follow the evolution of the high-energy (X-ray and UV) activity cycles of the nearby mid-F subgiant Procyon. This bright star has high-energy attributes that are similar to the Sun, yet it is a hotter star, at the edge of the region in the H-R diagram where surface convection occurs (the power source for stellar magnetic activity). The HST part is to record STIS UV spectra of the bright star on a semi-annual basis at high echelle resolution and high S/N, especially to capture the FUV Fe XII 124,134 nm coronal forbidden lines, which can tie together the non-simultaneous Chandra X-ray and HST pointings; as well as to record other key high-energy species like Si IV, C IV, and N V. The latter display Doppler-shifted, bimodal distorted emission profiles that signify high-powered dynamics in the interface regions of the stellar atmosphere between the super-hot corona (>1 MK) and the cold photosphere (<6000 K). The associated flows are a hot topic in contemporary solar physics, and one focus of a new space-based solar imaging spectrometer called IRIS. The solar and stellar FUV views are strongly complementary. The HST part of the program has two general objectives: (1) follow changes in the FUV spectra associated with any slowly evolving X-ray activity cycle of Procyon; and (2) combine the multiple epochs of echelle spectra to provide the highest possible S/N for identifying weak, but diagnostically important, emission lines (absorption, in some cases), and for decomposing the high-temperature line profiles (e.g., Si IV, C IV) into multiple dynamical components (which are though to be symptomatic of coronal heating and cooling processes). Title: CxO (x=16,17,18) isotopologue ratios in the solar photosphere Authors: Lyons, James; Gharib-Nezhad, Ehsan; Ayres, Thomas Bibcode: 2015DPS....4750709L Altcode: Determination of the oxygen isotope ratios in the solar photosphere is essential to constraining the formation environment of the solar system. The solar CO fundamental and first-overtone bands were previously measured by the shuttle-borne ATMOS Fourier transform spectrometer (FTS), and with the National Solar Observatory FTS on the McMath-Pierce telescope at Kitt Peak. Analyzing the rovibrational bands from these photospheric spectra, a 3D convection model was employed to calculate ratios with improved uncertainties (16O/17O=2738±118 and 16O/18O =511±10 Ayres et al. 2013), which fall between the terrestrial values and those inferred from solar wind measurements by the Genesis spacecraft. However, differences in published CO dipole moment functions yielded a range of isotopic ratios spanning ~ 3 % in δ18O. Here we re-evaluate the CO dipole moment function in order to obtain more accurate isotope ratios for the photosphere. We used a new set of dipole moments from HITEMP which were accurately determined by both semi-empirical and ab initio methods. Preliminary values of isotope ratios using the new dipole moments are in better agreement with the inferred photosphere values from Genesis, showing that the solar photosphere is isotopically similar to primitive inclusions in meteorites, but different from the terrestrial planets by ~ 6 %. New spectral observations are needed to reduce uncertainties in photospheric C17O abundances. Title: The High-Energy Environs of the Anomalous Coronal Source Alpha Persei Authors: Ayres, Thomas Bibcode: 2015hst..prop14349A Altcode: This is a joint Chandra/HST program to investigate the F-type supergiant Alpha Persei, brightest star in the young (50 Myr) open cluster that bears its name. The central question is whether the bright ROSAT X-ray source identified as Alpha Per truly is associated with the supergiant (which would make it quite an anomalous object in its class), or instead is due to a low-mass coronally active cluster member in the immediate vicinity of Alpha Per, but which has escaped detection owing to the glare of the very bright star nearby. In fact, the ROSAT LX is similar to that of active G dwarfs in the young cluster, and the X-ray source appears to be shifted slightly from the optical position of the bright star. Furthermore, a brief COS SNAPshot FUV spectrum of Alpha Per appeared to lack significant high-energy features (e.g., Si IV 140 nm) expected from a powerful X-ray source, although the bright FUV photospheric continuum of the warm supergiant was a major source of interference. The observational objectives of the HST part of the program are: (1) image the field with WFC3 to pin down positions of any faint, low-mass stars in the immediate vicinity of the supergiant (chromospherically active dwarfs have a large contrast advantage, for example, at Mg II 280 nm); and (2) take a deeper COS FUV spectrum than was possible in the Cycle 17 SNAPshot program, including the important Lyman Alpha region, which was forbidden in the SNAP program owing to safety issues. We now know that the Lyman Alpha observation would be safe, and access to the G130M side-B spectrum would capture key hot lines like N V 124 nm, where the FUV continuum is weaker, to help characterize the activity levels of the iconic supergiant. Title: Alpha Centauri at a Crossroads Authors: Ayres, Thomas Bibcode: 2015hst..prop14341A Altcode: Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized solar-like dwarf stars, which also have the best studied multi-MK coronal X-ray activity cycles, extending back to the 1970's. Objective is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual X-ray pointings in Chandra Cycles 16-18, as the system reaches a coronal crossroads: solar twin A rising toward starspot cycle maximum, K-type companion B sinking into a minimum. HST/STIS UV spectra will support and leverage the X-ray measurements by probing chromospheric and subcoronal dynamics, with connection to the corona through the FUV Fe XII 1242 forbidden line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen orbit also reaches a crossroads in 2016 (only 4 separation), and only HST/STIS can measure the bright Alpha Cen stars with sufficient UV spectral resultion and wavelength coherence. What's more, the recent validation of the STIS NDA,B,C long slits for echelle use now make feasible NUV E230H measurements (e.g., of key chromospheric tracers Mg II 2800 and Mg I 2852) which heretofore were not practical in a long-term program of this nature. Title: Procyon: A New Candidate for the Dynamo Clinical Trial Authors: Ayres, Thomas Bibcode: 2015cxo..prop.4728A Altcode: Procyon (Alp CMi; F5IV-V) is a bright, nearby subgiant; similar in X-ray emission to the Sun, but very different in mass, luminosity, and evolutionary status. Historical Mt Wilson CaII monitoring was inconclusive whether Procyon has a solar-like 11-yr magnetic cycle, or instead is a "flat-activity" star, as might be guessed from its late-MS-age. However, CaII is a poor magnetic proxy for F-types owing to low spectral contrast. X-rays are better. In fact, Procyon - with some X-ray/UV attention over the past two decades - is an excellent candidate for the ongoing "Dynamo Clinical Trial" sponsored by Chandra, XMM, and HST; ultimately to provide a "calibration" of novel theoretical models that seek to couple the inside Dynamo with the outside corona. Title: The High-Energy Environs of the Anomalous Coronal Source Alpha Persei Authors: Ayres, Thomas Bibcode: 2015cxo..prop.4590A Altcode: Alpha Persei (F5Ib) is brightest member of the eponymous young (50 Myr) cluster, and strong ROSAT source. Paradoxically, HST/COS found only weak FUV emissions, far out of line with the X-rays. Young clusters are teeming with active low-mass stars, so the "Alpha Per" source might be an unrelated object. Alternately, the anomaly might be genuine, signaling a novel pathway for coronal activity. Objectives: (1) image with HRC-I to obtain definitive detections of Alpha Per and any close-by sources; (2) extend earlier COS SNAPshot to capture crucial diagnostic spectra at shorter wavelengths; (3) image with WFC3 to characterize any active stars in Alp Per's neighborhood. F supergiants lie at the edge of convection; keystones for testing theories of coronal activity. Title: The Hubble Space Telescope Advanced Spectral Library Project Authors: Ayres, Thomas Bibcode: 2015IAUGA..2244967A Altcode: Advanced Spectral Library (ASTRAL) is a Hubble Large Treasury Project, whose aim is to collect high-quality ultraviolet (1150-3100 Å) spectra of bright stars, utilizing the echelle modes of powerful Space Telescope Imaging Spectrograph; with resolution and signal-to-noise rivaling the best that can be achieved at ground-based observatories in the visible. During HST Cycle 18 (2010-2011), ASTRAL was allocated 146 orbits to record eight representative late-type ("cool") stars, including well-known cosmic denizens like Procyon and Betelgeuse. In Cycle 21 (2013-2014), ASTRAL was awarded an additional 230 orbits to extend the project to the hot side of the H-R diagram: 21 targets covering the O-A spectral types, including household favorites Vega and Sirius. The second part of the program was completed in January 2015. I describe the scientific motivations for observing hot and cool stars in the UV; the unique instrumental characteristics of STIS that enabled a broad survey like ASTRAL; progress in the program to date; and prospects for the future. Title: The abundance pattern of heavy elements in Sirius: Impact of modern observations (STIS) and improved Atomic data Authors: Ramsay Cowley, Charles; Ayres, Thomas; Wahlgren, Glenn; Carpenter, Kenneth Bibcode: 2015IAUGA..2236931R Altcode: The abundance pattern of heavy elements in Sirius: Impact of modern observations (STIS) and improved atomic data. We determine abundances or upper limits for the 55 stable elements from copper to uranium for the A1 Vm star Sirius. The primary observational material consists of Hubble Space Telescope (HST) spectra taken with the Space Telescope Imaging Spectrograph (STIS) from the ASTRAL project (Ayres 2010, ApJS, 187, 149). We have also used archival material from COPERNICUS (retrieved from the MAST) and from HST/GHRS, as well as the ground-based Furenlid, Westin, and Kurucz Sirius Atlas (FWK). The GHRS observations were described by Wahlgren, et al. (1993, Bull. AAS, 25, 1321). We also used the monumental study of Sirius by Klaus Kohl (1964, Zs. f. Ap. 60, 115, 1964, see also 1964, Das Spektrum des Sirius, 3100 - 8863A, Kiel thesis). Abundance determinations are based on the photospheric model of Landstreet (2011, A&A, 528, 132). The atomic data base is significantly improved since the pioneering work by Sadakane (1988, PASP, 100, 811; 1991, 103, 355). The basic source was VALD3 (http://vald.inasan.ru/~vald3/php/vald.php), supplemented for all species by the essential NIST bibliographic data base (http://physics.nist.gov/cgi-bin/ASBib1/TransProbBib.cgi). We determine abundances and upper limits by synthesizing short wavelength regions around strong lines. Virtually all of the abundance/upper limit results show excesses over the solar composition of between 1 and 2 dex. This result is in general agreement with overall results for metallic line stars, though we have no information on possible severe depletions for most elements. We conclude that the mechanisms causing abundance anomalies in Sirius have not acted to produce the extreme excesses of 4 or more dex (Pt, Hg), or deficiencies (Zn) seen in many HgMn stars.CRC thanks Stefano Bagnulo for the UVESPOP Sirius spectrum. Robert Kurucz was most helpful with older Sirius UV and visual spectra. Title: CO isotopologue ratios in the solar photosphere Authors: Lyons, James; Gharib-Nezhad, Ehsan; Ayres, Thomas Bibcode: 2015IAUGA..2257564L Altcode: Determination of the oxygen isotope ratios in the solar photosphere is essential to constraining the formation environment of the solar system. The solar CO fundamental and first-overtone bands were previously measured by the shuttle-borne ATMOS Fourier transform spectrometer (FTS), and with the National Solar Observatory FTS on the McMath-Pierce telescope at Kitt Peak. Analyzing the rovibrational bands from these photospheric spectra, a 3D convection model was employed to calculate ratios with improved uncertainties (16O/17O=2738±118 and 16O/18O =511±10 Ayres et al. 2013), which fall between the terrestrial values and those inferred from solar wind measurements by the Genesis spacecraft. However, differences in published CO dipole moment functions yielded a range of isotopic ratios spanning ~ 3 % in δ18O. Here we re-evaluate the CO dipole moment function in order to obtain more accurate isotope ratios for the photosphere. We used a new set of dipole moments from HITEMP which were accurately determined by both semi-empirical and ab initio methods. Preliminary values of isotope ratios using the new dipole moments are in better agreement with the inferred photosphere values from Genesis, showing that the solar photosphere is isotopically similar to primitive inclusions in meteorites, but different from the terrestrial planets by ~ 6 %. New spectral observations are needed to reduce uncertainties in photospheric C17O abundances. Title: A Giant Far-Ultraviolet Flare on Young Solar Analog EK Draconis Authors: Ayres, Thomas Bibcode: 2015IAUGA..2244956A Altcode: A particularly impressive far-ultraviolet flare (corresponding to a GOES X25,000-class event: 50 is largest ever recorded on the Sun) was captured serendipitously by Hubble's Cosmic Origins Spectrograph, during a campaign on young (~50 Myr) solar analog EK Draconis. The large outburst was like a classical solar 2-ribbon flare: it lasted several hours and all the atmospheric temperature regimes -- from C II (30,000 K) through C IV (100,000 K), and up to Fe XXI (10 MK) -- were affected simultaneously. Scaling laws suggest that the EK Dra event was in the upper echelons of the historical sample of stellar high-energy outbursts, but the first to be captured in the FUV with the unprecedented sensitivity, spectral resolution, and high time cadence of an instrument like COS. Remarkably, time-resolved line profiles of hot species like Si IV and C IV displayed strong, highly redshifted components during the event; contrary to the blueshifts one might naively anticipate from an isotropic stellar explosion. Instead, the conspicuous redshifts probably are signatures of a post-flare cooling process, analogous to "coronal rain" or "super-arcade downflows" associated with large solar events. Flares of this magnitude probably are common on young hyperactive sunlike stars, occurring perhaps twice a day on EK Dra itself. The transient doses of FUV radiation probably are not a significant impediment to planetary habitability, compared with the "quiescent" FUV output of the star (if you can call an object with 1000 times the X-ray luminosity of the Sun "quiet"), but the associated very hard X-ray and γ-ray fluences could have a much larger impact on the ionization of a primitive planetary atmosphere, boosting its exposure to gas-stripping by stellar winds or coronal mass ejections. Title: Fluorescence Processes in the Outer Atmospheres of the Evolved M-Stars Alpha Ori (M2 Iab) and Gamma Cru (M3.4 III) Authors: Carpenter, Kenneth; Kober, Gladys; Nielsen, Krister; Ayres, Thomas; Wahlgren, Glenn Bibcode: 2015IAUGA..2242446C Altcode: The prototypical M-giant and M-supergiant stars, Gamma Cru (M3.4 III)) and Alpha Ori (M2Iab), have been observed as part of the "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres). "ASTRAL-Cool Stars" is an HST Cycle 18 Treasury Program designed to collect, using the Space Telescope Imaging Spectrograph (STIS), a definitive set of representative, high-resolution (R~46,000 in the FUV up to ~1700 Å, R~30,000 for 1700-2150 Å, and R~114,000 >2150 Å) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality UV echelle spectra are available from the HST archive and through the University of Colorado (http://casa.colorado.edu/~ayres/ASTRAL/). In this paper, we use the very rich emission-line spectra of the two evolved M stars in the sample, Gamma Cru (GaCrux) and Alpha Ori (Betelgeuse), to study the fluorescence processes operating in their outer atmospheres. We summarize the pumping transitions and fluorescent line products known on the basis of previous work and newly identified in our on-going analysis of these extraordinary new “Treasury” spectra. Detailed descriptions of selected processes are given to illustrate their operation. The wide variety of fluorescence processes in operation in these outer atmospheres, both molecular and atomic, suggest that there is a mixture of warm and cool plasmas present and that H I Ly-alpha in particular is locally very strong, even though, in the case of Alpha Ori, no flux is seen at earth due to strong circumstellar absorption at that wavelength. Many new fluorescence line products and several new processes have been identified in these spectra, which are more complete and of higher S/N than previously available for these stars. Title: The Flare-ona of EK Draconis Authors: Ayres, Thomas R. Bibcode: 2015AJ....150....7A Altcode: 2015arXiv150502320A EK Draconis (HD 129333: G1.5 V) is a well-known young (50 Myr) solar analog. In 2012, Hubble Space Telescope returned to EK Dra to follow up a far-ultraviolet (FUV) SNAPshot visit by Cosmic Origins Spectrograph (COS) two years earlier. The brief SNAP pointing had found surprisingly redshifted, impulsively variable subcoronal “hot-line” emission of Si iv 1400 Å (T ∼ 8 × 104 K). Serendipitously, the 2012 follow-on program witnessed one of the largest FUV flares ever recorded on a sunlike star, which again displayed strong redshifts (downflows) of 30-40 km s-1, even after compensating for small systematics in the COS velocity scales, uncovered through a cross-calibration by Space Telescope Imaging Spectrograph (STIS). The (now reduced, but still substantial) ∼10 km s-1 hot-line redshifts outside the flaring interval did not vary with rotational phase, so cannot be caused by “Doppler imaging” (bright surface patches near a receding limb). Density diagnostic O iv] 1400 Å multiplet line ratios of EK Dra suggest ne ∼ 1011 cm-3, an order of magnitude larger than in low-activity solar twin α Centauri A, but typical of densities inferred in large stellar soft X-ray events. The self-similar FUV hot-line profiles between the flare decay and the subsequent more quiet periods, and the unchanging but high densities, reinforce a long-standing idea that the coronae of hyperactive dwarfs are flaring all the time, in a scale-free way; a flare-ona if you will. In this picture, the subsonic hot-line downflows probably are a byproduct of the post-flare cooling process, something like “coronal rain” on the Sun. All in all, the new STIS/COS program documents a complex, energetic, dynamic outer atmosphere of the young sunlike star. Title: Characterizing the Habitable Zones of Exoplanetary Systems with a Large Ultraviolet/Visible/Near-IR Space Observatory Authors: France, Kevin; Shkolnik, Evgenya; Linsky, Jeffrey; Roberge, Aki; Ayres, Thomas; Barman, Travis; Brown, Alexander; Davenport, James; Desert, Jean-Michel; Domagal-Goldman, Shawn; Fleming, Brian; Fontenla, Juan; Fossati, Luca; Froning, Cynthia; Hallinan, Gregg; Hawley, Suzanne; Hu, Renyu; Kaltenegger, Lisa; Kasting, James; Kowlaski, Adam; Loyd, Parke; Mauas, Pablo; Miguel, Yamila; Osten, Rachel; Redfield, Seth; Rugheimer, Sarah; Schneider, Christian; Segura, Antigona; Stocke, John; Tian, Feng; Tumlinson, Jason; Vieytes, Mariela; Walkowicz, Lucianne; Wood, Brian; Youngblood, Allison Bibcode: 2015arXiv150501840F Altcode: Understanding the surface and atmospheric conditions of Earth-size, rocky planets in the habitable zones (HZs) of low-mass stars is currently one of the greatest astronomical endeavors. Knowledge of the planetary effective surface temperature alone is insufficient to accurately interpret biosignature gases when they are observed in the coming decades. The UV stellar spectrum drives and regulates the upper atmospheric heating and chemistry on Earth-like planets, is critical to the definition and interpretation of biosignature gases, and may even produce false-positives in our search for biologic activity. This white paper briefly describes the scientific motivation for panchromatic observations of exoplanetary systems as a whole (star and planet), argues that a future NASA UV/Vis/near-IR space observatory is well-suited to carry out this work, and describes technology development goals that can be achieved in the next decade to support the development of a UV/Vis/near-IR flagship mission in the 2020s. Title: RAISE (Rapid Acquisition Imaging Spectrograph Experiment): Results and Instrument Status Authors: Laurent, Glenn T.; Hassler, Donald; DeForest, Craig; Ayres, Tom; Davis, Michael; DePontieu, Bart; Diller, Jed; Graham, Roy; Schule, Udo; Warren, Harry Bibcode: 2015TESS....140203L Altcode: We present initial results from the successful November 2014 launch of the RAISE (Rapid Acquisition Imaging Spectrograph Experiment) sounding rocket program, including intensity maps, high-speed spectroheliograms and dopplergrams, as well as an update on instrument status. The RAISE sounding rocket payload is the fastest high-speed scanning-slit imaging spectrograph flown to date and is designed to observe the dynamics and heating of the solar chromosphere and corona on time scales as short as 100-200ms, with arcsecond spatial resolution and a velocity sensitivity of 1-2 km/s. The instrument is based on a class of UV/EUV imaging spectrometers that use only two reflections to provide quasi-stigmatic performance simultaneously over multiple wavelengths and spatial fields. The design uses an off-axis parabolic telescope mirror to form a real image of the sun on the spectrometer entrance aperture. A slit then selects a portion of the solar image, passing its light onto a near-normal incidence toroidal grating, which re-images the spectrally dispersed radiation onto two array detectors. Two full spectral passbands over the same one-dimensional spatial field are recorded simultaneously with no scanning of the detectors or grating. The two different spectral bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two intensified Active Pixel Sensor (APS) detectors whose focal planes are individually adjusted for optimized performance. RAISE reads out the full field of both detectors at 5-10 Hz, allowing us to record over 1,500 complete spectral observations in a single 5-minute rocket flight, opening up a new domain of high time resolution spectral imaging and spectroscopy. RAISE is designed to study small-scale multithermal dynamics in active region (AR) loops, explore the strength, spectrum and location of high frequency waves in the solar atmosphere, and investigate the nature of transient brightenings in the chromospheric network. Title: CxO (x=16,17,18) Isotopologue Ratios in the Solar Photosphere Authors: GharibNezhad, E.; Lyons, J. R.; Ayres, T. R. Bibcode: 2015LPI....46.1592G Altcode: 2015LPICo1832.1592G Using revised f-values of CO isotopologues, preliminary isotope ratios for the solar photosphere were determined, and are found to be similar to Genesis values. Title: Characterising exoplanets and their environment with UV transmission spectroscopy Authors: Fossati, L.; Bourrier, V.; Ehrenreich, D.; Haswell, C. A.; Kislyakova, K. G.; Lammer, H.; Lecavelier des Etangs, A.; Alibert, Y.; Ayres, T. R.; Ballester, G. E.; Barnes, J.; Bisikalo, D. V.; Collier, A.; Cameron; Czesla, S.; Desert, J. -M.; France, K.; Guedel, M.; Guenther, E.; Helling, Ch.; Heng, K.; Homstrom, M.; Kaltenegger, L.; Koskinen, T.; Lanza, A. F.; Linsky, J. L.; Mordasini, C.; Pagano, I.; Pollacco, D.; Rauer, H.; Reiners, A.; Salz, M.; Schneider, P. C.; Shematovich, V. I.; Staab, D.; Vidotto, A. A.; Wheatley, P. J.; Wood, B. E.; Yelle, R. V. Bibcode: 2015arXiv150301278F Altcode: Exoplanet science is now in its full expansion, particularly after the CoRoT and Kepler space missions that led us to the discovery of thousands of extra-solar planets. The last decade has taught us that UV observations play a major role in advancing our understanding of planets and of their host stars, but the necessary UV observations can be carried out only by HST, and this is going to be the case for many years to come. It is therefore crucial to build a treasury data archive of UV exoplanet observations formed by a dozen "golden systems" for which observations will be available from the UV to the infrared. Only in this way we will be able to fully exploit JWST observations for exoplanet science, one of the key JWST science case. Title: Serendipitous Discovery of a Dwarf Nova in the Kepler Field Near the G Dwarf KIC 5438845 Authors: Brown, Alexander; Neff, James E.; Ayres, Thomas R.; Kowalski, Adam; Hawley, Suzanne; Berdyugina, Svetlana; Harper, Graham M.; Korhonen, Heidi; Piskunov, Nikolai; Saar, Steven; Walkowicz, Lucianne; Wells, Mark A. Bibcode: 2015AJ....149...67B Altcode: The Kepler satellite provides a unique window into stellar temporal variability by observing a wide variety of stars with multi-year, near-continuous, high precision, optical photometric time series. While most Kepler targets are faint stars with poorly known physical properties, many unexpected discoveries should result from a long photometric survey of such a large area of sky. During our Kepler Guest Observer programs that monitored late-type stars for starspot and flaring variability, we discovered a previously unknown dwarf nova that lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This dwarf nova underwent nine outbursts over a 4 year time span. The two largest outbursts lasted ∼17-18 days and show strong modulations with a 110.8 minute period and a declining amplitude during the outburst decay phase. These properties are characteristic of an SU UMa-type cataclysmic variable. By analogy with other dwarf nova light curves, we associate the 110.8 minute (1.847 hr) period with the superhump period, close to but slightly longer than the orbital period of the binary. No precursor outbursts are seen before the super-outbursts and the overall super-outburst morphology corresponds to Osaki & Meyer “Case B” outbursts, which are initiated when the outer edge of the disk reaches the tidal truncation radius. “Case B” outbursts are rare within the Kepler light curves of dwarf novae. The dwarf nova is undergoing relatively slow mass transfer, as evidenced by the long intervals between outbursts, but the mass transfer rate appears to be steady, because the smaller “normal” outbursts show a strong correlation between the integrated outburst energy and the elapsed time since the previous outburst. At super-outburst maximum the system was at V ∼ 18, but in quiescence it is fainter than V ∼ 22, which will make any detailed quiescent follow-up of this system difficult. Title: The Far-Ultraviolet Ups and Downs of Alpha Centauri Authors: Ayres, Thomas R. Bibcode: 2015AJ....149...58A Altcode: Four years (2010-2014) of semiannual pointings by the Hubble Space Telescope Imaging Spectrograph (STIS) on nearby Alpha Centauri have yielded a detailed time history of far-ultraviolet (FUV: 1150-1700 Å) emissions of the solarlike primary (A: G2 V) and the cooler but more active secondary (B: K1 V). This period saw A climbing out of a prolonged coronal X-ray minimum, as documented contemporaneously by Chandra, while B was rising to, then falling from, a peak of its long-term (∼8 year) starspot cycle. The FUV fluxes of the primary were steady over most of the STIS period, although the [Fe xii] λ1242 coronal forbidden line (T∼ 1.5 MK) partly mirrored the slowly rising X-ray fluxes. The FUV emissions of the secondary more closely tracked the rise and fall of its coronal luminosities, especially the “hot lines” Si iv, C iv, and N v (T∼ 0.8-2 × 105 K), and coronal [Fe xii] itself. The hot lines of both stars were systematically redshifted, relative to narrow chromospheric emissions, by several km s-1, showing little change in amplitude over the four-year period, especially for α Cen B, despite the significant evolution of its coronal activity. Further, the hot lines of both stars, individually and epoch-averaged, displayed non-Gaussian shapes, which most trivially could be decomposed into two components, one narrow (FWHM ∼25-45 km s-1), the other broad (60-80 km s-1). A bimodal Gaussian strategy had been applied previously to the α Cen stars, but this was the first opportunity to evaluate any time dependence. In fact, not much variation of the component properties was seen, even over the major cycle changes of B. Curiously, the line fluxes were about equally divided between the narrow and broad components for both stars. The fact that there is minimal activity dependence of the narrow/broad flux partition, as well as densities derived from O iv] line ratios, either during the cycle evolution of B or between A and B, suggests that there is a dominant “quantum” of FUV surface activity that is relatively unchanged during the cycle, aside from the fractional area covered. Title: Predicting the Extreme-UV and Lyman-α Fluxes Received by Exoplanets from their Host Stars Authors: Linsky, Jeffrey L.; France, Kevin; Ayres, Thomas R. Bibcode: 2015csss...18..831L Altcode: Extreme-UV (EUV) radiation from the chromospheres, transition regions, and coronae of host stars (spectral types F, G, K, and M) ionize and heat the outer atmospheres of exoplanets leading to mass loss that is observed during transits and can change the exoplanet's atmosphere. Lyman-α emission from host stars controls the photochemistry in the upper layers of planetary atmospheres by photodissociating important molecules including H_2O, CO_2, CH_4, thereby increasing the oxygen and ozone mixing ratios important for habitability. Both the EUV and strong Lyman-α radiation are largely absorbed by the interstellar medium and must be reconstructed or estimated to understand the radiation environment of exoplanets. In two recent papers, tet{Linsky2013} and tet{Linsky2014}, we have presented robust methods for predicting the intrinsic Lyman-α and EUV fluxes from main sequence cool stars. Solar models and satellite observations (HST, FUSE, and EUVE) provide tests for the feasibility of these methods. Title: The HST Treasury ``Advanced Spectral Library'' (ASTRAL) Programs Authors: Carpenter, Kenneth G.; Ayres, Thomas R. Bibcode: 2015csss...18.1041C Altcode: 2014arXiv1411.1419C The ``Advanced Spectral Library (ASTRAL)'' Project (PI = T. Ayres) consists of two Treasury Programs: the Cycle 18 ``Cool Stars'' (GO-12278) Program and the Cycle 21 ``Hot Stars'' (GO-13346) Program. The primary goal of these programs is to collect, for the use of the astronomical community over the coming decades, a definitive set of representative, high-resolution (R∼30,000-100,000), high signal/noise (S/N>100) spectra, with full UV coverage (∼1150 - 3100 Å) of prototypical stars across the HR diagram, utilizing the high-performance Space Telescope Imaging Spectrograph (STIS). The Cycle 18 program obtained spectra of 8 F-M evolved late-type stars, while the Cycle 21 program is in the process of observing 21 early-type stars, which span a broad range of spectral types between early-O and early-A. All of these data will be available from the HST archive and, in post-processed and merged form, at http://casa.colorado.edu/ãyres/ASTRAL/. These data will enable investigations of a broad range of problems - stellar, interstellar, and beyond - for many years into the future. We describe here the details of the observing programs, including the program targets and the observing strategies utilized to optimize the quality of the spectra, and present some illustrative examples of the on-going scientific analyses, including a study of the outer atmospheres and winds of the two evolved M stars in the sample and a first look at a ``high definition'' UV spectrum of a magnetic chemically peculiar ``Ap'' star. Title: Mining the HST "Advanced Spectral Library (ASTRAL)": Winds of the Evolved M Stars Alpha Ori (M2 Iab) and Gamma Cru (M3.4 III) Authors: Carpenter, Kenneth G.; Nielsen, Krister E.; Kober, Gladys V.; Ayres, Thomas R. Bibcode: 2015AAS...22534408C Altcode: The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program that collected a definitive set of representative, high-resolution (R=30,000-100,000) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the ASTRAL website at the University of Colorado at http://casa.colorado.edu/~ayres/ASTRAL/ and will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years. In this paper, we examine the wealth of wind diagnostics contained in the very rich spectra of the two evolved M stars in the sample, the M3.4 III giant Gamma Crucis (GaCrux) and the M2 Iab supergiant Alpha Orionis (Betelgeuse) and characterize the winds at the time of these STIS observations in 2011 and compare the results with those obtained from more limited data taken at earlier epochs with HST/GHRS and IUE. In particular we study the variation of the numerous Fe II profiles with intrinsic strength in the two stars. The shifting wavelengths of the wind absorptions relative to the emission peaks and the changes in relative strengths of the emission peaks reflect the acceleration of the wind from the base of the chromosphere. Although the characteristics of the Gamma Cru wind are relatively stable with time, the Alpha Ori wind outflow appears significantly smaller than seen by Carpenter et al. (1997, ApJ, 479, 970) in GHRS observations taken in 1992 (and in earlier IUE observations). There might in fact be evidence in these STIS spectra that the outflow has turned into an inflow, as reported at epochs prior to IUE by Boesgaard and Magnan (1975 ApJ 198, 369) and Boesgaard (1979 ApJ 232, 485) based on a limited number of lines in the extreme blue end of ground-based spectra. Title: Flares and Antiflares on Young Solar Analog EK Draconis Authors: Ayres, Thomas R. Bibcode: 2015AAS...22513823A Altcode: EK Draconis (HD129333: G1.5 V) is a well-known young (50 Myr) solar analog. In 2012, Hubble Space Telescope returned to EK Dra to follow up a far-UV SNAPshot visit by HST's Cosmic Origins Spectrograph two years earlier. The brief SNAP pointing had found surprisingly redshifted subcoronal Si IV (T~ 8x104 K), which also displayed impulsive variability, curiously uncorrelated with species at lower temperatures (C II: 2x104K) or higher (Fe XXI: 1x107K). Serendipitously, the follow-on program witnessed one of the largest FUV flares ever recorded on a sun-like star, which nevertheless displayed even stronger redshifts (downflows) than had been seen earlier, contrary to the violent blueshifts expected from such explosive events. At the same time, a velocity cross-calibration by Space Telescope Imaging Spectrograph (STIS) uncovered systematic deviations in the wavelength scales of COS, that were partly, but not entirely, responsible for the previously reported SNAP redshifts. However, the (now smaller, but still about 10 km s-1) Si IV redshifts did not vary with rotational phase, so are not likely caused by "Doppler imaging' effects. Instead, the downflows might be signatures of catastrophic coronal cooling events (`"antiflares'). All in all, the new COS/STIS program documents a complex, energetic, dynamic outer atmosphere of the young solar analog. Title: X-ray Emission from Young Stars in the TW Hya Association Authors: Brown, Alexander; Herczeg, Gregory J.; Ayres, Thomas R.; France, Kevin; Brown, Joanna M. Bibcode: 2015csss...18..203B Altcode: 2014arXiv1408.4062B The 9 Myr old TW Hya Association (TWA) is the nearest group (typical distances of ∼50 pc) of pre-main-sequence (PMS) stars with ages less than 10 Myr and contains stars with both actively accreting disks and debris disks. We have studied the coronal X-ray emission from a group of low mass TWA common proper motion binaries using the Chandra and Swift satellites. Our aim is to understand better their coronal properties and how high energy photons affect the conditions around young stars and their role in photo-exciting atoms, molecules and dust grains in circumstellar disks and lower density circumstellar gas. Once planet formation is underway, this emission influences protoplanetary evolution and the atmospheric conditions of the newly-formed planets. The X-ray properties for 7 individual stars (TWA 13A, TWA 13B, TWA 9A, TWA 9B, TWA 8A, TWA 8B, and TWA 7) and 2 combined binary systems (TWA 3AB and TWA 2AB) have been measured. All the stars with sufficient signal require two-component fits to their CCD-resolution X-ray spectra, typically with a dominant hot (~2 kev (25 MK)) component and a cooler component at ~0.4 keV (4 MK). The brighter sources all show significant X-ray variability (at a level of 50-100% of quiescence) over the course of 5-15 ksec observations due to flares. We present the X-ray properties for each of the stars and find that the coronal emission is in the super-saturated rotational domain. Title: The Ups and Downs of Alpha Centauri Authors: Ayres, Thomas Bibcode: 2014fysc.confP...6A Altcode: Nearby Alpha Centauri is destined for a pivotal chapter in human history, as first stop of future starfarers from Earth: 3x closer than the next nearest star; three very different objects to visit -- Alpha Cen A (G2V), B (K1V), and C (M6V); and B hosts an Earth-mass companion, albeit in a hot, lifeless orbit. For its part, Chandra has been keeping intent watch on the high-energy starspot cycles of AB, with semi-annual pointings over the past decade. Only HRC-I can separate AB as they plunge toward a close approach of 4" in 2016; and LETGS has countered that an abrupt 50x drop in XMM count rate of sun-like A in early 2005, ominously reported as the "darkening of the solar twin," simply is a soft sensitivity issue, not an unprecedented, inexplicable case of corona interrupta. Title: Searching for a gas cloud surrounding the WASP-18 planetary system Authors: Fossati, L.; Ayres, T. R.; Haswell, C. A.; Jenkins, J. S.; Bisikalo, D.; Bohlender, D.; Flöer, L.; Kochukhov, O. Bibcode: 2014Ap&SS.354...21F Altcode: Near-UV (NUV) Hubble Space Telescope (HST) observations of the extreme hot-Jupiter WASP-12b revealed the presence of diffuse exospheric gas extending beyond the planet's Roche lobe. Furthermore the NUV observations showed a complete lack of the normally bright core emission of the Mg ii h&k resonance lines, in agreement with the measured anomalously low stellar activity index (log R' HK ). Comparisons with other distant and inactive stars, and the analysis of radio and optical measurements of the intervening interstellar medium (ISM), led us to the conclusion that the system is surrounded by a circumstellar gas cloud, likely formed of material lost by the planet. Similar anomalous log R' HK index deficiencies might therefore signal the presence of translucent circumstellar gas around other stars hosting evaporating planets; we identified five such systems and WASP-18 is one of them. Both radio and optical observations of the region surrounding WASP-18 point towards a negligible ISM absorption along the WASP-18 line of sight. Excluding the unlikely possibility of an intrinsic anomalously low stellar activity, we conclude that the system is probably surrounded by a circumstellar gas cloud, presumably formed of material lost by the planet. Nevertheless only a far-UV spectrum of the star would provide a definite answer. Theoretical modelling suggests WASP-18b undergoes negligible mass loss, in contrast to the probable presence of a circumstellar gas cloud formed of material lost by the planet. The solution might be the presence either of an extra energy source driving mass loss (e.g., the reconnection of the stellar and planetary magnetic fields inside the planet atmosphere) or of an evaporating third body (e.g., moon). Title: An HST COS "SNAPshot" Spectrum of the K Supergiant λ Vel (K4Ib-II) Authors: Carpenter, Kenneth G.; Ayres, Thomas R.; Harper, Graham M.; Kober, Gladys; Nielsen, Krister E.; Wahlgren, Glenn M. Bibcode: 2014ApJ...794...41C Altcode: We present a far-ultraviolet spectrum of the K4 Ib-II supergiant λ Vel obtained with the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) as a part of the SNAPshot program "SNAPing coronal iron" (GO 11687). The observation covers a wavelength region (1326-1467 Å) not previously recorded for λ Vel at a spectral resolving power of R ~ 20,000 and displays strong emission and absorption features, superposed on a bright chromospheric continuum. Fluorescent excitation is responsible for much of the observed emission, mainly powered by strong H I Lyα and the O I (UV 2) triplet emission near λ1304. The molecular CO and H2 fluorescences are weaker than in the early-K giant α Boo while the Fe II and Cr II lines, also pumped by H I Lyα, are stronger in λ Vel. This pattern of relative line strengths between the two stars is explained by the lower iron-group element abundance in α Boo, which weakens that star's Fe II and Cr II emission without reducing the molecular fluorescences. The λ Vel spectrum shows fluorescent Fe II, Cr II, and H2 emission similar to that observed in the M supergiant α Ori, but more numerous well-defined narrow emissions from CO. The additional CO emissions are visible in the spectrum of λ Vel since that star does not have the cool, opaque circumstellar shells that surround α Ori and produce broad circumstellar CO (A-X) band absorptions that hide those emissions in the cooler star. The presence of Si IV emission in λ Vel indicates a ~8 × 104 K plasma that is mixed into the cooler chromosphere. Evidence of the stellar wind is seen in the C II λλ1334,1335 lines and in the blueshifted Fe II and Ni II wind absorption lines. Line modeling using Sobolev with Exact Integration for the C II lines indicates a larger terminal velocity (~45 versus ~30 km s-1) and turbulence (~27 versus <21 km s-1) with a more quickly accelerating wind (β = 0.35 versus 0.7) at the time of this COS observation in 2010 than derived from Goddard High Resolution Spectrograph data obtained in 1994. The Fe II and Ni II absorptions are blueshifted by 7.6 km s-1 relative to the chromospheric emission, suggesting formation in lower levels of the accelerating wind and their widths indicate a higher turbulence in the λ Vel wind compared to α Ori.

Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. Title: The Far-Ultraviolet Ups and Downs of Alpha Centauri Authors: Ayres, Thomas R. Bibcode: 2014arXiv1411.0038A Altcode: Four years (2010-2014) of semiannual pointings by Hubble Space Telescope Imaging Spectrograph (STIS) on nearby Alpha Centauri have yielded a detailed time history of far-ultraviolet emissions of the solar-like primary (A: G2V) and the cooler, but more active, secondary (B: K1V). This period saw A climbing out of a prolonged coronal X-ray minimum, as documented by Chandra, while B was rising to, then falling from, a peak of its long-term (8 yr) starspot cycle. The FUV fluxes of the primary were steady over most of the STIS period, although the [Fe XII] 124 nm coronal forbidden line (T= 1.5 MK) partly mirrored the slowly rising X-ray fluxes. The FUV emissions of the secondary more closely tracked the rise and fall of its coronal luminosities, especially the "hot lines" like Si IV, C IV, and N V (T= 80,000-200,000 K), and coronal [Fe XII] itself. The hot lines of both stars were systematically redshifted, relative to narrow chromospheric emissions, by several km/s, showing little change in amplitude over the 4-year period; especially for Alpha Cen B, despite the significant evolution of its coronal activity. Further, the hot line profiles of both stars, individually and epoch-averaged, could be decomposed into two nearly equal components, one narrow (FWHM~ 25-45 km/s), the other broad (60-80 km/s). Not much variation of the component properties was seen over the 4-year period, even over the major cycle changes of B. This suggests that there is a dominant "quantum" of FUV surface activity that is relatively unchanged during the cycle, aside from the fractional area covered. Title: Molecular absorption in transition region spectral lines Authors: Schmit, D. J.; Innes, D.; Ayres, T.; Peter, H.; Curdt, W.; Jaeggli, S. Bibcode: 2014A&A...569L...7S Altcode: 2014arXiv1409.1702S
Aims: We present observations from the Interface Region Imaging Spectrograph (IRIS) of absorption features from a multitude of cool atomic and molecular lines within the profiles of Si IV transition region lines. Many of these spectral lines have not previously been detected in solar spectra.
Methods: We examined spectra taken from deep exposures of plage on 12 October 2013. We observed unique absorption spectra over a magnetic element which is bright in transition region line emission and the ultraviolet continuum. We compared the absorption spectra with emission spectra that is likely related to fluorescence.
Results: The absorption features require a population of sub-5000 K plasma to exist above the transition region. This peculiar stratification is an extreme deviation from the canonical structure of the chromosphere-corona boundary. The cool material is not associated with a filament or discernible coronal rain. This suggests that molecules may form in the upper solar atmosphere on small spatial scales and introduces a new complexity into our understanding of solar thermal structure. It lends credence to previous numerical studies that found evidence for elevated pockets of cool gas in the chromosphere.

Movies associated to Figs. 1 and 2 are available in electronic form at http://www.aanda.org Title: Alpha Centauri at a Crossroads Authors: Ayres, Thomas Bibcode: 2014cxo..prop.4335A Altcode: Nearby Alpha Centauri (G2V+K1V) contains the two best characterized solar-like dwarf stars, which also have the best studied X-ray activity cycles, extending back to the 1970's. Objective is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual HRC-I pointings in Cycles 16-18, as the system reaches a coronal crossroads: solar twin A rising toward cycle maximum, K-type companion B sinking into a minimum. HST/STIS UV spectra will support and leverage the X-ray measurements by probing subcoronal dynamics, with connection to the corona through the FUV Fe XII forbidden line. Only Chandra can resolve the AB X-ray sources as the Alpha Cen orbit also reaches a crossroads in 2016. Title: The Stellar-IRIS Connection: Four Years of FUV Measurements of Alpha Centauri by HST/STIS Authors: Ayres, Thomas R. Bibcode: 2014AAS...22432312A Altcode: Since 2010 January, shortly after the miraculous repair of Hubble's Space Telescope Imaging Spectrograph (STIS) by SM4, the two sun-like stars of Alpha Centauri ("A" [G2V] and "B" [K1V]) have been recorded on a semi-annual basis utilizing STIS's far-ultraviolet (115-170 nm) medium resolution mode (about 8 km/s FWHM resolving power), jointly with an X-ray imaging study of AB by the Chandra Observatory. Both efforts are intended to assess the long-term behavior of high-energy (multimillion K) coronal, and subcoronal, processes on the two relatively low-activity solar-age dwarfs. In fact, the near-solar-twin Alpha Cen A has been mired in a coronal lull since 2005, originally recognized by XMM-Newton, and only recently has begun to climb out of the extended X-ray minimum. Meanwhile, the lower mass, lower luminosity, but coronally more active secondary has displayed a clear 8-year X-ray cycle, extending from the mid-1990's ROSAT era. The current study focuses on properties of the "transition zone" lines ( 100,000 K) of the Alpha Centauri stars, namely the bulk redshifts exhibited by the Si IV, C IV, and N V doublets; the multi-component nature of the hot-line profiles; behavior of the Fe XII 124 nm coronal forbidden line; and variability of the FUV fluxes relative to the higher-energy X-ray time series. These stellar measurements, with their high precision in wavelength and flux, complement the detailed high-spatial and high-temporal resolution spectral mapping of the solar corona and lower atmosphere being carried out by NASA's Interface Region Imaging Spectrograph (IRIS). [This work supported by GO grants 12758, 13060, and 13465 from Space Telescope Science Institute.] Title: The Structure of the Local Interstellar Medium. VI. New Mg II, Fe II, and Mn II Observations toward Stars within 100 pc Authors: Malamut, Craig; Redfield, Seth; Linsky, Jeffrey L.; Wood, Brian E.; Ayres, Thomas R. Bibcode: 2014ApJ...787...75M Altcode: 2014arXiv1403.8096M We analyze high-resolution spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope toward 34 nearby stars (<=100 pc) to record Mg II, Fe II, and Mn II absorption due to the local interstellar medium (LISM). Observations span the entire sky, probing previously unobserved regions of the LISM. The heavy ions studied in this survey produce narrow absorption features that facilitate the identification of multiple interstellar components. We detected one to six individual absorption components along any given sight line, and the number of absorbers roughly correlates with the pathlength. This high-resolution near-ultraviolet (NUV) spectroscopic survey was specifically designed for sight lines with existing far-UV (FUV) observations. The FUV spectra include many intrinsically broad absorption lines (i.e., of low atomic mass ions) and are often observed at medium resolution. The LISM NUV narrow-line absorption component structure presented here can be used to more accurately interpret the archival FUV observations. As an example of this synergy, we present a new analysis of the temperature and turbulence along the line of sight toward epsilon Ind. The new observations of LISM velocity structure are also critical in the interpretation of astrospheric absorption derived from fitting the saturated H I Lyα profile. As an example, we reanalyze the spectrum of λ And and find that this star likely does have an astrosphere. Two stars in the sample that have circumstellar disks (49 Cet and HD141569) show evidence for absorption due to disk gas. Finally, the substantially increased number of sight lines is used to test and refine the three-dimensional kinematic model of the LISM and search for previously unidentified clouds within the Local Bubble. We find that every prediction made by the Redfield & Linsky kinematic model of the LISM is confirmed by an observed component in the new lines of sight. Title: Reconstructing the Stellar UV and EUV Emission that Controls the Chemistry of Exoplanet Atmospheres Authors: Linsky, Jeffrey L.; France, Kevin; Ayres, Tom Bibcode: 2014IAUS..293..309L Altcode: Lyman-α and extreme-ultraviolet radiation from exoplanet host stars are critically important for evaluating the phototchemistry of planetary atmospheres, but these emissions are largely or completely absorbed by hydrogen in the interstellar medium. We describe a new technique for estimating the intrinsic Lyman-α and EUV fluxes of F, G, K, and M stars using correlations with observable emission lines. Title: Superflares on Sun-Like Stars: Bane of Habitability? Authors: Ayres, T. Bibcode: 2014hwat.confE...1A Altcode: A key aspect of planetary habitability is the existence of rare, but catastrophic events. One Earthly example is the attribution of several geological mass extinctions to asteroid collisions. Indeed, the Late Heavy Bombardment, during which the 600 Myr old Earth was pummeled persistently by impactors over a period of perhaps a hundred Myr, likely significantly delayed the permanent foothold of life on our planet. Another, less well known, example is the proposed existence of "superflares" on Sun-like stars. Although the quantity of energy in a superflare is negligible compared with the time-integrated X-ray dose from the quiescent multi-MK corona, the quality of the radiation (i.e., composition dominated by gamma rays) released from the transient, but extreme, outburst is what could be of concern to the survival of primitive lifeforms struggling for existence on a semi-habitable world. However, existing reports of superflares mainly involve interpretations of historical materials, such as long-term astronomical plate collections; there are very few concrete examples of such events observed by modern techniques at the most relevant wavelengths, namely ultraviolet or X-rays. The lack of good examples is mostly because these rare events are, well, rare. However, a recent HST Cosmic Origins Spectrograph program to record the ultraviolet spectrum of young ( 50 Myr) solar analog EK Draconis, fortuitously captured a giant, hour-long FUV transient, in hot lines like the C IV 155 nm doublet (T 100,000 K), and very toasty Fe XXI 124 nm coronal forbidden line ( 10 MK). If translated into the equivalent GOES 0.1-0.8 nm X-ray fluence, the event would correspond to an X25000-class flare (most extreme observed on the Sun might reach as high as a mere X50). The EK Dra giant flare, as viewed with the excellent wavelength resolution, broad coverage, and high sensitivity of COS, provides the opportunity to deduce properties of such events to help inform possible impacts on planetary habitability, especially in the context of the early development of life on Earth-like planets orbiting young Sun-like stars. Title: The Ups and Downs of α Centauri Authors: Ayres, Thomas R. Bibcode: 2014AJ....147...59A Altcode: 2014arXiv1401.0847A The following is a progress report on the long-term coronal (T ~ 1 MK) activity of α Centauri A (HD 128620: G2 V) and B (HD 128621: K1 V). Since 2005, Chandra X-Ray Observatory has carried out semiannual pointings on AB, mainly with the High Resolution Camera, but also on two occasions with the Low-Energy Transmission Grating Spectrometer, fully resolving the close pair in all cases. During 2008-2013, Chandra captured the rise, peak, and initial decline of B's coronal luminosity. Together with previous high states documented by ROSAT and XMM-Newton, the long-term X-ray record suggests a period of 8.1 ± 0.2 yr, compared to 11 yr for the Sun, with a minimum-to-peak contrast of 4.5, about half the typical solar cycle amplitude. Meanwhile, the A component has been mired in a Maunder-Minimum-like low state since 2005, initially recognized by XMM-Newton. But now, A finally appears to be climbing out of the extended lull. If interpreted simply as an overlong cycle, the period would be 19.2 ± 0.7 yr, with a minimum-to-peak contrast of 3.4. The short X-ray cycle of B, and possibly long cycle of A, are not unusual compared with the diverse (albeit much lower amplitude) chromospheric variations recorded, for example, by the HK Project. Further, the deep low state of A also is not unusual, but instead is similar to the L X/L bol of the Sun during recent minima of the sunspot cycle. Title: Mining the HST "Advanced Spectral Library (ASTRAL) - Hot Stars": The High Definition UV Spectrum of the Ap Star HR 465 Authors: Carpenter, Kenneth G.; Ayres, T. R.; Nielsen, K. E.; Kober, G. V.; Wahlgren, G. M.; Adelman, S. J.; Cowley, C. R. Bibcode: 2014AAS...22315105C Altcode: The "Advanced Spectral Library (ASTRAL) Project: Hot Stars" is a Hubble Space Telescope (HST) Cycle 21 Treasury Program (GO-13346: Ayres PI). It is designed to collect a definitive set of representative, high-resolution ( 30,000-100,000), high signal/noise (S/N>100), and full UV coverage 1200 - 3000 A) spectra of 21 early-type stars, utilizing the high-performance Space Telescope Imaging Spectrograph (STIS). The targets span the range of spectral types between early-O and early-A, including both main sequence and evolved stars, fast and slow rotators, as well as chemically peculiar (CP) and magnetic objects. These extremely high-quality STIS UV echelle spectra will be available from the HST archive and, in post-processed and merged form, at http://casa.colorado.edu ayres/ASTRAL/. The UV "atlases" produced by this program will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years to come. We offer a first look at one of the earliest datasets to come out of this observing program, a "high definition" UV spectrum of the Ap star HR 465, which was chosen as a prototypical example of an A-type magnetic CP star. HR 465 has a global magnetic field of ~2200 Gauss. Earlier analyses of IUE spectra show strong iron-peak element lines, along with heavy elements such as Ga and Pt, while being deficient in the abundance of some ions of low atomic number, such as carbon. We demonstrate the high quality of the ASTRAL data and present the identification of spectral lines for a number of elements. By comparison of the observed spectra with calculated spectra, we also provide estimates of element abundances, emphasizing heavy elements, and place these measurements in the context of earlier results for this and other Ap stars. Title: The "Horns" of FK Comae and the Complex Structure of its Outer Atmosphere Authors: Saar, Steven H.; Ayres, T. R.; Kashyap, V. Bibcode: 2014AAS...22315116S Altcode: As part of a large multiwavelength campaign (COCOA-PUFS*) to explore magnetic activity in the unusual, single, rapidly rotating giant FK Comae, we have taken a time series of moderate resolution FUV spectra of the star with the COS spectrograph on HST. We find that the star has unusual, time-variable emission profiles in the chromosphere and transition region which show horn-like features. We use simple spatially inhomogeneous models to explain the variable line shapes. Modeling the lower chromospheric Cl I 1351 Å line, we find evidence for a very extended, spatial inhomogeneous outer atmosphere, likely composed of many huge "sling-shot" prominences of cooler material with embedded in a rotationally distended corona. We compare these results with hotter hotter transition region lines (Si IV) and optical spectra of the chromospheric He I D3 line. We also employ the model Cl I profiles, and data-derived empirical models, to fit the complex spectral region around the coronal Fe XXI 1354.1 Å line. We place limits on the flux of this line, and show these limits are consistent with expectations from the observed X-ray spectrum. *Campaign for Observation of the Corona and Outer Atmosphere of the Fast-rotating Star, FK Comae This work was supported by HST grant GO-12376.01-A. Title: The Advanced Spectral Library (ASTRAL) Project Authors: Ayres, Thomas R.; The ASTRAL I & Science Teams, II Bibcode: 2014AAS...22325437A Altcode: The Advanced Spectral Library (ASTRAL) is an HST Treasury Program whose aim is to secure definitive ultraviolet (115-310 nm) spectra of representative bright stars utilizing the venerable -- yet still state-of-the-art -- Space Telescope Imaging Spectrograph (STIS). The initial Cycle 18 installment of the program (146 orbits in 2010-2011) focused on late-type (``cool’’) stars, acquiring high-S/N, high spectral resolution measurements of eight pivotal targets, including iconic objects like Betelgeuse and Procyon. The latest episode, in current Cycle 21 (230 orbits in 2013-2014), is designed to record very high-S/N (>100) STIS echellegrams, at the highest resolution feasible ( 30,000-100,000), of 21 representative bright early-type (``hot’’) stars, including equally iconic objects like Vega, Sirius, Regulus, and Zeta Puppis. The targets span a broad range of spectral types between early-O and early-A, encompassing main sequence and evolved stars, fast and slow rotators, as well as chemically peculiar and magnetic objects. These high-quality STIS UV spectra will be publicly available immediately after observation from the HST archive; and, in post-processed and merged form, at the project website: http://casa.colorado.edu ayres/ASTRAL/. The UV "atlases" produced by the ASTRAL Program will enable investigations of a broad range of astrophysical problems -- stellar, interstellar, and beyond -- for many years to come. Supported by Guest Observer grants from STScI. Title: HST/STIS Advanced Spectral Library (ASTRAL) Authors: Ayres, T. R. Bibcode: 2014ASInC..13....1A Altcode: ASTRAL is a Hubble Space Telescope Large Treasury Program whose aim is to collect full-coverage ultraviolet (1150-3100 Å) echelle spectra of representative stars of spectral types O-M, with resolution and S/N comparable to the best now obtained routinely in optical observations from the ground. First part of the program - Cool Stars - was completed in 2011. Second part - Hot Stars - is in progress (2013-2014). Resulting high-level processed UV "atlases" are available from the ASTRAL site:

http://casa.colorado.edu/ ayres/ASTRAL/ Title: HST/STIS Advanced Spectral Library (ASTRAL) Authors: Ayres, T. R. Bibcode: 2014ASInC..11....1A Altcode: ASTRAL is a Hubble Space Telescope Large Treasury Program whose aim is to collect full-coverage ultraviolet (1150--3100 &Aring) echelle spectra of representative stars of spectral types O--M, with resolution and S/N comparable to the best now obtained routinely in optical observations from the ground. First part of the program -- Cool Stars -- was completed in 2011. Second part -- Hot Stars -- is in progress (2013--2014). Resulting high-level processed UV "atlases" are available from the ASTRAL site:

http://casa.colorado.edu/ ayres/ASTRAL/ Title: Advanced Spectral Library II: Hot Stars Authors: Ayres, Thomas Bibcode: 2013hst..prop13346A Altcode: Stars are the bright matter of the Universe. Without them, it would be a dull and dreary place indeed: no light, no heavy elements, no planets, no life. It also is safe to say that stellar spectroscopy is a cornerstone of astrophysics, providing much of what we know concerning temperatures and masses of stars, their compositions, planets, and the dynamics and evolution of the galaxies they inhabit. This is especially true for the satellite ultraviolet, owing to the rich collection of atomic and ionic transitions found there. Unfortunately, the archive of Space Telescope Imaging Spectrograph rarely achieves the high S/N of the best ground-based spectra, and relatively few objects have the full wavelength coverage for which the powerful, highly multiplexed, second generation Hubble instrument was designed. Our aim is to collect STIS UV echelle spectra - comparable in S/N and resolution to the best ground-based material - for a diverse sample of representative stars, to build an Advanced Spectral Library; a foundation for astrophysical exploration: stellar, interstellar, and beyond. Our first effort, in Cycle 18, involved cool stars. Now we turn attention to the hot side of the H-R diagram.Our Treasury program will provide detailed stellar "atlases," based on advanced processing of the STIS echellegrams. Members of our broad collaboration will analyze these data for specific purposes, such as dynamics of O-star mass-loss; detection of rare species in sharp-lined B stars; and properties and kinematics of local interstellar clouds; but public release {based on the "ASTRAL-I" model} will enable many other investigations by a much wider community, for decades to come. Title: Alpha Cen: Climbing out of a Coronal Recession? {year 3 continuation} Authors: Ayres, Thomas Bibcode: 2013hst..prop13465A Altcode: Nearby Alpha Centauri contains the two best characterized G and K dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. Alpha Cen A & B also have the best studied stellar X-ray activity cycles, extending back to the 1970's. Present proposal is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin A is expected to be rising to cycle maximum following an extended coronal recession. STIS E140M spectra will support and leverage the broad-band X-ray measurements by probing subcoronal dynamics and providing a low-T boundary condition for DEM modeling, with connection to the X-rays through the FUV Fe XII coronal forbidden line. Title: The Ups and Downs of Alpha Centauri Authors: Ayres, Thomas R. Bibcode: 2013SPD....44..152A Altcode: The nearby Alpha Centauri triple system has two solar-type stars in a relatively close orbit (20 au separation), and a dim red dwarf companion -- Proxima -- about 10,000 au away, on the Sun-ward side of the group. The heaviest star -- Alpha Cen A -- is a close twin of the Sun. Its slightly less massive companion -- Alpha Cen B -- is a K-type dwarf, and is the closest star thought to host an exoplanet (Earth-sized, but in a much tighter orbit). The close pair has been scrutinized for more than a decade in X-rays by XMM and Chandra, on a semiannual basis since 2003 and 2005, respectively. However, in recent years only Chandra has been able to cleanly separate the pair, which are approaching closest separation on the sky (only a few arcseconds) in their 80-year orbit. For the past 3 years, the HST STIS spectrograph has joined the crowd, also capturing FUV snapshots of the pair every six months. The Alpha Cen stars provide an important complement to long-term studies of the Sun at high energies. The K-star has displayed a clear 8-year cycle in recent years, while the G-star remains mired in a Maunder-like minimum. Title: Red Giant Atmospheres, through the Lens of UV Spectroscopy Authors: Ayres, Thomas R. Bibcode: 2013giec.conf10202A Altcode: UV spectra of normal red giants show many differences with the Sun. The usual high-excitation, coronal-related emissions like Si IV and C IV are weak or absent, but low-excitation species like O I and Mg II are conspicuous and often carry signatures of strong, chromospheric winds. In extreme cases, one even finds dusty molecule-rich circumstellar envelopes that absorb strongly in the FUV bands of CO. At higher energies -- X-rays -- the red giants are even more feeble, inhabiting was has been called the "coronal graveyard." One imagines that the general avoidance of high-energy emissions among the red giants is a consequence of lack of magnetic activity due to slow rotation. Indeed, if one considers tidally spun-up red giants in short-period binaries, such objects are among the most coronally active known. Still, even if the rotationally catalyzed "dynamo" is suppressed in the normal red giants, they should have some residual magnetic activity generated by surface convective processes. UV spectra can provide clues to where these putative fields are hiding; and their possible connection to the chromospheric winds. Title: Status of RAISE, the Rapid Acquisition Imaging Spectrograph Experiment Authors: Laurent, Glenn T.; Hassler, D. M.; DeForest, C.; Ayres, T. R.; Davis, M.; De Pontieu, B.; Schuehle, U.; Warren, H. Bibcode: 2013SPD....44..145L Altcode: The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) sounding rocket payload is a high speed scanning-slit imaging spectrograph designed to observe the dynamics and heating of the solar chromosphere and corona on time scales as short as 100 ms, with 1 arcsec spatial resolution and a velocity sensitivity of 1-2 km/s. The instrument is based on a new class of UV/EUV imaging spectrometers that use only two reflections to provide quasi-stigmatic performance simultaneously over multiple wavelengths and spatial fields. The design uses an off-axis parabolic telescope mirror to form a real image of the sun on the spectrometer entrance aperture. A slit then selects a portion of the solar image, passing its light onto a near-normal incidence toroidal grating, which re-images the spectrally dispersed radiation onto two array detectors. Two full spectral passbands over the same one-dimensional spatial field are recorded simultaneously with no scanning of the detectors or grating. The two different spectral bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two intensified Active Pixel Sensor (APS) detectors whose focal planes are individually adjusted for optimized performance. The telescope and grating are coated with B4C to enhance short wavelength (2nd order) reflectance, enabling the instrument to record the brightest lines between 602-622Å and 761-780Å at the same time. RAISE reads out the full field of both detectors at 5-10 Hz, allowing us to record over 1,500 complete spectral observations in a single 5-minute rocket flight, opening up a new domain of high time resolution spectral imaging and spectroscopy. We present an overview of the project, a summary of the maiden flight results, and an update on instrument status.Abstract (2,250 Maximum Characters): The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) sounding rocket payload is a high speed scanning-slit imaging spectrograph designed to observe the dynamics and heating of the solar chromosphere and corona on time scales as short as 100 ms, with 1 arcsec spatial resolution and a velocity sensitivity of 1-2 km/s. The instrument is based on a new class of UV/EUV imaging spectrometers that use only two reflections to provide quasi-stigmatic performance simultaneously over multiple wavelengths and spatial fields. The design uses an off-axis parabolic telescope mirror to form a real image of the sun on the spectrometer entrance aperture. A slit then selects a portion of the solar image, passing its light onto a near-normal incidence toroidal grating, which re-images the spectrally dispersed radiation onto two array detectors. Two full spectral passbands over the same one-dimensional spatial field are recorded simultaneously with no scanning of the detectors or grating. The two different spectral bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two intensified Active Pixel Sensor (APS) detectors whose focal planes are individually adjusted for optimized performance. The telescope and grating are coated with B4C to enhance short wavelength (2nd order) reflectance, enabling the instrument to record the brightest lines between 602-622Å and 761-780Å at the same time. RAISE reads out the full field of both detectors at 5-10 Hz, allowing us to record over 1,500 complete spectral observations in a single 5-minute rocket flight, opening up a new domain of high time resolution spectral imaging and spectroscopy. We present an overview of the project, a summary of the maiden flight results, and an update on instrument status. Title: Computing Intrinsic LYα Fluxes of F5 V to M5 V Stars Authors: Linsky, Jeffrey L.; France, Kevin; Ayres, Tom Bibcode: 2013ApJ...766...69L Altcode: 2013arXiv1301.5711L The Lyα emission line dominates the far-ultraviolet spectra of late-type stars and is a major source for photodissociation of important molecules including H2O, CH4, and CO2 in exoplanet atmospheres. The incident flux in this line illuminating an exoplanet's atmosphere cannot be measured directly as neutral hydrogen in the interstellar medium (ISM) attenuates most of the flux reaching the Earth. Reconstruction of the intrinsic Lyα line has been accomplished for a limited number of nearby stars, but is not feasible for distant or faint host stars. We identify correlations connecting the intrinsic Lyα flux with the flux in other emission lines formed in the stellar chromosphere, and find that these correlations depend only gradually on the flux in the other lines. These correlations, which are based on Hubble Space Telescope spectra, reconstructed Lyα line fluxes, and irradiance spectra of the quiet and active Sun, are required for photochemical models of exoplanet atmospheres when intrinsic Lyα fluxes are not available. We find a tight correlation of the intrinsic Lyα flux with stellar X-ray flux for F5 V to K5 V stars, but much larger dispersion for M stars. We also show that knowledge of the stellar effective temperature and rotation rate can provide reasonably accurate estimates of the Lyα flux for G and K stars, and less accurate estimates for cooler stars. Title: Absorbing Gas around the WASP-12 Planetary System Authors: Fossati, L.; Ayres, T. R.; Haswell, C. A.; Bohlender, D.; Kochukhov, O.; Flöer, L. Bibcode: 2013ApJ...766L..20F Altcode: 2013arXiv1303.3375F Near-UV observations of the planet host star WASP-12 uncovered the apparent absence of the normally conspicuous core emission of the Mg II h and k resonance lines. This anomaly could be due either to (1) a lack of stellar activity, which would be unprecedented for a solar-like star of the imputed age of WASP-12 or (2) extrinsic absorption, from the intervening interstellar medium (ISM) or from material within the WASP-12 system itself, presumably ablated from the extreme hot Jupiter WASP-12 b. HIRES archival spectra of the Ca II H and K lines of WASP-12 show broad depressions in the line cores, deeper than those of other inactive and similarly distant stars and similar to WASP-12's Mg II h and k line profiles. We took high-resolution ESPaDOnS and FIES spectra of three early-type stars within 20' of WASP-12 and at similar distances, which show the ISM column is insufficient to produce the broad Ca II depression observed in WASP-12. The EBHIS H I column density map supports and strengthens this conclusion. Extrinsic absorption by material local to the WASP-12 system is therefore the most likely cause of the line core anomalies. Gas escaping from the heavily irradiated planet could form a stable and thick circumstellar disk/cloud. The anomalously low stellar activity index (log R^{{\prime }}_{HK}) of WASP-12 is evidently a direct consequence of the extra core absorption, so similar HK index deficiencies might signal the presence of translucent circumstellar gas around other stars hosting evaporating planets.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Rechereche Scientifique of France, and the University of Hawaii. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Title: Is the Sun Lighter than the Earth? Isotopic CO in the Photosphere, Viewed through the Lens of Three-dimensional Spectrum Synthesis Authors: Ayres, Thomas R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.; Wedemeyer-Böhm, S. Bibcode: 2013ApJ...765...46A Altcode: 2013arXiv1301.5281A We consider the formation of solar infrared (2-6 μm) rovibrational bands of carbon monoxide (CO) in CO5BOLD 3D convection models, with the aim of refining abundances of the heavy isotopes of carbon (13C) and oxygen (18O, 17O), to compare with direct capture measurements of solar wind light ions by the Genesis Discovery Mission. We find that previous, mainly 1D, analyses were systematically biased toward lower isotopic ratios (e.g., R 23 ≡ 12C/13C), suggesting an isotopically "heavy" Sun contrary to accepted fractionation processes that were thought to have operated in the primitive solar nebula. The new 3D ratios for 13C and 18O are R 23 = 91.4 ± 1.3 (R ⊕ = 89.2) and R 68 = 511 ± 10 (R ⊕ = 499), where the uncertainties are 1σ and "optimistic." We also obtained R 67 = 2738 ± 118 (R ⊕ = 2632), but we caution that the observed 12C17O features are extremely weak. The new solar ratios for the oxygen isotopes fall between the terrestrial values and those reported by Genesis (R 68 = 530, R 67 = 2798), although including both within 2σ error flags, and go in the direction favoring recent theories for the oxygen isotope composition of Ca-Al inclusions in primitive meteorites. While not a major focus of this work, we derive an oxygen abundance, epsilonO ~ 603 ± 9 ppm (relative to hydrogen; log epsilon ~ 8.78 on the H = 12 scale). The fact that the Sun is likely lighter than the Earth, isotopically speaking, removes the necessity of invoking exotic fractionation processes during the early construction of the inner solar system. Title: Isotopic CO in the Solar Photosphere, Viewed Through the Lens of 3D Spectrum Synthesis Authors: Ayres, T. R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.; Wedemeyer-Bohm, S. Bibcode: 2013LPI....44.3038A Altcode: 2013LPICo1719.3038A New analyses of CO isotopologue abundances in the solar photosphere are now consistent with Genesis solar wind results, although ^17O error bars are still large. Title: Advanced Spectral Library (ASTRAL): Cool stars edition Authors: Ayres, T. R. Bibcode: 2013AN....334..105A Altcode: 2013csss...17..105A ASTRAL is a project to create high-resolution, high-S/N UV (1150-3200 Å) atlases of bright stars utilizing {HST}/STIS. During Cycle 18 (2010-2011), eight cool star targets were observed, including key objects like Procyon and Betelgeuse, churning through 146 orbits in the process. The new spectral atlases are publically available through the project website.

Data were obtained with the Hubble Space Telescope. Title: A Large Sample of Magnetically-Active Stars Observed With Kepler Authors: Wells, Mark; Neff, J. E.; Brown, A.; Ayres, T. R.; Basri, G. S.; Berdyugina, S.; Harper, G.; Hawley, S. L.; Korhonen, H.; Kowalski, A.; Micela, G.; Piskunov, N. E.; Ramsey, L. W.; Saar, S. H.; Walkowicz, L. M. Bibcode: 2013AAS...22135415W Altcode: We have observed about 325 stars in our Kepler Guest Observer programs (Cycles 1 through 4). For most of these targets, we are analyzing extremely high-precision light curves that have been continuously sampled every 30 minutes for up to 3 years. Our sample of candidate magnetically-active stars was selected primarily using GALEX colors. Starspots, pulsations, and variations due to eclipsing and contact binaries combine to produce a rich variety of light curves. We have developed semi-automated procedures to characterize this variability and thus to classify the targets and identify the physical mechanisms that dominate their Kepler light curves. We will describe these procedures and discuss the range of physical properties covered by our final classification scheme. We are using this Kepler database of variability over timescales of minutes to years to provide diagnostics of flares, starspot formation, evolution, migration, and ultimately of stellar cycles in general. This work contains results obtained using the NASA Kepler satellite and from the Apache Point Observatory, the MMT (using NOAO community access time), and the Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants NNX10AC51G, NNX11AC79G, and NNX12AC85G to the University of Colorado, by NSF grant AST-1109695 to the College of Charleston, and by a grant from the South Carolina Space Grant consortium. Title: Chromospheric thermal continuum millimetre emission from non-dusty K and M red giants Authors: Harper, G. M.; O'Riain, N.; Ayres, T. R. Bibcode: 2013MNRAS.428.2064H Altcode: 2012MNRAS.tmp..152H; 2012arXiv1210.2627H We examine the thermal free-free millimetre fluxes expected from non-dusty and non-pulsating K through mid-M giant stars based on our limited understanding of their inhomogeneous chromospheres. We present a semi-analytic model that provides estimates of the radio fluxes for the mm wavelengths [e.g. Combined Array for Research in Millimetre-wave Astronomy (CARMA), Atacama Large Millimetre/submillimetre Array (ALMA) and Karl G. Jansky Very Large Array (JVLA) Q band] based on knowledge of the effective temperatures, angular diameters and chromospheric Mg ii h & k emission fluxes. At 250 GHz, the chromospheric optical depths are expected to be significantly less than unity, which means that fluxes across the mm and submm range will have a contribution from the chromospheric material that gives rise to the ultraviolet emission spectrum, as well as the cool molecular material known to exist above the photosphere. We predict a lower bound to the inferred brightness temperature of red giants based on heating at the basal flux limit if the upper chromospheres have filling factor ≃1. Multifrequency mm observations should provide important new information on the structuring of the inhomogeneous chromospheres, including the boundary layer, and allow tests of competing theoretical models for atmospheric heating. We comment on the suitability of these stars as mm flux calibrators. Title: Ultraviolet and Extreme Ultraviolet Emission of Host Stars and Effects on Exoplanet Atmospheres Authors: Linsky, Jeffrey; France, K.; Ayres, T. R. Bibcode: 2013AAS...22132105L Altcode: The chemistry and mass-loss rates of exoplanet atmospheres are controlled by the radiative and particle emission of their host star. The host star's ultraviolet radiation, and especially the Lyman-alpha emission, photodissociate important molecules in exoplanet atmospheres including water, CO2, and methane. The intrinsic Lyman-alpha emission cannot be observed because of attenuation by neutral hydrogen in the interstellar medium and must therefore be reconstructed. We describe a new reconstruction method based on correlations of Lyman-alpha flux with the fluxes in other emission lines formed at similar temperatures in the stellar chromosphere. Except for low metal abundance stars, this technique provides estimates of the Lyman-alpha flux within 20 percent of the values obtained by Wood et al. (2005) for stars of spectral type F5 V to M5 V. We also show that the EUV flux in 100 A wide spectral bands from 300 to 1170 A is well correlated with the Lyman-alpha flux and therefore can be accurately estimated for these stars. This work is based on observations with the COS and STIS instruments on HST, and is supported by NASA grants to the Space Telescope Science Institute and the University of Colorado. Title: Solar carbon monoxide: poster child for 3D effects . Authors: Ayres, T. R.; Lyons, J. R.; Ludwig, H. -G.; Caffau, E.; Wedemeyer-Böhm, S. Bibcode: 2013MSAIS..24...85A Altcode: Photospheric infrared (2-6 mu m) rovibrational bands of carbon monoxide (CO) provide a tough test for 3D convection models such as those calculated using CO5BOLD. The molecular formation is highly temperature-sensitive, and thus responds in an exaggerated way to thermal fluctuations in the dynamic atmosphere. CO, itself, is an important tracer of the oxygen abundance, a still controversial issue in solar physics; as well as the heavy isotopes of carbon (13C) and oxygen (18O, 17O), which, relative to terrestrial values, are fingerprints of fractionation processes that operated in the primitive solar nebula. We show how 3D models impact the CO line formation, and add in a second constraint involving the near-UV Ca RIPTSIZE II line wings, which also are highly temperature sensitive, but in the opposite sense to the molecules. We find that our reference CO5BOLD snapshots appear to be slightly too cool on average in the outer layers of the photosphere where the CO absorptions and Ca RIPTSIZE II wing emissions arise. We show, further, that previous 1D modeling was systematically biased toward higher oxygen abundances and lower isotopic ratios (e.g., R23equiv 12C/13C), suggesting an isotopically ``heavy'' Sun contrary to direct capture measurements of solar wind light ions by the Genesis Discovery Mission. New 3D ratios for the oxygen isotopes are much closer to those reported by Genesis, and the associated oxygen abundance from CO now is consistent with the recent Caffau et al. study of atomic oxygen. Some lingering discrepancies perhaps can be explained by magnetic bright points. Solar CO demonstrates graphically the wide gulf that can occur between a 3D analysis and 1D. Title: Mining the Advanced Spectral Library (ASTRAL): Characterizing Winds of Evolved M-Stars Authors: Nielsen, Krister E.; Carpenter, K. G.; Kober, G. V.; Cheng, K.; Ayres, T. R.; Harper, G. Bibcode: 2013AAS...22135102N Altcode: The HST/STIS treasury program Advanced Spectral Library (ASTRAL) enables investigations of the character and dynamics of the wind and chromosphere of cool stars, using high quality spectral data. This paper present the analysis of the outflowing winds of the M3.4 giant Gamma Cru and the M2Iab supergiant Alpha Ori. The outer atmospheres of these objects show strong evidence for significant inhomogeneity in their thermal and kinematic structure, and are in general not well understood. The wind features are characterized by a strong chromospheric emission suppressed by a overlying wind absorption, for many transitions producing a double peak feature. The relative strengths and wavelength shifts between the absorption and emission components of the lines reflect the acceleration of the wind from the base of the chromosphere, as the self-absorption is due to the overlying wind absorption, whose velocity relative to the chromosphere varies with height and thus line opacity. The wind profiles are sensitive to the wind opacity, turbulence and flow velocity, and hence favorable to analyze with the Sobolev source function with Exact Integration of the transfer equation (SEI) code. This paper will show a velocity and intensity analysis of the wind profiles and modeling with the SEI code to derive an improved set of wind parameters, primarily, for Gamma Cru. Title: Young Star Populations in the Kepler Field Authors: Brown, Alexander; Neff, J. E.; Wells, M.; Saar, S.; Furesz, G.; Walkowicz, L. M.; Ayres, T. R.; Basri, G. S.; Berdyugina, S.; Harper, G.; Hawley, S. L.; Korhonen, H.; Kowalski, A.; Micela, G.; Piskunov, N. E.; Ramsey, L. W. Bibcode: 2013AAS...22135414B Altcode: The Kepler satellite is providing spectacular optical photometric light-curves of unprecedented precision and duration that routinely allow detailed studies of stellar magnetic activity on late-type stars that were difficult previously. Kepler provides multi-year duration light-curves that allow investigation of how activity phenomena -- such as the growth, migration, and decay of star-spots, differential rotation, activity cycles, and flaring -- operate on a wide variety of single and binary stars. The 105 square degree Kepler Field contains tens of thousands of late-type stars showing rotational modulation due to star-spots with periods ranging from one day to a ``solar-like'' month. Short rotation periods and high levels of magnetic activity are strongly correlated. However, there are only two basic reasons why stars with rotation periods of a few days possess such high angular momentum --- either they are close binaries or they are young stars. During Kepler GO Cycles 1 through 4 we have been studying the Long-cadence (30 minute sampling) photometry of hundreds of active late-type stars and as an absolutely essential complement we have been obtaining high resolution optical spectra to understand the physical properties of these stars. We present results from a spectroscopic survey using the MMT Hectochelle multi-object echelle of 4 square degrees of the Kepler Field. We have discovered a significant population of young stars with Li I absorption indicating ages of ~100 Myr or less at a spatial density of at least 20 stars per square degree. Our detected young star sample comprises at least 80 stars and represents a dramatic advance compared to the previously known sample over the full Kepler Field of three stars in this age range. Roughly one sixth of the stars observed are young and a similar number short-period binaries based on 2-4 radial velocities. We show how the rotational properties of the stars and their physical properties are related. This work is based on data obtained with the NASA Kepler satellite and the MMT Hectochelle spectrograph using NOAO community access time. Support by NASA Kepler grants to the University of Colorado and by NSF grant to the College of Charleston. Title: Mining the Advanced Spectral Library (ASTRAL): Fluorescence in Evolved M-Stars Authors: Carpenter, Kenneth G.; Nielsen, K. E.; Kober, G. V.; Cheng, K.; Ayres, T. R.; Wahlgren, G. M.; Harper, G. Bibcode: 2013AAS...22135101C Altcode: The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program designed to collect a definitive set of representative, high-resolution ( 46,000 in the FUV up to ~1700 Å, 30,000 for 1700-2150 Å, and 114,000 >2150 Å) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the University of Colorado (http://casa.colorado.edu ayres/ASTRAL/) and will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years. In this paper, we use the very rich emission-line spectra of the two evolved M stars in the sample, the M3.4 giant Gamma Crucis (GaCrux) and the M2Iab supergiant Alpha Orionis (Betelgeuse), to study the fluorescence processes operating in their outer atmospheres. We summarize the pumping transitions and fluorescent line products known on the basis of previous work (e.g. Carpenter 1988 and references therein) and newly identified in our current, on-going analysis and provide some comments on their implications for the structure of the outer atmospheres of these stars. Title: Near-ultraviolet Absorption, Chromospheric Activity, and Star-Planet Interactions in the WASP-12 system Authors: Haswell, C. A.; Fossati, L.; Ayres, T.; France, K.; Froning, C. S.; Holmes, S.; Kolb, U. C.; Busuttil, R.; Street, R. A.; Hebb, L.; Collier Cameron, A.; Enoch, B.; Burwitz, V.; Rodriguez, J.; West, R. G.; Pollacco, D.; Wheatley, P. J.; Carter, A. Bibcode: 2012ApJ...760...79H Altcode: 2013arXiv1301.1860H Extended gas clouds have been previously detected surrounding the brightest known close-in transiting hot Jupiter exoplanets, HD 209458 b and HD 189733 b we observed the distant but more extreme close-in hot Jupiter system, WASP-12, with Hubble Space Telescope (HST). Near-UV (NUV) transits up to three times deeper than the optical transit of WASP-12 b reveal extensive diffuse gas, extending well beyond the Roche lobe. The distribution of absorbing gas varies between visits. The deepest NUV transits are at wavelength ranges with strong stellar photospheric absorption, implying that the absorbing gas may have temperature and composition similar to those of the stellar photosphere. Our spectra reveal significantly enhanced absorption (greater than 3σ below the median) at ~200 individual wavelengths on each of two HST visits; 65 of these wavelengths are consistent between the two visits, using a strict criterion for velocity matching that excludes matches with velocity shifts exceeding ~20 km s-1. Excess transit depths are robustly detected throughout the inner wings of the Mg II resonance lines independently on both HST visits. We detected absorption in Fe II λ2586, the heaviest species yet detected in an exoplanet transit. The Mg II line cores have zero flux, emission cores exhibited by every other observed star of similar age and spectral type are conspicuously absent. WASP-12 probably produces normal Mg II profiles, but the inner portions of these strong resonance lines are likely affected by extrinsic absorption. The required Mg+ column is an order of magnitude greater than expected from the interstellar medium, though we cannot completely dismiss that possibility. A more plausible source of absorption is gas lost by WASP-12 b. We show that planetary mass loss can produce the required column. Our Visit 2 NUV light curves show evidence for a stellar flare. We show that some of the possible transit detections in resonance lines of rare elements may be due instead to non-resonant transitions in common species. We present optical observations and update the transit ephemeris.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from MAST at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 11651 and 11673. Title: Alpha Cen: Climbing out of a Coronal Recession? {year 2 continuation} Authors: Ayres, Thomas Bibcode: 2012hst..prop13060A Altcode: Nearby Alpha Centauri contains the two best characterized G and K dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. Alpha Cen A & B also have the best studied stellar X-ray activity cycles, extending back to the 1970â??s. Present proposal is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin A is expected to be rising to cycle maximum from an extended coronal recession. STIS E140M spectra will support and leverage the broad-band X-ray measurements by probing subcoronal dynamics and providing a low-T boundary condition for DEM modeling, with connection to HRC through the FUV Fe XII coronal forbidden line. Title: Ultraviolet Spectroscopy of Rapidly Rotating Solar-Mass Stars: Emission-line Redshifts as a Test of the Solar-Stellar Connection Authors: Linsky, Jeffrey L.; Bushinsky, Rachel; Ayres, Tom; France, Kevin Bibcode: 2012ApJ...754...69L Altcode: 2012arXiv1205.6498L We compare high-resolution ultraviolet spectra of the Sun and thirteen solar-mass main-sequence stars with different rotational periods that serve as proxies for their different ages and magnetic field structures. In this, the second paper in the series, we study the dependence of ultraviolet emission-line centroid velocities on stellar rotation period, as rotation rates decrease from that of the Pleiades star HII314 (P rot = 1.47 days) to α Cen A (P rot = 28 days). Our stellar sample of F9 V to G5 V stars consists of six stars observed with the Cosmic Origins Spectrograph on the Hubble Space Telescope (HST) and eight stars observed with the Space Telescope Imaging Spectrograph on HST. We find a systematic trend of increasing redshift with more rapid rotation (decreasing rotation period) that is similar to the increase in line redshift between quiet and plage regions on the Sun. The fastest-rotating solar-mass star in our study, HII314, shows significantly enhanced redshifts at all temperatures above log T = 4.6, including the corona, which is very different from the redshift pattern observed in the more slowly rotating stars. This difference in the redshift pattern suggests that a qualitative change in the magnetic-heating process occurs near P rot = 2 days. We propose that HII314 is an example of a solar-mass star with a magnetic heating rate too large for the physical processes responsible for the redshift pattern to operate in the same way as for the more slowly rotating stars. HII314 may therefore lie above the high activity end of the set of solar-like phenomena that is often called the "solar-stellar connection." Title: The Old Feeble Transition Regions and Coronae of Solar-like Dwarf Stars in the Arcturus Moving Group Authors: Brown, Alexander; Hodges-Kluck, E. J.; Ayres, T. R.; Harper, G. M. Bibcode: 2012AAS...22032804B Altcode: Old dwarf stars have generally spun down significantly thus dampening one of the main contributors (rotation) to solar-like alpha-omega magnetic dynamo activity. Studying how stellar activity on stars older than the Sun changes in terms of the chromospheric/transition-region/coronal temperature structure and how much energy is radiated as a function of temperature provides important constraints on how solar-like dynamos work. Stars with different metallicities provide information on how the radiative cooling channels control the temperature structure.

We have measured fluxes and profiles of FUV emission lines using the HST COS spectrograph and the broad-band X-ray fluxes using Chandra ACIS-S for a sample of old inactive dwarfs. Our sample comprises five members of the 7-8 Gyr Arcturus Moving Group --- HD90508/LHS2266 (F9 V/M4 V, [Fe/H] = -0.4), HD65583 (G8 V, Fe/H]=-0.7), and HD145417 (K0 V, [Fe/H]=-1.4) --- plus three well-studied comparison stars -- HD103095 (G8 V, [Fe/H]=-1.4), Tau Ceti (G8 V, [Fe/H]=-0.4), and the Quiet Sun (G2 V, [Fe/H]=0.0).

In this poster we provide estimates of atmospheric radiative losses as a function of temperature and metallicity. The atmospheres of these low-metallicity stars are more heavily weighted towards cooler temperatures than those of more active stars or even the Sun. Chromospheric emission lines, e.g. C I lines, are far stronger relative transition region lines, e.g C IV. Similarly the X-ray data provide detections for all the targets but with primarily very soft (0.3-0.5 keV) photons and imply "coronal" temperatures of less than 1 MK. While the temperature distributions are cooler, the overall integrated X-ray and FUV luminosities are similar to those of the "Quiet Sun" -- implying that similar amounts of non-radiative energy input are being dissipated.

This work is supported by NASA GALEX grant NNX06AB46G, HST grants GO-11555 and GO-11829, and Chandra grants GO6-7018X, GO7-8020X, and GO9-0021X to the University of Colorado. Title: Using Kepler Data to Characterize the Flare Properties of GK Stars Authors: Kowalski, Adam F.; Deitrick, Russell J.; Brown, Alex; Davenport, Jim R. A.; Hawley, Suzanne L.; Hilton, Eric J.; Ayres, Thomas R.; Berdyugina, Svetlana V.; Harper, Graham M.; Korhonen, Heidi; Walkowicz, Lucianne M. Bibcode: 2012decs.confE.120K Altcode: Due to their high occurrence rate and large contrast against the background stellar emission, white-light flares on a handful of very active low-mass M stars have been the primary source for our understanding of optical flare emission. Kepler's high-precision, long baseline light curves have opened up the characterization of white-light emission to new domains of stars, including active G dwarfs. We present the properties of white-light flares on GALEX-selected solar-type stars from GO data in Q1-Q7. The flares are discussed in relation to intrinsic stellar properties, which are constrained by a vast amount of follow-up characterization of the sample. We compare the flare properties to large white-light flares observed on the Sun. These high-precision state-of-the-art observations will provide important constraints for models of internal magnetic dynamos and NLTE radiative-hydrodynamic simulations of energy deposition in the lower atmospheric layers. Title: The Solar Oxygen Crisis, Revisited Authors: Ayres, Thomas R. Bibcode: 2012AAS...21914408A Altcode: For years, controversy has raged over what seemingly should be a well-established property of our Sun, the solar oxygen abundance. Spectroscopic estimates early last decade based on advanced 3D time-dependent photospheric convection simulations, suggested that the true oxygen abundance was almost 40% lower than the value (680 ppm relative to hydrogen) recommended only a few years prior. The unexpectedly low value sparked what has come to be called the ``Solar Oxygen Crisis,'' because the previous higher abundance was almost exactly what was required by helioseismology to reproduce the interior sound speed profile, well-characterized from surface p-mode measurements. Although in most other parts of Astronomy, agreement to within a factor of two is cause for celebration, in this case -- despite intense efforts on both sides -- there did not seem to be an easy way to reconcile the disparate results from the inside and outside of the Sun. In this study, I examine the surface spectroscopy side of the issue, bringing to bear additional diagnostics, such as center-to-limb behavior, on the one hand to validate the thermal properties of the 3D convection models, and on the other to provide additional leverage on the abundance issue. The main conclusion is that existing 3D models can reproduce the key continuum center-limb effect in the visible, showing that the mean thermal gradient in the deep atmosphere is accurate, but the same models misunderestimate intensities in the inner wings of the H and K resonance lines of ionized calcium, a signature of too-low temperatures in the middle photosphere (where key oxygen bearing CO and OH reside). Implications for a unified description of the oxygen abundance from atomic and molecular species are discussed. This work supported by NSF. Title: Far-ultraviolet Continuum Emission: Applying This Diagnostic to the Chromospheres of Solar-mass Stars Authors: Linsky, Jeffrey L.; Bushinsky, Rachel; Ayres, Tom; Fontenla, Juan; France, Kevin Bibcode: 2012ApJ...745...25L Altcode: 2011arXiv1109.5653L The far-ultraviolet (FUV) continuum flux is recognized as a very sensitive diagnostic of the temperature structure of the Sun's lower chromosphere. Until now analysis of the available stellar FUV data has shown that solar-type stars must also have chromospheres, but quantitative analyses of stellar FUV continua require far higher quality spectra and comparison with new non-LTE chromosphere models. We present accurate far-ultraviolet (FUV, 1150-1500 Å) continuum flux measurements for solar-mass stars, made feasible by the high throughput and very low detector background of the Cosmic Origins Spectrograph on the Hubbble Space Telescope. We show that the continuum flux can be measured above the detector background even for the faintest star in our sample. We find a clear trend of increasing continuum brightness temperature at all FUV wavelengths with decreasing rotational period, which provides an important measure of magnetic heating rates in stellar chromospheres. Comparison with semiempirical solar flux models shows that the most rapidly rotating solar-mass stars have FUV continuum brightness temperatures similar to the brightest faculae seen on the Sun. The thermal structure of the brightest solar faculae therefore provides a first-order estimate of the thermal structure and heating rate for the most rapidly rotating solar-mass stars in our sample. Title: The Amazing COS FUV (1320 - 1460 Å) Spectrum of λ Vel (K4Ib-II)1 Authors: Carpenter, K. G.; Ayres, T.; Brown, A.; Harper, G. M.; Wahlgren, G. M. Bibcode: 2011ASPC..448.1083C Altcode: 2011csss...16.1083C The FUV spectrum (1320-1460 Å) of the K4 Ib-II supergiant λ Vel was observed with the Cosmic Origins Spectrograph (COS) on HST, as part of the Ayres and Redfield Cycle 17 SNAP program "SNAPing Coronal Iron." This spectrum covers a region not previously recorded in λ Vel at high resolution and, in a mere 20 minutes of exposure, reveals an amazing treasure trove of information. It shows a wide variety of strong emission lines and multiple absorption lines, superposed on a bright chromospheric continuum, with contributions from both atomic and molecular species. These features provide diagnostics of the chromosphere and wind of the star, and by comparison with spectra of stars of similar Teff and/or geff, will improve our knowledge of the heating processes in the chromospheres and the forces driving the stellar wind in cool evolved stars. We present the details of this spectrum, in comparison with stars of similar temperature or luminosity, and discuss our initial interpretation of the data. Title: Bridging STIS's Neutral Density Desert Authors: Ayres, Thomas Bibcode: 2011hst..prop12567A Altcode: This is a calibration proposal focused on a set of unsupported ND-filtered long slits {31X0.05NDA,B,C} that can be used with the STIS echelles, and which provide attenuations intermediate between the standard spectroscopic slits {0.2X0.06, 0.2X0.09, or 0.1X0.03} and the {only two} supported ND slits: 0.2X0.05ND {ND=2} and 0.3X0.05ND {ND=3}. These intermediate NDs {0.6-1.4} potentially are valuable for bright continuum sources, mainly hot stars, for which currently the supported ND slits must be used to mitigate MAMA global count rate violations. Because there is such a large jump from the normal clear spectroscopic slits {ND 0} to the next supported ND step {ND=2}, there are many cases where an observation just barely exceeds the global rate with a clear aperture, and therefore must shift to the ND=2 slit, but now requires something like 100 times the exposure duration to achieve a target S/N. Adding the currently unsupported slits to STIS's toolkit will pave the way for more efficient future projects involving echelle spectroscopy, especially for the top tier of bright hot stars not yet observed by this powerful instrument.To qualify the 31X0.05ND slit set, HST standard G191B2B {DA} will be measured to determine wavelength dependent throughputs across the FUV+NUV range, and across the full field of each MAMA camera. Pole-on rapid rotator Vega {A0V} - well-known visible photometric standard, and which has a bright, rich, and complex FUV spectrum - will provide a test for any lineshape degradation by the long slits in the high-res echelle configuration. The high-S/N Vega FUV echelle spectra will have unique scientific value as well. Title: Alpha Cen: Climbing out of a Coronal Recession? Authors: Ayres, Thomas Bibcode: 2011hst..prop12758A Altcode: Nearby Alpha Centauri contains the two best characterized G and K dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. Alpha Cen A & B also have the best studied stellar X-ray activity cycles, extending back to the 1970A?s. Present proposal is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin A is expected to be rising to cycle maximum from an extended coronal recession. STIS E140M spectra will support and leverage the broad-band X-ray measurements by probing subcoronal dynamics and providing a low-T boundary condition for DEM modeling, with connection to HRC through the FUV Fe XII coronal forbidden line. Title: EK Draconis: Warm Coronal Rain? Authors: Ayres, Thomas Bibcode: 2011hst..prop12566A Altcode: A remarkable FUV spectrum of young solar analog EK Draconis {G1.5V} was taken by COS in Cycle 17. The mere 20-min SNAPshot captured two distinct Si IV flares {T 60,000 K}; very broad profiles of Si IV and C II {T 30,000 K}; and prominent Fe XXI coronal forbidden line emission {T 10 MK}. Curiously, the bright Si IV features were significantly redshifted, suggesting that warm gas must be continually accreting onto the lower atmosphere. This possibly meshes with a new understanding of the solar "coronal heating paradox," whereby the lacy loop-like magnetic structures that define the Sun's "quiet" corona {away from active regions} are very close to potential, and thus cannot carry enough magnetic free energy to heat themselves: the heating must come from elsewhere. That elsewhere possibly has been discovered recently: needle-like jets of hot gas, called Type II Spicules, have been observed blasting from deep in the chromosphere out into the corona, where the ambient magnetic loops trap the upward streaming hot gas, which then cools and eventually falls back to the surface. Ironically, then, the corona was the wrong place to seek the roots of coronal heating: the chromosphere is where the action really is. The EK Dra redshifts perhaps are a glimpse of a super-sized version of the cooling phase of the solar process. The purpose of this proposal is to utilize STIS and COS to solidify the observational basis for the apparent coronal downdrafts on EK Dra. If the "coronal rain" hypothesis is borne out, it will be an important step toward resolving the long-standing mystery of coronal heating in the Sun and stars. Title: Alpha Cen: Climbing out of a Coronal Recession? Authors: Ayres, Thomas Bibcode: 2011cxo..prop.3466A Altcode: Nearby Alpha Centauri contains the two best characterized G and K dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. Alpha Cen A & B also have the best studied stellar X-ray activity cycles, extending back to the 1970's. Present proposal is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual HRC-I pointings in Cycles 13-15, as solar twin A is expected to be rising to cycle maximum from an extended coronal recession. STIS E140M spectra will support and leverage the broad-band X-ray measurements by probing subcoronal dynamics and providing a low-T boundary condition for DEM modeling, with connection to HRC through the FUV Fe XII coronal forbidden line. Title: The Curious Case of the Alpha Persei Corona: A Dwarf in Supergiant's Clothing? Authors: Ayres, Thomas R. Bibcode: 2011ApJ...738..120A Altcode: Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290-1430 Å far-ultraviolet (FUV) spectrum of α Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si IV 1400 Å doublet (T ~ 8 × 104 K), are very weak, as are the chromospheric C II 1335 Å multiplet (T ~ 3 × 104 K) and O I 1305 Å triplet. In fact, the Si IV features of α Per are not only narrower than those of later, G-type supergiants of similar L X/L bol, but are also fainter (in L Si IV /L bol) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on α Per finds the X-ray centroid offset from the stellar position by 9'', at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star. Title: FK Com Multi-wavelength Campaign Authors: Kashyap, Vinay; Ayres, T.; Korhonen, H.; Saar, S.; Drake, J.; Garcia-Alvarez, D.; Huenemoerder, D. Bibcode: 2011HEAD...12.1004K Altcode: FK Com (G5 III) is an ultrafast-rotating single yellow giant. It is the eponymous member of its class, and is suspected to have been a coalesced binary that has spun up. Here we present preliminary results from a multi-wavelength campaign we have carried out in April-May 2011. We observe the corona with X-rays with the high-resolution HETG spectrometer on Chandra, the corona and chromosphere FUV with HST/COS, and obtain surface magnetic information via Zeeman Doppler and Doppler Imaging with ground-based observations. The X-ray light curve exhibits significant variability, but unlike previous observations, is not dominated by large flares. The FUV lines show broad profiles, and considerable jitter.

This study has been supported by Chandra and HST grants. Title: Starspot variability and evolution from modeling Kepler photometry of active late-type stars Authors: Brown, Alexander; Korhonen, Heidi; Berdyugina, Svetlana; Tofany, Barton; Ayres, Thomas R.; Kowalski, Adam; Hawley, Suzanne; Harper, Graham; Piskunov, Nikolai Bibcode: 2011IAUS..273...78B Altcode: The Kepler satellite provides a unique opportunity to study the detailed optical photometric variability of late-type stars with unprecedentedly long (several year) continuous monitoring and sensitivity to very small-scale variations. We are studying a sample of over two hundred cool (mid-A - late-K spectral type) stars using Kepler long-cadence (30 minute sampling) observations. These stars show a remarkable range of photometric variability, but in this paper we concentrate on rotational modulation due to starspots and flaring. Modulation at the 0.1% level is readily discernable. We highlight the rapid timescales of starspot evolution seen on solar-like stars with rotational periods between 2 and 7 days. Title: Kepler Observations of Starspot Evolution, Differential Rotation, and Flares on Late-Type Stars Authors: Brown, Alexander; Korhonen, H.; Berdyugina, S.; Walkowicz, L.; Kowalski, A.; Hawley, S.; Neff, J.; Ramsey, L.; Redman, S.; Saar, S.; Furesz, G.; Piskunov, N.; Harper, G.; Ayres, T.; Tofany, B. Bibcode: 2011AAS...21820502B Altcode: 2011BAAS..43G20502B The Kepler satellite is providing spectacular optical photometric light-curves of unprecedented precision and duration that routinely allow detailed studies of stellar magnetic activity on late-type stars that were difficult, if not impossible, to attempt previously. Rotational modulation due to starspots is commonly seen in the Kepler light-curves of late-type stars, allowing detailed study of the surface distribution of their photospheric magnetic activity. Kepler is providing multi-year duration light-curves that allow us to investigate how activity phenomena -- such as the growth, migration, and decay of starspots, differential rotation, activity cycles, and flaring -- operate on single and binary stars with a wide range of mass and convection zone depth.

We present the first results from detailed starspot modeling using newly-developed light-curve inversion codes for a range of GALEX-selected stars with typical rotation periods of a few days, that we have observed as part of our 200 target Kepler Cycle 1/2 Guest Observer programs. The physical properties of the stars have been measured using high resolution optical spectroscopy, which allows the Kepler results to be placed within the existing framework of knowledge regarding stellar magnetic activity. These results demonstrate the powerful diagnostic capability provided by tracking starspot evolution essentially continuously for more than 16 months. The starspots are clearly sampling the stellar rotation rate at different latitudes, enabling us to measure the differential rotation and starspot lifetimes. As would be expected, stars with few day rotation show frequent flaring that is easily seen as "white-light" flares in Kepler light-curves. We compare the observed flare rates and occurrence with the starspot properties.

This work contains results obtained using the NASA Kepler satellite and from the Apache Point Observatory, the MMT (using NOAO community access time), and the Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants NNX10AC51G and NNX11AC79G. Title: Advanced Spectral Library (ASTRAL): Cool Stars Authors: Ayres, Thomas R.; Co-Investigators, ASTRAL Bibcode: 2011AAS...21832814A Altcode: 2011BAAS..43G32814A The Advanced Spectral Library (ASTRAL) is a Hubble Space Telescope (HST) Cycle 18 (2010-2011) Large Treasury Project, whose aim is to collect high-quality ultraviolet echelle spectra of bright stars utilizing the high-performance Space Telescope Imaging Spectrograph (STIS). In Cycle 18, ASTRAL focuses on eight iconic late-type objects -- all well-known bright stars with vaguely unpronounceable names like Procyon and Betelgeuse -- and will devote 146 HST orbits for the purpose. The objective is to record each of the targets with broad uninterrupted UV coverage (1150-3100 Angstroms) at the highest signal-to-noise and highest spectral resolution achievable within the available spacecraft time, and given a variety of observing constraints. The broad ultraviolet coverage will be achieved by splicing together echellegrams taken in multiple FUV and NUV prime echelle settings of STIS. The observing strategy was designed to maximize S/N, ensure accurate wavelength scales, and preserve the radiometric level of the UV spectral energy distribution. This is a progress report on the observational status of ASTRAL. Up-to-date information can be found at the project website:http://casa.colorado.edu/ ayres/ASTRAL/.

Supported by grants from the Space Telescope Science Institute, operated by AURA for NASA. Title: Wavelength Calibration Accuracy for the STIS CCD and MAMA Modes Authors: Pascucci, Ilaria; Hodge, Phil; Proffitt, Charles R.; Ayres, T. Bibcode: 2011stis.rept....1P Altcode: Two calibration programs were carried out to determine the accuracy of the wavelength solutions for the most used STIS CCD and MAMA modes after Servicing Mission 4. We report here on the analysis of this dataset and show that the STIS wavelength solution has not changed after SM4. We also show that a typical accuracy for the absolute wavelength zero-points is 0.1 pixels while the relative wavelength accuracy is 0.2 pixels. Title: The Discovery of a Photoevaporation-Driven Molecular Outflow from the T Tauri Transitional Disk GM Aur Authors: Hornbeck, Jeremy; Grady, C. A.; Brown, A.; Ayres, T.; Apai, D.; Brittain, S.; Brown, J. M.; Hamaguchi, K.; Henning, T.; Herczeg, G.; Kamp, I.; Perrin, M.; Petre, R.; Schneider, G.; Sitko, M.; Walter, F.; Williger, G.; Wisniewski, J.; Woodgate, B. Bibcode: 2011AAS...21734029H Altcode: 2011BAAS...4334029H Circumstellar disks are not only a byproduct of star formation, but are also the place where planets form and migrate. The dominant gas-phase constituent of disks early in their evolution is H2, and its lifetime in the disk limits the time available for gas giant planet formation and migration. A number of mechanisms have been proposed to remove gas, including photoevaporation in the presence of the stellar X-ray, EUV, and FUV radiation field, but the relative importance of these different components and the point in disk evolution where they become significant remain uncertain. Some models predict enhanced evaporation of gas in the outer disk once the inner portions of the disk have begun to clear. One such system is the T Tauri star GM Aur which hosts a large disk with an r=20 AU central cavity. We have carried out the first high-contrast FUV imaging of this star+disk using HST ACS/SBC and report the detection of the inner 1" (140 AU) of the disk in the FUV and the discovery of a roughly cylindrical structure 90 AU in radius and extending 200 AU orthogonal to the disk, aligned with the previously reported red, polar lobes. The structure is brightest at wavelengths where there are numerous fluorescent molecular hydrogen transitions, both in our imagery and in an archival HST/STIS long-slit spectrum. The cylinder is marginally detected in the ACS/SBC F165LP band indicating that there is some sub-0.2 micron-sized dust entrained in it, but is not detected in ACS/SBC F122M imagery. The radial scale of the footprint of the cylinder on the disk and the absence of atomic emission lines associated with the structure exclude a conventional jet, but are consistent with a photoevaporation-driven outflow. We compare the properties of this outflow with predictions of X-ray, EUV, and FUV-driven disk winds. Title: λ Vel (K4 Ib-II): Fluorescence on a PAR with Other Luminaries Authors: Wahlgren, G. M.; Carpenter, K. G.; Ayres, T. R.; Brown, A.; Harper, G. M. Bibcode: 2011AAS...21715406W Altcode: 2011BAAS...4315406W The ultraviolet spectral region of cool, luminous stars contains emission features that originate from fluorescent mechanisms via PAR (photo-excitation by accidental resonance). These mechanisms can account for numerous emission lines, downward transitions from upper energy levels pumped by strong transitions, such as H Ly-α, O I 1302, C II 1335, and Mg II h&k. A new, high S/N observation of the cool giant star λ Vel (K4 Ib-II) was obtained with the HST/COS instrument at a resolving power of R 20000 and covers the wavelength region from 132 nm to 147 nm. High-quality spectra (COS and GHRS) are now available from 128 nm to 147 nm, and at 12 moderate and high resolution observations from the HST/GHRS, the latter covering approximately a third of the wavelength interval from 189 nm to 285 nm. Using these data, together with observations from FUSE and IUE, we investigate PAR processes in the spectra of Cr II and Fe II and make comparisons with other stars. The presence of additional atomic (O I, S I, and Cl I) and molecular (H2, CO) PAR processes in the spectrum of λ Vel is briefly discussed. Title: The Potential of High Angular Resolution and Contrast FUV Imagery for Studies of Star and Planetary System Formation Authors: Grady, C. A.; Brown, A.; Woodgate, B.; Hornbeck, J.; Williger, G.; Herczeg, G.; Brown, J.; Brittain, S.; Wisniewski, J.; Perrin, M.; Hamaguchi, K.; Henning, T.; Kamp, I.; Petre, R.; Schneider, G.; Sitko, M.; Walter, F.; Apai, D.; Ayres, T. Bibcode: 2011AAS...21734019G Altcode: 2011BAAS...4334019G High contrast and high angular resolution imagery has opened new viewpoints on the formation and early evolution of planetary systems, revealing features of protoplanetary and young planetary systems which would go undetected in the integrated measures of the systems. Much of the power of such studies has resulted from pan-chromatic data, but the majority of studies to date have been limited to optical and longer wavelengths, despite the wealth of atomic, ionic, and molecular tracers of circumstellar material in the FUV. As with high-contrast imaging at longer wavelengths, realizing the full potential of FUV imagery of young stars requires subtraction of PSF template data, which are now available for 3 of the HST ACS/SBC bandpasses. Such imagery has resulted in the first imagery of the circumstellar disk around the Herbig Ae star PDS 144S and can trace the geometry of the molecular gas disk for T Tauri stars. FUV imaging data also provide exquisite detail for molecular outflows for systems like T Tauri, complementing studies in the FIR with Herschel. Such data can also reveal the presence of previously unsuspected disk winds, as seen in GM Aur. Since FUV imagery is sensitive to extinction, FUV data preferentially detect circumstellar material on the near side of disks and the approaching components of outflows, removing ambiguities in disk viewing geometry, and can map, at the highest angular resolution achievable with HST, where disks are shadowed. This is a capability which future UV/Optical telescopes optimized for studies of planetary system formation should not be without.

This study is based on data obtained with the Hubble Space Telescope under GO programs 10864, 11336, and 12016. Title: FUV Spectroscopy Of Outflows And Disks Around The Intermediate Mass Pre-main-sequence Stars HD135344B And HD104237 Authors: Brown, Alexander; Herczeg, G.; Brown, J. M.; Walter, F. M.; Ayres, T. R.; DAOof TAU Team Bibcode: 2011AAS...21734034B Altcode: 2011BAAS...4334034B The intermediate-mass, pre-main-sequence (Herbig Ae/Fe) stars HD135344B (F4) and HD104237 (A8 IV-V) are both still surrounded by almost face-on circumstellar disks. The disk around HD135344B is a ``transitional'' disk with a 25 AU radius cleared inner hole but still with some gas and dust very close to the star. We have obtained FUV spectra of these stars using the HST COS and STIS spectrographs that show that both stars have dramatic high-velocity (terminal velocity = 300-400 km/s) outflows and rich fluorescently-excited molecular hydrogen emission, originating primarily from warm gas in their disks. We present these FUV spectra and outline the outflow and disk properties implied by the observed emission and absorption line profiles. The profiles and widths of the molecular hydrogen lines provide strong constraints on the location of the emitting regions.

This work is supported by HST grants for GO projects 11828 and 11616, and Chandra grant GO9-0015X to the University of Colorado. Title: The Chromospheric Structure and Wind of the K-Supergiant Lambda Velorum Authors: Carpenter, Kenneth G.; Ayres, T. R.; Brown, A.; Harper, G. M.; Wahlgren, G. M. Bibcode: 2011AAS...21715407C Altcode: 2011BAAS...4315407C Recently, the 1326-1466 Å region of the FUV spectrum of the K4 Ib-II supergiant Lambda Vel was observed with the Cosmic Origins Spectrograph (COS) on HST, as part of the Ayres and Redfield Cycle 17 SNAP program "SNAPing Coronal Iron.” This spectrum covers a region not previously recorded in Lambda Vel at high resolution and, in a mere 20 minutes of exposure, reveals an amazing treasure trove of information. It shows a wide variety of strong atomic and molecular emission lines formed in the chromosphere and multiple atomic absorption lines formed in the stellar wind, both superposed on a bright chromospheric continuum. Further evidence of the stellar wind is seen in the P Cygni profiles presented by the C II (UV 1) lines near 1335 Å. We combine this COS data with archival GHRS spectra of other selected FUV and NUV regions to better characterize the outer atmospheric structure of the star and its massive, outflowing wind. Title: Warm Coronal Rain on Young Solar Analog EK Draconis? Authors: Ayres, Thomas; France, Kevin Bibcode: 2010ApJ...723L..38A Altcode: We report a moderate-resolution, 1290-1430 Å spectrum of young solar analog EK Draconis (HD 129333: G1.5 V), obtained by Cosmic Origins Spectrograph on Hubble Space Telescope. The 20 minute observation, remarkably, captured two distinct "flares" in the Si IV 1400 Å doublet (T ~ 6 × 104 K); very broad profiles of Si IV and the C II 1335 Å multiplet (T ~ 3 × 104 K); and prominent Fe XXI λ1354 coronal forbidden line emission (T ~ 10 MK). The bright Si IV features are significantly redshifted compared to the milder, although still redshifted, equivalent components of solar-twin α1 Cen (HD 128620: G2 V). The broad, shifted, flaring hot-line profiles of EK Dra indicate not only that the subcoronal plasma of the young sun is highly dynamic, but also that the Si IV-bearing gas must be continually accreting onto the lower atmosphere, perhaps the stellar equivalent of warm "coronal rain." Title: SpS1-Digging in the solar COmosphere with NAC Authors: Ayres, Thomas R. Bibcode: 2010HiA....15..547A Altcode: The solar “COmosphere” is an enigmatic region of cold gas (temperatures as low as ~3500 K) coexisting in the low chromosphere with plasma much hotter (~7000 K). This zone probably consists of patchy clouds of cool gas, seen readily in off-limb emissions of CO 4667 nm lines, threaded by hot gas entrained in long-lived magnetic filaments as well as transient shock fronts. The COmosphere was not anticipated in classical 1D models of the solar outer atmosphere, but is quite at home in the contemporary 3D highly dynamic view, which one might call the Magnetic Complexity Zone. Title: Alpha Cen to the Max Authors: Ayres, Thomas Bibcode: 2010cxo..prop.3047A Altcode: Nearby Alpha Centauri contains the two best characterized G and K dwarfs, next to the Sun itself, thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. Alpha Cen A & B also have the best studied stellar X-ray activity cycles, extending back to the 1970's. In fact, Chandra LETGS spectra of the double star are superior to any existing solar material in the crucial 2-20 nm band, accounting for bulk of Sun's XUV emission (relevant to Space Weather). Present proposal is to continue the evolving coronal narrative with dual HRC-I pointings in Cycle 12, and an LETGS spectrum of the sun-like pair close to the peaks of their X-ray cycles. STIS FUV spectra will leverage the coronal line measurements (e.g., dynamics and low-T B.C. for DEM modeling). Title: Deep Lamp Too Authors: Ayres, Thomas Bibcode: 2010hst..prop12280A Altcode: This is a calibration proposal that addresses a significant obstacle to ongoing efforts to enhance the quality of the dispersion solutions implemented in the STIS echelle pipeline. Namely, the wavecal material representing many of the secondary grating "tilts" is in relatively poor shape. With solid lamp calibrations in all 37 supported high-res {E140H and E230H} settings, STIS itself can be exploited to bootstrap {by means of an empirical wavelength distortion correction} a "laboratory calibration" to the many lines emitted by the STIS lamps, mainly chromium, that were missing from the GHRS flight-spare units originally measured at NIST in the 1990's, and more recent work with STIS-type lamps that unfortunately only covers the FUV band. The prototype distortion correction significantly improves the quality of the pipeline spectra, to the great benefit of the many types of GO programs that require accurate velocity measurements - stellar, interstellar, and even intergalactic - and thus have turned to STIS in the past. {And now again, during its "second life."} The proposed exposure depth enhancements for the 28 {of 44} tilts require seven orbits, with no impact on science time. The total exposure duration {10 hours} is only 1/4 that already expended on "deep" wavecals {texp>60 s}, and essentially would complete the fundamental wavelength calibration of this enormously valuable spectroscopic machine. The program should have negligible impact on lamp life, which is measured in many hundreds of hours. Title: FK Comae, King of Spin: the Movie Authors: Ayres, Thomas Bibcode: 2010hst..prop12279A Altcode: FK Comae is an ultra-fast rotating, single yellow giant, product of a recent W UMa merger. Extraordinary levels of FUV and X-ray emission rate FK Comae a coronal powerhouse on par with the most extreme of the better known activity heavyweights: short-period RS CVn binaries. As a single star, FK Comae has clear advantages as a laboratory for exploring the outer limits of magnetospheric activity among the coronal cool stars. FK Comae has a long history of attention at optical and X-ray wavelengths, thanks to its generously spotted surface, and proclivity to flare regularly at high energies. FUSE discovered ultra-broad, redshifted profiles of O VI and C III, but unfortunately the singular observation could not be repeated, thanks to the satellite's flaky attitude system. The remarkable FUV spectrum was taken just a few months before STIS failed in 2004, so there was no opportunity to turn the more powerful gaze of Hubble to the task. Now, finally, the amazing sensitivity of Cosmic Origins Spectrograph can be brought to bear: a single orbit can capture an FUV spectrum of FK Comae with S/N at instrumental limits for bright lines, and digging down to faint Fe XXI 1354 {bridge to the coordinated Chandra HETGS pointing we also are proposing}.We will trace how the bright FUV regions relate spatially to the photospheric dark spots, to inform ideas of coronal structure and heating in these advanced objects. We will probe whether a global magnetosphere exists, and whether the field lines are loaded with hot coronal gas {>10 MK}, as well as the cooler 0.3 MK material already suggested by highly broadened FUSE O VI. Further, we will test whether the striking 100 km/s redshifts of the FUV lines, and similar shifts seen in Ne X by Chandra HETGS, are caused by a massive coronal outflow {perhaps implicated in magnetic braking}. Our method is to exploit, on the one hand, emission-line "Doppler imaging," whereby bright surface regions are mapped onto specific locations in the global profile, according to the line-of-sight rotational velocity. On the other hand, we compare features of different opacity and excitation {e.g., Si III 1206 and Si IV 1393} to deduce whether, say, a red asymmetry is caused by blueshifted absorption, or alternatively by infall of the entire feature. Multiple epochs spaced over two rotation periods break the degeneracy between profile distortions caused by disk passage of hot patches {Doppler imaging part}, and those caused by large-scale flows. Contemporaneous spot maps from the ground will provide a fundamental magnetic context for the coordinated FUV and X-ray "movies." Title: FK Comae, King of Spin: the Movie Authors: Ayres, Thomas Bibcode: 2010cxo..prop.3035A Altcode: FK Comae is an ultra-fast rotating, single yellow giant, product of a recent W UMa merger. Extraordinary levels of FUV and X-ray emission rate FK Comae a coronal powerhouse on par with the most extreme short-period RS CVn binaries. As a single star, FK Comae has clear advantages as a laboratory for exploring high-energy activity. We will bring to bear Hubble's powerful Cosmic Origins Spectrograph, together with Chandra HETGS and groundbased Zeeman Doppler Imaging, to trace -- over two stellar rotations -- spatial relationships between bright FUV patches, extended X-ray emission zones, and the photospheric dark spots, to inform ideas of coronal structure and heating at the outer limits of magnetospheric activity among the coronal cool stars. Title: Advanced Spectral Library Project: Cool Stars Authors: Ayres, Thomas Bibcode: 2010hst..prop12278A Altcode: Stars are the luminous backbone of the Universe, and without them, it would be a dull and dreary place indeed: no light, no heavy elements, no planets, no life. It also is safe to say that stellar spectroscopy is a cornerstone of astrophysics, providing much of what we know concerning temperatures and masses of stars, their compositions, planets, and the dynamics and evolution of the galaxies they inhabit. The proper interpretation of stellar spectra thus is fundamental to modern astronomy. This is especially true for the satellite ultraviolet, owing to the rich collection of atomic and ionic transitions found there. Unfortunately, the existing archive of Space Telescope Imaging Spectrograph rarely achieves the high S/N of the best ground-based spectra, and relatively few objects have the full wavelength coverage for which the powerful, highly multiplexed, second generation Hubble instrument was designed. With UVES at ESO and ESPaDOnS at CFHT, for example, astronomers routinely are obtaining broad-coverage optical spectra with S/N > 100 and resolving power of 100,000 to fuel ground-breaking analyses. Our objective is to collect comparable STIS UV echelle spectra for a diverse sample of representative stars, to build an Advanced Spectral Library; a foundation for astrophysical exploration: stellar, interstellar, and beyond. Our first effort involves cool stars, whose main contribution to the UV is through magnetic activity, an enigmatic phenomenon subject to close scrutiny on the Sun, and of undeniable importance to a broad range of cosmic situations: Space Weather, T-Tauri disk winds, red dwarf flares, erosion of exoplanet atmospheres, and so forth.The main product of our Treasury program will be detailed stellar "atlases," based on advanced processing of the STIS echellegrams. Members of our broad collaboration will analyze these data for specific purposes, such as detection of rare species in sharp-lined F stars, properties and kinematics of local interstellar clouds, and dynamics of chromospheres, coronae, and winds of cool stars; but rapid public release {based on the "StarCAT" model} will enable many other investigations by a much wider community, for decades to come. Title: Alpha Cen to the Max Authors: Ayres, Thomas Bibcode: 2010hst..prop12374A Altcode: This is the HST part of a joint Chandra/HST observing program. The objective for HST is to obtain new UV spectra of both components of the Alpha Centauri binary: the primary {"Alpha Cen A"} is a near twin of the Sun, while the companion {"B"} is an early K dwarf, slightly less massive, smaller and less luminous than the Sun {but coronally more active}. The orbital period is 80 yr, and the two stars currently are separated by about 7". The Alpha Cen system has been the subject of long term coronal X-ray monitoring by four successive generations of space observatories, and extensive UV measurements were obtained periodically during the IUE era, from the late 1970's to late 1990's. The present program will obtain new STIS echelle spectra of both stars, which each were observed in selected wavelength windows by GHRS in the mid-1990's, and Alpha Cen A later by STIS in an extensive high-res program in 1999, then both stars this past HST Cycle 17 with STIS, as a part of a previous joint Chandra-HST program with similar objectives. Title: Ironing Out the Wrinkles in STIS Authors: Ayres, Thomas R. Bibcode: 2010hstc.workE...7A Altcode: The echelle wavelength scales of Space Telescope Imaging Spectrograph were evaluated based on a novel high-density line list for the on-board Pt/Cr-Ne emission lamps. The new reference wavelengths were obtained by a bootstrapping technique that exploited the space-borne instrument as its own laboratory spectrometer.

A number of strategies were explored to mitigate subtle wavelength scale deviations identified in the process (known from earlier work), either by modifying the pipeline dispersion relations directly, or by a post-facto distortion correction. The main conclusion is that the STIS echelle wavelengths can be significantly improved with only modest changes to the current dispersion model. Title: The solar photospheric abundance of carbon. Analysis of atomic carbon lines with the CO5BOLD solar model Authors: Caffau, E.; Ludwig, H. -G.; Bonifacio, P.; Faraggiana, R.; Steffen, M.; Freytag, B.; Kamp, I.; Ayres, T. R. Bibcode: 2010A&A...514A..92C Altcode: 2010arXiv1002.2628C Context. The analysis of the solar spectra using hydrodynamical simulations, with a specific selection of lines, atomic data, and method for computing deviations from local thermodynamical equilibrium, has led to a downward revision of the solar metallicity, Z. We are using the latest simulations computed with the CO5BOLD code to reassess the solar chemical composition. Our previous analyses of the key elements, oxygen and nitrogen, have not confirmed any extreme downward revision of Z, as derived in other works based on hydrodynamical models.
Aims: We determine the solar photospheric carbon abundance with a radiation-hydrodynamical CO5BOLD model and compute the departures from local thermodynamical equilibrium by using the Kiel code.
Methods: We measured equivalent widths of atomic C I lines on high-resolution, high signal-to-noise ratio solar atlases of disc-centre intensity and integrated disc flux. These equivalent widths were analysed with our latest solar 3D hydrodynamical simulation computed with CO5BOLD. Deviations from local thermodynamic equilibrium we computed in 1D with the Kiel code, using the average temperature structure of the hydrodynamical simulation as a background model.
Results: Our recommended value for the solar carbon abundance relies on 98 independent measurements of observed lines and is A(C)=8.50 ± 0.06. The quoted error is the sum of statistical and systematic errors. Combined with our recent results for the solar oxygen and nitrogen abundances, this implies a solar metallicity of Z = 0.0154 and Z/X = 0.0211.
Conclusions: Our analysis implies a solar carbon abundance that is about 0.1 dex higher than what was found in previous analyses based on different 3D hydrodynamical computations. The difference is partly driven by our equivalent width measurements (we measure, on average, larger equivalent widths than the other work based on a 3D model), in part because of the different properties of the hydrodynamical simulations and the spectrum synthesis code. The solar metallicity we obtain from the CO5BOLD analyses is in slightly better agreement with the constraints of helioseismology than the previous 3D abundance results. Title: Commission 36: Theory of Stellar Atmospheres Authors: Asplund, Martin; Puls, Joachim; Landstreet, John; Allende Prieto, Carlos; Ayres, Thomas; Berdyugina, Svetlana; Gustafsson, Bengt; Hubeny, Ivan; Ludwig, Hans Günter; Mashonkina, Lyudmila; Randich, Sofia Bibcode: 2010IAUTB..27..197A Altcode: The members of the Commission 36 Organizing Committee attending the IAU General Assembly in Rio de Janeiro met for a business session on August 7. Both members from the previous (2006-2009) and the new (2009-2012) Organizing Committee partook in the discussions. Past president John Landstreet described the work he had done over the past three years in terms of supporting proposed conferences on the topic. He has also spent significant amount of time establishing an updated mailing list of all >350 members of the commission, which is unfortunately not provided automatically by the IAU. Such a list is critical for a rapid dissemination of information to the commission members and for a correct and smooth running of elections of IAU officials. Everyone present thanked John effusively for all of his hard work over the past three years to stimulate a high level of activity within the discipline. Title: A Fresh Hubble Perspective on Sun-Like Dwarfs, Young and Old Authors: Ayres, Thomas R.; Redfield, S. Bibcode: 2010AAS...21640013A Altcode: 2010BAAS...41..856A Far-ultraviolet spectra of three sun-like stars have been obtained recently by HST, utilizing its two powerful UV spectrographs: STIS and COS. A 3.6 ks STIS E140M echellegram of nearby, bright Alpha Cen A was taken as part of a joint Chandra-HST program to study the coronal cycles of the solar twin, which has been mired in an activity low-state the past several years, much like the Sun (although recovery for our star apparently is imminent). As part of an HST Cycle 17 Guest Observer program ("SNAPing Coronal Iron"), COS acquired short (20M) G130M snapshots of two young-sun analogs: Hyades G star HD25825 and Pi1 UMa, an early-G dwarf in the Ursa Major Stream, comparable in age to the Hyades. The COS pointing on HD25825 represents the first high-resolution (R=20,000) FUV spectrum of such a faint solar-type dwarf, albeit a hyperactive one befitting its youth (600 Myr). The COS spectra are spectacular, given the brief integrations, rivaling previous STIS efforts (on brighter objects) that required equivalently 20X the exposure depth. A comparison of these spectra show the evolution of chromospheric, transition zone, and even coronal (FeXII 1349 and FeXXI 1354) line profiles from the pinnacles to the depths of activity.

This work supported by grants HST-GO-11687.01 and HST-GO-11839.01 from STScI. Title: VizieR Online Data Catalog: StarCAT: STIS UV echelle spectra of stars (Ayres, 2010) Authors: Ayres, T. R. Bibcode: 2010yCat..21870149A Altcode: StarCAT is a Cycle 14 Legacy Archival project supported by the Guest Investigator program of Hubble Space Telescope (HST). The objective of StarCAT was to create an easily accessible catalog of high resolution spectral observations of targets broadly identified as "stars," collected by Space Telescope Imaging Spectrograph (STIS) from the time of its installation in 1997, during Hubble Servicing Mission 2, to its shutdown in 2004 August. StarCAT is available through an interface maintained at the Multimission Archive at Space Telescope (MAST): http://archive.stsci.edu/prepds/starcat

(3 data files). Title: Chandra and HST Observations of the High Energy (X-ray/UV) Radiation Fields for an Evolutionary Sequence of Pre-Main-Sequence Stars Authors: Brown, Alexander; Herczeg, G. J.; Brown, J. M.; Walter, F. M.; Valenti, J.; Ardila, D.; Hillenbrand, L. A.; Edwards, S.; Johns-Krull, C. M.; Alexander, R.; Bergin, E. A.; Calvet, N.; Bethell, T. J.; Ingleby, L.; Bary, J. S.; Audard, M.; Baldovin, C.; Roueff, E.; Abgrall, H.; Gregory, S. G.; Ayres, T. R.; Linsky, J. L. Bibcode: 2010HEAD...11.1709B Altcode: 2010BAAS...42..684B Pre-main-sequence (PMS) stars are strong X-ray and UV emitters and the high energy radiation from the central stars directly influences the physical and chemical processes in their protoplanetary disks. Gas and dust in protoplanetary systems are excited by these photons, which are the dominant ionization source for hundreds of AU around the star. X-rays penetrate deep into disks and power complex chemistry on grain surfaces. ``Transitional disks'' are an important short-lived evolutionary stage for PMS stars and protoplanetary systems. These disks have transformed most of the dust and gas in their inner regions into planetesimals or larger solid bodies. As dust disks disappear after ages of roughly 5 Myr high levels of stellar magnetic activity persist and continue to bathe the newly-forming protoplanetary systems with intense high energy radiation.

We present new X-ray and UV spectra for a sample of PMS stars at a variety of evolutionary stages, including the classical T Tauri stars DE Tau and DK Tau, the transitional disk stars GM Aur and HD135344B, the Herbig Ae star HD104237, and the weak-lined T Tauri star LkCa4, the Eta Cha cluster [age 7 Myr] members RECX1, RECX-11, and RECX-15, and TW Hya association [age 8 Myr] member TWA-2. These include the first results from our 111 orbit HST Large project and associated X-ray data. New and archival Chandra, XMM, and Swift X-ray spectra and HST COS+STIS FUV spectra are being used to reconstruct the full high energy (X-ray/EUV/FUV/NUV) spectra of these stars, thus allowing detailed modeling of the physics and chemistry of their circumstellar environments. The UV spectra provide improved emission line profiles revealing details of the magnetically-heated plasma and accretion and outflow processes.

This work is supported by Chandra grants GO8-9024X, GO9-0015X and GO9-0020B and proposal 11200754 and HST GO grants 11336, 11616, and 11828. Title: StarCAT: A Catalog of Space Telescope Imaging Spectrograph Ultraviolet Echelle Spectra of Stars Authors: Ayres, Thomas R. Bibcode: 2010ApJS..187..149A Altcode: StarCAT is a catalog of high resolution ultraviolet spectra of objects classified as "stars," recorded by Space Telescope Imaging Spectrograph (STIS) during its initial seven years of operations (1997-2004). StarCAT is based on 3184 echelle observations of 545 distinct targets, with a total exposure duration of 5.2 Ms. For many of the objects, broad ultraviolet coverage has been achieved by splicing echellegrams taken in two or more FUV (1150-1700 Å) and/or NUV (1600-3100 Å) settings. In cases of multiple pointings on conspicuously variable sources, spectra were separated into independent epochs. Otherwise, different epochs were combined to enhance the signal-to-noise ratio (S/N). A post-facto correction to the calstis pipeline data sets compensated for subtle wavelength distortions identified in a previous study of the STIS calibration lamps. An internal "fluxing" procedure yielded coherent spectral energy distributions (SEDs) for objects with broadly overlapping wavelength coverage. The best StarCAT material achieves 300 m s-1 internal velocity precision; absolute accuracy at the 1 km s-1 level; photometric accuracy of order 4%; and relative flux precision several times better (limited mainly by knowledge of SEDs of UV standard stars). While StarCAT represents a milestone in the large-scale post-processing of STIS echellegrams, a number of potential improvements in the underlying "final" pipeline are identified. Title: The Cycles of Alpha Centauri Authors: Ayres, Thomas R. Bibcode: 2010IAUS..264..146A Altcode: The main AB pair of the nearby Alpha Centauri triple system has one of the most extensive X-ray records of any cosmic object, stretching over three decades. The primary, α Cen A (G2V), is a near twin of the Sun, with a similarly soft (1-2 MK) corona. The secondary, α Cen B (K1V), is more active than the Sun, with a generally harder coronal spectrum. Here, spatially resolved measurements of the pair by Chandra's High Resolution Camera are compared, on a common basis, with previous pointings from ROSAT and XMM-Newton. Title: High Energy (X-ray/UV) Radiation Fields of Young, Low-Mass Stars Observed with Chandra and HST Authors: Brown, Alexander; Brown, J. M.; Herczeg, G.; Bary, J.; Walter, F. M.; Ayres, T. R. Bibcode: 2010AAS...21542928B Altcode: 2010BAAS...42R.354B Pre-main-sequence (PMS) stars are strong UV and X-ray emitters and the high energy (UV/X-ray) radiation from the central stars directly influences the physical and chemical processes in their protoplanetary disks. Gas and dust in protoplanetary systems are excited by these photons, which are the dominant ionization source for hundreds of AU around the star. X-rays penetrate deep into disks and power complex chemistry on grain surfaces. ``Transitional disks'' are a crucial and important evolutionary stage for PMS stars and protoplanetary systems. These disks have transformed most of the dust and gas in their inner regions into planetesimals or larger solid bodies. The disks show clear inner ``holes'' that almost certainly harbor infant planetary systems, given the very sharp gap boundaries inferred. Transitional disks are rare and represent a short-lived phase of PMS disk evolution. We have observed a sample of PMS stars at a variety of evolutionary stages, including the transitional disk stars GM Aur (K5) and HD135344B (F4). Chandra ACIS CCD-resolution X-ray spectra and HST STIS and COS FUV spectra are being used to reconstruct the full high energy (X-ray/EUV/FUV/NUV) spectra of these young stars, so as to allow detailed modeling of the physics and chemistry of their circumstellar environments, thereby providing constraints on the formation process of planetary systems.

This work is supported by Chandra grants GO8-9024X, GO9-0015X and GO9-0020B and HST grants for GO projects 11336, 11828, and 11616 to the University of Colorado. Title: A stellar perspective on chromospheres. Authors: Ayres, T. Bibcode: 2010MmSAI..81..553A Altcode: The Sun is not alone in hosting a chromosphere: virtually all convective stars (F-types and later) possess them. Properties can vary wildly from object to object. Historically, three key systemic behaviors were recognized. First is the strong preference of chromospheres for the cool half of the H-R diagram. Second is the so-called rotation-age-activity connection (``Skumanich law''). Third is the Ca II H & K emission width-luminosity relation (``Wilson-Bappu effect''). In the modern era of ultraviolet and X-ray telescopes in space, additional phenomenology has been recognized; mainly concerning energetic relationships between chromosphere and corona, importance of atmospheric dynamics, and the curious ``buried coronae'' of red giant stars. Collectively, these pieces of evidence hint that ``relentlessly dynamic'' stellar chromospheres are the rule, not the exception. Title: The Cycles of Alpha Centauri Authors: Ayres, Thomas Bibcode: 2009cfdd.confE..64A Altcode: The main AB pair of the nearby Alpha Centauri triple system has an extensive X-ray history, covering three decades. Alpha Cen A (G2V) is a near twin of the Sun, with a similarly soft (1-2 MK) corona. Alpha Cen B (K1V) is more active than the Sun, with a generally harder X-ray spectrum. Here, spatially resolved measurements from ROSAT, XMM-Newton, and Chandra are compared on a common basis. In the combined time series, Alpha Cen B shows a distinct X-ray modulation with a period of about eight years and a factor of 5 cycle depth (the latter is similar to the Sun's). Alpha Cen A showed minimal variability 1995-2000, a decrease in the initial XMM epoch 2003-2005, and nearly constant behavior in the subsequent Chandra segment (late-2005 to present), although down a factor of 2 from the mid-1990's level. A remarkable ``smoking gun'' LETGS spectrum in mid-2007 emphasized that much of the coronal luminosity of solar-activity objects falls at longer wavelengths than recorded efficiently by contemporary instruments. This makes cycle depth strongly dependent on the energy bandpass of the measurement (here 0.2-2 keV), and complicates assessments of coronal heating requirements. Title: The Ups and Downs of Alpha Centauri Authors: Ayres, Thomas Bibcode: 2009cxo..prop.2756A Altcode: Nearby Alpha Centauri hosts two of the best characterized late-type dwarfs, besides the Sun itself; thanks to the accurate orbit, resolved angular diameters, and well understood co-evolutionary state. The G and K components of the system have X-ray measurements extending back to the late-1970's; in some sense superior to the solar high-energy irradiance. The latter is not routinely measured in the normal cosmic energy bands, and must be reconstructed from proxies. The present proposal is to continue this ongoing twin coronal narrative with additional HRC-I pointings in Cycle 11, including an attempt to assess the importance of rotational modulation effects. FUV spectroscopy by HST-COS will leverage the unique coronal activity record. Title: Ironing Out the Wrinkles Authors: Ayres, Thomas Bibcode: 2009hst..prop11743A Altcode: This is a Calibration Archival proposal to develop, implement, and test enhancements to the pipeline wavelength scales of STIS echelle spectra, to take full advantage of the extremely high performance of which the instrument is capable. The motivation is a recent extensive investigation--The Deep Lamp Project--which identified systematic wavelength distortions in all 44 primary and secondary settings of the four STIS echelle modes: E140M, E140H, E230M, and E230H. The method was to process deep exposures of the onboard Pt/Cr-Ne calibration source as if they were science images, and measure deviations of the lamp lines from their laboratory wavelengths. An approach has been developed to correct the distortions post facto, but it would be preferable to implement a more robust dispersion model in the pipeline itself. The proposed study will examine a more extensive set of WAVECALs than in the exploratory Deep Lamp effort, and will benefit from a new laboratory line list specifically for the STIS lamps. Ironing out the wrinkles in the STIS wavelength scales will impact many diverse science investigations, especially the Legacy Archival project "StarCAT." Title: The Cycles of Alpha Centauri Authors: Ayres, Thomas Bibcode: 2009hst..prop11839A Altcode: This is the HST part of a joint Chandra/HST observing program. The objective of the HST part is to obtain new UV spectra of both components of the Alpha Centauri binary: the primary {"Alpha Cen A"} is a near twin of the Sun, while the companion {"B"} is an early K dwarf, slightly less massive, smaller and less luminous than the Sun. The orbital period is 80 yr, and the two stars currently are separated by about 8". The Alpha Cen system has been the subject of long term coronal X-ray monitoring by four successive generations of space observatories, and extensive UV measurements were obtained periodically during the IUE era, from thelate 1970's to late 1990's. The present program will obtain new STIS echelle spectra of both stars, which each were observed in selected wavelength windows by GHRS in the mid-1990's, and Alpha Cen A later by STIS in an extensive high-res program in 1999, although B unfortunately never was recorded by STIS. Title: SNAPing Coronal Iron Authors: Ayres, Thomas Bibcode: 2009hst..prop11687A Altcode: This is a Snapshot Survey to explore two forbidden lines of highly ionized iron in late-type coronal sources. Fe XII 1349 {T 2 MK} and Fe XXI 1354 {T 10 MK} - well known to Solar Physics - have been detected in about a dozen cool stars, mainly with HST/STIS. The UV coronal forbidden lines are important because they can be observed with velocity resolution of better than 15 km/s, whereas even the state-of-the-art X-ray spectrometers on Chandra can manage only 300 km/s in the kilovolt band where lines of highly ionized iron more commonly are found. The kinematic properties of hot coronal plasmas, which are of great interest to theorists and modelers, thus only are accessible in the UV at present. The bad news is that the UV coronal forbidden lines are faint, and were captured only in very deep observations with STIS. The good news is that 3rd-generation Cosmic Origins Spectrograph, slated for installation in HST by SM4, in a mere 25 minute exposure with its G130M mode can duplicate the sensitivity of a landmark 25-orbit STIS E140M observation of AD Leo, easily the deepest such exposure of a late-type star so far. Our goal is to build up understanding of the properties of Fe XII and Fe XXI in additional objects beyond the current limited sample: how the lineshapes depend on activity, whether large scale velocity shifts can be detected, and whether the dynamical content of the lines can be inverted to map the spatial morphology of the stellar corona {as in "Doppler Imaging''}. In other words, we want to bring to bear in the coronal venue all the powerful tricks of spectroscopic remote sensing, well in advance of the time that this will be possible exploiting the corona's native X-ray radiation. The 1290-1430 band captured by side A of G130M also contains a wide range of key plasma diagnostics that form at temperatures from below 10,000 K {neutral lines of CNO}, to above 200,000 K {semi-permitted O V 1371}, including the important bright multiplets of C II at 1335 and Si IV at 1400; yielding a diagnostic gold mine for the subcoronal atmosphere. Because of the broad value of the SNAP spectra, beyond the coronal iron project, we waive the normal proprietary rights. Title: The Cycles of α Centauri Authors: Ayres, Thomas R. Bibcode: 2009ApJ...696.1931A Altcode: The main AB pair of the nearby α Centauri triple system has one of the most extensive X-ray records of any cosmic object, stretching over 30 years. The primary, α Cen A (G2 V), is a near twin of the Sun, with a similarly soft (1-2 MK) corona. The secondary, α Cen B (K1 V), is more active than the Sun, with a generally harder coronal spectrum. Here, more than a decade of spatially resolved measurements from ROSAT, XMM-Newton, and Chandra are compared on a common basis, with careful attention to conversion factors that translate count rates of the different instruments into absolute energy fluxes. For the latter purpose, two epochs of Chandra transmission grating spectra, which fully resolve the binary, were modeled using a differential emission measure formalism. The aggregate time series suggests that α Cen B was near X-ray maximum in the mid-1990s, minimum in the late-1990s, then peaked again in 2004-2005, and more recently has been declining toward another minimum. Meanwhile, α Cen A showed minimal variability 1995-2000, and like the secondary presently is mired in an activity lull (in fact, as seen by XMM-Newton, the primary "fainted" from view in the 2005 time frame). Comparisons between X-ray luminosities in the 0.2-2 keV (6-60 Å) ROSAT "WGACAT" band and a softer counterpart 0.06-1.2 keV (10-200 Å) reinforce the idea that cycle depth is strongly dependent on the energy span of the measurement, and that much of the coronal luminosity of cool-corona objects like the Sun falls at longer wavelengths than are recorded efficiently by contemporary instruments. Consequently, one must be careful in discussing X-ray cycles, their amplitudes, and coronal heating requirements unless one can demonstrate good control over the out-of-band component. Title: Chandra and GALEX Observations of Stellar Activity on the 7 Gyr Old Arcturus Moving Group Dwarfs Authors: Brown, Alexander; Hodges-Kluck, Edmund; Harper, Graham M.; Ayres, Thomas R. Bibcode: 2009AIPC.1094..908B Altcode: 2009csss...15..908B We present observations of the X-ray and ultraviolet emission from a sample of dwarf stars in the Arcturus Moving Group. The Arcturus Moving Group is very likely a remnant of the merger of a dwarf galaxy with the Milky Way Galaxy in the distant past. This kinematically distinct group has members located very close to the Sun, allowing study of stellar activity on very old (7-8 Gyr), low metallicity stars that would typically not be possible. Our sample has metallicities between 0.4 and 0.04 solar, spectral types F9-mid-M, and distances less than 25 pc from the Sun. We have detected X-ray emission from five AMG dwarfs with the Chandra ACIS-S S3 back-illuminated detector and for four stars have measured or placed upper limits on the C IV UV1 emission flux using GALEX GRISM spectra. The measured X-ray luminosities are comparable to the minimum solar Lx (range 6-20 1026 erg s-1 for 0.24-2.0 keV) and for the late G/early K stars are also similar to that of the inactive, more metal rich ([Fe/H] = -0.42] G8 dwarf Tau Cet. However, a major difference from the Sun and Tau Cet is that the soft X-ray emitting plasma is far cooler. The detected source X-rays are generally very soft with energies of 0.2-0.3 keV, and the bulk of this emission originates from upper transition region emission lines, such as C V, rather than a conventional solar-like corona. Title: Mass-Loss and Magnetic Fields as Revealed Through Stellar X-ray Spectroscopy Authors: Osten, Rachel A.; Audard, Marc; Ayres, Tom; Brown, Alex; Drake, Jeremy; Drake, Steve; Gagné, Marc; Huenemoerder, Dave; Kashyap, Vinay; Leutenegger, Maurice; Linsky, Jeff; Oskinova, Lidia; Schulz, Norbert; Schmitt, Jurgen; Sciortino, Salvatore; Stelzer, Beate; Tuellmann, Ralph; Waldron, Wayne; Wolk, Scott Bibcode: 2009astro2010S.228O Altcode: No abstract at ADS Title: The Solar Chromosphere: Old Challenges, New Frontiers Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger, T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White, S.; Solanki, S. Bibcode: 2009astro2010S...9A Altcode: No abstract at ADS Title: Dynamos and magnetic fields of the Sun and other cool stars, and their role in the formation and evolution of stars and in the habitability of planets Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres, Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen; Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov, Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier, Klaus; Walter, Fred Bibcode: 2009astro2010S.262S Altcode: No abstract at ADS Title: Chandra's Darkest Bright Star: not so Dark after All? Authors: Ayres, Thomas R. Bibcode: 2008AJ....136.1810A Altcode: The Chandra High Resolution camera (HRC) has obtained numerous short exposures of the ultraviolet (UV)-bright star Vega (α Lyrae; HD 172167: A0 V), to calibrate the response of the detector to out-of-band (non-X-ray) radiation. A new analysis uncovered a stronger "blue leak" in the imaging section (HRC-I) than reported in an earlier study of Vega based on a subset of the pointings. The higher count rate—a factor of nearly 2 above prelaunch estimates—raised the possibility that genuine coronal X-rays might lurk among the out-of-band events. Exploiting the broader point-spread function of the UV leak compared with soft X-rays identified an excess of counts centered on the target, technically at 3σ significance. A number of uncertainties, however, prevent a clear declaration of a Vegan corona. A more secure result would be within reach of a deep uninterrupted HRC-I pointing. Title: Solar Forbidden Oxygen, Revisited Authors: Ayres, Thomas R. Bibcode: 2008ApJ...686..731A Altcode: Recent large reductions in the solar oxygen abundance, based on synthesis of photospheric O I, OH, and CO absorptions with 3D convection models, have provoked consternation in the helioseismology community: the previous excellent agreement between measured p-mode oscillation frequencies and predictions based on the recommended epsilonO of a decade ago (680 parts per million [ppm] relative to hydrogen) unravels at the new low value (460 ppm). In an attempt to reconcile these conflicting results, the formation of pivotal [O I] λ6300, which is blended with a weak Ni I line, has been reconsidered, exploiting an alternative 3D model (albeit only a single temporal snapshot). And while there are several areas of agreement with the earlier [O I] studies of Allende Prieto, Asplund, and others, there is one crucial point of disagreement: the epsilonO derived here is significantly larger, 650 +/- 65 ppm (although at the expense of a ~30% weaker Ni I line than expected from the recommended nickel abundance). One innovation is a more robust treatment of the solar wavelengths: the balance between the components of the [O I] + Ni I blend is sensitive to velocity errors of only a few hundred m s-1. A second improvement is enforcement of a "continuum calibration" to ensure a self-consistent 3D temperature scale. Because of the renewed agreement between the linchpin tracer [O I] and seismic oxygen, the proposed downward slump of the solar metallicity and the perceived "oxygen crisis" now can be said to rest on less secure footings. Title: A New Era in Solar Thermal-IR Astronomy: the NSO Array Camera (NAC) on the McMath-Pierce Telescope Authors: Ayres, T.; Penn, M.; Plymate, C.; Keller, C. Bibcode: 2008ESPM...12.2.74A Altcode: The U.S. National Solar Observatory Array Camera (NAC) is a cryogenically cooled 1Kx1K InSb ``Aladdin" array that recently became operational at the McMath-Pierce facility on Kitt Peak, a high dry site in the southwest U.S. (Arizona). The new camera is similar to those already incorporated into instruments on nighttime telescopes, and has unprecedented sensitivity, low noise, and excellent cosmetics compared with the Amber Engineering (AE) device it replaces. (The latter was scavenged from a commercial surveillance camera in the 1990's: only 256X256 format, high noise, and annoying flatfield structure). The NAC focal plane is maintained at 30 K by a mechanical closed-cycle helium cooler, dispensing with the cumbersome pumped--solid-N2 40 K system used previously with the AE camera. The NAC linearity has been verified for exposures as short as 1 ms, although latency in the data recording holds the maximum frame rate to about 8 Hz (in "streaming mode"). The camera is run in tandem with the Infrared Adaptive Optics (IRAO) system. Utilizing a 37-actuator deformable mirror, IRAO can--under moderate seeing conditions--correct the telescope image to the diffraction limit longward of 2.3 mu (if a suitable high contrast target is available: the IR granulation has proven too bland to reliably track). IRAO also provides fine control over the solar image for spatial scanning in long-slit mode with the 14 m vertical "Main" spectrograph (MS). A 1'X1' area scan, with 0.5" steps orthogonal to the slit direction, requires less than half a minute, much shorter than p-mode and granulation evolution time scales. A recent engineering test run, in April 2008, utilized NAC/IRAO/MS to capture the fundamental (4.6 mu) and first-overtone (2.3 mu) rovibrational bands of CO, including maps of quiet regions, drift scans along the equatorial limbs (to measure the off-limb molecular emissions), and imaging of a fortuitous small sunspot pair, a final gasp, perhaps, of Cycle 23. Future work with the NAC will emphasize pathfinding toward the next generation of IR imaging spectrometers for the Advanced Technology Solar Telescope, whose 4 m aperture finally will bring sorely needed high spatial resolution to daytime infrared astronomy. In the meantime, the NAC is available to qualified solar physicists from around the world to conduct forefront research in the 1-5 mu region, on the venerable--but infrared friendly--McMath-Pierce telescope. Title: The Cycles of Alpha Centauri Authors: Ayres, T. Bibcode: 2008ESPM...12..4.1A Altcode: As the nearest system of Sun-like stars, ? Centauri (G2 V + K1 V) is a "poster child" of the solar-stellar connection. This is especially true in coronal soft X-rays, where a parade of successive high-energy observatories has imaged the binary over the past three decades. I report a new analysis of ROSAT, XMM-Newton, and Chandra pointings covering 1995-2008. Although XMM-Newton found a dramatic decline in the coronal luminosity of first A in 2005, then more recently B in 2007, the "Fainting of ? Cen" now is recognized as an instrument calibration issue. Nevertheless, cycles of both stars clearly are evident in the long term record, surprisingly synchronized in the current epoch. Title: The photospheric solar oxygen project. I. Abundance analysis of atomic lines and influence of atmospheric models Authors: Caffau, E.; Ludwig, H. -G.; Steffen, M.; Ayres, T. R.; Bonifacio, P.; Cayrel, R.; Freytag, B.; Plez, B. Bibcode: 2008A&A...488.1031C Altcode: 2008arXiv0805.4398C Context: The solar oxygen abundance has undergone a major downward revision in the past decade, the most noticeable one being the update including 3D hydrodynamical simulations to model the solar photosphere. Up to now, such an analysis has only been carried out by one group using one radiation-hydrodynamics code.
Aims: We investigate the photospheric oxygen abundance considering lines from atomic transitions. We also consider the relationship between the solar model used and the resulting solar oxygen abundance, to understand whether the downward abundance revision is specifically related to 3D hydrodynamical effects.
Methods: We performed a new determination of the solar photospheric oxygen abundance by analysing different high-resolution high signal-to-noise ratio atlases of the solar flux and disc-centre intensity, making use of the latest generation of CO5BOLD 3D solar model atmospheres.
Results: We find 8.73 ≤ log (N_O/N_H) +12 ≤ 8.79. The lower and upper values represent extreme assumptions on the role of collisional excitation and ionisation by neutral hydrogen for the NLTE level populations of neutral oxygen. The error of our analysis is ± (0.04± 0.03) dex, the last being related to NLTE corrections, the first error to any other effect. The 3D “granulation effects” do not play a decisive role in lowering the oxygen abundance.
Conclusions: Our recommended value is log (N_O/N_H) = 8.76 ± 0.07, considering our present ignorance of the role of collisions with hydrogen atoms on the NLTE level populations of oxygen. The reasons for lower O abundances in the past are identified as (1) the lower equivalent widths adopted and (2) the choice of neglecting collisions with hydrogen atoms in the statistical equilibrium calculations for oxygen.

This paper is dedicated to the memory of Hartmut Holweger. Title: The Cycles of Alpha Centauri Authors: Ayres, Thomas Bibcode: 2008cxo..prop.2547A Altcode: Alpha Centauri (G2V + K1V) is the nearest system of Sun-like stars; the primary long regarded a solar twin. The binary has been a popular target for previous X-ray missions, although the shrinking orbit now is resolvable only by Chandra. The 25 year X-ray record has revealed striking long term changes in the Alpha Cen coronae, including a deep X-ray minimum of the primary spotted by XMM in 2004-05. A recent LETGS pointing showed that the G star had become quite deficient in >2 MK emissions, but the softer 1 MK spectrum was little changed. Two additional 10 ks HRC-I snapshots in 2009 will continue this remarkable coronal narrative. We also propose key HST FUV spectra of the pair, to constrain emission measures and probe subcoronal dynamics. Title: The Deep Lamp Project: An Investigation of the Precision and Accuracy of the Echelle Wavelength Scales of Space Telescope Imaging Spectrograph Authors: Ayres, Thomas R. Bibcode: 2008ApJS..177..626A Altcode: The precision and absolute accuracy of the echelle mode wavelength scales of Space Telescope Imaging Spectrograph (STIS) are investigated. The method is to measure deep exposures of the onboard Pt/Cr-Ne hollow cathode calibration lamp. The standard deviation of emission spots from their laboratory wavelengths in a single image is a measure of the internal precision of the pipeline-assigned scales. The average shift of the image as a whole is a measure of the absolute accuracy. While systematic patterns can be identified in all four echelle modes (E140M, E140M, E230M, and E230H), the overall precision (even without compensating for long-range trends with λ) is excellent: of order one-tenth of the resolution element (σ ~ 600 and 300 m s-1, for medium- [M] and high- [H] resolution modes, respectively). Furthermore, the absolute accuracy and its repeatability (assessed in a time series of WAVECAL images) is of order a remarkable 100 m s-1, aside from one of the E230M modes (secondary tilt λ2269) that shows a systematic offset 10 times larger. The excellent precision of the STIS echelle wavelengths could be improved by adding higher order terms to the biquadratic polynomial currently implemented in the CALSTIS pipeline. On the other hand, the existing small distortions might be resolved more naturally by a "physical instrument model," currently under development by the Space Telescope European Coordinating Facility's STIS Calibration Enhancement Project. Title: The Fainting of α Centauri A, Resolved Authors: Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt, Jürgen H. M. M. Bibcode: 2008ApJ...678L.121A Altcode: Beginning in 2003, XMM-Newton snapshot monitoring of α Centauri (HD 128620, 128621: G2 V, K1 V) documented a steady fading of the primary's X-ray corona, which had all but disappeared by early 2005. The steep decline in LX was at odds with the previous two decades of high-energy measurements, which showed only modest variability of the Sun-like star. A Chandra LETGS spectrum in 2007 June, however, fully resolved the source of the curious X-ray darkening: a depletion of plasma above ~2 MK had substantially depressed the line spectrum where the XMM-Newton response peaks (λ lesssim 30 Å), even though the overall coronal luminosity, dominated by longer wavelength emissions, had declined only slightly. This is reminiscent of the Sun's magnetic activity cycle, where the 2-3 MK active regions of sunspot maximum give way to the spatially pervasive, but cycle-independent, 1 MK "quiet corona" at minimum. This emphasizes that any discussion of cyclic coronal variability in low-activity stars will depend crucially on the energy coverage of the measurements. Title: The Solar Oxygen Problem: Crisis, Catastrophe, or Opportunity? Authors: Ayres, T. R. Bibcode: 2008ASPC..384...52A Altcode: 2008csss...14...52A A proposed large reduction in the solar oxygen abundance--motivated by spectral synthesis of weak forbidden O I absorptions using 3D convection models--has provoked consternation in the helioseismology community: the spectacular agreement between measured interior sound speed profiles and predictions based on the historical ɛ_{O} completely unravels at the new lower value. In an effort to validate low-O, two generic tests of the 3D models are outlined. A snapshot from the CO^5BOLD class of convection simulations is shown to meet some of the requirements, but fail others. Implications for the solar carbon monoxide (CO) spectrum--alternative O tracer--are discussed. Title: Instruments: HRC Authors: Kraft, Ralph; Kenter, Almus; Ayres, Thomas R.; Judge, Philip G.; Saar, Steven H.; Schmitt, Jurgen H. M. M.; Anderson, Gemma; Gaensler, Bryan; Chicago Team Bibcode: 2008ChNew..15...13K Altcode: No abstract at ADS Title: Commission 36: Theory of Stellar Atmospheres Authors: Spite, Monique; Landstreet, John D.; Asplund, Martin; Ayres, Thomas R.; Balachandran, Suchitra C.; Dravins, Dainis; Hauschildt, Peter H.; Kiselman, Dan; Nagendra, K. N.; Sneden, Christopher; Tautvaišiené, Grazina; Werner, Klaus Bibcode: 2007IAUTB..26..160S Altcode: The business meeting of Commission 36 was held during the General Assembly in Prague on 16 August. It was attended by about 15 members. The issues presented included a review of the work made by members of Commission 36, and the election of the new Organising Committee. We note that a comprehensive report on the activities of the commission during the last triennium has been published in Reports on Astronomy, Transactions IAU Volume XXVIA. The scientific activity of the members of the commission has been very intense, and has led to the publication of a large number of papers. Title: The Solar Oxygen Crisis: a Goldilocks Solution Authors: Ayres, Thomas R. Bibcode: 2007AAS...211.5908A Altcode: 2007BAAS...39..842A The recent recommended large reduction in the solar oxygen abundance--mainly motivated by spectral synthesis of a weak forbidden O I absorption (6300 A) using 3D convection models---has provoked consternation in the helioseismology community: the spectacular agreement between measured interior sound speed profiles and predictions based on the historical abundance (850 ppm relative to hydrogen) completely unravels at the new lower value (450 ppm). At the same time, molecular tracers of the oxygen abundance, such as CO, indicate a value closer to 700 ppm, when the photospheric temperatures in the region of peak molecular concentration are carefully adjusted to match the temperature sensitive wings of the Ca II H and K lines. (One does derive 450 ppm when the unaltered 3D models are used, but these simulations are too cool in the upper photosphere where the molecular diagnostics arise.) In order to reconcile these disparate results, I have reconsidered the formation of the [O I] 6300 feature using an alternative 3D convection model that matches key observational constraints such as the visible continuum center-limb behavior, and calibrated continuum intensities at disk center. As compared with the previous work of Allende Prieto, Asplund, and collaborators, I find that the so-called "1D-to-3D abundance correction" not only is very small, contrary to their study, but also goes in the opposite direction. The consequence is an oxygen abundance of about 650 ppm from 3D [O I]: not too high, not too low, but just right (in the middle). This work was supported by NSF. I thank the CO5BOLD collaboration for making available snapshots from their 3D time dependent solar convection simulations. Title: The Further Fainting of Alpha Cen A Authors: Ayres, Thomas Bibcode: 2007cxo..prop.2330A Altcode: 2007cxo..prop.2286A Alpha Centauri (G2V + K1V) is the nearest system of solar-like stars. The primary has long been regarded a solar twin. Previous X-ray missions have been able to separate the coronal point sources (14" apart in Y2000), although the orbit now is closing rapidly and beyond 2006 can only be resolved easily by Chandra. The 25 year X-ray record has revealed striking long term changes in the Alpha Cen coronae, likely related to analogs of the still mysterious solar sunspot cycle. Recent work suggests that the K star is falling into a cycle minimum, while the G star is relapsing following a brief recovery from an unprecedented deep X-ray minimum in 2005 (that fully challenges our understanding of stellar dynamos). Two 10 ks HRC-I snapshots in 2008 will build on this remarkable coronal narrative. Title: Filling in the Coronal Graveyard Authors: Ayres, Thomas Bibcode: 2007cxo..prop.2333A Altcode: 2007cxo..prop.2289A 20 ks Chandra HRC-I pointings on 5 late-type G/K supergiants in the depths of the "coronal graveyard" will complete a survey of the limits of X-ray activity in evolved cool stars. Our ambition is to gain insight into magnetic generation in the absence of sensible rotation, and the disposition of hot coronal structures in the extended outer envelopes of these objects, possibly partially smothered under a "cool absorber." Such buried activity might be the long sought initiator of chromospheric winds in the giant branch. Coronal activity is important to the Sun-Earth connection, the fate of primitive planetary atmospheres, and a broad reaching set of magnetic phenomena in diverse cosmic environments. Understanding the activity, and its evolution, is a key objective of stellar astrophysics. Title: X-Ray and Ultraviolet Spectroscopy of Intermediate-Mass, First Crossing Giants Authors: Ayres, Thomas R.; Hodges-Kluck, Edmund; Brown, Alexander Bibcode: 2007ApJS..171..304A Altcode: Chandra, FUSE, and HST STIS jointly have obtained spectra of four intermediate-mass giants (<~3 Msolar) crossing the Hertzsprung gap for the first time, passing through a ``rapid braking phase'' analogous to, but much briefer than, the more gradual prolonged decay of magnetic activity experienced by single low-mass stars like the Sun. All four giants display hot, dense coronal plasmas (6-30 MK, ~1012 cm-3), with near solar abundances. The UV spectra show a remarkable congruence of shapes of the 0.06-0.2 MK lines of Si IV, C IV, and N V, which further can be decomposed into narrow and broad Doppler components. The profile isomorphism extends to the yellow dwarf α1 Cen (G2 V), utilized as a solar surrogate. The broad component fraction of the total increases with LX/Lbol and is suggestive of persistent ``microflaring.'' Indeed, the most active of the targets, HR 9024 (G1 III), experienced a macroflare during the Chandra pointing, reaching a remarkable 100 MK. In prebraking phase 31 Com (G0 III) and solar proxy α1 Cen emission levels in the 0.03-0.3 MK ``transition zone'' regime are very similar to those of the 1-10 MK corona, but in the three cooler giants, the hotter plasma is dominant. The high coronal densities of all four giants contrast to much lower values (~1010 cm-3) at 0.15 MK from O IV line ratios, contrary to expectations for isobaric magnetic loops, but possibly analogous to the bimodal pressure behavior of certain solar impulsive flares. Title: α TrA Junior Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. Bibcode: 2007ApJ...658L.107A Altcode: The ``hybrid chromosphere'' star α Trianguli Australis (K2 Ib-IIa) displays atypical coronal properties for its class: elevated soft X-ray emission, flare outbursts, and a superhot (T~10 MK) spectrum. The Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST) now has found a faint object close to the red supergiant, 0.4" nearly due south and about 1% its intensity in the F160BW ultraviolet filter, consistent with a G0 dwarf. Potentially, the ``young sun'' companion to the massive primary could completely dominate the coronal luminosity. The X-ray centroid in a contemporaneous Chandra High-Resolution Camera (HRC) pointing is offset in the direction of the faint UV secondary, but measurements of the radio counterpart of a serendipitous X-ray source 12" southeast (SE) of α TrA, obtained with the Australia Telescope Compact Array (ATCA), suggest a conflicting offset. Title: Commission 36: Theory of Stellar Atmospheres Authors: Spite, Monique; Landstreet, John; Asplund, M.; Ayres, T.; Balachandran, S.; Dravins, D.; Hauschildt, P.; Kiselman, D.; Nagendra, K. N.; Sneden, C.; Tautvaišiené, G.; Werner, K. Bibcode: 2007IAUTA..26..215S Altcode: Commission 36 covers all the physics of stellar atmospheres. The scientific activity in this large field has been very intense during the last triennium and led to the publication of a large number of papers which makes an exhaustive report practically not feasible. As a consequence we decided to keep the format of the preceding report: first a list of areas of current research, then web links for obtaining further information. Title: Deep GRISM Survey of the Hyades Cluster. Ii. Authors: Ayres, Thomas Bibcode: 2007galx.prop...65A Altcode: The nearby, young (600 Myr) Hyades cluster is an important testing ground for theories of stellar activity and flares, whose associated chromospheric and coronal emissions are particularly conspicuous at high energies. The Hyades region has been imaged numerous times by soft X-ray observatories, beginning a quarter century ago with Einstein, continuing with ROSAT, and more recently Chandra and XMM-Newton. However, FUV observations -- particularly of key energy balance and flare tracer C IV 1550 -- have been hampered by faintness of the cluster members and the usual limitation to observe them one at a time. Here, we propose to continue our Cycle 3 program by imaging three rich fields in the Hyades with the GALEX grisms to capture C IV (and Mg II 2800) in 30, or more, cluster members of late spectral type (F-K), mostly main sequence stars. The controlled sample will strongly leverage our understanding of high energy processes and flare outbursts in Sun-like stars, especially in the crucial age range of our own solar system when primitive planetary atmospheres were strongly eroded by coronal ionizing radiations and mass ejections. The spatial multiplex advantage, high sensitivity, spectral isolation, and long stare capability of GALEX are ideally suited to the project." Title: The Old Feeble Coronae of Solar-like Dwarf Stars in the Arcturus Moving Group Authors: Brown, Alexander; Hodges-Kluck, E.; Ayres, T. R.; Harper, G. M. Bibcode: 2006AAS...209.8905B Altcode: 2006BAAS...38Q1025B The Arcturus Moving Group (AMG) is very likely a remnant of the merger of a dwarf galaxy with the Milky Way Galaxy in the distant past. This kinematically distinct group has members located very close to the Sun, allowing study of coronal activity on very old stars that would typically not be possible. We are investigating a sample of nearby AGM dwarfs to study the properties of stellar magnetic activity on old (7-8 Gyr), low metallicity stars. Our sample has metallicities between 0.4 and 0.04 solar, spectral types F9 K0, and distances less than 35 pc from the Sun. We have detected X-ray emission from two AMG dwarfs with the Chandra ACIS-S S3 BI detector during Cycle 7 and two further stars have been approved for observation in Cycle 8. The detected stars are HD199288 (G0 V, V=6.6, d = 21.6 pc, [Fe/H] = -0.68) and HD65583 (G8 V, V=6.9, d = 16.8 pc, [Fe/H] = -0.68) and their derived X-ray luminosities are 4.4 and 1.9 1026 erg s-1 respectively. These X-ray luminosities are somewhat less than the minimum solar Lx (range 6 -20 1026 erg s-1 ) but are comparable with that of the inactive, more metal rich ([Fe/H] = -0.42] G8 dwarf Tau Cet. All the detected source X-rays are very soft with energies of 0.2-0.3 keV, indicating very cool (∼ 1 MK) coronal temperatures.

These results were obtained and funded by CXO project 7200977. Title: The Coronae of γ Draconis Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. Bibcode: 2006ApJ...651.1126A Altcode: The Chandra X-Ray Observatory has detected coronal (T>~106 K) emission from the red giant γ Draconis (HD 164058: K5 III; d=45 pc), now fully resolved from a stronger source 21" to the SE that had confused earlier measurements by Röntgensatellit (ROSAT). The second source is coincident with the 13th magnitude visual component ADS 10923B (γ Dra B), possibly a dM star in a wide orbit around the red giant. The 0.2-2 keV luminosity of γ Dra is LX~1.2+0.4-0.2×1027 ergs s-1 (1 σ confidence interval), assuming log(Tcor)>~6.5 K, while that of the faint optical companion is 3.2+0.7-0.5×1027 ergs s-1, assuming the same distance. Both sources have an intermediate spectral hardness within the range displayed by coronal stars. γ Dra has LX/Lbol an order of magnitude brighter than the other red giants previously imaged by Chandra, Arcturus (α Boo: K1.5 III) and Aldebaran (α Tau: K5 III), despite having an only 2 × elevated LC IV/Lbol (T~105 K). Title: Strip-Mining the Coronal Graveyard Authors: Ayres, Thomas Bibcode: 2006xmm..prop...95A Altcode: XMM-Newton pointings on 5 late-type G/K supergiants in the outskirts of the coronal graveyard will explore the midrange of X-ray activity in evolved late-type stars. Our ambition is to gain insight into magnetic field generation in the absence of sensible rotation, and the disposition of hot coronal structures in the extended outer envelopes of these objects, possibly partially smothered beneath a cool absorber. Such buried activity might be the long sought initiator of chromospheric winds in the giant branch. The project will capture the remaining most promising candidates from UV and X-ray flux limited samples identified in the ROSAT era. Understanding the broad reaches of coronal activity, and its evolution, are key objectives of cool star astrophysics. Title: The Fainting of Alpha Cen A Authors: Ayres, Thomas Bibcode: 2006cxo..prop.2108A Altcode: Alpha Centauri (G2V+K1V) is the nearest system of solar-like stars; the primary has long been regarded a solar twin. Historical X-ray missions have been able to separate the coronal point sources (14" apart in Y2000), although the orbit now is closing rapidly and beyond 2006 can only be resolved by Chandra. The 35 year X-ray record has revealed striking long term changes in the Alpha Cen coronae, likely related to analogs of the still mysterious solar sunspot cycle. Recent work suggests that the K star is rising out of a cycle minimum, while the G star has experienced a startling, unprecedented plunge in its X-ray luminosity that calls into question our understanding of stellar dynamos. A deep LETGS spectrum, and two short HRC-I snapshots, will build on this remarkable coronal narrative. Title: Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and Their Isotopes Authors: Ayres, Thomas R.; Plymate, Claude; Keller, Christoph U. Bibcode: 2006ApJS..165..618A Altcode: 2006astro.ph..6153A A solar photospheric ``thermal profiling'' analysis is presented, exploiting the infrared (2.3-4.6 μm) rovibrational bands of carbon monoxide (CO) as observed with the McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum intensities and center-limb behavior constrained the temperature profile of the deep photosphere, while CO center-limb behavior defined the thermal structure at higher altitudes. The oxygen abundance was self-consistently determined from weak CO absorptions (for C/O≡0.5). Our analysis was meant to complement recent studies based on three-dimensional (3D) convection models, which, among other things, have revised the historical solar oxygen (and carbon) abundance downward by a factor of nearly 2, although in fact our conclusions do not support such a revision. Based on various considerations, an ɛO=700+/-100 ppm (parts per million relative to hydrogen) is recommended; the large uncertainty reflects the model sensitivity of CO. New solar isotopic ratios also are reported: 12C/13C=80+/-1, 16O/17O=1700+/-220, and 16O/18O=440+/-6-all significantly lower than terrestrial. CO synthesis experiments utilizing a stripped down version of the 3D model-which has large temperature fluctuations in the middle photosphere, possibly inconsistent with CO ``movies'' from the Infrared Imaging Spectrometer (IRIS), and a steeper mean temperature gradient than matches visible continuum center-limb measurements-point to a lower oxygen abundance (~500 ppm) and isotopic ratios closer to terrestrial. A low oxygen abundance from CO-and other molecules like OH-thus hinges on the reality of the theoretically predicted midphotospheric convective properties. Title: Those Cool Stars...So Hot Right Now Authors: Ayres, T. R. Bibcode: 2006ASPC..348..145A Altcode: I offer four (out of many possible) examples of FUSE programs focussing on late-type ("cool") stars: (1) a survey of coronal forbidden lines; (2) the buried coronae of red giants; (3) super-rotational UV line broadening in Hertzsprung gap stars; and (4) FUV time series as a gauge of activity. Title: A Cycle-4 Survey of RS CVn Binary Systems Authors: Redfield, S.; Linsky, J. L.; Ayres, T. R.; Brown, A.; Herczeg, G. J. Bibcode: 2006ASPC..348..269R Altcode: RS CVn systems are detached late-type binaries that are very active as a result of their tidally enforced rapid rotation. They are actively studied and bright at X-ray and ultraviolet (UV) wavelengths, but very few have been observed in the far-UV. We present multiple orbital phase observations of RS CVn systems taken by the Far Ultraviolet Spectroscopic Explorer (FUSE) through a survey program in Cycle 4. Located in the FUSE spectral range are emission lines formed in plasma at 50,000--300,000 K (e.g., C III and O VI). We present an analysis of the strong emission line profiles. By monitoring the change in the profile shape over the course of an orbital period we can measure the fractional contributions of each star in the RS CVn binary system at different plasma temperatures. In addition, the spectral resolution and wavelength scale of FUSE permit us to measure the width and velocity shift of the O VI and C III lines, providing a new window on stellar atmospheric dynamics and structure. Title: The Remarkable Far-Ultraviolet Spectrum of FK Comae Berenices: King of Spin Authors: Ayres, Thomas R.; Harper, Graham M.; Brown, Alexander; Korhonen, Heidi; Ilyin, Ilya V.; Redfield, Seth; Wood, Brian E. Bibcode: 2006ApJ...644..464A Altcode: A Far Ultraviolet Spectroscopic Explorer (FUSE) pointing on the ultrafast rotating yellow giant FK Comae Berenices (HD 117555; vsini~163 km s-1) recorded emission profiles of C III λ977 (T~8×104 K) and O VI λ1031 (T~3×105 K) that are exceptionally broad and asymmetric, but nearly identical in shape, aside from a blueward absorption component in the latter (identified as interstellar O I, rather than, say, a C III outflow feature). The FWHMs exceed 500 km s-1, twice the broadest far-UV line shape of any normal late-type star observed to date, but similar to the Hα profiles of FK Com, and following the trend of other fast spinning early G giants that often display ``superrotational'' broadening of their UV ``hot'' lines. Although the red-asymmetric O VI λ1031 profile is suggestive of an outflow at ~3×105 K, the weaker member of the doublet, λ1037, does not display the differential absorption pattern expected from a warm wind. Furthermore, at times the chromospheric Mg II λ2796 + λ2803 composite profile, from a collection of International Ultraviolet Explorer (IUE) echellegrams obtained two decades earlier, is nearly identical in shape to red-asymmetric O VI λ1031. A contemporaneous optical Doppler map places the photospheric dark spots mainly in the polar regions of the approaching hemisphere. The dominantly redward biased profiles of C III and O VI could be explained if the associated emission zones were leading the starspots in phase and partially rooted in lower latitudes. Title: Key problems in cool-star astrophysics Authors: Pagano, Isabella; Ayres, Thomas R.; Lanzafame, Alessandro C.; Linsky, Jeffrey L.; Montesinos, Benjamín; Marcello-Rodonò Bibcode: 2006Ap&SS.303...17P Altcode: Selected key problems in cool-star astrophysics are reviewed, with emphasis on the importance of new ultraviolet missions to tackle the unresolved issues. UV spectral signatures are an essential probe of critical physical processes related to the production and transport of magnetic energy in astrophysical plasmas ranging, for example, from stellar coronae, to the magnetospheres of magnetars, and the accretion disks of protostars and Active Galactic Nuclei. From an historical point of view, our comprehension of such processes has been closely tied to our understanding of solar/stellar magnetic activity, which has its origins in a poorly understood convection-powered internal magnetic dynamo. The evolution of the Sun's dynamo, and associated magnetic activity, affected the development of planetary atmospheres in the early solar system, and the conditions in which life arose on the primitive Earth. The gradual fading of magnetic activity as the Sun grows old likewise will have profound consequences for the future heliospheric environment. Beyond the Sun, the magnetic activity of stars can influence their close-in companions, and vice versa. Cool star outer atmospheres thus represent an important laboratory in which magnetic activity phenomena can be studied under a wide variety of conditions, allowing us to gain insight into the fundamental processes involved. The UV range is especially useful for such studies because it contains powerful diagnostics extending from warm (∼ 104 K) chromospheres out to hot (1 10 MK) coronae, and very high-resolution spectroscopy in the UV has been demonstrated by the GHRS and STIS instruments on HST but has not yet been demonstrated in the higher energy EUV and X-ray bands. A recent example is the use of the hydrogen Lyα resonance line—at 110 000 resolution with HST STIS—study, for the first time, coronal winds from cool stars through their interaction with the interstellar gas. These winds cannot be detected from the ground, for lack of suitable diagnostics; or in the X-rays, because the outflowing gas is too thin. A 2m class UV space telescope with high resolution spectroscopy and monitoring capabilities would enable important new discoveries in cool-star astronomy among the stars of the solar neighborhood out to about 150 pc. A larger aperture facility (4 6 m) would reach beyond the 150 pc horizon to fainter objects including young brown dwarfs and pre-main sequence stars in star-forming regions like Orion, and magnetic active stars in distant clusters beyond the Pleiades and α Persei. This would be essential, as well, to characterize the outer atmospheres of stars with planets, that will be discovered by future space missions like COROT, Kepler, and Darwin. Title: Stellar Activity on Young Stars in the Local Association: FUSE Observations of the Beta Pic and Tucana-horologium Moving Groups Authors: Brown, Alexander; Harper, G. M.; Ayres, T. R. Bibcode: 2006AAS...208.1003B Altcode: 2006BAAS...38...89B A significant number of the nearby single active dwarf stars are members of the Local Association, which is a widespread aggregate of young stars related to star formation in the Sco-Cen association. The ages of stars within the Local Association span a range of 8-150 Myr, but the subgroups have much narrower age spreads. The older portions of the Local Association include the Pleiades and Alpha Per clusters. Younger subgroupings of the Local Association include the Beta Pic [age 12Myr] and Tucana-Horologium [age 30Myr] moving groups. By ages of 12 Myr, circumstellar disks and associated protoplanetary systems are at an extremely interesting stage of evolution with gas giant formation well under way and terrestrial planets starting to form. The high energy radiation and particle (wind+flare) emission from the central star plays an important role in the evolution of these disks. The crucial EUV radiation field that photoioizes protoplanetary disks and atmospheres is dominated by transition region ( 105 K) emission lines, such as He I 584, 537 A, He II 304 A, N III 686 A, O III 600, 703 A, O IV 556, 610, 790 A, O V 630, 760 A, Ne VIII 780 A, and sub-coronal emissions such as Mg IX 368 A and Mg X 610, 625 A. These emission lines are unobservable because of strong absorption by the interstellar medium and their strengths must be estimated from UV observations of other emission lines from the same ions or ions formed at similar temperatures. We are currently undertaking a FUSE Cycle 6/7 Legacy project to study the Beta Pic moving group and a large Cycle 7 Survey project to investigate the Tucana-Horologium moving group. We present the current status of these projects and discuss the O VI and C III emission line properties observed. Title: Exploring High Time Resolution Coronal Dynamics with the Rapid Acquisition Imaging Spectrograph (RAISE) Sounding Rocket Program Authors: Hassler, Donald W.; DeForest, C. E.; McIntosh, S.; Slater, D.; Ayres, T.; Thomas, R.; Scheuhle, U.; Michaelis, H.; Mason, H. Bibcode: 2006SPD....37.3706H Altcode: The Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation high resolution imaging spectrograph to study the dynamics of the solar chromosphere and corona on time scales as short as 100 ms. High speed imaging from TRACE has shown that rapid motions and reconnection are central to the physics of the transition region and corona, but cannot resolve the differences between propagating phenomena and bulk motion. SoHO/CDS and SoHO/SUMER have yielded intriguing measurements of motion and heating in the solar atmosphere, and Solar-B/EIS will capture EUV spectra of flares in progress; but no currently planned instrument can capture spectral information in the chromosphere, transition region, or cool corona on the 1-10 Hz time scale required for few-second cadence spectral imaging or rapid wave motion studies. RAISE is uniquely suited to exploring this hard-to-reach domain.The first flight of RAISE is scheduled for October 24, 2006 (Flight 36.219 US) and will focus on the study of high frequency, small-scale dynamics of active region structures and the high frequency wave structure associated with these active regions. Title: Deep Grism Survey of the Hyades Cluster Authors: Ayres, Thomas Bibcode: 2006galx.prop...81A Altcode: The nearby, young (600 Myr) Hyades cluster is an important testing ground for theories of stellar activity and flares, whose associated chromospheric and coronal emissions are particularly conspicuous at high energies. The Hyades region has been imaged numerous times by soft X-ray observatories, beginning a quarter century ago with Einstein, continuing with ROSAT, and more recently Chandra and XMM-Newton. However, FUV observations--particularly of key energy balance and flare tracer C IV 1550--have been limited by faintness of the cluster members and the usual limitation (of slit spectrographs) to observe them one at a time. Here, we propose to image four rich fields in the Hyades with the GALEX grisms to capture C IV (and Mg II 2800) in about 30 cluster members of late spectral type (F-K), mostly main sequence stars. The highly controlled sample will strongly leverage our understanding of high energy processes and flare outbursts in Sun-like stars, especially in the crucial age range of the young Sun relevant to the erosion of primitive planetary atmospheres by coronal ionizing radiations and mass ejections. The spatial multiplex advantage, sensitivity, spectral isolation, and long stare capability of GALEX are ideally suited to the project. Title: Seven Days in the Life of AR Lac Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Korhonen, H.; Redfield, S.; Hawley, S. L.; Optical Support Team Bibcode: 2005AAS...20717505A Altcode: 2005BAAS...37.1445A A week-long pointing on the short-period eclipsing RS CVn binary AR Lac (K0IV+G4IV; P=2d) by the Far-Ultraviolet Spectroscopic Explorer was coordinated with groundbased optical Doppler mapping, to provide an unprecedented view of structure, energetics, and dynamics of subcoronal activity, through time-resolved measurements of FUV diagnostics like C III λ 977, O VI λ 1031, and (coronal forbidden line) Fe XVIII λ 974. The observation was carried out over the period 29 November to 7 December 2004, with a total exposure of 225 ks, covering four revolutions of the binary. Three large flares were captured during this period, and numerous smaller ones, mainly on the K subgiant primary. We discuss the appearance of the FUV activity on the surfaces of the two hyperactive companions, with special emphasis on the eclipse intervals.

This work was supported by a FUSE Guest Investigator grant. Title: Anomalous Coronae of Yellow Giants and Supergiants Authors: Ayres, Thomas Bibcode: 2005xmm..prop...47A Altcode: EPIC-pn spectra of "X-ray deficient" yellow giants and supergiants will explore why these stars display anomalous coronal behavior compared with cooler giants only slightly further advanced in their evolution. Among the class-III objects, the sharp transition in coronal properties on the way to helium flash might be caused by disruption of a "fossil" magnetosphere by a newly born solar-like dynamo. But, the class-I supergiants are post-flash, and a second deficiency mechanism likely applies, perhaps highly extended chromospheric envelopes obscuring X-rays from submerged magnetic loops. A key discriminator is the coronal energy distribution, especially the presence of enhanced soft absorption. Title: Further Resolving the Puzzle of Hybrid Star X-rays Authors: Ayres, Thomas Bibcode: 2005cxo..prop.1897A Altcode: 2005chan.prop.1829A; 2005cxo..prop.1829A Do Alpha TrA (K2II) and Beta Ind (K1II) have previously unrecognized X-ray active dwarf companions, leading us astray concerning the coronal properties of the "hybrid-chromosphere" class? Establishing the true X-ray luminosities of the hybrids is a basis for understanding magnetic field generation in evolved supergiants, the driving of their winds, and the seeding of coronal conditions in their extended outer envelopes. It also bears on the issue of late-type dwarfs orbiting main sequence B stars, the evolutionary predecessors of K bright giants. We propose to directly image the putative hybrid companions using Chandra, with supporting observations from HST/WFPC2. We also propose to obtain a coronal temperature for the archetype hybrid Alpha Aqr (G2Ib), recently detected by HRC-I. Title: Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. Bibcode: 2005ApJ...627L..53A Altcode: We report Chandra detections of coronal X-rays from the early G supergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD 204867: G0 Ib). Previous ROSAT observations of these archetypical ``hybrid chromosphere'' stars were inconclusive, in the case of α Aqr owing to a 38' mispointing, and for β Aqr because of a small positional discrepancy of the apparent source. The Chandra High Resolution Camera (HRC-I), with its superior spatial resolution and sensitivity, has obtained a positive detection of α Aqr and recovered faint emission at the location of β Aqr, now well separated from the stronger source to the southeast that dominated the earlier ROSAT image. The coronal LX/LC IV luminosity ratios of both supergiants are extremely depressed relative to early G main-sequence stars, continuing the ``X-ray deficiency syndrome'' originally identified in late F/early G luminosity class III giants of the Hertzsprung gap. Title: StarCAT Authors: Ayres, Thomas Bibcode: 2005hst..prop10638A Altcode: StarCAT is a two-year Legacy Archival project to assemble all of the STIS ultraviolet echelle exposures of normal stars into a broad-ranging UV spectral library. The STIS echelle collection will be unique for the decade, or more, that it will take to reproduce the lost UV high-resolution capability in space. Consequently, StarCAT will be an important resource for a wide variety of investigations, for years to come. It follows-on an earlier Cycle 11 effort-CoolCAT-focussing on late-type stars, which stands as a successful demonstration project. But, StarCAT will capture as many as 300 targets and 2000 individual spectra {6X CoolCAT}, so it will have much further reach and impact. Equally important, we can improve upon the CoolCAT post-processing procedures and employ the definitive version of the STIS pipeline when it becomes available. StarCAT will serve a broad cross-section of the community beyond the familiar stellar enterprises, supporting work on the interstellar medium, asterospheres, circumstellar environments, exoplanets, and more. Now, at the end of STIS operations, is the time to undertake such a UV preservation effort for the benefit of future researchers, before the current expertise with the instrument inevitably fades away. Title: Further Resolving the Puzzle of Hybrid Star X-rays Authors: Ayres, Thomas Bibcode: 2005hst..prop10767A Altcode: Do Alpha TrA {K2II} and Beta Ind {K1II} have previously unrecognized X-ray active dwarf companions, leading us astray concerning the coronal properties of the "hybrid-chromosphere" class? Establishing the true X-ray luminosities of the hybrids is a basis for understanding magnetic field generation in evolved supergiants, the driving of their winds, and the seeding of coronal conditions in their extended outer envelopes. It also bears on the issue of late-type dwarfs orbiting main sequence B stars, the evolutionary predecessors of K bright giants. We propose to directly image the putative hybrid companions using Chandra, with supporting observations from HST/WFPC2. Title: The Solar Oxygen Abundance, and the Rare Isotopes of C and O, Derived from Infrared Spectra of Carbon Monoxide Authors: Ayres, T. R.; Plymate, C.; Keller, C.; Kurucz, R. L. Bibcode: 2005AGUSMSP41B..09A Altcode: A detailed abundance analysis is presented for solar oxygen based on the ΔV=1 fundamental (4.6~μm) and ΔV=2 (2.3~μm) first-overtone rovibrational bands of carbon monoxide observed above the Earth's atmosphere at very high spectral resolution and high signal-to-noise by the Shuttle-borne ATMOS Fourier transform spectrometer (FTS). Additional observations to define the reference photospheric thermal structure were taken of the CO fundamental bands in an atmospheric window at 2145~cm-1 (4.6~μm) using the 1~m FTS of the McMath-Pierce telescope at Kitt Peak and a fast tip/tilt image stabilization system. The latter allowed measurements at the extreme limb where the highly slanted rays probe into the outer layers of the photosphere. High spatial resolution "movies" of weak CO lines at disk center taken under excellent seeing conditions with the Infrared Imaging Spectrometer (IRIS), also on the McMath-Pierce telescope, further constrained thermal and velocity fluctuations in the layers in which the abundance-sensitive CO lines form. This work is meant to complement a series of recent studies which have revised the previously recommended solar oxygen abundance downward by nearly a factor of two; although in fact our conclusions do not support such a revision. The oxygen abundance recovered in the present work is 700±70~ppm (parts per million relative to hydrogen) compared with the proposed downward revision to 460±60~ppm, and the recommended value of 650±100~ppm of a decade ago. In our analysis, a fixed C/O ratio of 0.5, derived in independent work, was assumed; so the associated carbon abundance is 350~ppm. New accurate values for the solar abundance ratios of the rare isotopes of C and O also are reported: 12C/13C= 70, 16O/17O= 400, and 16O/18O= 2000. All three ratios are lower than terrestrial or meteoritic values (indicating higher isotopic abundances). We find no evidence in the ATMOS3 spectra for measurable 14C16O lines. Title: XMM-Newton observations of Pleiades-age K dwarfs Authors: Brown, A.; Day, F.; Ayres, T. R.; Ambruster, C. Bibcode: 2005ESASP.560..465B Altcode: 2005csss...13..465B No abstract at ADS Title: CoolCAT Authors: Ayres, T. R. Bibcode: 2005ESASP.560..419A Altcode: 2005csss...13..419A No abstract at ADS Title: Ultraviolet Atlas of the Arcturus Spectrum, 1150-3800 A Authors: Hinkle, Kenneth; Wallace, Lloyd; Valenti, Jeff; Ayres, Thomas Bibcode: 2005uaas.book.....H Altcode: 2005ASPMP...3.....H The third volume of a set of atlases covering the infrared through ultraviolet spectrum of the K giant Arcturus. This volume covers the ultraviolet spectrum observed from the ground as well as moderate and high resolution ultraviolet spectra observed with STIS on the HST. The wavelength coverage of this volume is 1150 to 3800 A. In addition to the spectrum of Arcturus, the solar spectrum or the spectrum of the solar proxy alpha Cen A are shown. Each atlas page covers 10 to 15 A of spectrum with line identifications shown. Tables are included summarizing the line identifications. Title: COmospheres and Beyond Authors: Ayres, Thomas Bibcode: 2005hris.conf..353A Altcode: There is an unexpectedly cool atmospheric layer on top of the Sun’s photosphere, likely present in virtually all stars of solar temperature and cooler. The main diagnostic of this mysterious layer is the = 1 (fundamental) rovibrational band system of carbon monoxide in the thermal infrared, near 5 μm. It is thought that strong radiative cooling by the CO bands, themselves, is directly responsible for the depressed thermal structure of the cold layer, thus the moniker “COmosphere.” Here, three different views of stellar COmospheres are presented: a survey of the 5 μm CO bands in late-type stars with the PHOENIX cryogenic echelle spectrometer at the Kitt Peak 2.1 m telescope; recent studies of the off-limb CO emissions in the Sun exploiting the McMath-Pierce Fourier transform spectrometer (FTS); and time-resolved integral field spectroscopy of solar surface dynamics using the Imaging Infrared Spectrograph (IRIS) and a new IR adaptive optics system, also on the McMath-Pierce at Kitt Peak. Title: X-Rays from Hybrid Stars Authors: Ayres, Thomas R. Bibcode: 2005ApJ...618..493A Altcode: The late-type giants and supergiants of the ``hybrid chromosphere'' class display signatures of cool (T<~2×104 K) winds together with hot emission lines from species like C IV (T~105 K). A survey of such stars by Reimers et al. using ROSAT reported numerous X-ray detections (T~106 K), strengthening the (then heretical) idea that hot coronae and cool winds can coexist in luminous giants. However, several of the candidate sources were offset from the predicted stellar coordinates, calling into question the identifications. In an effort to secure better knowledge of the X-ray luminosities of the hybrids, the ROSAT fields from the Reimers et al. survey were reexamined, exploiting the USNO-A2.0 astrometric catalog to register the pointings to a few arcseconds accuracy. On the basis of positional mismatches, at least two of the previously reported detections of key hybrid stars-γ Dra (K5 III) and β Aqr (G0 Ib)-must be rejected. The new X-ray upper limits for these stars, combined with the remaining candidate detections (and nondetections) from the original survey, place the hybrids into the same ``X-ray deficient'' category as the ``noncoronal'' red giants like Arcturus (α Boo: K1.5 III) and Aldebaran (α Tau: K5 III). A few of the hybrid X-ray sources are exceptional, however. The archetype α TrA (K2 II-III), in particular, is securely detected in terms of positional coincidence, but its anomalous, contradictory coronal properties suggest that an unseen companion-a young hyperactive G dwarf-might dominate the X-ray emission. Title: The Soho-Stellar Re-Connection Authors: Ayres, T. R. Bibcode: 2004ESASP.575..279A Altcode: 2004soho...15..279A No abstract at ADS Title: FK Comae: King of Spin Authors: Ayres, T. R.; Korhonen, H.; Harper, G. M.; Brown, A.; Redfield, S. Bibcode: 2004AAS...205.1202A Altcode: 2004BAAS...36.1356A Fast-rotating early-G giants often display ultraviolet profiles of ``hot lines,'' like O VI (3×105 K), up to twice as broad as anticipated from the photospheric υsin {i}. This peculiar behavior has been attributed to highly extended coronal outer atmospheres.

FUSE recently has contributed fundamentally to the exploration of these ``super-rotational'' effects by observing the fascinating object FK Comae Berenices (G5 III). It is prototype of a class of rapidly rotating single giants which display spectacular emission activity from X-rays to radio. FK Com has a spin period of only 2.4 d, and a remarkable υsin {i} of 160 km s-1. The origins of such ultra-fast--rotating stars are controversial. They might result from a coalesced contact binary, cannibalism of a ``hot Jupiter,'' or simply represent the top of the natural spin distribution of moderate-mass Hertzsprung gap giants.

In February 2004, FUSE obtained a 13 ks exposure of FK Com in the 920--1180 Å range, the first UV observation of this unusual object since the IUE era a decade ago, and by far the best quality spectrum to date. The FUV emissions of O VI λ 1031 and C III λ 977 are enormously broad, asymmetric, but nearly identical in shape, aside from a blue-shifted absorption component in the latter. The FHWM's are a remarkable 600 km s-1, about twice the broadest FUV profile of any late-type star observed up to that point.

The blueshifted C III feature might represent a wind at ∼ 3×104 K, or alternatively a scattering structure in the highly extended coronal envelope, something like the ``prominences'' seen already in Hα . The asymmetric O VI profile might indicate an outflow at higher ∼ 3× 105 K temperatures; or simply reflects a skewed distribution of high-altitude activity in the equatorial zones of FK Com. The relationship between the hot lines and photospheric active regions---deduced from contemporaneous optical Doppler mapping---also will be discussed.

This work was supported by FUSE Guest Investigator grant NNG04GH25G. Title: HRC Imaging of the `Fainted' Primary of the Alpha Centauri System Authors: Ayres, Thomas Bibcode: 2004cxo..prop.1874A Altcode: The famous Alpha Centauri binary (G2V+K1V) has been regularly observed in X-rays since first resolved by Einstein 25 years ago, later by ROSAT/HRI, and more recently by XMM. The latest EPIC-pn imaging uncovered an extremely odd result: solar twin Alp Cen A has nearly disappeared in X-rays. This behavior had not been encountered in the previous quarter century of X-ray work on the system, and is quite unlike anything ever seen on the Sun, except perhaps the curious 18th-century "Maunder minimum," when sunspots vanished from the solar disk for decades at a time, and coronal activity likely was severely depressed; although, of course, we don't have any X-ray observations from then to confirm the true coronal behavior. The AB orbit now has closed below the resolution of EPIC, although still is easy for Chandra to separate. I therefore propose to continue the crucial X-ray time series on this important solar analog using Chandra's HRC-I. Title: Resolving the Puzzle of Hybrid Star Coronal X-rays Authors: Ayres, Thomas Bibcode: 2004cxo..prop.1644A Altcode: We propose 20 ks HRC-I pointings to detect 3 members of the so-called "hybrid star" class, and 50 ks to confirm a previous HRC-I detection of the archetype noncoronal giant Arcturus. Coronal activity, mirrored in X-ray emission, is important to the Sun-Earth connection, the fate of primitive planetary atmospheres, and a broad reaching set of magnetic phenomena in diverse cosmic environments. Our program will explore the limits of X-ray activity across the "coronal dividing line," focussing on targets for which ROSAT-era detections have been challenged recently. Assessing the true levels of coronal activity in these objects has important implications for understanding the initiation of chromospheric winds in red giants, a key phenomenon whose origins remain elusive. Title: A Multiwavelength Perspective of Flares on HR 1099: 4 Years of Coordinated Campaigns Authors: Osten, Rachel A.; Brown, Alexander; Ayres, Thomas R.; Drake, Stephen A.; Franciosini, Elena; Pallavicini, Roberto; Tagliaferri, Gianpiero; Stewart, Ron T.; Skinner, Stephen L.; Linsky, Jeffrey L. Bibcode: 2004ApJS..153..317O Altcode: 2004astro.ph..2613O We report on four years of multiple wavelength observations of the RS CVn system V711 Tau (HR 1099) from 1993, 1994, 1996, and 1998. This combination of radio, ultraviolet, extreme ultraviolet, and X-ray observations allows us to view, in the most comprehensive manner currently possible, the coronal and upper atmospheric variability of this active binary system. We report on the changing activity state of the system as recorded in the EUV and radio across the four years of the observations, and study the high energy variability using an assemblage of X-ray telescopes. (Longer abstract in paper). Title: The Deep Lamp Project Authors: Ayres, Thomas Bibcode: 2004hst..prop10203A Altcode: Space Telescope Imaging Spectrograph is the most sophisticated space-borne spectrometer ever built, probably the last of its kind for some time to come. A key virtue of STIS is that its medium- and high-resolution echelle modes provide access to broad intervals of the vacuum ultraviolet spectrum in a single shot. Another virtue is the validation of the wavelength scales by periodic observations of an onboard hollow-cathode emission line source. Tying together the different echelle orders by means of the accurately known lamp spectrum enables a wide range of studies that exploit differential comparisons of velocity diagnostics in stellar, interstellar, and even extragalactic spectra. Despite the importance of the wavelength calibrations, however, they are done only infrequently {once a year}. While STIS undoubtedly must be one of the most stable orbiting spectrographs ever designed, possible thermal distortions of the instrument might cause small nonlinear deviations of the wavelength scales and thereby impact the velocity precision. The existing wavecal data sets are separated too far apart in time to isolate short-term thermal fluctuations from long-term secular behavior, and the routine WAVELINEs taken with every grating switch are too underexposed to reveal any differential behavior across the spectrum, aside from a simple zero-point offset. I therefore propose to obtain a series of deep lamp exposures in a few representative modes of the NUV and FUV MAMAs to search for and characterize short-term differential distortions of the echelle formats. This work also will provide an important dataset to test new approaches to derive the basic dispersion relations, such as the effort underway by the Physical Modeling Group at ESA's ST-ECF. The calibration campaign can be scheduled in pure parallel mode with no loss of orbits from the Cycle 13 science program. Title: A Comparison of the Outer Atmosphere of the ``Flat Activity'' Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A (G2 V) Authors: Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres, Thomas R. Bibcode: 2004ApJ...609..392J Altcode: Driven by the desire to understand the roles of acoustic and magnetic mechanisms in heating the outer atmospheres of Sun-like stars, we compare solar UV spectra with archival STIS spectra from the Hubble Space Telescope of α Cen A (G2 V) and new STIS spectra of the extremely inactive dwarf star τ Cet (G8 V, V=3.5). The activity of τ Cet shows occasional rotational modulations but no long-term cyclic variation. It may be in a phase analogous to the solar Maunder minimum. Solar disk center intensities from both the HRTS instrument and the SUMER instrument on SOHO were converted to Sun-as-a-star fluxes by using center-to-limb data from Dammasch and colleagues. The derived solar flux spectrum represents conditions near the minimum of the solar magnetic activity cycle. We find that the τ Cet line profiles differ systematically from those of the Sun and α Cen A. While lines formed in the middle chromospheres appear similar, the entire emission from the upper chromosphere to the middle transition region of τ Cet has lower flux densities by factors of ~2, the line widths are significantly narrower, and, uniquely, the transition region lines are not significantly redshifted. The soft X-ray surface flux of τ Cet, measured between 0.1 and 2.4 keV, is ~9×103 ergs cm-2 s-1, several times smaller than the median solar value. We also find that the UV spectrum of α Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun is in an intermediate phase of its activity cycle but that its coronal emission may be somewhat smaller. We discuss the implications of these results for magnetic fields and heating mechanisms in the stars and speculate that τ Cet's UV spectrum might represent the solar spectrum during a grand minimum phase. Title: Fossil Magnetospheres Confront Newborn Dynamos in the Rapid Braking Zone Authors: Ayres, T. R. Bibcode: 2004IAUS..215..280A Altcode: No abstract at ADS Title: Positional Uncertainties and Detection Limits of ROSAT X-Ray Sources Authors: Ayres, Thomas R. Bibcode: 2004ApJ...608..957A Altcode: This study addresses, primarily, positional uncertainties of sources imaged by the X-ray cameras on the Röntgensatellit (ROSAT). Monte Carlo simulations are exploited to estimate the precision of centroiding point-source ``photon clouds'' in ROSAT event lists. Measurements of bright coronal stars demonstrate that the design specification 6" accuracy of a ROSAT pointing center was achieved in practice. Furthermore, the accuracy often can be improved to 2" or better by matching serendipitous X-ray sources to an optical catalog like the US Naval Observatory A2. Even a low signal-to-noise detection usually can be localized well enough to obtain a unique identification with a cataloged object or to establish that no bright optical counterpart is present. Secondarily, and in a more general context, the study addresses detection significance and flux limits in the sparse counting regime. Building on previous work by Gehrels and Kraft, Burrows, & Nousek, scaling laws are developed to estimate detection thresholds and lower and upper bounds on possible source fluxes. Although the specific application of ROSAT was in mind, the flux limit approximations apply to other situations governed by Poisson statistics; including ultraviolet and X-ray spectra with low source counts and nonnegligible backgrounds. Title: Coronal Activity on Rapidly-Rotating Solar-Like Stars: Chandra Observations of ER Vul Authors: Brown, A.; Brown, J. M.; Osten, R. A.; Ayres, T. R.; Guinan, E. Bibcode: 2004IAUS..215..334B Altcode: No abstract at ADS Title: High Time Cadence Observations with the Rapid Acquisition Imaging Spectrograph (RAISE) Rocket Program Authors: Ayres, T. R.; Hassler, D. M.; Slater, D.; DeForest, C. E.; Mason, H.; McIntosh, S.; Thomas, R. J. Bibcode: 2004AAS...204.9704A Altcode: 2004BAAS...36..828A The Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation high resolution imaging spectrograph scheduled to fly on a NASA sounding rocket in 2006 to study the dynamics of the solar chromosphere and corona on time scales as short as 100 ms. High speed imaging from TRACE has shown that rapid motions and reconnection are central to the physics of the transition region and corona, but cannot resolve the differences between propagating phenomena and bulk motion. SoHO/CDS and SoHO/SUMER have yielded intriguing measurements of motion and heating in the solar atmosphere, and Solar-B/EIS will capture EUV spectra of flares in progress; but no currently planned instrument can capture spectral information in the chromosphere, transition region, or cool corona on the ∼ 1-10 Hz time scale required for few-second cadence spectral imaging or rapid wave motion studies. RAISE is uniquely suited to exploring this hard-to-reach domain.

This work is supported by NASA Grant NNG04WC01G to the Southwest Research Institute. Title: The Stellar-Solar Connection Authors: Ayres, T. R. Bibcode: 2004AAS...204.3601A Altcode: 2004BAAS...36..707A Many solar-stellar astronomers believe that the solar-stellar connection primarily is a one-way street: the exquisitely detailed studies of the solar surface, interior, and heliosphere strongly mold our views of the distant, unresolved stars. Perhaps many solar physicists have gone so far as to adopt the myopic view that stellar astronomy, by and large, is merely sponging up the fabulous insights from ever deeper examinations of our local star, but the ``dark side'' is not really capable of returning the favor. What could we possibly learn from the stars, that we don't already know from much better observations of the Sun?

In my Introduction to this Topical Session, I will discuss two broad issues: (1) the present divergence between solar and stellar physics (driven by the different goals and tools of the two disciplines); and (2) the diversity of stars in the H-R diagram, to help inform our understanding of solar processes. Today, there are observations of stars that greatly exceed the quality of analogous solar measurements: e.g., HST/STIS UV echelle spectra of Alpha Cen A; Chandra transmission grating spectra of solar-type stars; and only recently have we obtained a definitive understanding of the Sun's soft X-ray luminosity in the key ROSAT/PSPC band. The lack of equivalent solar observations hinders practical applications of the solar-stellar connection. On the more informative side, the evolutionary paths of other stars can be quite different from the Sun's, with potentially dramatic influences on phenomena such as magnetic activity. Equally important, examples of Sun-like stars can be found at all stages of evolution, from proplyds to red giants, in the volume of nearby space out to 500 pc. In short, the solar-stellar connection need not be a one-way street, but rather a powerful tool to explore solar processes within the broader context of stars and stellar evolution.

This work was supported by NASA grant NAG5-13058. Title: A New Spin on FK Comae Authors: Ayres, T. Bibcode: 2004fuse.prop.D075A Altcode: FUSE observations of the ultra-fast rotating Hertzsprung gap giant FK Comae (G5 III; v-sin-i= 160 km/s) will exploit the phenomenon of super-rotational broadening to test whether such stars have extended co-rotating regions of 100,000 K subcoronal gas. Extended emission zones are expected in a magnetospheric scenario that describes a possible fundamental dramatic change in magnetic activity as rapidly evolving moderate-mass giants first enter the convective part of the H-R diagram. A 15 ks exposure will obtain moderate S/N profiles of O VI 1032 and C III 977, suitable to test the super-rotation hypothesis. Title: The Giant Star Ca II Ionization Problem: Mass Loss Revisited Authors: Harper, G. M.; Brown, A.; Ayres, T.; Sim, S. A. Bibcode: 2004IAUS..219..651H Altcode: 2003IAUS..219E.143H Pioneering studies of winds from non-coronal evolved late-type stars were plagued by uncertainties in the Ca ionization balance that resulted in very large uncertainties in derived mass-loss rates. Here we re-examine the Ca II ionization balance in these stellar winds using FUSE spectra which reveal for the first time the flux from the photoionizing radiation field shortward of 1045 Angstroms.

We present a FUSE 912-1185 Angstrom spectroscopic survey of evolved late-K and M stars; including the M giants alpha Cet (M1.5 III) gamma Cru (M3.5 III) beta Gru (M4.5 III) and R Dor (M8e III). Trends are presented of the high excitation emission of C III fluorescent Fe II pumped by H Lyman alpha and continuum fluxes with spectral-type. Using FUSE spectra of alpha Tau (K5 III) supplemented with partial redistribution calculations of H Lyman alpha and beta together with UV and radio data we present a detailed study of alpha Tau's wind ionization balance and derive new limits on its mass-loss rate Title: Future Observations with the Rapid Acquisition Imaging Spectrograph (RAISE) Authors: Hassler, D. M.; Deforest, C. E.; Slater, D.; Ayres, T.; Mason, H.; McIntosh, S.; Thomas, R. Bibcode: 2004cosp...35.2280H Altcode: 2004cosp.meet.2280H The Rapid Acquisition Imaging Spectrograph (RAISE) is a next-generation high resolution imaging spectrograph scheduled to fly on a NASA sounding rocket in 2006 to study the dynamics of the solar chromosphere and corona on time scales as short as 100 ms. High speed imaging from TRACE has shown that rapid motions and reconnection are central to the physics of the transition region and corona, but cannot resolve the differences between propagating phenomena and bulk motion. SoHO/CDS and SoHO/SUMER have yielded intriguing measurements of motion and heating in the solar atmosphere, and Solar-B/EIS will capture EUV spectra of flares in progress; but no currently planned instrument can capture spectral information in the chromosphere, transition region, or cool corona on the ~1-10 Hz time scale required for few-second cadence spectral imaging or rapid wave motion studies. RAISE is uniquely suited to exploring this hard-to-reach domain. Title: Multi-Wavelength Observations of EV Lacertae Authors: Osten, R. A.; Hawley, S. L.; Allred, J.; Johns-Krull, C. M.; Roark, C.; Ambruster, C.; Brown, A.; Ayres, T. R.; Linsky, J. L. Bibcode: 2004IAUS..219..249O Altcode: 2003IAUS..219E.207O We present an analysis of simultaneous radio optical UV and X-ray observations of the dMe flare star EV Lacertae taken in 2001 September. The analysis is time-resolved and concentrates on determining flare-related changes in each spectral region. Temporal correlations in different wavelength regions are examined. Numerous X-ray flares were observed; two X-ray flares are accompanied by UV enhancements in a pattern reminiscent of the Neupert effect seen in solar flares where UV bursts are interpreted as a product of nonthermal heat input to the lower atmosphere and soft X-ray emission occurs as a result of the heating. An extemely large radio flare seen at two frequencies and representing a factor of 100 increase in quiescent radio flux density has an optical counterpart with an enhancement of about 3 magnitudes in the U filter. There is no corresponding increase in soft X-ray flux. We investigate scenarios which could give rise to the observed multi-wavelength correlations. The run of electron density with temperature in the outer atmosphere (transition region through corona) is investigated and implications for coronal structure are given. Title: COmospheric Waves Authors: Ayres, T. R. Bibcode: 2004ESASP.547..119A Altcode: 2004soho...13..119A The puzzling cool "COmosphere" is an important interface between the radiatively controlled outer photosphere and the dynamics-dominated chromosphere. Highresolution spectroscopy of the thermal infrared rovibrational bands of carbon monoxide is a key tool to elucidate the physical properties of the cool gas, and to search for dynamical signatures of the waves that shock at higher altitudes to excite the Ca II "K grains" and other phenomena. An adaptive optics system developed for the McMath-Pierce telescope has shown exceptional promise for improving thermal infrared observations, particularly with the very high-resolution Fourier transform spectrometer. At the same time, AO and integral field units now are allowing high-quality imaging spectroscopy (albeit at lower spectral resolution) of the CO lines over 10 × 10 areas with high enough cadence to measure the wave field down to periods of about 10 s. Title: Seven Days in the Life of AR Lac Authors: Ayres, T. Bibcode: 2004fuse.prop.E542A Altcode: A week-long FUSE stare at short-period eclipsing RS CVn binary AR Lac K0IV+G4IV; P2d), coordinated with groundbased radio imaging and optical Doppler mapping, will provide an unprecedented view of structure, energetics, and dynamics of hot-gas activity, through time-resolved measurements of FUV diagnostics like C III 977, O VI 1031, and (coronal forbidden line) Fe XVIII 974. As a class, RS CVns are notorious for extreme high-energy emissions even during quiescent periods, but are most spectacular during flare outbursts. Our project is the cool star equivalent of a Hubble Deep Field, in the time domain; a new window on magnetic activity in extreme environments ubiquitous in the Cosmos, but only now beginning to be characterized and understood. (Although the FUSE program is stand-alone, we plan to broaden and enhance the campaign by requesting Chandra HETGS and HST STIS time to be coordinated with the FUV spectroscopy.) Title: The Holely Coronal Graveyard Authors: Ayres, T. Bibcode: 2004fuse.prop.D115A Altcode: A 100 ks FUSE pointing will probe the O VI and C III emissions of an archetype denizen of the coronal graveyard--Aldebaran (Alpha Tauri; K5 III). HST spectra suggest the possible--surprising--presence of solar-like magnetic activity on the old, spun-down red giant. But, many of the characteristic 1150-1500 A UV emissions apparently are extinguished by a cool absorber overlying the hot (100,000 K) structures. Detection of O VI by FUSE suggests that the cool absorber opacity thins out just above the LyC edge, so O VI 1032 (and C III 977) could be a sensitive probe of the submerged activity through the far-UV opacity hole. The deep pointing will achieve high S/N, to search for discrete absorption structure in the hot lines, impressed on them by the cool absorber; and will allow an assessment of temporal variability due to the heating process, which might be convective-acoustic but probably is magnetic. If the latter, the buried magnetic activity on red giants possibly plays a key role in driving their winds--a long-standing astrophysical mystery, and a crucial component of galactic chemical evolution. The existing FUSE spectrum is too low in S/N to unambiguously measure discrete absorption components, and its singular nature precludes any variability analysis. Title: A Far-Ultraviolet Spectroscopic Survey of RS CVn Binary Systems Authors: Redfield, S.; Linsky, J. L.; Ayres, T. R.; Brown, A.; Herczeg, G. J. Bibcode: 2003AAS...203.1218R Altcode: 2003BAAS...35.1224R RS CVn systems are detached late-type binaries that are very active as a result of their tidally-enforced rapid rotation. They are actively studied and bright at X-ray and ultraviolet (UV) wavelengths, but very few have been observed in the far-UV. We present multiple orbital phase observations of RS CVn systems taken by the Far Ultraviolet Spectroscopic Explorer (FUSE). Located in the FUSE spectral range are emission lines formed in plasma at 50,000-300,000 K (e.g., C III and O VI). We present an analysis of the strong emission line profiles. By monitoring the change in the profile shape over the course of an orbital period we can measure the fractional contributions of each star in the RS CVn binary system at different plasma temperatures. In addition, the spectral resolution and wavelength scale of FUSE permit us to measure the width and velocity shift of the O VI and C III lines, providing a new window on stellar atmospheric dynamics and structure. Title: Hybrid-Star Coronal X-ray Sources Authors: Ayres, T. R. Bibcode: 2003AAS...203.4805A Altcode: 2004BAAS...36R.580A ``Hybrid chromosphere'' stars show evidence of cool winds together with hot emission lines like C 4 λ 1548 (T ∼ 105 K), originally thought to be mutually exclusive in ``noncoronal'' giants and supergiants to the red of the Linsky-Haisch coronal dividing line near K1 III. Several surveys of such stars by the Roentgensatellit (ROSAT ) reported numerous X-ray detections and concluded that the hybrids as a class are legitimate coronal sources, in some cases strong. However, several of the detected sources were displaced from the predicted stellar positions, calling into question the identifications. I have reexamined the issue, using the U.S. Naval Observatory A2 Catalog to astrometrically register deep pointings by the ROSAT Position Sensitive Proportional Counter (PSPC) and High-Resolution Imager (HRI) to ∼few arcsecond accuracy. At least two of the previously proposed detections of key hybrid stars---γ Draconis (K5 III) and β Aquarii (G0 Ib)---must be rejected on the basis of lack of positional coincidence. (Together with HR 4289 [K5 III] whose identification originally was challenged by Huensch, Reimers, & Schmitt [1996, A&A, 313, 755], who found that the ∼ 30'' displaced X-ray source coincided with a faint, previously unknown galaxy.) Given that many of the original survey sample were not even detected by ROSAT in the first place, and that several of the secure detections plausibly can be attributed to low-mass active MS companions, the conclusion is that hybrid stars generally are very weak coronal sources, at best. The hybrids possibly fall into the same category as the ``noncoronal'' red giants like α Boo (K1 III) and α Tau (K5 III) whose hot-line emitting regions appear to be buried deep in their X-ray opaque chromospheres.

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This work was supported by grant NAG5-13058 from NASA to the University of Colorado. The study made extensive use of the ROSAT public archive at the HEASARC of NASA's Goddard Space Flight Center, and the USNO-A2 astrometric catalog, as accessed from the Catalogue Server of the ESO/ST-ECF Archive. Title: Buried Alive in the Coronal Graveyard Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. Bibcode: 2003ApJ...598..610A Altcode: We have used the High Resolution Camera (HRC-I) of the Chandra X-Ray Observatory to search for coronal (T~106 K) emission from the archetype ``noncoronal'' red giants Arcturus (α Bootis=HD 124897, K1 III) and Aldebaran (α Tauri=HD 29139, K5 III). Our program follows up previous detections of ultraviolet coronal proxies such as C IV λ1548 (T~1×105 K) and O VI λ1031 (T~3×105 K). The deep (~19 ks) HRC-I pointings obtained a tentative 3 σ detection of Arcturus, with fX(0.2-2keV)=1.0+1.8-0.8×10-15 ergs cm-2 s-1 (95% confidence limits [CLs]), but failed to record Aldebaran, with an upper limit of <~1.5×10-15 ergs cm-2 s-1 (also at 95% CL). The corresponding LX/Lbol ratios are a factor of ten thousand less than the Sun, a low-activity coronal dwarf. At the same time, Hubble Space Telescope Imaging Spectrograph far-ultraviolet spectra suggest the presence of a ``cool absorber,'' probably near the base of the red giant chromosphere, imprinting discrete low-excitation absorptions on top of highly ionized features such as Si IV λ1393. The hot emission zones thus are at least partially buried under a large column of chromospheric material, which would severely attenuate any soft X-rays that might be emitted. The submerged hot structures presumably are magnetic because of their high temperatures and broad C IV profiles (FWHM~130 km s-1). Perhaps these structures are analogous to small-scale ephemeral bipolar regions seen ubiquitously on the Sun throughout the sunspot cycle and thought to be of direct convective origin. If small-scale magnetic fields indeed are present in the lower atmospheres of red giants such as Arcturus and Aldebaran, they might play a role in initiating the cool winds of such stars, perhaps through a mechanism similar to solar spicules. Title: High Resolution Infrared, Visible and Ultraviolet Spectral Atlases of the Sun and Arcturus Authors: Hinkle, K.; Wallace, L.; Livingston, W.; Ayres, T.; Harmer, D.; Valenti, J. Bibcode: 2003csss...12..851H Altcode: Various groups of the co-authors have produced series of solar and stellar atlases. Some atlases are listed below and the most recent products described. Title: Dynamics of Coronal Iron Lines in Cool Stars based on FUSE and HST/STIS Observations Authors: Redfield, S.; Ayres, T. R.; Linsky, J. L.; Guinan, E. F. Bibcode: 2003csss...12..863R Altcode: We present UV observations of coronal forbidden lines of highly ionized iron. Fe XXI λ1354 and Fe XII λ1242 have been observed by spectrographs on board the Hubble Space Telescope (HST), and Fe XVIII λ975 recently has been identified in spectra taken by the Far Ultraviolet Spectroscopic Explorer (FUSE). Mass motions of hot gas in the corona provide information on the heating mechanism and magnetic field strength in the corona. Observations of forbidden iron lines with these moderate to high resolution spectrographs provide a unique opportunity to study high temperature dynamics of the hot coronal plasmas. We positively detect the forbidden iron line of Fe XVIII λ975 in five stars. β Ceti shows the strongest Fe XVIII emission, and since it is a single star system, it is an ideal target to study stellar coronal dynamics. We find that the hot coronal plasma is confined, in contrast to observed downflows at the temperatures where the 105 K lines like C III λ977 form. Title: The Future of Cool-Star Astrophysics Authors: Brown, A.; Harper, G. M.; Ayres, T. R. Bibcode: 2003csss...12.....B Altcode: No abstract at ADS Title: An Estimate of the Sun's ROSAT-PSPC X-Ray Luminosities Using SNOE-SXP Measurements Authors: Judge, Philip G.; Solomon, Stanley C.; Ayres, Thomas R. Bibcode: 2003ApJ...593..534J Altcode: Using solar soft X-ray irradiance measurements from the SXP instrument on the SNOE satellite, we relate the solar surface flux densities and their variability to those of stars as measured with the PSPC instrument on ROSAT. We translate SNOE-SXP measurements into equivalent ROSAT-PSPC counts using model spectra calculated from the CHIANTI package. Using the SNOE-SXP measurements has significant advantages over earlier studies: the absolute calibration is known to +/-25%, SNOE measures the Sun as if it were an unresolved star, it has operated over a significant fraction of the solar cycle, and its three wavelength channels overlap substantially with that of the ROSAT-PSPC instrument. The predicted solar X-ray luminosities and surface flux densities are compared with measurements from the ROSAT database. We find that we can estimate the luminosity of the Sun as seen in the 0.1-2.4 keV (``RASS'') passband of ROSAT-PSPC to within +/-50%, not counting sources of systematic uncertainty mentioned in an appendix: the result lies between 1027.1 and 1027.75 ergs s-1 (measured in the existing data set, only partially covering a full solar cycle) and between 1026.8 and 1027.9 ergs s-1 (extrapolated to the full activity range of a typical solar cycle). The solar luminosities lie close to the median behavior found for a volume-limited (d<13 pc) sample of G stars studied in 1997 by Schmitt, revealing the Sun to be a normal or slightly inactive G dwarf. A factor of 1.5 peak-to-peak variation in the RASS passband is predicted due simply to rotational modulations (i.e., those filtered to include periods P<81 days). The ratio of maximum/minimum RASS luminosities from the magnetic activity cycle (filtered to include periods P>81 days) are estimated to be 0.7-0.8 in log10LRASS, a ratio of 5 or 6. These variations are much smaller than both recent estimates of solar X-ray variability and the range of X-ray luminosities seen within Schmitt's sample. It is suggested that the reported absence of ``solar-like'' cyclic emission in stellar X-rays might partly arise because the Sun is less variable than assumed in some earlier work. Repeated ROSAT observations of α Cen A during 1995-1998 show X-ray behavior reminiscent of the Sun during activity minimum conditions. Title: The Outer Atmosphere of Canopus: Detection of a Fast Stellar Wind from an F Supergiant Authors: Brown, A.; Harper, G. M.; Ayres, T. R.; Brown, J. M. Bibcode: 2003AAS...202.3211B Altcode: 2003BAAS...35..745B We have investigated the outer atmospheric structure of the F0 Ib supergiant Canopus using HST, Chandra and FUSE and have discovered a number of unexpected properties, including the presence of an unusually fast stellar wind from this post-M supergiant.

Our observations consist of 96 ksec of Chandra HETGS spectroscopy obtained on 2000 July 21, a set of HST-STIS (E140M, E230M, E230H) UV spectra obtained on 2002 June 11, and three FUSE FUV spectra obtained in 2000 December and 2001 October. The STIS and FUSE spectra provide full coverage of the 900-3000 Å spectrum and the first UV emission line profiles from the transition region of an F supergiant. These high signal-to-noise profiles allow detailed study of the physical conditions in Canopus' outer atmosphere from photospheric temperatures up to 5 105 K. Of particular interest is the hydrogen Lyman alpha line at 1215 Å ; this line shows clear evidence of high velocity (up to 400 km s-1) wind absorption, which is a surprisingly high value for a cool star wind. Investigating the winds from F supergiants, lying between the fast (thousands km s-1) hot star winds and the slow (tens km s-1) red supergiant winds, is particularly important because the wind structure and driving mechanisms for such stars is currently unknown. We see no evidence for wind absorptions in any other UV emission lines observed by STIS or FUSE. The Chandra spectrum shows the presence of a corona whose emission measure peaks at 7 MK and contains temperatures up to 20 MK. Other coronal properties including elemental abundances are presented. No coronal variability was seen.

This work was supported by HST grant GO-06783.01-A, SAO Chandra grant GO0-1087X, and NASA grant NAG5-4804 to the University of Colorado. Title: CoolCAT Authors: Ayres, T. R. Bibcode: 2003AAS...202.2504A Altcode: 2003BAAS...35..732A CoolCAT is a cool-star UV spectral catalog derived from the rich stellar archive of STIS E140M/H and E230M/H exposures. There are approximately 50 more-or-less normal late-type stars in the HST STIS archive with at least one E140M spectrogram, providing full UV wavelength coverage from 1150--1700 Å at a resolution of R≡ λ /Δ λ ∼ 4*E4. About 70% of these stars also have one or more E230M/H exposures, covering all, or part, of the interval 1700--3000 Å. Approximately 150 E140M exposures have been reduced for CoolCAT, and a comparable number of E230's, split nearly equally between the medium-res (M: R ∼ 3*E4) and high-res (H: R ∼ 1*E5) modes. CoolCAT consists of a collection of digital spectral atlases---echellograms processed to the same uniform standard, multiple observations graded and coadded, and adjacent wavelength regions concatenated---and a supporting catalog of line identifications, wavelengths, widths, and fluxes. Semiautonomous line fitting procedures ensure a homogeneous and uniform treatment of the diverse spectral material. A wide range of investigations---from the photochemical evolution of primitive planetary atmospheres, the dynamics of cool star atmospheres, to galactic population synthesis---will be enabled by CoolCAT. The database will reside at the Multimission Archive at Space Telescope (MAST).

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This work was supported by grant HST--AR--09550.01--A from STScI to the University of Colorado. Title: A Far Ultraviolet Spectroscopic Explorer Survey of Coronal Forbidden Lines in Late-Type Stars Authors: Redfield, Seth; Ayres, Thomas R.; Linsky, Jeffrey L.; Ake, Thomas B.; Dupree, A. K.; Robinson, Richard D.; Young, Peter R. Bibcode: 2003ApJ...585..993R Altcode: 2002astro.ph.11363R We present a survey of coronal forbidden lines detected in Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of nearby stars. Two strong coronal features, Fe XVIII λ974 and Fe XIX λ1118, are observed in 10 of the 26 stars in our sample. Various other coronal forbidden lines, observed in solar flares, also were sought but not detected. The Fe XVIII feature, formed at logT=6.8 K, appears to be free of blends, whereas the Fe XIX line can be corrupted by a C I multiplet. FUSE observations of these forbidden iron lines at spectral resolution λ/Δλ~15,000 provides the opportunity to study dynamics of hot coronal plasmas. We find that the velocity centroid of the Fe XVIII feature deviates little from the stellar rest frame, confirming that the hot coronal plasma is confined. The observed line widths generally are consistent with thermal broadening at the high temperatures of formation and show little indication of additional turbulent broadening. The fastest rotating stars, 31 Com, α Aur Ab, and AB Dor, show evidence for excess broadening beyond the thermal component and the photospheric vsini. The anomalously large widths in these fast-rotating targets may be evidence for enhanced rotational broadening, consistent with emission from coronal regions extending an additional ΔR~0.4-1.3R* above the stellar photosphere, or represent the turbulent broadening caused by flows along magnetic loop structures. For the stars in which Fe XVIII is detected, there is an excellent correlation between the observed Röntgensatellit (ROSAT) 0.2-2.0 keV soft X-ray flux and the coronal forbidden line flux. As a result, Fe XVIII is a powerful new diagnostic of coronal thermal conditions and dynamics that can be utilized to study high-temperature plasma processes in late-type stars. In particular, FUSE provides the opportunity to obtain observations of important transition region lines in the far-UV, as well as simultaneous measurements of soft X-ray coronal emission, using the Fe XVIII coronal forbidden line. Title: XMM-Newton Proposal 02015603 Authors: Ayres, Thomas Bibcode: 2003xmm..prop...86A Altcode: Objectives of the proposal are twofold: (1) obtain EPIC-pn spectra of three key "X-ray deficient" Hertzsprung gap stars, to explore why these F2-G0 giants display anomalous coronal behavior compared with G/K dwarfs; and (2) record deep RGS spectra of four other gap giants, 3 of which were observed previously by Chandra, to capture the O VII He-like triplet and other faint, but important, diagnostics beyond the reach of H/LETGS. Interpretations will be based on comparisons of derived emission measure distributions, and FIP, MAD, inverse-FIP abundance behavior, with RGS and H/LETGS X-ray spectra of stars previously collected. A sharp transition in coronal properties on the way to He-flash might be due to disruption of a "fossil" magnetosphere by a nascent solar-like dynamo. Title: Space Telescope Imaging Spectrograph Survey of Far-Ultraviolet Coronal Forbidden Lines in Late-Type Stars Authors: Ayres, Thomas R.; Brown, Alexander; Harper, Graham M.; Osten, Rachel A.; Linsky, Jeffrey L.; Wood, Brian E.; Redfield, Seth Bibcode: 2003ApJ...583..963A Altcode: We describe an extensive search with the Space Telescope Imaging Spectrograph (STIS) for ultraviolet coronal (T>106 K) forbidden lines in a sample of 29 F-M dwarfs, giants, and supergiants. Measuring coronal lines in the 1150-1700 Å band with STIS has important advantages of superior velocity resolution and an absolute wavelength calibration compared with using the Chandra or XMM-Newton grating spectrometers to observe permitted transitions of the same ion stages in the kilovolt X-ray region. Fe XII λλ1242, 1349 (T~2×106 K) and Fe XXI λ1354 (107 K) are well known from solar studies and have been reported in previous stellar work. A search for other coronal forbidden lines in the 1200-1600 Å region was largely negative. The few candidate identifications (e.g., Ar XIII λ1330 and Ca XV λ1375) are too faint to be diagnostically useful. We add new dwarfs to the list of Fe XII detections, including the nearby solar twin α Cen A (G2 V). Clear detections of Fe XXI were obtained in dMe stars, active giants, a short-period RS CVn binary, and possibly in active solar-type dwarfs. We developed a semiempirical method for removing the C I blend that partially affects the Fe XXI λ1354 profile. As discussed recently by Johnson et al., Capella (α Aur; G8 III+G1 III) displays clear Fe XXI variability between Goddard High-Resolution Spectograph (GHRS) and STIS observations 4 yr apart, which is apparently due to a substantial decline in the contribution from the G8 primary. We present an alternative model of the GHRS and STIS era profiles using information in the two sets of line shapes jointly, as well as knowledge of the behavior of Fe XXI profiles of other late-G ``clump'' giants similar to Capella G8. The full survey sample also provides a context for the apparent variability: the Fe XXI flux of the G8 star in the GHRS spectrum is nearly identical (in LFeXXI/Lbol) to other clump giants of similar LX/Lbol, but it had dropped at least a factor of 6 in the STIS measurement. The He II λ1640 Bα feature-which is thought to be responsive to coronal irradiation-also showed significant changes between the GHRS and STIS epochs, but the decrease in the G8 star was much smaller than Fe XXI. The Fe XII flux displays a correlation with the ROSAT 0.2-2 keV X-ray flux that can be described by an α=0.5 power law. Fe XXI exhibits a steeper, perhaps linear (α=1), correlation with the ROSAT flux down to an activity level of LX/Lbol~10-5, below which detections of the coronal forbidden line are rare. There is no evidence of large, systematic Doppler shifts in either Fe XII λ1242 or Fe XXI λ1354. This suggests that the emissions arise dominantly in confined structures, analogous to magnetic loops on the Sun, rather than, say, in a hot wind. The Fe XII and Fe XXI line widths generally are close to thermal (FWHM~40-90 km s-1 at T~106.2-107.0 K), except for the Hertzsprung-gap giants 31 Comae (G0 III) and Capella G1 and the K1 subgiant primary of HR 1099, all of which show evidence for excess broadening in Fe XXI (Fe XII is obscured in these objects by broad N V λ1242 features). If the excess broadening is rotational, it implies that the hot coronae of ``X-ray-deficient'' 31 Com and Capella G1 are highly extended, contrary to the compact structures suggested by recent density estimates in a number of active coronal sources. Title: Accuracy and Precision of Measuring Emission Line Velocities with the Space Telescope Imaging Spectrograph Authors: Ayres, T. R. Bibcode: 2003hstc.conf..170A Altcode: I describe some of the issues connected with measurements of emission line velocities in STIS spectra, primarily in the key E140M band. These issues are important not only in studies of the magnetodynamics of stellar outer atmospheres, but also to gain insight into ways of bootstrapping calibrations onto solar FUV instruments, which typically have avoided internal wavecal lamps (like those flown in all of the HST spectrometers) in favor of using in situ spectral "standards" (such as the average velocity of weak chromospheric emission lines to set the zero point offset). I address the issue of accuracy by comparing apparent emission line radial velocities, as measured by STIS in the FUV, with high-quality optical measurements of photospheric spectra, for a large sample of late-type stars. I address the issue of precision by conducting a series of numerical experiments to simulate Gaussian line fitting in the presence of Poisson noise. I also discuss generalization of these principles to the next generation HST spectrometer, the Cosmic Origins Spectrograph. Title: Resolution of the COmosphere Controversy Authors: Ayres, T. R. Bibcode: 2003ASPC..286..431A Altcode: 2003ctmf.conf..431A No abstract at ADS Title: Chandra, Extreme Ultraviolet Explorer, and Very Large Array Observations of the Active Binary System σ2 Coronae Borealis Authors: Osten, Rachel A.; Ayres, Thomas R.; Brown, Alexander; Linsky, Jeffrey L.; Krishnamurthi, Anita Bibcode: 2003ApJ...582.1073O Altcode: We present the results of a coordinated observing campaign on the short-period RS CVn binary σ2 Coronae Borealis (F6V+G0V Porb=1.14 days) with the Very Large Array, the Extreme Ultraviolet Explorer, and the Chandra X-Ray Observatory High-Energy Transmission Grating Spectrometer. The radio emission is consistent with previously determined quiescent gyrosynchrotron properties. Multiple flares were seen with Extreme Ultraviolet Explorer, five occurring within two consecutive orbital periods. The first of these flares was observed with Chandra. The Chandra observations of σ2 CrB showed no systematic variations of line fluxes, widths, or Doppler shifts with orbital phase, nor any response in line width or offset due to the flare. This is consistent with both stars being equally active coronal emitters. We have developed a self-consistent method of spectral analysis to derive information from the line and continuum emissions concerning the distribution of plasma with temperature and elemental abundances. A bimodal temperature distribution is appropriate for both quiescent and flare intervals, with a stable peak at 6-8 MK and another variable enhancement at higher temperatures, with evidence for significant contribution from temperatures up to 50 MK during the flare, compared to 30 MK during quiescence. The iron abundance is subsolar during quiescence but is enriched by about a factor of 2 during a large flare seen with Chandra. The noble gas elements neon and argon show elevated abundances with respect to iron, but there is no clear evidence for any first ionization potential-based abundance pattern during quiescence or the flare. We have determined coronal electron densities from the helium-like ions O VII, Ne IX, Mg XI, and Si XIII, which imply densities >=1010 cm-3. There is a small enhancement in the electron densities derived for the flare, but it is not statistically significant. We call attention to electron temperature constraints provided by the ratios of 1s2 1S0-1snp 1P1 transitions of the helium-like ions O VII, Ne IX, Mg XI, and Si XIII. The derived coronal electron pressures change by 1-2 orders of magnitude over a 25% change in temperature, implying nonisobaric coronal conditions. We find no evidence for significant departures from the effectively thin coronal assumption. The electron densities inferred from the soft X-ray spectra are inconsistent with cospatial gyrosynchrotron emission; further observations are necessary to discriminate the relative locations of the radio and soft X-ray-emitting plasma. Title: A Far Ultraviolet Spectroscopic Explorer Survey of Late-Type Dwarf Stars Authors: Redfield, Seth; Linsky, Jeffrey L.; Ake, Thomas B.; Ayres, Thomas R.; Dupree, A. K.; Robinson, Richard D.; Wood, Brian E.; Young, Peter R. Bibcode: 2002ApJ...581..626R Altcode: We describe the 910-1180 Å spectra of seven late-type dwarf stars obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. The stars include Altair (A7 IV), Procyon (F5 IV-V), α Cen A (G2 V), AB Dor (K1 V), α Cen B (K2 V), ɛ Eri (K2 V), and AU Mic (M0 V). We present line identifications, fluxes, Doppler shifts, and widths. Doppler shifts are measured with respect to heliocentric wavelength scales determined from interstellar absorption lines, and are compared with transition region line shifts seen in Hubble Space Telescope (HST) ultraviolet spectra. For the warmer stars the O VI lines extend the trend of increasing redshift with line formation temperature, but for the cooler stars the O VI line redshifts are essentially zero. The C III and O VI lines of most stars in the sample are best fit with two Gaussians, and we confirm the correlation of increasing importance of the broad component with increasing stellar activity. The nonthermal velocities of the narrow component are subsonic and exhibit a trend toward larger velocities with decreasing surface gravity, while the nonthermal velocities of the broad components show no obvious trend with stellar gravity. The C III and O VI lines of Altair show unique broad horned profiles. Two flares were observed on AU Mic. One shows increasing continuum flux to shorter wavelengths, which we interpret as free-free emission from hot plasma, and relatively narrow, redshifted C III and O VI emission. The other shows very broad line profiles. Title: The Quiescent and Flaring Atmosphere of the dMe Flare Star EV Lacertae Authors: Osten, R. A.; Hawley, S. L.; Johns-Krull, C. M.; Brown, A.; Ayres, T. R.; Ambruster, C. Bibcode: 2002AAS...201.1207O Altcode: 2002BAAS...34.1113O We report on a multi-wavelength campaign to observe flares on the dM4.5e flare star, EV Lac, in 2001 September. The campaign utilized the Chandra ACIS-HETGS, HST-STIS, VLA, and optical photometry and spectroscopy with the McDonald Observatory's 2.1 and 2.7m telescopes. The goal of the campaign was to characterize EV Lac's dynamic outer atmosphere and study the characteristics of magnetic energy release processes in a completely convective star. X-ray grating observations confirm the quiescent underabundance of iron deduced from previous low spectral resolution observations and show evidence of enhanced and variable Ne/Fe abundance ratios. Numerous flares were observed in the 100 ksec X-ray pointing; UV observations overlap one impulsive event, while radio and optical observations reveal impulsive flare signatures during a moderate X-ray flare. Preliminary results from a time-resolved spectroscopic analysis of the X-ray data will be presented, including determination of changing abundances, density, and temperature structure of the coronal plasma in EV Lac. The timing of flares in radio, UV, and optical will be compared against X-ray variations. A discussion of the observed multi-wavelength temporal trends will be given, and comparison made to solar flares. RAO acknowledges support from Chandra grant G01-2014A and HST grant GO-08880.04-A, as well as support from NRAO through a Jansky fellowship. Title: Buried Alive in the Coronal Graveyard Authors: Ayres, T. R.; Brown, A.; Harper, G. M. Bibcode: 2002AAS...201.1204A Altcode: 2002BAAS...34Q1113A We have used the highly sensitive ``solar-blind'' Chandra High Resolution Camera (HRC-I) to search for 0.2--10 keV coronal X-ray emission from the key ``noncoronal'' red giants Arcturus (α Boo: K1 III) and Aldebaran (α Tauri: K5 III). Our program follows up previous detections of subcoronal (T ~ 105 K) emission lines, such as C 4 λ 1548, by HST STIS, and its predecessor GHRS. The two deep (19 ks) HRC-I pointings failed to detect either red giant, however, with 3 σ upper limits of 1x 10-4 cnts s-1 and 2x 10-4 cnts s-1 for Arcturus and Aldebaran, respectively. The corresponding 0.2--2.0 keV L X/L bol levels are a factor of a thousand lower than the Sun (itself already an inconspicuous coronal object), establishing new limits of coronal futility among late-type stars. At the same time, STIS far-ultraviolet spectra suggest the presence of a ``cool absorber'' in the red giant atmosphere capable of selectively extinguishing the subcoronal spectrum shortward of ~ 1500 Å. The cool absorber must lie beneath the extensive chromospheric (T ~ 7000 K) envelope, because the chromospheric lines lack absorption signatures from the cool layer. As a result, the hot-line structures must be doubly buried under a large column of neutral hydrogen, undoubtedly smothering any soft X-ray emission that might be present. If small-scale magnetic active regions indeed exist in the lower atmospheres of red giants like Arcturus and Aldebaran, they might in some way be responsible for initiating and sustaining the cool outflows of such stars. The source of the near surface magnetism could be analogous to that of the small-scale ephemeral bipolar regions seen ubiquitously on the Sun throughout the sunspot cycle, and thought to be of direct convective origin. [-3mm] This work was supported by Chandra grant G02-3014X and HST grant GO-09273.01--A to the University of Colorado. Title: Coordinated Chandra HETGS and VLA Radio Observations of the Active Coronae on the Short-Period Binary ER Vul (G0 V + G5 V) Authors: Brown, A.; Osten, R. A.; Ayres, T. R.; Harper, G.; Guinan, E. Bibcode: 2002ASPC..277..223B Altcode: 2002sccx.conf..223B No abstract at ADS Title: Chandra HETGS Observations of the Active Binary σ2 Coronae Borealis Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Linsky, J. L. Bibcode: 2002ASPC..277..239O Altcode: 2002sccx.conf..239O No abstract at ADS Title: Limits on Chromospheres and Convection among the Main-Sequence A Stars Authors: Simon, Theodore; Ayres, Thomas R.; Redfield, Seth; Linsky, Jeffrey L. Bibcode: 2002ApJ...579..800S Altcode: In deeply convective stars, the nonthermal energy required to heat the chromosphere ultimately is supplied by turbulent magnetoconvection. Because the early and middle A stars have very shallow convective layers, they are not expected to produce enough magnetoconvective power to sustain luminous chromospheres or hot coronae. Here we describe a search for chromospheric emission in the far-ultraviolet (905-1185 Å) spectra of seven main-sequence A stars, based on observations from the Far Ultraviolet Spectroscopic Explorer (FUSE) telescope. Our survey spans the interval in effective temperature along the main sequence over which powerful subsurface convection zones and hence chromospheric emission are expected to vanish. The presence or absence of high-temperature emissions in our FUSE spectra therefore can be used to identify the locus for the transition from convective to radiative envelopes-a change in stellar structure that is difficult to assess by other means. We present our observations and analysis of the subcoronal emission lines of C III λλ977, 1175 and O VI λλ1032, 1037, which bracket a range in formation temperatures from 50,000 to 300,000 K. To supplement our FUSE observations, we also report Goddard High Resolution Spectrograph measurements of Si III λ1206 and H I Lyα λ1215, obtained from archival observations of the Hubble Space Telescope, as well as X-ray measurements from previous ROSAT survey and pointed observations. We detected C III and O VI emission features in the FUSE spectra of the coolest stars of our sample, at Teff<~8200 K. When normalized to the bolometric luminosities, the detected emission-line fluxes are comparable to solar values. We detected none of the hotter stars in our survey at Teff>=8300 K. Upper limits on the normalized flux in some instances approach 40 times less than solar. Within an uncertainty in the effective temperature scale of up to several hundred kelvins, our FUSE observations indicate that the transition between convective and radiative stellar envelopes takes place at, or very near, the point along the main sequence where stellar structure models predict and, moreover, that the changeover occurs very abruptly, over a temperature interval no greater than ~100 K in width. Our FUSE sample also includes two binary stars. In both cases, the narrow UV line profiles we have observed suggest that the high-temperature emission is most likely associated with the late-type companions rather than the A stars themselves. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, operated for NASA by Johns Hopkins University under NASA contract NAS5-32985. Title: Does the Sun Have a Full-Time COmosphere? Authors: Ayres, Thomas R. Bibcode: 2002ApJ...575.1104A Altcode: Off-limb emissions of solar 4.7 μm rovibrational bands of carbon monoxide, recorded under excellent observing conditions with the Infrared Imaging Spectrograph at the McMath-Pierce telescope, are compared with theoretical translimb CO simulations based on time slices from the Carlsson & Stein dynamical model of chromospheric ``K grains.'' In the Carlsson-Stein view, the solar outer atmosphere-in nonmagnetic internetwork regions-is a spatially and temporally intermittent wave-driven phenomenon, yielding an average thermal profile in the classical low chromosphere that is cool, not hot. Recent papers by Kalkofen and collaborators have criticized the dynamical model in favor of traditional ``layered'' stratifications, in which temperatures vary smoothly with altitude and are warm throughout the chromosphere. The present work sharpens the controversy by reiterating that traditional models with warm thermal profiles in the altitude range 500-1000 km fail two key ``infrared CO'' tests. The same tests reveal that the Carlsson-Stein dynamical model-which Kalkofen et al. argue is too cool in the low chromosphere-is not cold enough. Equally important, there need not be any contradiction between the existence of cool gas above the classical temperature minimum and observations of ubiquitous ultraviolet emission from the solar outer atmosphere, a central criticism by Kalkofen and collaborators of a full-time cold ``COmosphere.'' Title: CoolCAT Authors: Ayres, Thomas Bibcode: 2002hst..prop.9550A Altcode: 2002hst..prop.5895A A cool-star UV spectral catalog--CoolCAT-- will improve dramatically the accessibility and utility of the rich stellar archive of STIS E140M/H and E230M/H exposures. CoolCAT will contain digital spectral atlases--echellograms processed to the same uniform standard, multiple observations graded and coadded, and adjacent wavelength regions concatenated--and a supporting catalog of line identifications, wavelengths, widths, and fluxes. Semiautonomous line fitting procedures will ensure a homogeneous and uniform treatment of the diverse spectral material. Valuable experience already has been gained with cycle 8 project 8280, which obtained full UV echelle coverage {1150-3000 Angstrom} of 13 representative late-type stars. My personal interest in these data involves studies of gas dynamics in stellar outer atmospheres, traced by emission line Doppler widths and shifts. However, a wide range of other investigations--from the photochemical evolution of primitive planetary atmospheres to galactic population synthesis--will be enabled by CoolCAT. Title: Comparison of the spectrum of a sunspot-like star with a sunspot Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Osten, R. A. Bibcode: 2002AN....323..321L Altcode: A typical sunspot umbra has an effective temperature, gravity, and strong magnetic field strength similar to the dM1e star AU Microscopii. We compare STIS, Chandra, EUVE, and FUSE spectra of AU Mic with typical spectra of sunspots to characterize the major differences and then compare models of AU Mic with sunspot models. We find that the emission, heating rates, and differential emission measure distributions are very different for AU Mic and sunspots, and conclude that the root cause of the difference lies in the very different geometries of the two magnetic fields. Title: Chandra HETGS Observes Tortured Coronae in the Rapid Braking Zone Authors: Ayres, T. R.; Osten, R. A.; Brown, A.; Gagne, M.; Linsky, J. L. Bibcode: 2002AAS...200.7419A Altcode: 2002BAAS...34..773A We have obtained Chandra High Energy Transmission Grating Spectrometer observations of five moderate mass (2--3 Msun) giants straddling the portion of the Hertzsprung gap where early-G III stars---evolving rapidly toward the red giant branch---suffer strong rotational braking and dramatic changes in their X-ray emitting coronae. G0 III giants prior to the braking epoch are fast rotators (υ rot ~ 50-100 km s-1) and display very hot (T> 107 K) coronae, but nevertheless have curiously depressed X-ray luminosities. The post-braking giants are slow rotators (υ rot< 10 km s-1) with cooler coronae (T ~ 106.8 K), but nevertheless manage a healthy level of X-ray emission. We believe the differences reflect the violent replacement of a ``fossil'' magnetosphere---inherited from the late-B or early-A MS progenitor---by a solar-like regenerative magnetic dynamo. The latter becomes dominant when the initially shallow surface convection in yellow giants at the blue edge of the Hertzsprung gap gives way to deep convective layers as the stars evolve to the red edge. Three of the targets were observed in Cycle 2: 31 Com (G0 III) on 2001-03-12 [132.0 ks]; HR 9024 (G1 III) on 2001-08-11 [96.9 ks]; and μ Vel (G5 III) on 2001-09-24 [19.9 ks], 2001-10-29 [58.1 ks], and 2001-12-18 [57.7 ks]. (The first μ Vel observation was scheduled for 80 ks, but was cut short by a solar flare. The second pointing was intended to complete the exposure, but was affected by ``threshold crossing plane'' latchup in the ACIS CCDs, and was repeated two months later, accounting for the third pointing.) The remaining two stars are: Cycle 3 target 24 UMa (G4 III; ~50 ks pointings on 2002-03-26 and 2002-03-29); and GTO target β Ceti (K0 III) observed on 2001-06-29 [87.5 ks]. We describe the HETGS spectra and our efforts to infer plasma conditions (temperature/density models), chemical fractionation, gas dynamics (through emission line Doppler shifts), and coronal variability. [-3mm] This work was supported by Chandra grant GO1-2018X to the University of Colorado. Title: Four Years of Multi-Wavelength Observations of the RS CVn System HR 1099 (V711 Tau) Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Linsky, J. L. Bibcode: 2002ASPC..264..156O Altcode: 2002ccea.conf..156O No abstract at ADS Title: Glimmers of Life in the Coronal Graveyard Authors: Ayres, Thomas R. Bibcode: 2002fuse.prop.C106A Altcode: Red giants represent the final stage in the life cycle of normal stars. Those evolving from low-mass dwarfs like the Sun were magnetically active for most of their main sequence phase, thanks to a spin-catalyzed convective dynamo. At the same time, such stars also experienced significant rotational braking by their coronal winds. Once they expanded into red giants, their spins further plummeted, and they should have become magnetically dead; an expectation seemingly confirmed by a conspicuous lack of coronal X-ray detections. However, reports of the deaths of red giant coronae were premature - far-UV C IV emissions (an important coronal proxy) have been detected in archetype members of the class by HST, and now O VI has been seen by FUSE in at least one case. Curiously, however, features formed at similar temperatures -- Si IV and N V -- are absent, apparently removed by a mysterious cool absorber. Our objective is to obtain additional detections of the O VI doublet in key red giants, to help address the question of the nature of the cool absorber, and the implications for smothering any coronal X-ray emission. If we can show that there is lingering magnetic activity on the red giants, we might have found a possible link to the acceleration of their chromospheric winds, which chemically enrich the ISM and themselves are a long-standing astrophysical puzzle. Title: Coronal Iron Survey The Yellow Giants Authors: Ayres, Thomas R. Bibcode: 2002fuse.prop.C107A Altcode: We propose a small survey of yellow giants to study the Fe XVIII lambda 974 coronal forbidden line, discovered recently in several late-type stars by FUSE. We selected candidate targets from an extensive HST STIS survey of the analogous Fe XXI lambda 1354 feature. Active yellow giant stars (G0--G9 III) are the best choice, because their coronal emission measures narrowly peak at approx. 6x106 K, where Fe L-shell species -- such as Fe XVIII -- are most prominent. Measurements of Doppler widths and shifts of the lambda 974 feature, at the high velocity resolution afforded by FUSE, will revolutionize the study of stellar coronal dynamics in ways that the current generation of orbiting X-ray observatories cannot. A novel aspect of our program is use of the interstellar absorption feature in the adjacent bright C III lambda 977 emission core to calibrate the velocity scale. Title: X-ray coronae of stars: recent results from Chandra Authors: Linsky, J.; Ayres, T.; Brown, A.; Osten, R. Bibcode: 2002cosp...34E1302L Altcode: 2002cosp.meetE1302L The Chandra X-ray Observatory has opened up the new field of astronomical X-ray spectroscopy and has also provided beautiful X-ray images of young star clusters with unprecedented angular resolution. We will summarize some of the important discoveries coming from the HETG and LETG observations of many active stars and binary systems as well as early-type stars. For the active late-type stars, we will intercompare derived differential emission measures and coronal electron densities of stars with different properties and consider the main uncertainties that enter such analyses. We will also discuss whether coronae are geometrically extended and how coronae change when a star flares. Chandra has also provided important new information on differences between coronal and photospheric abundances. For early-type stars we will summarize the evidence for and against coronal vs wind emission mechanisms. The final topic will be the question of how the coronae of pre-main sequence stars differ from older but still active stars as a result of the presence of magnetic disks and accretion flows. Deep ACIS images of young star clusters like the Trapezium in Orion and M16 are providing insights on this topic. Title: \it HST STIS Observations of Fluoresced Molecular Hydrogen Emission in Diverse Stellar Environments Authors: Ayres, T. R.; Wood, B. E.; Herczeg, G. J.; Linsky, J. L. Bibcode: 2001AAS...19915805A Altcode: 2002BAAS...34..567A The broad coverage, high sensitivity, and precise wavelength calibration of the Space Telescope Imaging Spectrograph's E140M medium-resolution echelle mode make it ideal for studies of broadly dispersed spectral features, such as molecular band systems, in the 1150--1700 Å far-UV interval. The present work focuses on the B--X electronic rovibration bands of H 2, which can be radiatively pumped by H I λ 1215 Lyα resonance emission in stellar environments where cold molecular gas (T< 4000 K) is irradiated by hotter, chromospheric (T ~ 104 K) material. We compare three very different stellar objects whose only common feature appears to be extensive fluoresced H 2 bands: The 10 Gyr old red giant Arcturus (α Bootis; K2 III); the 10 Myr young T-Tauri star TW Hya; and the enigmatic accretion/wind source Mira B, which apparently was caught in a low state during the 1999 August STIS observations. We discuss implications of spectral differences among these objects concerning physical properties (temperatures and column densities) in the different environments where the molecular hydrogen is pumped (stellar ``COmosphere,'' PMS accretion disk, and wind-shock interaction zone), as well as intrinsic profiles of the Lyα irradiation field, which can be deduced free from the usual strong interstellar absorption that affects the H I emission core. This work was supported by STScI grant GO-08614.02-02A to the University of Colorado, and NASA grant S-56500-D to NIST and CU. Observations were from the NASA/ESA HST, collected at the STScI, operated by AURA, under contract NAS5-26555. Title: 3 Ms in the Life of β Ceti: Sustained Flare Activity on a Clump Giant Detected by the Extreme Ultraviolet Explorer Authors: Ayres, Thomas R.; Osten, Rachel A.; Brown, Alexander Bibcode: 2001ApJ...562L..83A Altcode: A 34 day Extreme Ultraviolet Explorer (EUVE) pointing on the ``clump'' giant β Ceti (HD 4128; K0 III) recorded a series of striking coronal flare events, reminiscent of a singular outburst seen previously from μ Velorum (HD 93497; G6 III + dF). The recent flaring episode contrasts with a more placid behavior in a 6 day EUVE observation of β Cet 6 years earlier. The average 70-180 Å Deep Survey count rate in the new observation is twice as high, and the 75-150 Å spectrum displays a distinct hardening. The discovery of sustained flare activity on β Cet raises the possibility that such episodes are more common than suspected among the core helium-burning giants and sharpens the puzzle of the survival of magnetic activity beyond helium flash. Title: Long-Slit Observations of Extended C II λ1335 Emission around V854 Centauri and RY Sagittarii Authors: Clayton, G. C.; Ayres, T. R. Bibcode: 2001ApJ...560..986C Altcode: 2001astro.ph..6529C We have obtained long-slit far-ultraviolet (1150-1730 Å) spectra of the R Coronae Borealis (RCB) stars V854 Cen and RY Sgr near maximum light and pulsational phase zero with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. The far-UV spectrum of each star shows a photospheric continuum rising steeply toward longer wavelengths and a prominent emission feature at C II λ1335. RY Sgr displays a second, but fainter, emission attributed to Cl I λ1351 (which is radiatively fluoresced by C II λ1335), but Cl I is weak or absent in V854 Cen. Most surprisingly, the C II emission of V854 Cen is significantly extended along the slit by +/-2.5", about 6×103 AU at the distance of the star. The C II feature of RY Sgr exhibits no such gross extension. Nevertheless, subtle broadenings of the C II emissions beyond the point response profile suggest inner clouds of radius ~0.1" (250 AU) around both stars. V854 Cen is only the third RCB star after R CrB and UW Cen known to have a resolved shell. Based on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by STScI for the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Title: a tale of Two G Stars Authors: Ayres, Thomas Bibcode: 2001cxo..prop..767A Altcode: 2001chan.prop..723A; 2001cxo..prop..723A High-quality HETGS exposures of key coronal stars are presenting a unique, novel view of some of the most ubiquitous high-energy phenomena in the galaxy; and taking crucial steps toward making X-ray spectroscopy an indispensable remote-sensing tool for Astronomy. We will focus on the influence of stellar surface gravity by adding to our ongoing program the active G dwarf Chi1 Orionis (G0V) and the active G giant 24 Ursae Majoris (G4III). Chandra transmission grating spectroscopy offers a new way to determine temperatures and densities in the hot outer atmospheres of cool stars, probe chemical fractionation processes, and explore plasma dynamics. Our program will add to the Chandra Emission Line Project and help interpret lower-res XMM-Newton/RGS spectra of fainter stars. Title: Buried Alive in the Coronal GRAVEYARD?! Authors: Ayres, Thomas Bibcode: 2001cxo..prop..759A Altcode: 2001cxo..prop..713A; 2001chan.prop..713A We propose 20 ks pointings with Chandra HRC-I to obtain detections of 3 red giants in the depths of the "coronal graveyard." Stellar coronal activity is important to the Sun-Earth connection, to the fate of primitive planetary atmospheres, and to a broad reaching set of magnetic phenomena in many cosmic environments. Understanding the activity, and its evolution, therefore is a key objective in astrophysics. The birth of magnetic activity in young stars is well-studied; the death of coronae in highly evolved stars is not. Our program ultimately will test the hypothesis that significant coronal activity persists on the red giants, but smothered beneath a "cool absorber" in the chromospheric envelope. Such activity might be the long-sought initiator of red giant winds. Title: Chandra HETGS and VLA Radio Observations of the Active Coronae on the Short-Period Binary ER Vul (G0 V + G5 V) Authors: Brown, Alexander; Osten, Rachel A.; Ayres, Thomas R.; Harper, Graham Bibcode: 2001tysc.confE..46B Altcode: We present results from a long (114 ksec) Chandra HETGS observation of the short period (Porb = 0.69 d) active binary ER Vul, which consists of two solar-like dwarfs with rotation rates ~ 40 times that of the Sun. X-ray spectra were obtained on 2001 March 29-30 along with 12 hours of simultaneous VLA monitoring at 3.6 and 20 cm. The Chandra Medium Energy Grating (MEG) covers the wavelength range 1.8 - 25 Å in first order, while the High Energy Grating (HEG) covers 1.8-18 Å. ER Vul showed continuous low-level variability throughout the observation with the largest flare peaking at slightly more than twice the ``quiescent'' level. Contrary to the behaviour of most longer period active binaries, no large, long-duration flares were detected, consistent with previous X-ray observations of this binary. The largest flare detected has a duration of only ~ 30 minutes, and appears to be very ``solar-like''. Unfortunately this flare was not observed in the radio. The 20 cm radio emission does show a highly polarized (LCP) flare that has at best only a weak X-ray resonse. We characterise the flare-related variability seen in the coronal line and continuum emission, place limits on any orbital phase-related variability, and quantify the quiescent coronal temperature and density distributions. Title: Buried Alive in the Coronal Graveyard? Authors: Ayres, Thomas Bibcode: 2001hst..prop.9273A Altcode: We propose 20 ks pointings with Chandra HRC-I to obtain detections of two red giants in the depths of the "coronal graveyard." Our program will test the hypothesis that significant coronal activity persits on the red giants, but smothered beneath a "cool absorber" in the chromospheric envelope. Such activity might be the long-sought initiator of red giant winds. HST/STIS E140M spectra are proposed for one of the targets-alpha Tau {K5 III}; to help probe conditions in the cool absorber. High-S/N STIS spectra already are available for the other target, alpha Boo {K2 III}. Title: HST STIS Coronal Iron Survey Authors: Ayres, T. R.; Brown, A.; Linsky, J. L. Bibcode: 2001AAS...198.4404A Altcode: 2001BAAS...33..845A The broad coverage, high sensitivity, and precise wavelength calibration of the Space Telescope Imaging Spectrograph's medium-resolution echelle mode, coupled with the growing collection of GO and GTO E140M exposures, are ideal for surveys of specific spectral diagnostics across a diversity of stellar types, luminosities, and activity levels. Of great current interest are the weak coronal forbidden lines that appear in the far-UV, which are well known from solar flare work. Measuring coronal lines with STIS in the 1150--1700 Å band has significant advantages over using, say, Chandra HETGS or XMM-Newton RGS in the 1 keV range, because the STIS velocity resolution is 40x, or more, higher; STIS has an absolute wavelength calibration established by an onboard emission lamp; and the large effective area of the HST telescope compensates for the faintness of the forbidden lines. Here, we report a survey of Fe XXI λ 1354 in a sample of ~25 stars. The forbidden iron feature forms at a temperature of about 107 K, characteristic of very active or flaring coronal conditions. Clear detections of the coronal iron line are made in active M dwarfs (AU Mic, AD Leo), active giants (α Aur, β Cet, ι Cap, 24 UMa, HR 9024), short-period RS CVn binaries (e.g., HR 1099), and possibly in active solar-type dwarfs (ζ Dor, χ1 Ori). We describe our semi-empirical method for removing the C I blend that partially corrupts the Fe XXI profile, and our measurements of coronal line widths and Doppler shifts. Although α Aur displays clear variability between Fe XXI profiles obtained at the same orbital phase, but four years apart; the hyperactive HR 1099 system showed virtually no change in its coronal iron feature during a sequence of 14 spectra taken over a 7 hr period in 1999 September, despite the occurrence of two large flares in far-UV lines such as Si IV and C IV. This work was supported by grant GO-08280.01-97A from STScI. Observations were from the NASA/ESA HST, collected at the STScI, operated by AURA, under contract NAS5-26555. We thank the other collaborators in HST program 8280 for their help in carrying out the STIS stellar survey upon which the present study is based. Title: Chandra, EUVE, HST, and VLA Multiwavelength Campaign on HR 1099: Instrumental Capabilities, Data Reduction, and Initial Results Authors: Ayres, Thomas R.; Brown, Alexander; Osten, Rachel A.; Huenemoerder, David P.; Drake, Jeremy J.; Brickhouse, Nancy S.; Linsky, Jeffrey L. Bibcode: 2001ApJ...549..554A Altcode: In mid-September of 1999, a multiwavelength campaign was carried out on the coronally active RS Canum Venaticorum binary HR 1099 (K1 IV+G5 V P=2.84 days), during commissioning of the High Energy Transmission Grating Spectrometer (HETGS) of the Chandra X-ray Observatory (CXO). The coordinated program involved the Extreme Ultraviolet Explorer (EUVE), the Hubble Space Telescope Imaging Spectrograph (STIS), and the Very Large Array (VLA). The objective was to study the system in quiescence, across as much of the electromagnetic spectrum as practical, and to catch any flares that might occur. The EUVE 80-180 Å light curve of HR 1099, covering the period September 13-22, showed only a single impulsive outburst, which occurred at the very end of the 9 day pointing. The 3-25 Å bremsstrahlung continuum displayed an overall decay during the 1.5 day Chandra observation on September 14-16, with a few superimposed mild enhancements. The VLA 3.5 cm and 20 cm radio light curves, obtained during a 10 hr period on September 15 immediately before the HST pointing, similarly revealed normal quiescent gyrosynchrotron emission and an absence of impulsive events. In contrast, the 7 hr STIS time series later on September 15 contained two distinct flares. The first was accompanied by intensification of the preexisting broad wings of the medium excitation species (e.g., Si IV λ1393 and C IV λ1548), while the second involved primarily the narrow cores of the lines, and even cooler temperatures. The Fe XXI λ1354 forbidden line showed little response to either flare, consistent with the contemporaneous soft X-ray and EUV light curves. The lack of coronal counterparts to the ultraviolet flares is unusual and suggests that they belong to a separate class of outbursts, sharing some similarities with the ``transition zone explosive events'' seen on the Sun. The density sensitive O IV λ1400 multiplet was not affected by either flare. The density sensitive Si III λ1300 multiplet showed little response to the first flare, but a dramatic brightening in the second, likely due to the lower peak temperature of that event. The O IV line ratios were near their low-density limits and suggest ne~1010 cm-3 for the duration of the HST observations. The Si III ratios during the second flare rise indicate ne~7×1010 cm-3. The far-UV diagnostics jointly imply electron pressures of neT~2×1015 K cm-3, if formed close to their respective ionization equilibrium temperatures. The helium-like triplets of O VII, Ne IX, and Mg XI in the HETGS spectra have forbidden-to-intercombination line ratios consistent with average coronal electron densities of <~1011 cm-3 at T~0.3-1×107 K over the duration of the Chandra pointing. Fe XXI λ102/λ128 and λ142/λ128 ratios from EUVE suggest ne<~1012-1013 cm-3, near 107 K. Thus, the coronal electron pressures could be as much as several orders of magnitude larger than those of the lower atmosphere. We constructed time-resolved spectra from the HETGS event lists and measured the centroids of the three brightest X-ray lines of HR 1099 in 60 minute bins. In high-S/N Ne X λ12.1, we believe that we can see the changing radial velocity of the K1 IV star over the half an orbital cycle recorded by Chandra. The amplitude of the velocity change is only ~100 km s-1 over the 1.5 day interval, a small fraction of the 300-500 km s-1 resolution of the HETGS at 12 Å. Ne X λ12.1 also displayed a transient blueshift of ~60 km s-1 immediately prior to the first STIS flare, during which the far-UV lines briefly exhibited blueshifts of similar magnitude. The apparent displacement of Ne X appears independently in the -1 and +1 orders of the medium energy band (MEG), but there was no confirmation in the redundant high energy band (HEG), nor in other X-ray lines. Fe XXI λ1354 showed a blueshift about 30 minutes later at the beginning of the second HST orbit, but only at the 20 km s-1 level. Analogous HETGS time series of the brightest lines of comparison star Capella (α Aurigae G8 III+G1 III) exhibited steady behavior, consistent with measurement uncertainties, without the transient Doppler ``bursts'' seen in HR 1099. Although the reality of the Ne X Lyα blueshift is in doubt, there is no question that the Chandra HETGS velocity scales are stable and free from large systematic errors. Title: Stellar Coronae: New Insights into Fundamental Questions (Invited) Authors: Linsky, Jeffrey L.; Ayres, Tom; Brown, Alec; Osten, Rachel; Skinner, Steve; Gagne, Marc Bibcode: 2001ASPC..251...22L Altcode: 2001ncxa.conf...22L No abstract at ADS Title: Cool Flares on HR 1099 (A Saga of Joint Observations with Chandra and HST) Authors: Ayres, T. R. Bibcode: 2001ASPC..234...93A Altcode: 2001xras.conf...93A No abstract at ADS Title: Far-UV Echelle Spectroscopy of Arcturus with HST STIS (CD-ROM Directory: contribs/ayres) Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.; Linsky, J. L.; Carpenter, K. G.; Robinson, R. D. Bibcode: 2001ASPC..223.1079A Altcode: 2001csss...11.1079A No abstract at ADS Title: Cool Star Chromospheres and the Sun Authors: Linsky, J.; Redfield, S.; Ayres, T.; Brown, A.; Harper, G. Bibcode: 2001ASPC..242..247L Altcode: 2001ecom.conf..247L No abstract at ADS Title: STIS Observations of the Transition Region of ζ Doradus (CD-ROM Directory: contribs/redfield) Authors: Redfield, S.; Linsky, J. L.; Ayres, T. R.; STIS Cycle 8 Cool Star Survey Team Bibcode: 2001ASPC..223.1045R Altcode: 2001csss...11.1045R No abstract at ADS Title: STIS Observations of the Hybrid-Chromosphere Star alpha TrA (CD-ROM Directory: contribs/linsky2) Authors: Linsky, J. L.; Redfield, S.; Harper, G.; Ayres, T.; Brown, A. Bibcode: 2001ASPC..223.1626L Altcode: 2001csss...11.1626L No abstract at ADS Title: Magnetospheres and Winds in the Rapid Braking Zone Authors: Ayres, Thomas Bibcode: 2001fuse.prop.B072A Altcode: FUSE exposures of five late-Fearly-G giants will probe fundamental plasma dynamics in their hot magnetized outer atmospheres; as encoded in spectral line widths, Doppler shifts, broad components, asymmetries, and wind-induced circumstellar absorptions. The giants lie in or near the Rapid Braking Zone where moderate mass stars undergo a radical transformation of their coronal outer atmospheres. We also will explore the even more extreme extension of the RBZ to higher masses two G0 supergiants in the so-called hybrid region where hot coronae mix freely with cool stellar winds. FUSE spectra of the key O VI λ1032 and CIII λ977 features will allow us to separate the influences of temperature and opacity on the super-rotational broadening of the RBZ subcoronal emissions; and will strongly complement an ongoing HST STIS (1150--3100 A) survey of late-type stars. Our ultimate objective is to understand stellar magnetic activity; crucial to solar-terrestrial relations, the early evolution of solar system, and one face of a myriad of hydromagnetic phenomena that occur in many cosmic environments protostellar envelopes, neutron star magnetospheres, the accretion disks of cataclysmics, and those of AGN. The dramatic, rapid magnetic evolution of the RBZ stars allows us to view many fundamental aspects of stellar activity---coronal structuring, heating, and angular momentum loss---from an entirely different perspective than afforded by the highly accessible---but singular---case of our Sun. It is through these different perspectives that we can hope to gain new insights into the underlying physical processes. Title: "Coronal" vs. "Noncoronal" Giants: A Spectral Comparison of α Boo and β Gem (CD-ROM Directory: contribs/osten) Authors: Osten, R. A.; Ayres, T. R.; Brown, A.; Linsky, J. L. Bibcode: 2001ASPC..223.1102O Altcode: 2001csss...11.1102O No abstract at ADS Title: On the Temperature Structure of α TrA's Wind Authors: Harper, G. M.; Brown, A.; Ayres, T. R.; Osten, R. A. .; Bennett, P. D.; Linsky, J. L.; Skinner, S. L.; Redfield, S.; Baade, R.; Reimers, D.; Andersson, B. -G. Bibcode: 2000AAS...197.0803H Altcode: 2000BAAS...32.1406H; 2000AAS...197..803H We present new constraints on the wind temperature structure of the hybrid bright-giant α TrA (K2 II) based on multi-wavelength datasets (ATCA, HST/GHRS & STIS, FUSE, ASCA). A previous study by Dupree & Brickhouse (1998), based on an ORFEUS-SPAS II spectrum, suggested that α TrA's wind temperature was 3 x 105 K but this appears inconsistent with the line profile shapes of lower excitation species observed in GHRS spectra. The GHRS profiles indicate an ionization temperature at the base of the wind of Tion <= 20,000 K (Harper 2001). We present new high sensitivity and R ~ 20,000 spectral resolution FUSE spectra which allow us to examine the C III 977Å and O VI line profiles in detail. Contrary to the ORFEUS-SPAS II spectra, the O VI lines show no evidence that they are physically associated with the stellar wind. To within the inherent uncertainties in the FUSE wavelength scale, the O VI 1031.9Å line is symmetric when centered on the photospheric rest frame. This indicates that (i) O VI photons are not created within a 3 x 105 K outflow, and (ii) there is no significant material at this temperature to scatter photons within the wind. We also investigate the suggestion by Ayres & Kashyap (1994) that the large asymmetry observed in the H Lyα line, which is also observed in the FUSE Lyβ profile, is a result of trace neutral hydrogen in a high velocity (400\>km\>s-1) coronal wind. This research is funded by NASA grants NAG5-9010 & NAG5-3226. Title: Radio, X-Ray, and Extreme-Ultraviolet Coronal Variability of the Short-Period RS Canum Venaticorum Binary σ2 Coronae Borealis Authors: Osten, Rachel A.; Brown, Alexander; Ayres, Thomas R.; Linsky, Jeffrey L.; Drake, Stephen A.; Gagné, Marc; Stern, Robert A. Bibcode: 2000ApJ...544..953O Altcode: We present the results of a coordinated observing campaign on the short-period (1.14 days) RS CVn binary σ2 Coronae Borealis with the VLA, ASCA, and RXTE. We also discuss earlier observations of the same system obtained by the Extreme Ultraviolet Explorer (EUVE). Dramatic coronal variability is present in all of these observations across the electromagnetic spectrum. σ2 CrB undergoes frequent large flares that occur close together in time. Radio flares are unambiguously correlated with X-ray flares; the X-ray flares peak as much as 1.4 hr before the corresponding radio maxima. Response to flares is more rapid in higher energy X-ray bandpasses, signaling an increase in temperature during the course of the flare. Flares are seen more frequently in the harder RXTE bandpass than in simultaneously taken ASCA observations. There is greater contrast between flaring and nonflaring conditions in the RXTE light curve. Complex flaring is seen in the radio at 3 and 6 cm, consistent with optically thin nonthermal gyrosynchrotron emission for most of the duration of the observation. Bursts of left-circularly polarized emission at 20 cm lasting <=15 minutes appear to be due to a coherent emission process. EUVE spectra reveal coronal material at ne<=1012 cm-3, with no discernible density differences between flaring and quiescent time intervals. Quiescent ASCA spectra show lower than solar photospheric abundances with iron depleted by a factor of 4 from the solar photospheric value. The abundances increase during a large flare observed with ASCA, with iron enhanced to the solar photospheric value during the rise phase of the flare. Two-temperature fits to extracted spectra show a low-temperature quiescent value of 8 MK and a high-temperature component that varies from 22 MK during quiescence to 50 MK at the peak of the flare. Emission measure distributions measured from the ASCA observations are consistent with the temperatures derived from the discrete two-temperature fits and indicate the presence of very hot (>100 MK) plasma during the rise phase of the ASCA flare. Many of the flares observed with EUVE, ASCA, and RXTE show a double exponential decay phase, further highlighting the importance of this phenomenon in diagnosing flaring conditions. We also find that the observed second decay timescale cannot be explained by some of the currently used flare parameterizations. Title: Origins, Structure, and Evolution of Magnetic Activity in the Cool Half of the H--R Diagram: Progress Report on a Major HST STIS Stellar Survey Authors: Ayres, T. R.; Brown, A.; Drake, S. A.; Dupree, A. K.; Guedel, M.; Guinan, E.; Harper, G. M.; Jordan, C.; Linsky, J. L.; Reimers, D.; Schmitt, J. H. M. M.; Simon, T. Bibcode: 2000AAS...197.4407A Altcode: 2000BAAS...32.1472A In early October 2000, HST completed a year and a half long ultraviolet spectral survey of late-type stars with its Space Telescope Imaging Spectrograph (STIS). Thirteen stars were observed, ranging over spectral types F7--K0 on the main sequence, F8--G8 in the giant branch, and G0--G8 in the supergiants. A total of 72 observation sequences were executed, some consisting of several independent exposures (up to 13: in the case of HR 1099, recorded during a long grating observation by Chandra ). Spectra were taken in the medium resolution echelle modes (E140M, E230M: R ~ 30--40,000) below about 2500 Å, and in the high-resolution echelle mode (E230H: R ~ 105) between 2500--3000 Å. For each target, about 70% of the exposure time was devoted to the key E140M interval (1150--1700 Å). Although the observations were collected primarily to study the magnetically disturbed outer atmospheres of late-type stars, they also are valuable for investigating the local interstellar medium through UV absorptions in H 1, O 1, Fe 2, and Mg 2, and for measuring the cosmologically significant D/H ratio. We present examples of the superb spectra resulting from the program, and discuss some of the new insights we have gained concerning plasma dynamics in the 105 K layers of the stellar ``transition zone;'' the super-rotational broadening of the Si 4, C 4, and N 5 emissions in Hertzsprung gap giants; and the spectral peculiarities of the ``hybrid chromosphere'' supergiants. This work was supported by grant GO-08280.01-97A from STScI. Observations were from the NASA/ESA HST, collected at the STScI, operated by AURA, under contract NAS5-26555. Title: Solar Spectroscopy: Infrared Emission Authors: Ayres, T. Bibcode: 2000eaa..bookE2231A Altcode: The solar infrared spectrum extends from 1 μm to 1 mm, nestled between the well-studied visible and radio bands. The infrared is rich in spectral proxies of temperature, velocity and magnetic field. These range from high-excitation He I 1.083 μm, to low-excitation molecules like carbon monoxide, hydroxyl, and even water vapor (in sunspots), to magnetically sensitive atomic iron absorptions near 1... Title: Chromosphere: Thermal Bifurcation Authors: Ayres, T. Bibcode: 2000eaa..bookE2259A Altcode: Thermal bifurcation refers to the existence of `cool clouds' of gas (T<3500 K) at high altitudes in the solar atmosphere, within what was thought to be a uniformly hot (T∼7000 K) CHROMOSPHERE. It also refers to a cooling instability, promoted by carbon monoxide molecules, which operates in places where the chromospheric mechanical heating is weak. The cool clouds were discovered through the anoma... Title: Capella Authors: Ayres, T. Bibcode: 2000eaa..bookE2397A Altcode: Capella—the `Goat Star' in the constellation Auriga, the `Charioteer'—is the sixth brightest star in the sky, third in the Northern hemisphere. It is a well-known spectroscopic binary of yellow giants, appears to form a physical system with Capella HL, an outlying pair of RED DWARFS, and is a member of the extended Hyades MOVING GROUP (coeval with the nuclear region of the nearby young cluster).... Title: Chandra HETG Spectroscopy of the F0 Ib Supergiant Canopus Authors: Brown, A.; Ayres, T. R.; Osten, R. A.; Harper, G. M. Bibcode: 2000HEAD....5.4216B Altcode: 2000BAAS...32.1257B The F0 supergiant Canopus (α Car) was observed by the Chandra X-ray Observatory on 2000 July 21 for 96 ksec using the High Energy Transmission Grating (HETG) and the ACIS-S detector. Canopus is the nearest supergiant star at a distance of only 96 pc and undergoing He-burning, post-M-supergiant evolution. It has a hot (107 K) corona with log Lx ~ 29.8 erg s-1, even though it has only a thin convection zone. The HETG data show a coronal emission line spectrum with the strongest lines being from Fe XVII, Ne X, and O VIII. We shall present a detailed analysis of the HETG spectra and the first accurate description of this star's coronal temperature distribution. These coronal properties will be compared with those implied by earlier ASCA, EUVE, ROSAT, and Einstein observations. This work is supported by NASA LTSA grant NAG5-3226, NASA GSRP fellowship NGT5-50241, and the Chandra Guest Observer program. Title: Coordinated Observations of the Active Binary σ 2 CrB with Chandra, EUVE, and the VLA Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Krishnamurthi, A.; Linsky, J. L. Bibcode: 2000HEAD....5.4214O Altcode: 2000BAAS...32.1257O We report on coordinated observations of the short-period active binary σ 2 CrB (F6V + G0V, P orb=1.14 d) taken with the Chandra X-ray Observatory, the Extreme Ultraviolet Explorer, and the Very Large Array. EUVE observations span more than 7 orbital periods of the system. Centered in the middle of the nine day EUVE observation is a Chandra ACIS-S+HETGS grating observation lasting 85 ks and an overlapping 12 hour multifrequency VLA observation. We discuss the coronal variability, present high-resolution X-ray spectra and preliminary analysis including the search for flares, and tie the thermal high temperature emission together with nonthermal coronal emission. RAO acknowledges funding from a NASA GSRP fellowship, grant NGT5-50241. AB and TRA acknowledge funding from NASA grant NAG5-3226, and JLL acknowledges support from NASA through grants S-56500-D and H-04630D. Title: Tortured Coronae in the Rapid Braking Zone Authors: Ayres, Thomas Bibcode: 2000cxo..prop..561A Altcode: 2000cxo..prop..430A; 2000chan.prop..430A Deep HETGS exposures of four key G0-G5 giants will address fundamental questions concerning their hot magnetized coronae by determining temperatures and densities, probing chemical fractionation processes, and exploring plasma dynamics. The giants lie in or near the "Rapid Braking Zone" where moderate mass stars undergo a radical transformation of their outer atmospheres, perhaps as a relic magnetosphere is disrupted by the onset of a solar-like dynamo. ACIS-I CCD spectra of five G/K supergiants will explore the even more extreme extension of the RBZ to higher masses: where hot coronae mix freely with cool stellar winds. These are ideal targets to exploit the experience gained in the Emission Line Project studies of the active binaries Capella and HR 1099. Title: 71 Tauri: Hyades Enigma Resolved? Authors: Simon, Theodore; Ayres, Thomas R. Bibcode: 2000ApJ...539..325S Altcode: 71 Tauri (HD 28052; F0 IV-V) is an enigmatic object for two reasons: (1) it is the second brightest X-ray source in the Hyades, yet early F stars as a rule are not strong coronal emitters; and (2) it lies a magnitude above the cluster main sequence, but radial velocity studies and speckle imaging suggest that it is single. Recently, long-slit ultraviolet spectra of the star, obtained with the Space Telescope Imaging Spectrograph (STIS), serendipitously have revealed the presence of a stellar companion at a distance of 0.1" directly south of the primary. The companion is seen only in its far-UV chromospheric emission lines. The nature of this object cannot be determined from our STIS spectra alone, but its high emission levels are most readily explained if it is a close binary of coronally active dG/dK stars. The presence of the secondary can account for the striking X-ray properties of 71 Tau but not its unusual location in the cluster color-magnitude diagram. It is conceivable that the primary itself is a close double of nearly equal stars, making 71 Tau a possible quadruple system. The alternative-that 71 Tau is ~150 Myr older than other members of the Hyades, approaching the end of core hydrogen burning for a 2 Msolar star-would challenge the presumed synchrony of star formation in the cluster. Title: Tortured Coronae in the Rapid Breaking Zone Authors: Ayres, Thomas Bibcode: 2000hst..prop.8889A Altcode: Deep Chandra X-ray Observatory high energy transmission grating {HETGS} exposures of three key G0-G5 giants will address fundamental questions concerning their hot magnetized coronae by determining temperatures and densities, probing chemical fractionation processes, and exploring plasma dynamics. The giants lie in or near the "Rapid Braking Zone" where moderate mass stars undergo a radical transformation of their outer atmospheres, perhaps as a relic magnetosphere is disrupted by the onset of a solar-like dynamo. These are ideal targets to exploit the experience gained in the CXO "Emission Line Project" studies of the active binaries Capella and HR 1099. For two of the targets-31 Comae and Mu Velorum-we will obtain contemporaneous medium-resolution far-UV echelle spectra using the HST/STIS E140M mode for 3 orbits each. The far-UV spectra will provide a snapshot of the physical state of the subcoronal atmosphere during each long X-ray grating exposure, and will tie directly into the 2-25 A HETGS spectra by recording the key Fe XXI 1354 A coronal forbidden line. Title: Chandra Sees Its First Stellar Flares: Results from Coordinated {Chandra, EUVE, HST} STIS, and VLA Observations of HR 1099 Authors: Osten, R. A.; Ayres, T. R.; Brown, A.; Huenemoerder, D.; Drake, J. J.; Linsky, J. L.; Brickhouse, N. Bibcode: 2000AAS...19511214O Altcode: 1999BAAS...31.1541O; 2000BAAS...32..877O On September 15, 1999, the Chandra X-ray Observatory began a 36 hour pointing on the coronally active RS CVn binary system HR 1099 (V711 Tau; K1 IV {+} dG) as part of the Emission Line Project. The High Energy Transmission Grating Spectrometer delivered time-tagged moderate resolution (E/Δ {E} 500--1000) spectra between 2--18 Angstroms (HEG) and 6--30 Angstroms (MEG). Other space-based and ground facilities participated in the campaign -- the Extreme Ultraviolet Explorer provided 10 days of 70--170 Angstroms Deep Survey photometry and 70--300 Angstroms spectroscopy beginning September 14; HST STIS contributed five orbits of echelle-resolution spectroscopy in the 1150--1700 Angstroms region, beginning 16 UT September 15; and the VLA recorded 9 1/2 hours of emission at 3, 6, and 20 cm just before the HST window. The coordinated program represented an unprecedented opportunity to study the energetics and kinematics of stellar flares, a trademark of active binaries like HR 1099. Sporadic flaring activity was recorded by all the observatories, from radio to X-ray. The Chandra MEG light curves of hydrogenic Ne X λ 12.1 and O VIII λ 19.0, derived from 15-minute-binned spectra, exhibit a number of impulsive rises and decays. The bright Ne X feature follows an overall velocity pattern consistent with the 50 km s-1 orbital motion of the active primary star during the long Chandra observation, which covered half a binary cycle. There are a few ``bursts'' of Ne X velocity, including a sustained 45 minute period of apparent 150--200 km s-1 blueshifts; immediately prior to the detection by HST STIS of a dramatic hypersonic event in Si IV λ 1393 and C IV λ 1548, with Doppler broadening up to +/-500 km s-1. Chandra's ability to measure directly plasma motions in stellar coronal flare events is a key diagnostic advance. Highlights of our initial studies of the campaign data sets will be presented. [2mm] {Supported by NASA (NAG5-3226) and STScI (GO-08280.01-97A).} Title: Probing the Multi-Wavelength Nature of Stellar Flares Authors: Osten, R. A.; Brown, A.; Ayres, T. R.; Linsky, J. L. Bibcode: 2000AAS...196.1304O Altcode: 2000BAAS...32..691O The Extreme Ultraviolet Explorer has been instrumental in advancing our understanding of flares on late-type stars. Its long observations of coronal sources for > 100 ks are perfectly matched for studying flaring variability on active binary systems, whose flaring time scales can last for tens of hours. This ability makes EUVE an ideal companion for multi-wavelength observations of flares, as it can place the shorter observations of other satellites and telescopes in perspective of the coronal variability. For example, EUVE recently participated in a campaign to observe the RS CVn binary HR 1099 (V711 Tau) during a calibration observation with the Chandra X-ray Observatory, with accompanying high-resolution UV coverage from HST/STIS and radio coverage from the VLA. I will discuss the results of this campaign as well as earlier multi-wavelength observations involving EUVE and other satellites such as ASCA, RXTE, and BeppoSAX of flaring variability on active binary systems. RAO acknowledges funding from a NASA GSRP fellowship, grant number NGT5-50241. AB and TRA acknowledge funding from NASA grant NAG5-3226 and JLL acknowledges support from NASA through grants S-56500-D and H-04630D. Title: Stellar Activity and Outer Atmospheric Structure of Yellow Supergiants from HST STIS and GHRS Spectroscopy Authors: Brown, A.; Ayres, T. R.; Harper, G. M.; Osten, R. A.; Linsky, J. L.; Dupree, A. K.; Jordan, C. Bibcode: 2000AAS...196.4013B Altcode: 2000BAAS...32..739B Yellow supergiants with spectral types F-G show a complex pattern of outer atmospheric structure with stellar wind and activity indicators varying significantly for stars with similar positions in the H-R diagram. The efficiency of the processes driving their stellar winds and heating their atmospheres is critically dependent on the evolutionary position and surface gravity of each star. We present high-resolution ultraviolet HST/STIS and HST/GHRS spectra for a range of intermediate mass F and G supergiants, including Alpha Car (F0 Ib), Beta Cam (G0 Ib), Beta Dra (G2 Ib), and Epsilon Gem (G8 Ib), and compare the atmospheric properties of these stars with lower luminosity giants and bright giants. We provide a systematic overview of the supergiant atmospheric properties dealing particularly with activity levels, the presence of hot ``transition region'' plasma, signatures of wind outflow, and the role of overlying cool absorbing plasma that becomes increasingly prominent for the cooler stars like Epsilon Gem. This work is supported by HST grants for program GO-08280 and by NASA grant NAG5-3226. Title: Does the Sun have a Full Time COmosphere? Authors: Ayres, T. R. Bibcode: 2000SPD....31.1104A Altcode: 2000BAAS...32R.843A Strong lines of the 5 μ m bands of carbon monoxide display surprisingly cool brightness temperatures at the extreme edge of the solar disk, and curious off-limb emissions protruding hundreds of kilometers into the supposedly hot chromosphere, an environment too hostile for molecules to exist. A straightforward---but controversial---proposal is that the low chromosphere is not pervasively hot at all, but instead is permeated by cool clouds, a ``COmosphere'' if you will (because the formation mechanism originally envisioned was a CO-inspired autocatalytic ``molecular cooling catastrophe''). More recently, Carlsson & Stein have invoked a purely dynamical process to explain the existence of molecule-laden gas at high altitudes. In their view, the solar chromosphere is a spatially and temporally intermittent wave-driven phenomenon; the time average thermal structure in the classical chromospheric layers is cool, not hot. Nevertheless, Kalkofen, Ulmschneider, & Avrett have criticized several of the key assumptions of the dynamical simulation, calling into question the existence of a cool ``part time'' COmosphere. The cause of the supraphotospheric molecular gas thus remains controversial. Here, I will describe measurements of the off-limb emissions of CO, obtained under exceptional observing conditions in May 1996 with the Infrared Imaging Spectrometer (IRIS) on the 1.5-m McMath-Pierce telescope at Kitt Peak. I will compare these data with theoretical off-limb CO simulations based on time slices from the Carlsson-Stein dynamical model. Finally, I will demonstrate through simple UV continuum formation models that there need not be any contradiction between the existence of substantial amounts of cool gas well above the classical temperature minimum, and the observation of ubiquitous ultraviolet line and continuum emission from the solar outer atmosphere. This work was supported by NSF grant AST-9618505. Title: The SOHO-Stellar Connection Authors: Ayres, Thomas R. Bibcode: 2000SoPh..193..273A Altcode: The `solar- stellar connection' bridges the daytime and nighttime communities; an essential link between the singular, but detailed, views of our Sun, and the broad, but coarse, glimpses of the distant stars. One area in particular - magnetic activity - has profited greatly from the two way traffic in ideas. In that spirit, I present an evolutionary context for coronal activity, focusing on the very different circumstances of low-mass main-sequence stars like the Sun, compared with more massive stars. The former are active mainly very early in their lives, whereas the latter become coronal only near the end of theirs, during the brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow, then red, giants. I describe tools at the disposal of the stellar astronomer; especially spectroscopy in the ultraviolet and X-ray bands where coronae leave their most obvious imprints. I compare HST STIS spectra of solar-type dwarfs - ζ Dor (F7 V), an active coronal source, and α Cen A (G2 V), near twin of the Sun - to the SOHO SUMER UV solar atlas. I also compare the STIS line profiles of the active coronal dwarf to the corresponding features in the mixed activity `hybrid chromosphere' bright giant α TrA (K2 II) and the archetype `non-coronal' red giant Arcturus (α Boo; K2 III). The latter shows dramatic evidence for a `cool absorber' in its outer atmosphere that is extinguishing the `hot lines' (like Si iv λ1393 and N v λ1238) below about 1500 Å; the corona of the red giant seems to lie beneath its extended chromosphere, rather than outside as in the Sun. I present an early taste of the moderate resolution spectra we can expect from the recently launched Chandra X-ray Observatory (CXO), and contemporaneous STIS high resolution UV measurements of the CXO calibration star Capella (α Aur; G8 III + G1 III). Last, I describe preliminary results from a May 1999 observing campaign involving SOHO SUMER, TRACE, and the Kitt Peak Infrared Imaging Spectrometer (IRIS). The purpose was to explore the dynamics of the quiet solar atmosphere through the key `magnetic transition zone' that separates the kinetically dominated deep photosphere from the magnetically dominated coronal regime. Linking spatially and temporally resolved solar phenomena to properties of the average line shapes (widths, asymmetries, intensity ratios, and Doppler shifts) is a crucial step in carrying physical insights from the solar setting to the realm of the distant stars. Title: High Resolution IR, Visible, and UV Spectroscopy of the Sun and Arcturus Authors: Hinkle, K.; Wallace, L.; Harmer, D.; Ayres, T.; Valenti, J. Bibcode: 2000IAUJD...1E..26H Altcode: As part of our series of solar and stellar atlases, we have produced high-resolution atlases in the infrared and visible for both the sun and Arcturus. Samples of the spectra will be shown and information provided on obtaining the spectra in both electronic and printed formats. We are currently extending the spectral coverage of both atlases into the 1200-3000 Å region of the ultraviolet. In this region line identification can be difficult due to both unidentified spectral features, some of which are modestly strong, and the transition of the spectrum from absorption to emission. Selected segments from the UV atlas will be shown. We will present a summary of atomic and molecular features identified in cool star spectra as well as suggestions for atomic and molecular species that need additional laboratory work. Title: The Fundamental Physical Processes Producing and Controlling Stellar Coronal/Transition Region/Chromospheric Activity and Structure Authors: Ayres, T. R.; Brown, A. Bibcode: 2000STIN...0269131A Altcode: Our LTSA (Long Term Space Astrophysics) research has utilized current NASA and ESA spacecraft, supporting ground-based IR, radio, and sub-mm telescopes, and the extensive archives of HST (Hubble Space Telescope), IUE (International Ultraviolet Explorer), ROSAT, EUVE (Extreme Ultraviolet Explorer), and other missions. Our research effort has included observational work (with a nonnegligible groundbased component), specialized processing techniques for imaging and spectral data, and semiempirical modelling, ranging from optically thin emission measure studies to simulations of optically thick resonance lines. In our previous LTSA efforts, we have had a number of major successes, including most recently: organizing and carrying out an extensive cool star UV survey in HST cycle eight; obtaining observing time with new instruments, such as Chandra and XMM (X-ray Multi-Mirror) in their first cycles; collaborating with the Chandra GTO program and participating with the Chandra Emission Line Project on multi-wavelength observations of HR 1099 and Capella. These are the main broad-brush themes of our previous investigation: a) Where do Coronae Occur in the Hertzsprung-Russell Diagram? b) Winds of Coronal and Noncoronal Stars; c) Activity, Age, Rotation Relations; d) Atmospheric Inhomogeneities; e) Heating Mechanisms, Subcoronal Flows, and Flares; f) Development of Analysis and Modelling Tools. Title: Origins, Structure, and Evolution of Magnetic Activity in the Cool Half of the H--R Diagram: an HST STIS Survey Authors: Ayres, T. R.; Brown, A.; Drake, S. A.; Dupree, A. K.; Guedel, M.; Guinan, E.; Harper, G. M.; Jordan, C.; Linsky, J. L.; Reimers, D.; Schmitt, J. H. M. M.; Simon, T. Bibcode: 1999AAS...195.5013A Altcode: 1999BAAS...31Q1449A In HST's cycle 8, we are carrying out a major ultraviolet spectral survey of late-type stars using the powerful capabilities of the Space Telescope Imaging Spectrograph (STIS). The origin of the hot UV emissions of otherwise cool stars is a fundamental puzzle in astrophysics. Magnetic phenomena---at the heart of chromospheric and coronal activity, and perhaps wind driving as well---play a central role in many cosmic settings. Our objective is to obtain high-quality ultraviolet spectra of a diverse collection of F--K stars, of all luminosity classes. Such a major project was unthinkable before STIS, but now is practical given the high resolution, broad spectral coverage, and sensitivity of the second generation spectrograph. Here, we discuss our choice of the thirteen targets; the observing strategy (which captures the entire UV spectrum between 1150--3000 Angstroms at resolutions λ /δ λ 30--100*E3 with good S/N); and preliminary results for the several targets observed to date (ζ Dor, F7 V, 1 May 1999, 2 CVZ orbits; V711 Tau, K1 IV+G5 IV, 15 September 1999, 5 orbits; β Cam, G0 I, 19 September 1999, 4 CVZ orbits). The observation of V711 Tau (HR 1099) was carried out during a long transmission grating pointing by the Chandra X-ray Observatory, in support of its ``Emission Line Project.'' This work was supported by grant GO-08280.01-97A from STScI. Observations were from the NASA/ESA HST, collected at the STScI, operated by AURA, under contract NAS5-26555. Title: Detections of CO in the Circumstellar Shells of R Coronae Borealis Stars Authors: Clayton, G. C.; Hanson, M. M.; Gordon, K. D.; Ayres, T. R. Bibcode: 1999AAS...195.4513C Altcode: 1999BAAS...31Q1438C It has been known for 60 years that the declines of R Coronae Borealis (RCB) stars are caused by circumstellar dust formation. The declines occur suddenly and without warning. No spectroscopic changes have yet been noted near the beginning of the decline, which might be linked to the cooling gas that must be condensing to form the dust. The mechanism of mass loss and dust formation is still a mystery. New observational evidence along with models of the carbon chemistry around RCB stars suggest that dust may condense close to the star. Shocks propagating through the outer atmospheres encourage non-equilibrium conditions where the conditions for carbon nucleation may be present. CO is thought to be a critical gas coolant in this process. We report detections of the CO 4th positive system lines in STIS UV spectra of two RCB stars and of the CO v=2 bands in the near-IR for several RCB stars. These observations are being used to model the temperature and density of condensing gas around these stars. Title: The Rise and Fall of μ Velorum: A Remarkable Flare on a Yellow Giant Star Observed with the Extreme Ultraviolet Explorer Authors: Ayres, Thomas R.; Osten, Rachel A.; Brown, Alexander Bibcode: 1999ApJ...526..445A Altcode: The close visual double μ Velorum (HD 93497; G6 III+dF) consists of a yellow giant and a fainter companion currently 2" apart. Recently μ Vel was the source of a large flare recorded by the Extreme Ultraviolet Explorer. The long 1.5 day decay phase was like the extremes seen on hyperactive RS CVn-type binaries. The primary, μ Vel A is a 3 Msolar star, in the ``rapid braking zone'' redward of G0 III. Yellow giants are not commonly reported as flare stars, perhaps because the first-crossers are relatively rare and not well represented in the observational samples. The secondary star is classified G2 V, but the 1700 Å energy distribution places it earlier on the main sequence, probably F4 or F5 V, in a class also not usually known for coronal variability. The long duration of the μ Vel event suggests that it occurred in a significantly elongated structure of moderate density, ne<~109 cm-3. If it was a magnetic plasmoid, like a coronal mass ejection on the Sun, then such events might play a role in shedding angular momentum from active evolved stars. The associated spin-down could control the activity survival time of red giants (in later stages of evolution than the first-crosser μ Vel) whose dynamos were rejunvenated by dredge-up of angular momentum from the interior, or more exotic sources, such as cannibalism of close-in substellar companions during the first or second ascent. Title: Sleuthing the Dynamo. II. Hubble Space Telescope Goddard High Resolution Spectrograph Observations of Solar-Type Dwarfs in Young Galactic Clusters Authors: Ayres, Thomas R. Bibcode: 1999ApJ...525..240A Altcode: Far-ultraviolet (1150-1670 Å) spectra of three solar-type dwarfs in the young galactic clusters α Persei and the Pleiades were obtained with the Hubble Space Telescope Goddard High-Resolution Spectrograph (G140L mode). Time series of Si IV λ1393 show erratic variability on timescales of tens of minutes. An X-ray/C IV flux-flux diagram displays a power-law slope of ~2, up to the level of the most active cluster stars. These fall systematically below the extrapolation owing to X-ray ``saturation.'' In rotation-activity diagrams, the X-rays plateau above ~15 km s-1 (P~3 days), while C IV continues to rise until ~35-50 km s-1 (P~1-1.5 days). Such behavior is significant for understanding the magnetic ``dynamo'' at high rotational velocities and is relevant for predicting the ionizing environment bathing newly formed planets around low-mass main-sequence stars. Title: Digging Deeper in the Coronal Graveyard: Postscript Authors: Ayres, Thomas R. Bibcode: 1999ApJ...525.1009A Altcode: An X-ray upper limit--from the ROSAT High Resolution Imager--is presented for ɛ Corvi (HD 105707), a K2 giant that lies in the ``noncoronal'' zone of the Hertzsprung-Russell diagram, but which previously was detected by the Hubble Space Telescope Goddard High Resolution Spectrograph in far-ultraviolet coronal proxies. The new measurement strengthens the anticorrelation between coronal X-rays and λ1380 carbon monoxide emission among the red giants. Title: Origins, Structure and Evolution of Magnetic Activity in the Cool Half of the H-R Diagram: A STIS Survey Authors: Ayres, Thomas Bibcode: 1999hst..prop.8280A Altcode: 1999hst..prop.4614A We propose to carry out a major ultraviolet spectral survey of "coronal" late-type stars using the powerful capabilities of STIS. The origin of the hot UV emissions of otherwise cool stars is a fundamental puzzle in astrophysics, and is linked closely with another long-standing mystery, that of late-type winds. Stars are the powerhouses and chemical factories of galaxies. The source of their ionizing radiations and the driving of their mass loss are of paramount importance in studies ranging from population synthesis, galactic chemical evolution, and cosmic rays to planetary atmospheres and terrestrial "space weather." Magnetic phenomena--at the heart of coronal activity and perhaps wind driving as well--are crucial in many cosmic settings, particularly dynamic environments such as associated with accretion and mass-transfer. Stars are accessible "laboratories without walls" in which to study the interplay of magnetic and plasma processes, and seek a unification with the h ig hly refined--but singular--portrait of the Sun painted by an array of recent orbiting observatories. The missing link: high-quality ultraviolet spectra of a diverse collection of late-type stars. Such a major project was unthinkable before STIS, but the high resolution, broad spectral coverage, and sensitivity of the second generation spectrograph can capture the stellar equivalent of a Hubble Deep Field. Title: STIS UV Atlas of the Red Giant Arcturus(1) Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.; Linsky, J. L.; Carpenter, K. G.; Robinson, R. D. Bibcode: 1999AAS...194.6701A Altcode: 1999BAAS...31..930A The Space Telescope Imaging Spectrograph (STIS) conducted a series of observations of the archetype ``noncoronal'' red giant Arcturus (HD 124897; alpha Boo; K1 III) on 24 August 1998, 17--23 UT. The STIS program was the result of a failed cycle 5 pointing, which could not be rescheduled during the abbreviated cycle 6, and was carried over to cycle 7. Three grating settings---E230H (t_exp= 1340 s), E230M (2493 s), and E140M (5208 s)---covered the ultraviolet spectrum from 1150--2850 Angstroms, at resolutions between R ~ 4*E(4) - 1*E(5) , with essentially no gaps. The resulting spectrograms are stunning. The resolution is very high, as is the S/N; the spectral coverage is broad and comprehensive. The far-UV interval (1150--1700 Angstroms) is a rich emission line spectrum, dominated by the broad resonance transitions of atomic hydrogen (lambda 1215) and oxygen (lambda 1305 triplet). There are numerous narrow emissions, mostly from low-excitation species such as Si I, Fe II, and fluoresced bands of carbon monoxide. Surprisingly, high-excitation species---Si IV (lambda 1393: 6*E(4) K) and C IV (lambda 1548: 1*E(5) K)---are present as well (as seen in the earlier ``failed'' GHRS spectra). The mid-UV (1700--2600 Angstroms) shows additional emission lines, particularly [C II] and [Si II] in the 2325 Angstroms region; the photospheric continuum rises strongly toward the longer wavelengths. The 2600--2850 Angstroms interval is mostly a photospheric absorption spectrum, although the bright chromospheric emission doublet of Mg II lords over the 2800 Angstroms region. We present a comprehensive spectral atlas based on our reductions of the STIS echellograms. We discuss the processing strategies, line identifications, and some of the preliminary results from our analysis of this windy, noncoronal giant. (1) This work was supported by grants GO-06066.01-94A from STScI, and NAG5-3226 from NASA. Observations were from the NASA/ESA HST, collected at the STScI, operated by AURA, under contract NAS5-26555. Title: The Magnetic Lives of Giant Stars Authors: Ayres, T. R.; Brown, A. Bibcode: 1999HEAD....4.0904A Altcode: 1999BAAS...31..705A After two decades of study by high-energy missions---beginning with HEAO-1 and Einstein, and extending more recently to ROSAT, EUVE, ASCA and BeppoSAX---the evolution of coronal magnetic activity of evolved stars has come into sharper focus. We present a synthesis of ideas advanced to explain the various coronal peculiarities of late-type giants, ranging from the ``X-ray deficiency'' of the F--G0 III Hertzsprung gap stars, the ``rapid braking zone'' in the yellow giants (mid-G), and the ``coronal graveyard'' redward of K0 III. The main source of the diversity of coronal behavior among the giant stars is the wide range of main sequence progenitors whose post-MS evolution converges in the relatively small region of the H--R diagram appropriately called the red giant ``clump.'' Common threads are: relic magnetospheres from hot-star predecessors; the tension between direct convectively generated magnetic flux (the so-called ``magnetic carpet'' fields on the Sun) and the large scale rotation-catalyzed ``dynamo;'' activity-assisted mass loss and spindown; and coronal rejuvenation (through spin-up via internal redistribution of angular momentum, or engulfment of a substellar companion). The new generation of X-ray missions---AXAF and XMM---can test many of these ideas through moderate-resolution spectroscopy of the coronal plasmas, to complement ongoing high-resolution dissection of the subcoronal layers by HST (earlier GHRS, now STIS) and soon FUSE. This work was supported by grant NAG5-3226 from NASA to the University of Colorado. Title: First Observations of an R Coronae Borealis Star with the Space Telescope Imaging Spectrograph: RY Sagittarii near Maximum Light Authors: Clayton, Geoffrey C.; Ayres, T. R.; Lawson, Warrick A.; Drilling, John S.; Woitke, P.; Asplund, Martin Bibcode: 1999ApJ...515..351C Altcode: We describe the far-UV (1140-1740 Å) spectrum of the hydrogen-deficient R Coronae Borealis (RCB) star RY Sgr, obtained near maximum light (pulsational phase ~0.1) by the Space Telescope Imaging Spectrograph (STIS) on Hubble Space Telescope. The far-UV spectrum shows a photospheric continuum rising steeply toward longer wavelengths and two prominent emission features at the shorter wavelengths: C II λ1335 and Cl I λ1351 (the latter is radiatively fluoresced by the 10 times stronger C II multiplet). We also find evidence for CO A-X 4th-positive system absorption band heads and possible weak CO fluorescent emissions pumped by C II λ1335, but the inferred column densities are low (~few times 1016 cm-2), consistent with formation in a warm (~5000 K) atmospheric layer. The detection of CO molecules, if confirmed, would be significant, because they are thought to play a key role in the dust ejection episodes of RCB stars through the initiation of ``molecular cooling catastrophes.''

Based on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by STScI for the Association of Universities for Research in Astronomy Inc. under NASA contract NAS 5-26555. Title: High-Resolution Thermal Infrared Imaging of the Sun: A Pipe Dream? Authors: Ayres, T. Bibcode: 1999ASPC..183..186A Altcode: 1999hrsp.conf..186A No abstract at ADS Title: The SOHO-Stellar Connection Authors: Ayres, Thomas R. Bibcode: 1999STIN...9914314A Altcode: I discusses practical aspects of the so-called "solar-stellar" connection; namely, the fundamental principles, the tools at the disposal of the stellar astronomer, and a few recent examples of the connection in action. I provide an overall evolutionary context for coronal activity, calling attention to the very different circumstances of low mass main sequence stars like the Sun, which are active mainly early in their lives; compared with more massive stars, whose coronally active phase occurs near the end of their lives, during their brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow and then red giants. On the instrumental slide, I concentrate primarily on spectroscopy, in the ultraviolet and X-ray bands where coronae leave their most obvious signatures. I present an early glimpse of the type of moderate resolution spectra we can expect from the recently launched Chandra observatory, and contemporaneous HST STIS high-resolution UV measurements of the CXO calibration star Capella (alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A (G2 V), a near twin of the Sun-to a trace obtained with the SOHO SUMER imaging UV spectrometer. I also compare STIS line profiles of the active coronal dwarf to the corresponding features in the mixed-activity "hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype "noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows dramatic evidence for a "cool absorber" in its outer atmosphere that is extinguishing the "hot lines" (like Si IV lambda1393 and N V lambda1238) below about 1500 A, probably through absorption in the Si I lambda1525 and C I lambda1240 photoionization continua. The disappearance of coronae across the "Linsky-Haisch" dividing line near K1 III thus apparently is promoted by a dramatic overturning in the outer atmospheric structure, namely the coronae of the red giants seem to lie beneath their extended chromospheres, rather than outside as in the Sun. I then discuss an intriguing long-slit STIS low-resolution observation of an X-ray active late-A dwarf in the nearby Hyades cluster: the spatially resolved UV spectroscopy clearly shows that a previously unseen close companion (a dKe or dMe) likely is responsible for the coronal activity, rather than some unexplained departure of the A dwarf from its expected state of X-ray dormancy. Finally, I describe early results from a joint observing campaign involving SOHO SUMER, TRACE, and the Kitt Peak Infrared Imaging Spectrometer, conducted May 1999, to explore the dynamics of the quiet solar atmosphere through the key "magnetic transition zone" that separates the kinetically dominated deep photosphere from the magnetically dominated coronal regime. Linking spatially and temporally resolved solar properties to aspects of the averaged lineshapes (for example: widths, asymmetries, intensity ratios, and Doppler shifts) is a crucial step in carrying any physical wisdom we develop in the solar setting to the distant stars. Title: The SOHO-Stellar Connection Authors: Ayres, Thomas R. Bibcode: 1999STIN...9914301A Altcode: Objective was to conduct a variety of observing programs with the SUMER spectrometer on SOHO, in order to further the understanding of the solar-stellar connection. The program was a continuation of SOHO GO program NAG5-6124 of the previous year. Title: A Search for an Emission-Line Region in the Hydrogen-deficient Carbon Star HD 182040 Authors: Brunner, Andrew R.; Clayton, Geoffrey C.; Ayres, T. R. Bibcode: 1998PASP..110.1412B Altcode: A long-exposure short-wavelength IUE spectrum of the hydrogen-deficient carbon (HdC) star HD 182040 does not show any detectable emission in the C II lambda1335 line. It is not certain whether this absence of emission is intrinsic or due to the large uncertainties in the distance, absolute luminosity, and reddening toward HD 182040. If intrinsic, this absence of emission along with the absence of an IR excess from circumstellar dust imply that little or no mass loss is occurring at present from this star even though it is very similar spectroscopically to the R Coronae Borealis (RCB) stars. This result also suggests that the emission-line gas and the circumstellar dust may result from the same mass-loss mechanism in the RCB stars. Title: The Rise and Fall of MU Velorum Authors: Ayres, T. R.; Osten, R. A.; Brown, A. Bibcode: 1998AAS...193.4602A Altcode: 1998BAAS...30.1320A Mu Velorum (HD 93497) is a close visual pair consisting of a G5 III primary and a fainter companion, currently 2'' apart, with an orbital period of about 140 yr. The distance to the system is 36 pc. Mu Vel A is a 3 Msun giant, in the Hertzsprung gap beyond the ``rapid braking zone'' just redward of G0 III. Mu Vel recently was the source of a giant EUV flare, caught during a 12-day pointing in March 1998 by the Deep Survey telescope of the Extreme Ultraviolet Explorer. The outburst rose in less than half a day, and decayed with an e-folding time of several days. The peak flux, ~ 0.3 cnts s(-1) in the DS band 80--180 Angstroms, was approximately twice the quiescent level recorded during the previous ten days of observation. The size and long duration of the event are very unusual for a mid-G giant; in fact, more typical of the extremes seen among the hyperactive short-period RS Canum Venaticorum binaries. Although the secondary star is classified as a G2 V, published visual magnitude differences, and the enhanced 1900 Angstroms continuum (mu Vel was detected by IUE, but AB were not resolved), suggest that it falls earlier on the MS (perhaps F5 V) and indeed itself might be a pair. If mu Vel B is a short-period double, then arguably it could be the source of the giant flare. Unfortunately, little is known about the secondary owing to the small separation of the visual components of mu Vel, and their large difference in brightness. We discuss the flare event, EUV spectra obtained in quiescence and during the flare decay, and the nature of the puzzling secondary. [2mm] This work was supported by NASA grant NAG5-3226. Title: High-Excitation Emission Lines in the Far-Ultraviolet Spectrum of the Late A Star α Cephei Authors: Simon, Theodore; Ayres, Thomas R. Bibcode: 1998ApJ...500L..37S Altcode: The A7 V star α Cephei lies in a region of the Hertzsprung-Russell diagram that is generally thought to be devoid of solar-like magnetic activity. The far-ultraviolet spectrum of this star was observed with the Berkeley spectrograph during the 1996 ORFEUS-SPAS II mission. We detected emission lines of Si III, C III, and O VI in the 900-1200 Å interval, spanning formation temperatures of 2×104-3×105 K. The normalized strengths of these lines, \RscrL≡fL/fbol, are within a factor of 2 of solar values. Lines of two C III multiplets in the ORFEUS spectrum yield an electron density estimate, ne~109.4+/-0.3, at a temperature of ~6×104 K. The corresponding electron pressure, p≡neT~1014.2+/-0.3, is similar to that of the average Sun, but several times smaller than previous estimates made for other late-type G-K stars. At higher temperatures, the normalized flux ratio for coronal soft X-rays is 20 times less for α Cep than it is for the Sun. This greatly reduced X-ray brightness suggests that the outer atmosphere of α Cep differs strikingly from that of the average Sun, being more akin to a low-density ``coronal hole.'' Title: PHOENIX IR Spectra of CO in the Sun and the Stars Authors: Ayres, T. R.; Valenti, J. A.; Hinkle, K. H.; Johns-Krull, C. M.; Wiedemann, G. R. Bibcode: 1998AAS...192.6709A Altcode: 1998BAAS...30..918A We report high-resolution (R ~ 5*E(4) ) spectra of the 2143 cm(-1) (4.7 mu m) interval---containing lines from the fundamental (Delta v =1) bands of carbon monoxide---in the Sun and other late-type stars, obtained with the PHOENIX cryogenic infrared spectrometer. The solar work was conducted at the McMath-Pierce telescope during the period 21--26 April 1997, while the stellar observations were obtained on the night of 6 December 1997 at the Kitt Peak 2.1-m. Comparisons of spatially-averaged spectra from the long-slit observations of the Sun with very high-resolution Fourier transform spectrometer scans permitted an evalution of the PHOENIX instrumental profile (affected by flexing of the grating owing to unequal thermal coefficients of the epoxy replica and the silicon substrate). The profile information subsequently was applied in comparisons of the stellar data sets with CO spectra synthesized using a variety of prototype thermal structure models. On the stellar side, we concentrated on bright K-type giants whose broad CO profiles are fully resolved at PHOENIX resolution. Our intent was to test the degree of thermal heterogeneity in the outer layers of the red giant atmospheres; analogous to the ``thermal bifurcation'' effects deduced in the solar context (namely, the dichotomy between classical hot chromosphere and the controversial cool ``COmosphere''). Our spectral analyses provide a preview of the power of PHOENIX for high-resolution infrared spectroscopy of stars; to be realized in the coming months when the original grating is replaced with an improved version. [-2mm] The observations were obtained at the National Optical Astronomy Observatories, which is operated by AURA, Inc., under a cooperative agreement with the National Science Foundation. This work was supported by NSF grant AST-9618505. Title: The Coronae of Moderate-Mass Giants in the Hertzsprung Gap and the Clump Authors: Ayres, Thomas R.; Simon, Theodore; Stern, Robert A.; Drake, Stephen A.; Wood, Brian E.; Brown, Alexander Bibcode: 1998ApJ...496..428A Altcode: We have used the Röentgensatellit (ROSAT), the Extreme Ultraviolet Explorer (EUVE), and the Hubble Space Telescope (HST) to measure X-ray and ultraviolet emissions of moderate-mass (~2-3 M⊙) giants in the Hertzsprung gap (spectral types early F to mid-G) and the post-helium flash ``clump'' (~G8-K0). Our motivation was to document the evolution of hot coronae (T > 106 K) along the post-main-sequence trajectories traveled by such stars in order to gain insight concerning the ``X-ray deficiency'' of the F-G0 giants and the strong braking of stellar rotation at the red edge of the Hertzsprung gap.

With few exceptions, Hertzsprung gap and clump giants observed by ROSAT PSPC show hot (T ~ 107 K) coronal energy distributions, regardless of any X-ray deficiency. EUVE spectra of gap star 31 Com (G0 III) indicate a broad coronal emission measure hump at ~107.2 K, while the active clump giant β Ceti (K0 III) displays a sharp peak at ~106.8 K, as seen previously in the mixed clump/gap binary Capella (α Aur: G8 III + G0 III). The gap giants υ Peg (F8 III) and 24 UMa (G4 III) have EUV emissions of intermediate temperature (~107.0 K).

The stars 31 Com, ψ3 Psc (G0 III), and β Cet exhibit redshifted transition zone (TZ: ~105 K) lines in HST GHRS spectra, as reported earlier in Procyon (α CMi: F5 IV-V) and Capella G0. Such redshifts on the Sun are thought to signify flows in magnetic loops. β Cas (F2 III)--a rare soft coronal source among the gap stars--displays blueshifts of C IV and O IV], although emissions at cooler and hotter temperatures are near the photospheric velocity. The remarkably broad line profiles of the fastest rotating gap giants suggest that the 105 K ``subcoronal'' emission zones extend to h~R* above the photosphere, about 50 scale heights.

In contrast to the TZ line redshifts, the upper chromospheric emissions (e.g., Mg II and Si III) of 31 Com and ψ3 Psc have blueshifted cores. Blue-asymmetric peaks in the solar Mg II lines are thought to indicate dynamical heating in the chromosphere. Observations of the H I Lyα feature of 31 Com taken 9 months apart reveal striking profile changes, reminiscent of those noted previously in the Lyα blue peak of the Capella G0 star.

We used the far-ultraviolet diagnostics, in combination with ROSAT X-ray photometry and EUVE high-excitation line strengths, to constrain physical models of the stellar outer atmospheres. Quasi-static magnetic loops can simulate the empirical coronal emission measures of the giant stars, but the inferred pressures for sensible loop lengths conflict with direct measurements of subcoronal densities. Furthermore, the high rate of emission at ~105 K cannot be explained by thermal conduction down the legs of hot quasi-static loops.

On the other hand, the possible existence of elongated (l ~ R*) emission structures on the gap giants leads to a speculative scenario to explain the X-ray deficiency. It is based on the increased importance of the dynamical filling phase (``explosive evaporation'') of the loop life cycle; conductive cooling, yielding TZ emissions at the footpoints, when the heating is interrupted; and the possibility for transitions between ``hot'' and ``cool'' energy balance solutions owing to dynamical suspension and centrifugal trapping of the cooling gas. The long loops might represent a vestigial global ``magnetosphere'' inherited from the main-sequence phase, which ultimately is disrupted near ~G0 by the deepening convective envelope and growth of a more solar-like dynamo. Coronal emissions might be boosted temporarily as the X-ray deficiency is removed but soon would be quenched by wind braking previously inhibited by the magnetospheric ``dead zone.'' Title: Flaring on RS CVn systems: Results from EUVE Photometry Authors: Osten, R. A.; Brown, A.; Ayres, T. R. Bibcode: 1998ASPC..154.1540O Altcode: 1998csss...10.1540O We present broadband EUV photometry for a sample of RS CVn systems observed with the Deep Survey Spectrometer and Right Angle Program (RAP) Scanners on the Extreme Ultraviolet Explorer (EUVE). We have developed robust data analysis and light curve software for the interpretation of these data. Large-scale flaring activity is seen on 15 of the 18 systems studied. These binaries cover a range in orbital period of 0.7 days to 21 days and include a mixture of giant, subgiant, and dwarf luminosity classes. For many systems the photometric coverage extends over several orbital periods and flaring is unambiguously characterized. We present statistics on the distribution of variability in the survey. Correlations of flaring with binary properties are examined. Title: Chromospheric Structure and Dynamics-Observations Authors: Ayres, Thomas R. Bibcode: 1998ASPC..140..209A Altcode: 1998ssp..conf..209A No abstract at ADS Title: CO and the temperature structure of the solar atmosphere Authors: Ayres, T. R. Bibcode: 1998IAUS..185..403A Altcode: The surface layers of the Sun provide a crucial boundary condition for many of the processes that occur in the deep interior. The stratification of the outer solar atmosphere once was thought to be well understood. However, studies of thermally sensitive molecular absorptions in the infrared revealed puzzling anomalies. Strong lines of the CO fundamental vibration-rotation bands near 5 microns showed very cool temperatures at the extreme limb, and remarkable off-limb emissions extending well into the supposedly hot chromosphere. The conflicting pictures of the photosphere/chromosphere interface, from the widely separated wavelength regimes, has raised suspicions that those ``layers'' of the atmosphere are much more inhomogeneous than previously suspected. One proposal is that the low chromosphere is dominated by cool gas---the ``COmosphere,'' if you will---which is threaded by a network of persistent small-scale hot magnetic filaments and occasionally disrupted by localized acoustic disturbances. The COmosphere is capped by the merged fields of the network elements in the chromospheric ``canopy.'' I will describe the evidence in favor of that model, including recent work at the NSO McMath-Pierce telescope (including use of the new ``Phoenix'' spectrometer) and translimb far-UV spectroscopy by SOHO/SUMER. Title: Why Solar Analogs? Authors: Ayres, Thomas R. Bibcode: 1998saco.conf..155A Altcode: No abstract at ADS Title: Thirty Days in the Life of Beta Ceti Authors: Ayres, Thomas R. Bibcode: 1998euve.prop...23A Altcode: Coronal flares are common among short-period RS CVn-type binaries; easy and valuable targets for EUVE. Less well known, but equally enigmatic, are flares on normal single stars; particularly G/K giants, whose coronal variability has been poorly documented. For such stars, flare-associated mass ejections might promote angular momentum loss, thereby controlling the lifetime of their magnetic activity (which possibly can be rejuvenated by cannibalism of hot Jupiters!). We propose to obtain an unprecedented 30-day history of the EUV behavior of the archetype active single K0 III giant, Beta Ceti. DS photometry will enable an inventory of flare sizes and frequencies, while the spectrometers will secure high-S/N emission line diagnostics during the quiescent periods, and hopefully also flare decays, for use in semiempirical modeling. The ability to record high-quality spectra over usefully-long time intervals is a unique, vital advantage of EUVE that should be exploited to the fullest extent possible during its final cycle. The study of magnetic activity, and its natural variability, impacts diverse fields of research including: stellar evolution, Sun-Earth relations, and ionizing radiation environments of evolving planetary systems. Title: Digging Deeper in the Coronal Graveyard Authors: Ayres, Thomas R.; Brown, Alexander; Harper, G. M.; Bennett, P. D.; Linsky, J. L.; Carpenter, K. G.; Robinson, R. D. Bibcode: 1997ApJ...491..876A Altcode: Soft X-ray detections of stellar coronae (T ~ 106 K) are rare in the giant branch redward of ~K1 III. We have conducted a less direct--but more sensitive--search using the Hubble Space Telescope Goddard High-Resolution Spectrograph to probe for far-ultraviolet proxies of the hot coronal gas in representative ``noncoronal'' red giants. In every target so far examined, we find weak but statistically significant Si IV emission, as well as, commonly, C IV and, in some cases, N V. Si IV is not affected by the CNO anomalies produced by the first dredge-up, which can deplete the carbon abundance and weaken C IV. In the low-activity giants, the λ1393 component of the Si IV doublet must be corrected for sharp absorptions, which we believe are caused by carbon monoxide in overlying cool material.

The normalized flux ratios (\Rscr≡f/fbol) of Si IV and X-rays among the ``coronal'' yellow giants (lying just blueward of the ``noncoronal'' zone) fall on a uniform track, \RscrX~\Rscr2SiIV. In the noncoronal zone, however, the Si IV index is nearly constant (\RscrSiIV~10-8), independent of \RscrX (which ranges from ~10-8 to <~10-10). The mechanism that diminishes X-ray activity in the red giants is highly sensitive to an as yet unidentified stellar property. Photoelectric absorption by cool gas might play a more important role than previously suspected, particularly if hot magnetic loops are partly or completely buried in the chromosphere. Title: Far-UV Spectra of Solar Proxies in Young Galactic Clusters Authors: Ayres, T. R. Bibcode: 1997AAS...191.1307A Altcode: 1997BAAS...29.1230A Solar magnetic activity is of special interest to solar-system physicists who study its influence on planetary atmospheres, and to stellar astronomers who study its analogs on other stars. The stars, in particular, tell us what solar activity might have been like in the Sun's youth, or its distant future; and provide insights into the fundamental stellar parameters---and underlying physical mechanisms---that drive it. I describe recent HST GHRS low-resolution ( ~ 1 Angstroms) far-ultraviolet spectra, and archival ROSAT X-ray photometry, of two G-type dwarf stars in the young open cluster alpha Persei (t ~ 50 Myr), and of the Pleiades G dwarf H II 314 (t ~ 70 Myr). The young galactic cluster stars provide convenient surrogates for the hyperactive neonatal Sun, corresponding to the Hadean era when planetary surfaces were forming. I compare the new results with previous measurements of field and cluster stars of a range of activity levels, including earlier FOS spectra of alpha Per, Pleiades, and Hyades members. The solar-type stars follow a nonlinear (alpha =2 power law) relation in an X-ray/C IV flux-flux diagram, although the most active members of the sample fall away from the main trend, showing a saturation in X-rays. Stellar rotation is a key factor setting the activity level, presumably via the dynamo. The decline of rotation with advancing age in single stars (owing to wind-induced spindown) leads to the age--activity relation. The subcoronal f_C IV/f_bol flux ratio apparently follows a simple power law up to v_rot ~ 50 km s(-1) , and only the very fast rotating alpha Per star HE 699 appears to deviate. In contrast, saturation (away from the alpha ~ 3 power law) occurs in the X-ray diagram at only ~ 20 km s(-1) , affecting all of the alpha Per stars, and the Pleiad H II 314. Unlike the previous FOS measurements of H II 314, there did not appear to be any dramatic flare activity during the more recent GHRS exposures. This work was supported by grant GO-06795.01-95A from STScI. Title: Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XI. Intensive Monitoring of the Ultraviolet Spectrum of NGC 7469 Authors: Wanders, I.; Peterson, B. M.; Alloin, D.; Ayres, T. R.; Clavel, J.; Crenshaw, D. M.; Horne, K.; Kriss, G. A.; Krolik, J. H.; Malkan, M. A.; Netzer, H.; O'Brien, P. T.; Reichert, G. A.; Rodríguez-Pascual, P. M.; Wamsteker, W.; Alexander, T.; Anderson, K. S. J.; Benitez, E.; Bochkarev, N. G.; Burenkov, A. N.; Cheng, F. -Z.; Collier, S. J.; Comastri, A.; Dietrich, M.; Dultzin-Hacyan, D.; Espey, B. R.; Filippenko, A. V.; Gaskell, C. M.; George, I. M.; Goad, M. R.; Ho, L. C.; Kaspi, S.; Kollatschny, W.; Korista, K. T.; Laor, A.; MacAlpine, G. M.; Mignoli, M.; Morris, S. L.; Nandra, K.; Penton, S.; Pogge, R. W.; Ptak, R. L.; Rodríguez-Espinoza, J. M.; Santos-Lleó, M.; Shapovalova, A. I.; Shull, J. M.; Snedden, S. A.; Sparke, L. S.; Stirpe, G. M.; Sun, W. -H.; Turner, T. J.; Ulrich, M. -H.; Wang, T. -G.; Wei, C.; Welsh, W. F.; Xue, S. -J.; Zou, Z. -L. Bibcode: 1997ApJS..113...69W Altcode: From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 2.3d-3.1d for Lyα, 2.7d for C IV λ1549, 1.9d-2.4d for N V λ1240, 1.7d-1.8d for Si IV λ1400, and 0.7d-1.0d for He II λ1640. The most remarkable result, however, is the detection of apparent time delays between the different UV continuum bands. With respect to the UV continuum flux at 1315 Å, the flux at 1485 Å, 1740 Å, and 1825 Å lags with time delays of 0.21d, 0.35d, and 0.28d, respectively. Determination of the significance of this detection is somewhat problematic since it depends on accurate estimation of the uncertainties in the lag measurements, which are difficult to assess. We attempt to estimate the uncertainties in the time delays through Monte Carlo simulations, and these yield estimates of ~0.07d for the 1 σ uncertainties in the interband continuum time delays. Possible explanations for the delays include the existence of a continuum-flux reprocessing region close to the central source and/or a contamination of the continuum flux with a very broad time-delayed emission feature such as the Balmer continuum or merged Fe II multiplets. Title: Distant Futures of Solar Activity Authors: Ayres, Thomas Bibcode: 1997hst..prop.7733A Altcode: 1997hst..prop.4070A We will explore possible future fates of solar magnetic activity through high-S/N ultraviolet spectra of the ancient Sun analog, Arcturus {K2 III}. The fundamental mechanisms that drive the hot {T>10^6 K} coronae of cool stars remain elusive. Solving the mystery is a central theme of the ``solar-stellar connection;'' whose importance extends beyond astronomy to areas ranging from basic plasma physics to solar-terrestrial relations. A significant property of the activity is that it subsides with age: G dwarfs in young clusters are intense coronal sources, whereas old low mass K giants are so feable in soft X-rays that most are below current detection limits. For that reason, historical studies of activity have been biased towards the younger stars. Now HST/STIS easily can record faint coronal proxies {like Si IV and C IV} in nearby cool subgiants and giants, thereby mitigating the de facto age discrimination. In the solar neighborhood the brightest single star of advanced age {9-11 Gyr} is Alpha Bootis {K2 III}. Previous studies have placed the archetype red giant firmly in the ``coronal graveyard.'' Our project focuses on understanding the ``basal'' chromosphere; molecular cooling catastrophes and the structure of the passive ``COmosphere;'' the dynamics and energy balance of the residual subcoronal gas; and mass loss mechanisms. {This program is a carryover from a failed Cycle 5 GHRS observation.} Title: Translimb Spectroscopy with SOHO/SUMER Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi, I.; Solanki, S. Bibcode: 1997SPD....28.0104A Altcode: 1997BAAS...29..879A We have used SUMER to obtain deep exposures of the 1300--1400 Angstroms spectrum, at the extreme limb and off-limb. Previous ``translimb'' studies in the thermal infrared had revealed remarkable extensions of cold material (T ~ 3000 K)---traced by carbon monoxide emission lines---into the heart of the hot chromosphere. A main objective of our program was to search for corresponding far-UV signatures of the ``thermally-bifurcated'' low chromosphere; for example, radiatively fluoresced emissions of the CO A--X 4th-positive system (collisional excitation would be negligible in cold gas). We conducted two separate observing programs with SUMER. Both made use of the 1('') -diameter circular aperture, translated across the limb in the minimum motor step increments of 0.('') 375, along the central meridian in the Northern polar coronal hole. The first program executed for nine hours beginning 19UT 25 Oct 1996. The full wavelength range was 1340--1400 Angstroms. It was recorded in two overlapping segments, placing key regions of the spectrum alternately on the KBr and bare parts of the detector, to help isolate 2nd-order features. Each segment was integrated for 500 s, and 32 pairs were obtained to span a 12('') swath centered on the optical limb. The second program was conducted 00--09UT 01 Dec 1996. It consisted of a single wavelength setting (1300--1340 Angstroms) with exposure time 500 s, but twice the spatial coverage of the earlier series: 64 steps, for a total displacement of 24('') . The strong chromospheric resonance lines of atomic oxygen (1302--1305 Angstroms) and ionized carbon (1334--1335 Angstroms) were observed on the bare part of the MCP camera. We report our progress in cataloging the rich, diverse translimb emission spectrum; and our efforts to deduce fundamental properties of the thermally heterogeneous chromosphere. [-3mm] SOHO is a project of international cooperation; the participation of TRA was supported by NASA grant NAG5-3226. Title: Multiwavelength Coronal Studies of the RS CVn Binaries sigma (2) CrB and HR1099 Authors: Brown, A.; Osten, R. A.; Ayres, T. R.; Drake, S. A. Bibcode: 1997AAS...190.2509B Altcode: 1997BAAS...29..807B We have used the ASCA, XTE, and EUVE satellites and the VLA radio array to study the coronal emission from the RS CVn binaries sigma (2) CrB, observed 1997 March 11-13, and HR1099 (V711 Tau), observed 1996 September 1-11 with additional, more limited, observations during the period 1996 October 9-22. We present time-resolved analyses of the variable coronal emission, including flares, from these systems. sigma (2) CrB was observed simultaneously by ASCA, XTE, and VLA, while simultaneous observations of HR1099 were obtained by XTE, EUVE, and VLA. During these observations HR1099 underwent a very large flare lasting 3 days. In addition we present a synopsis of the coronal variability seen for HR1099 from a total EUVE coverage lasting 34 days obtained between 1992 and 1996. This work is supported by NASA Grants NAG5-2259, NAG5-2530, & NAG5-3226 to the University of Colorado. Title: Evaluating Possible Heating Mechanisms Using the Transition Region Line Profiles of Late-Type Stars Authors: Wood, Brian E.; Linsky, Jeffrey L.; Ayres, Thomas R. Bibcode: 1997ApJ...478..745W Altcode: Our analysis of high-resolution Goddard High-Resolution Spectrograph (GHRS) spectra of late-type stars shows that the Si IV and C IV lines formed near 105 K can be decomposed into the sum of two Gaussians, a broad component and a narrow component. We find that the flux contribution of the broad components is correlated with both the C IV and X-ray surface fluxes. For main-sequence stars, the widths of the narrow components suggest subsonic nonthermal velocities, and there appears to be a tight correlation between these nonthermal velocities and stellar surface gravity (ξNC ~ g-0.68+/-0.07). For evolved stars with lower surface gravities, the nonthermal velocities suggested by the narrow components are at or just above the sound speed. Nonthermal velocities computed from the widths of the broad components are always highly supersonic. We propose that the broad components are diagnostics for microflare heating. Turbulent dissipation and Alfvén waves are both viable candidates for the narrow component heating mechanism.

A solar analog for the broad components might be the ``explosive events'' detected by the High-Resolution Telescope and Spectrograph (HRTS) experiment. The broad component we observe for the Si IV λ1394 line of α Cen A, a star that is nearly identical to the Sun, has a FWHM of 109 +/- 10 km s-1 and is blueshifted by 9 +/- 3 km s-1 relative to the narrow component. Both of these properties are consistent with the properties of the solar explosive events. However, the α Cen A broad component accounts for 25% +/- 4% of the total Si IV line flux, while solar explosive events are currently thought to account for no more than 5% of the Sun's total transition region emission. This discrepancy must be resolved before the connection between broad components and explosive events can be positively established.

In addition to our analysis of the Si IV and C IV lines of many stars, we also provide a more thorough analysis of all of the available GHRS data for α Cen A (G2 V) and α Cen B (K1 V). We find that the transition region lines of both stars have redshifts almost identical to those observed on the Sun: showing an increase with line formation temperature up to about log T = 5.2 and then a rapid decrease. Using the O IV] lines as density diagnostics, we compute electron densities of log ne = 9.65 +/- 0.20 and log ne = 9.50 +/- 0.30 for α Cen A and α Cen B, respectively.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy Inc., under NASA Contract NAS5-26555. Title: CO and the Temperature Structure of the Solar Atmosphere Authors: Ayres, Thomas R. Bibcode: 1997STIN...9914335A Altcode: The surface layers of the Sun provide a crucial boundary condition for many of the processes that occur in the deep interior. The stratification of the outer solar atmosphere once was thought to be well understood. However, studies of thermally sensitive molecular absorptions in the infrared revealed puzzling anomalies. Strong lines of the CO fundamental vibration-rotation bands near 5 microns showed very cool temperatures at the extreme limb, and remarkable off-limb emissions extending well into the supposedly hot chromosphere. The conflicting pictures of the photosphere/chromosphere interface, from the widely separated wavelength regimes, has raised suspicions that those "layers" of the atmosphere are much more inhomogeneous than previously suspected. One proposal is that the low chromosphere is dominated by cool gas--the "COmosphere," if you will--which is threaded by a network of persistent small-scale hot magnetic filaments and occasionally disrupted by localized acoustic disturbances. The COmosphere is capped by the merged fields of the network elements in the chromospheric "canopy." I will describe the evidence in favor of that model, including recent work at the NSO McMath-Pierce telescope (including use of the new "Phoenix" spectrometer) and translimb far-UV spectroscopy by SOHO/SUMER. Title: Chromospheric Structure and Dynamics--Observations Authors: Ayres, Thomas R. Bibcode: 1997STIN...9914312A Altcode: The chromosphere is a highly structured dynamic 'layer' of the solar outer atmosphere. Here, not only are the effects of mechanical heating first evident (moving upward in altitude from the deep photosphere), but also the amount of nonradiative energy deposited is far greater than in the albeit much hotter overlying transition region and corona. Further, the chromosphere is by far the thickest zone of the solar atmosphere with respect to the pressure scale height. A major goal of stellar astrophysics is to understand how the chromosphere is heated and why it adopts its peculiar structure. A cursory examination of solar filtergrams and high-resolution movies demonstrates that much of the chromospheric "action" must be occurring on fine spatial scales and short times; particularly in the cell interior transient brightenings, but also in the longer-lived network fragments. That regime of investigation is far removed from what one usually associates with "synoptic" measurements. Nevertheless, synoptic observations of chromospheric indices, filtergrams, and globally-averaged profile parameters (e.g., for Ca II) not only can provide important insight concerning the crucial role of the cycle-variable part of the solar magnetic field; but they also can forge a key link with analogous measurements of the stars, where often the phenomena can be significantly exaggerated from the solar case, but high spatial resolution reconnaissance is not even a remote possibility. In addition to discussing the synoptic aspects of chromospheric structure and dynamics, I will summarize new insights into the general problem of the solar chromosphere that have been obtained recently with the SUMER far-ultraviolet spectrometer on SOHO. Title: The Solar-Stellar Connection (NAG5-6124: SOHO Guest Investigator Program) Authors: Ayres, Thomas R. Bibcode: 1997STIN...9932584A Altcode: The following is a final report from the SOHO Guest Investigator program to use the SUMER far-UV spectrometer to obtain imaging spectroscopy in support of the goals of the so-called "solar-stellar connection." In particular, a major emphasis was utilization of the long-slit time-resolved maps of the solar surface in bright far-UV emission lines to deduce how particular aspects of the temporally and spatially averaged line profiles trace back to individual structural features of the magnetically disturbed outer atmosphere; to help interpret the unresolved line profiles from high quality stellar observations (say, with the Space Telescope Imaging Spectrograph). The researchers served two tours of duty in the SOHO Operations Center as SUMER planners, during which time we conducted an extensive series of observing programs. These can be divided into three general categories: surface mapping, translimb spectroscopy, and active region diagnostics. We have analyzed some of the large volumes of data to the point where we have presented them in poster papers, and in invited papers at national and international meetings. Listed below are the titles of the preliminary publications we have written, including brief abstracts to indicate the main results. (1) Chromospheric structure and Dynamics-- Observations -- The chromosphere is a highly structured dynamic 'layer' of the solar outer atmosphere. Here, not only are the effects of mechanical heating first evident (moving upward in altitude from the deep photosphere), but also the amount of nonradiative energy deposited is far greater than in the albeit much hotter overlying transition region and corona. Further, the chromosphere is by far the thickest zone of the solar atmosphere with respect to the pressure scale height. A major goal of stellar astrophysics is to understand how the chromosphere is heated and why it adopts its peculiar structure. A cursory examination of solar filtergrams and high-resolution movies demonstrates that much of the chromospheric "action" must be occurring on fine spatial scales and short times; particularly in the cell interior transient brightenings, but also in the longer-lived network fragments. That regime of investigation is far removed from what one usually associates with "synoptic" measurements. Nevertheless, synoptic observations of chromospheric indices, filtergrams, and globally-averaged profile parameters not only can provide important insight concerning the crucial role of the cycle-variable part of the solar magnetic field; but they also can forge a key link with analogous measurements of the stars, where often the phenomena can be significantly exaggerated from the solar case, but high spatial resolution reconnaissance is not even a remote possibility. In addition to discussing the synoptic aspects of chromospheric structure and dynamics, I summarized new insights into the general problem of the solar chromosphere that have been obtained recently with the SUMER far-ultraviolet spectrometer on SOHO. (2) CO and the Temperature Structure of the Solar Atmosphere -- The surface layers of the Sun provide a crucial boundary condition for many of the processes that occur in the deep interior. The stratification of the outer solar atmosphere once was thought to be well understood. However, studies of thermally sensitive molecular absorptions in the infrared revealed puzzling anomalies. Strong lines of the CO fundamental vibration-rotation bands near 5 microns showed very cool temperatures at the extreme limb, and remarkable off-limb emissions extending well into the supposedly hot chromosphere. The conflicting pictures of the photosphere/chromosphere interface, from the widely separated wavelength regimes, has raised suspicions that those "layers" of the atmosphere are much more inhomogeneous than previously suspected. One proposal is that the low chromosphere is dominated by cool gas, the "COmosphere," which is threaded by a network of persistent small-scale hot magnetic filaments and occasionally disrupted by localized acoustic disturbances. The COmosphere is capped by the merged fields of the network elements in the chromospheric "canopy." (3) Translimb Spectroscopy with SOHO/SUMER -- We have used SUMER to obtain deep exposures of the 1300-1400 A spectrum, at the extreme limb and off-limb. Previous "translimb" studies in the thermal infrared had revealed remarkable extensions of cold material (T is approximately equal to 3000 K)-traced by carbon monoxide emission lines-into the heart of the hot chromosphere. A main objective of our program was to search for corresponding far-UV signatures of the "thermally-bifurcated" low chromosphere; for example, radiatively fluoresced emissions of the CO A-X 4th-positive system (collisional excitation would be negligible in cold gas). We conducted two separate observing programs with SUMER. Both made use of the 1 inch-diameter circular aperture, translated across the limb in the minimum motor step increments of 0."375, along the central meridian in the Northern polar coronal hole. The first program executed for nine hours beginning 19UT 25 Oct 1996. The full wavelength range was 1340-1400 A. It was recorded in two overlapping segments, placing key regions of the spectrum alternately on the KBr and bare parts of the detector, to help isolate 2nd-order features. Each segment was integrated for 500 s, and 32 pairs were obtained to span a 12" swath centered on the optical limb. The second program was conducted 00-09UT 01 Dec 1996. It consisted of a single wavelength setting (1300-1340 A) with exposure time 500 s, but twice the spatial coverage of the earlier series: 64 steps, for a total displacement of 24". The strong chromospheric resonance lines of atomic oxygen (1302-1305 A) and ionized carbon (1334-1335 A) were observed on the bare part of the MCP camera. Title: A Final Look at the Gap and Clump Giants Authors: Ayres, Thomas R. Bibcode: 1997euve.prop...51A Altcode: Our objective is to develop insight into the X-ray deficiency of stars at the blue edge of the Hertzsprung gap, possibly a result of fossil magnetospheres preserved from the main sequence phase. EUVE spectra of representative stars in, and beyond, the Hertzsprung gap will be utilized to test models of the hot coronae. Several targets were observed by EUVE previously. We propose in Cycle 6 to revisit the two brightest single stars of our sample, 31 Com (G0 III) and Beta Cet (K0 III). Long pointings (500 ks) not only would improve existing spectral material, attaining sufficient S/N to detect weak density diagnostic lines, but also would secure unique medium-term records of coronal variability. Title: Hertzsprung Gap Coronae: ASCA Guest Investigator Program Authors: Ayres, Thomas R. Bibcode: 1997cub..rept.....A Altcode: The objective was a deep (40 ks) SIS/GIS pointing on the bright stellar X-ray source 31 Comae (G0 III) to record the 1-10 keV spectrum and obtain a lightcurve over the approx. 1 day duration of the observation. Title: Evolution of the solar ionizing flux Authors: Ayres, Thomas R. Bibcode: 1997JGR...102.1641A Altcode: A young magnetically active Sun, with enhanced ionizing radiations and an elevated solar wind, might have contributed to erosion of the primordial atmosphere of Mars (which is particularly vulnerable to dissociative recombination and sputtering by solar wind pickup ions). Spacecraft and ground based observations of solar-type dwarfs in young galactic clusters have yielded a unified view of the early evolution and subsequent systematic decline of magnetic activity with age. Rotational braking by the coronal wind ultimately quenches the spin-catalyzed ``dynamo'' at the heart of stellar magnetism. Decay of the 106-107K corona is much faster than the 104K chromosphere, but XUV emissions of both can be predicted reliably, and photoionization of key planetary atmospheric constituents can be modeled. The early Martian atmosphere (age ~1Gyr) probably was subjected to photoionization rates ~5 times contemporary peak values (sunspot maximum), possibly more if the ages of galactic clusters have been underestimated. Title: Ultraviolet variability in active galaxies: a systematic survey of the IUE archives. Authors: Edelson, R.; Penton, S.; Shull, J. M.; Ayres, T. R.; Pike, G. Bibcode: 1996BAAS...28.1287E Altcode: No abstract at ADS Title: Sleuthing the Dynamo: Hubble Space Telescope Faint Object Spectrograph Observations of Solar-Type Dwarfs in Young Galactic Clusters Authors: Ayres, Thomas R.; Simon, Theodore; Stauffer, J. R.; Stern, R. A.; Pye, J. P.; Brown, Alexander Bibcode: 1996ApJ...473..279A Altcode: We have used the Faint Object Spectrograph of the Hubble Space Telescope to record the ultraviolet emissions of solar-type [(B - V)0 ∼0.6 mag] dwarf stars in young galactic clusters: five in the Hyades (t 600 Myr); three in the Pleiades (t ∼ 70 Myr); and two in αPersei (t ∼ 50 Myr). Despite high levels of scattered light in the G130H (1140-1606 Å) spectra, the key C IV λ1549 blend was detected in all of the targets. The 105 K emission displays a dramatic decline from the youngest to the oldest stars of the sample, well correlated with rotational velocity; evidence of flaring in the most active of the G dwarfs; a wide spread in intensity among the Pleiades stars; but a small dispersion among the Hyades stars. The Mg II λ2800 emission is strongly enhanced in the younger stars, and the 2000 Å continuum is significantly elevated in the Hyades stars compared with the Sun. The hyperactive stars of the sample show an apparent saturation of their C IV emission at high rotational velocities, analogous to that seen in X-rays. The rotation-activity relations possibly exhibit mild curvature, in addition to the saturation, which nevertheless maps onto a simple power law in fX/fbol versus fCIV/fbol. The Sun apparently tracks a similar power law over the course of its magnetic activity cycle.

We discuss these results in terms of simple magnetic loop models. We show that the nonlinear power- law variation of CIV/fbol with rotational velocity (slope ∼1.5, contrary to the suspected linear dependence of the magnetic filling factor) very likely arises from a systematic increase in the base pressures of the dominant coronal loops compared with their counterparts on the Sun. The nonlinear X-ray/C IV power law (slope ∼1.7) separately indicates a significant increase in the mean apex temperature of the dominant coronal loops. We argue that the distribution of loop structures might change character from inactive stars like the Sun (dominated by X-ray-bright points and Active Region loops) to the hyperactive cluster stars (dominated by interregion large-scale structures or postflare loops). Title: Ultraviolet Variability in Active Galaxies: A Systematic Survey of the IUE Archives Authors: Edelson, R.; Penton, S.; Shull, J. M.; Ayres, T.; Pike, G. Bibcode: 1996AAS...189.1101E Altcode: 1996BAAS...28R1287E Now that the mission of IUE has been completed, the Colorado IUEAGN group is using the TOMSIPS software to systematically re-extract all of the AGN data in the archives. The spectra are then fitted with a multi-parameter model in order to measure continuum and line fluxes. We then compile a database of fluxes in a number of bands for each observation. In this talk, we present continuum variability data for all AGN with at least 12 SWP observations. These data are generally sensitive to long-term variations, as the IUE satellite was operational for almost 20 yr. For certain objects that were the subjects of intensive monitoring campaigns (e.g., NGC 5548, NGC 4151, etc.), shorter time scale data also exist. We will report the results of a number of studies. First, for individual well-observed objects, we determine the relation between variability amplitude and wavelength, on both long and short time scales. Second, for entire classes of objects (e.g., Seyfert 1s or BL Lacs), we measure the correlation between mean object luminosity and variability amplitude. Finally, we compare the variability properties of different classes of objects. Title: Fishing in the Coronal Graveyard Authors: Ayres, T. R.; Brown, A.; Harper, G. M.; Bennett, P. D.; Linsky, J. L.; Carpenter, K. G.; Robinson, R. D. Bibcode: 1996AAS...189.7815A Altcode: 1996BAAS...28.1379A Hot coronae (T ~ 10(6) K) are thought to be rare among single giant stars to the right of the ``Linsky--Haisch dividing line'' near K0 in the H--R diagram. K and M giants are such slow rotators that absence of dynamo generated magnetic activity would be natural. Nevertheless, gamma Dra (K5 III) unexpectedly was detected in FUV coronal proxies---hot lines Si IV lambda 1393 and C IV lambda 1548---by HST /GHRS during Science Verification, and subsequently was discovered as a faint X-ray source in a deep ROSAT /PSPC pointing. Is gamma Dra anomalous, or is the lack of coronal detections among the K giants simply a matter of insufficient sensitivity? We have used the GHRS low resolution mode to search for additional examples of hot lines among inactive single red giants. Si IV provides a clean diagnostic of subcoronal material because it falls near the peak sensitivity of the G140L mode and does not suffer from abundance depletions that can affect C IV in red giants. X-ray/Si IV ratios are such that HST can reach to much fainter limiting ``coronal'' magnitudes than even very deep ROSAT pointings. In every target so far examined, we find weak---but statistically significant---Si IV emission. These include: the ancient red giant Arcturus (alpha Boo: K1 III), recorded at the end of Cycle 5; and epsilon Crv (K2.5 III) and epsilon Sco (K2 III) observed in Cycle 6. X-ray/Si IV ratios of red giants (for which measurements, or upper limits, of both diagnostics are available) fall on a uniform track, extending downward from active K0 ``Clump'' giants like beta Ceti all the way to Arcturus itself, in the depths of the ``coronal graveyard.'' The systematic behavior argues that magnetic dynamo action continues even when long term angular momentum loss has slowed the stellar spin to a crawl. This work was supported by grant GO-06066.01-94A from STScI. Title: Mg Emission from Hybrid-Chromosphere Stars: 1.5 Decades of Chromospheric Variability Monitoring Authors: Brown, Alexander; Deeney, Bryan D.; Ayres, Thomas R.; Veale, Anthony; Bennett, Philip D. Bibcode: 1996ApJS..107..263B Altcode: We present an analysis of the available long-wavelength, high-dispersion spectra of seven hybrid-chromosphere stars obtained with the International Ultraviolet Explorer between 1978 and 1993. Our investigation of the variability of the Mg II h and k resonance doublet demonstrates that the emission- line fluxes are not rotationally modulated with the periods previously suggested by Brosius, Mullan, & Stencel. Furthermore, we find no evidence in the Mg II data to corroborate the multiple periodicities reported in the Ca II emissions of hybrid stars by Rao et al. Examination of 40 pairs of closely spaced Mg II observations failed to reveal the presence of any strong chromospheric flaring on the sample stars. Significant (20%-40%) nonperiodic Mg II flux variability, on time scales of days to years, is observed in six of the seven stars. The flux variations occasionally are accompanied by dramatic changes in the morphology of the Mg II profiles, indicating variable stellar-wind absorption. We argue that the variability observed is consistent with stochastic changes associated with the slow growth and decay of chromospheric active regions and the gradual evolution of the physical conditions in the winds. It is our opinion that no compelling argument has yet been made for periodic variability in the chromospheric diagnostics of hybrid stars. Title: Multiwavelength Observations of Short-Timescale Variability in NGC 4151. IV. Analysis of Multiwavelength Continuum Variability Authors: Edelson, R. A.; Alexander, T.; Crenshaw, D. M.; Kaspi, S.; Malkan, M. A.; Peterson, B. M.; Warwick, R. S.; Clavel, J.; Filippenko, A. V.; Horne, K.; Korista, K. T.; Kriss, G. A.; Krolik, J. H.; Maoz, D.; Nandra, K.; O'Brien, P. T.; Penton, S. V.; Yaqoob, T.; Albrecht, P.; Alloin, D.; Ayres, T. R.; Balonek, T. J.; Barr, P.; Barth, A. J.; Bertram, R.; Bromage, G. E.; Carini, M.; Carone, T. E.; Cheng, F. -Z.; Chuvaev, K. K.; Dietrich, M.; Dultzin-Hacyan, D.; Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hemar, S.; Ho, L. C.; Huchra, J. P.; Hutchings, J.; Johnson, W. N.; Kazanas, D.; Kollatschny, W.; Koratkar, A. P.; Kovo, O.; Laor, A.; MacAlpine, G. M.; Magdziarz, P.; Martin, P. G.; Matheson, T.; McCollum, B.; Miller, H. R.; Morris, S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.; Pike, G.; Pogge, R. W.; Ptak, R. L.; Qian, B. -C.; Recondo-Gonzalez, M. C.; Reichert, G. A.; Rodriguez-Espinoza, J. M.; Rodriguez-Pascual, P. M.; Rokaki, E. L.; Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo, M.; Shields, J. C.; Shull, J. M.; Smith, D. A.; Smith, S. M.; Snijders, M. A. J.; Stirpe, G. M.; Stoner, R. E.; Sun, W. -H.; Ulrich, M. -H.; van Groningen, E.; Wagner, R. M.; Wagner, S.; Wanders, I.; Welsh, W. F.; Weymann, R. J.; Wilkes, B. J.; Wu, H.; Wurster, J.; Xue, S. -J.; Zdziarski, A. A.; Zheng, W.; Zou, Z. -L. Bibcode: 1996ApJ...470..364E Altcode: 1996astro.ph..5082A; 1996astro.ph..5082E This paper combines data from the three preceding papers in order to analyze the multi-wave-band variability and spectral energy distribution of the Seyfert I galaxy NGC 4151 during the 1993 December monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths; The strongest variatIons were seen in medium-energy (~1.5 keV) X-rays, with a normalized variability amplitude (NVA) of 24%. Weaker (NVA = 6%) variations (uncorrelated with those at lower energies) were seen at soft gamma ray energies of ~100 keV. No significant variability was seen in softer (0.1-1 keV) X-ray bands. In the ultraviolet/optical regime the NVA decreased from 9% to 1% as the wavelength increased from 1275 to 6900 A. These data do not probe extreme ultraviolet (1200 A to 0.1 keV) or hard X ray (2-50 keV) variability. The phase differences between variations in different bands were consistent with zero lag, with upper limits of <~ 0.15 day between 1275 A and the other ultraviolet bands, <~0.3 day between 1275 A and 1.5 keV, and <~1 day between 1275 and 512 A. These tight limits represent more than an order of magnitude improvement over those determined in previous multi wave band AGN monitoring campaigns. The ultraviolet fluctuation power spectra showed no evidence for periodicity, but were instead well fitted with a very steep, red power law (a <= -2.5). If photons emitted at a "primary" wave band are absorbed by nearby material and "reprocessed" to produce emission at a secondary wave band, causality arguments require that variations in the secondary band follow those in the primary band. The tight interband correlation and limits on the ultraviolet and medium-energy X-ray lags indicate that the reprocessing region is smaller than ~0.15 lt-day in size. After correcting for strong (a factor of ~> 15) line-of-sight absorption, the medium-energy X-ray luminosity variations appear adequate to drive the ultraviolet/optical variations. However the medium-energy X-ray NVA is 2- 4 times that in the ultraviolet, and the single-epoch absorption- corrected X-ray/gamma ray luminosity is only about one third of that of the ultraviolet optical/infrared, suggesting that at most about a third of the total low energy flux could be reprocessed high-energy emission. The strong wavelength dependence of the ultraviolet NVAs is consistent with an origin in an accretion disk, with the variable emission coming from the hotter inner regions and nonvariable emission from the cooler outer regions. These data, when combined with the results of disk fits indicate a boundary between these regions near a radius of order R ~ 0.07 lt-day. No interband lag would be expected, as reprocessing (and thus propagation between regions) need not occur, and the orbital timescale of 1 day is consistent with the observed variability timescale. However, such a model does not immediately explain the good correlation between ultraviolet and X-ray variations. Title: Multiwavelength Observations of Short-Timescale Variability in NGC 4151. I. Ultraviolet Observations Authors: Crenshaw, D. M.; Rodriguez-Pascual, P. M.; Penton, S. V.; Edelson, R. A.; Alloin, D.; Ayres, T. R.; Clavel, J.; Horne, K.; Johnson, W. N.; Kaspi, S.; Korista, K. T.; Kriss, G. A.; Krolik, J. H.; Malkan, M. A.; Maoz, D.; Netzer, H.; O'Brien, P. T.; Peterson, B. M.; Reichert, G. A.; Shull, J. M.; Ulrich, M. -H.; Wamsteker, W.; Warwick, R. S.; Yaqoob, T.; Balonek, T. J.; Barr, P.; Bromage, G. E.; Carini, M.; Carone, T. E.; Cheng, F. -Z.; Chuvaev, K. K.; Dietrich, M.; Doroshenko, V. T.; Dultzin-Hacyan, D.; Filippenko, A. V.; Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hutchings, J.; Kazanas, D.; Kollatschny, W.; Koratkar, A. P.; Laor, A.; Leighly, K.; Lyutyi, V. M.; MacAlpine, G. M.; Malkov, Yu. F.; Martin, P. G.; McCollum, B.; Merkulova, N. I.; Metik, L.; Metlov, V. G.; Miller, H. R.; Morris, S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.; Pike, G.; Pogge, R. W.; Pronik, I.; Pronik, V. I.; Ptak, R. L.; Recondo-Gonzalez, M. C.; Rodriguez-Espinoza, J. M.; Rokaki, E. L.; Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo, M.; Sergeev, S. G.; Smith, S. M.; Snijders, M. A. J.; Sparke, L. S.; Stirpe, G. M.; Stoner, R. E.; Sun, W. -H.; van Groningen, E.; Wagner, R. M.; Wagner, S.; Wanders, I.; Welsh, W. F.; Weymann, R. J.; Wilkes, B. J.; Zheng, W. Bibcode: 1996ApJ...470..322C Altcode: 1996astro.ph..5079A; 1996astro.ph..5079C We present the results of an intensive ultraviolet monitoring campaign on the Seyfert I galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously With the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days Prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 A went through four significant and well-defined events of duration 2-3 days during the continuous-monitoring period. We find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines. Title: Teaching materials: stellar atmospheres/radiative transfer. Authors: Hawley, S. L.; Ayres, T. R. Bibcode: 1996BAAS...28Q.883H Altcode: No abstract at ADS Title: Fishing in the Coronal Graveyard Authors: Ayres, Thomas Bibcode: 1996hst..prop.6551A Altcode: 1996hst..prop.2962A We propose a far-UV spectroscopic survey of K2-K4 giants. Hotcoronae (T> 10^6 K) are rare or absent in single giant starsto the right of a boundary in the H-R diagram near K0(``Linsky-Haisch dividing line''). The early-K giants aresuch slow rotators that the absence of Dynamo-generatedmagnetic activity is natural. Nevertheless, Gamma Draconis(K5 III) unexpectedly was detected in the coronal proxy C IVby HST/GHRS, and subsequently was discovered as a faintX-ray source in a deep ROSAT pointing. The basis for thecoronal emission is unknown, given the presumed lack of Dynamoaction. However, the X-ray/C IV ratio of Gamma Dra falls on acontinuum of values; extending from the active K0 ``Clump''giants like Beta Ceti, down to the old red giant Alpha Boo (K1III) in the depths of the ``coronal graveyard.'' GHRS/G140Lreconnaissance of high-excitation FUV emissions (Si IV, C IV,and N V) can be conducted at sensitivity levels orders ofmagnitude better than possible prior to HST. Such a surveyof single red giants would provide a unique perspective on thebreadth of activity to the right of the L-H boundary. Italso would record the fluoresced 4th-positive system of CO,a key tracer of thermal inhomogeneities in late-typeatmospheres. Seven candidates fall in the magnitude rangeV < 3. Three--Beta UMi, Epsilon Sco, and Epsilon Crv--willbe observed, consistent with the TAC allocation. Title: Sleuthing the Dynamo: the Final Frontier Authors: Ayres, Thomas Bibcode: 1996hst..prop.6795A Altcode: 1996hst..prop.3206A Innovative technologies are opening new windows into the Sun;from its hidden interior to the far reaches of its turbulentouter envelope: rare-earth detectors for solar neutrinos; theGONG project for helioseismology; SOHO for high-resolutionXUV spectroscopy, and YOHKOH for coronal X-ray imaging. Atthe same time, a fleet of space observatories--ROSAT, EUVE,ASCA, and HST itself--are providing unprecedented views ofthe vacuum-UV and X-ray emissions of stars in our Galacticneighborhood. These seemingly unrelated developments are infact deeply connected. A central issue of solar-stellarphysics is the nature and origin of magnetic activity: thelink between the interior dynamics of a late-type star and theviolent state of its outermost coronal layers. As solarphysicists are unlocking the secrets of the hydromagneticDynamo deep inside the Sun, we and others have beendocumenting the early evolution of the Dynamo and itsassociated external gas-dynamic activity. In particular, wehave obtained HST/FOS spectra of ten young solar-type starsin three nearby open clusters--the Hyades, Pleiades, andAlpha Persei--ranging in age from 50 Myr to 600 Myr. We havesupplemented the HST spectroscopy with deep ROSAT pointings, and ground-based studies. Here, we will continue the HSTside of our project by obtaining FUV spectra of two AlphaPerseids from our original program (but not yet observed),and high-S/N follow-up measurements of the hyperactive PleiadH II 314. Title: Teaching Materials: Stellar Atmospheres/Radiative Transfer Authors: Hawley, S. L.; Ayres, T. R. Bibcode: 1996AAS...188.3905H Altcode: 1996BAAS...28..883H We will present a selection of modern teaching materials for courses in Stellar Atmospheres and Radiative Transfer that have been collected from a wide variety of sources. We will provide brief synopses of each book, or set of of notes, and endeavor to compare and contrast the different presentations of the material. One of the newer additions to the literature is ``Radiative Transfer in Stellar Atmospheres,'' lecture notes from R.J. Rutten based on courses taught at Utrecht University. In addition, I. Hubeny and D. Mihalas presently are writing a new edition of Mihalas' famous ``Stellar Atmospheres.'' Other books we are aware of range from the planning stages to near completion. We will emphasize the diversity of styles and presentation techniques, but will try to make clear the central themes around which any successful Stellar Atmospheres/Radiative Transfer course must be built. Title: 2-D Inhomogeneous Modeling of the Solar CO Bands Authors: Ayres, T. R. Bibcode: 1996AAS...188.3904A Altcode: 1996BAAS...28R.882A The recent discovery of off-limb emissions in the mid-IR ( ~ 5 mu m) vibration-rotation bands of solar carbon monoxide (CO) has sparked new interest in the formation of the molecular lines, and their ability to diagnose thermal conditions at high altitudes. The off-limb extensions of the strong CO lines indicate the penetration of cool material (T ~ 3500 K) several hundred kilometers into the otherwise hot (T ~ 6000 K) chromosphere. The origin of the cool gas, and its role in the thermal energy balance, remain controversial. The interpretation of the CO observations must rely heavily upon numerical modeling, in particular highly-inhomogeneous thermal structures arrayed in a 2-D scheme that can properly treat the geometry of the grazing rays at the solar limb. The radiation transport, itself, is especially simple for the CO off-limb emissions, because the fundamental bands form quite close to LTE (high collision rates; low spontaneous decay rates) and the background continuum is purely thermal as well (f--f transitions in H(-) and H). Thus, the geometrical aspects of the problem can be treated in considerably more detail than would be practical for typical NLTE scattering lines. I describe the recent modeling efforts, and the diagnostic potential of the CO bands for future observational studies of inhomogeneous surface structure on the Sun, and on other stars of late spectral type. This work was supported by NSF grant AST-9218063 to the University of Colorado. Title: Observations of Solar Carbon Monoxide with an Imaging Infrared Spectrograph. I. Thermal Bifurcation Revisited Authors: Ayres, Thomas R.; Rabin, Douglas Bibcode: 1996ApJ...460.1042A Altcode: We describe long-slit spectroscopy of the solar 4.7 μm carbon monoxide (CO) Δυ = 1 bands at the Main spectrograph of the NSO McMath-Pierce telescope. We utilized stigmatic imaging of the temperature- and velocity-sensitive CO absorptions to map quiet regions near disk center and at the extreme limb. At Sun center the dominant long-lived spatial structures are small-scale hot spots associated with fragments of the supergranulation network seen in cotemporal Ca II filtergrams. Oscillatory thermal and velocity fluctuations of the global p-mode interference pattern are a pervasive feature of the maps, but the rms amplitudes (≍70 K and ≍240 m s-1) are perturbations on a relatively unstructured outer photosphere. We occasionally see small-scale transient cooling episodes longer lived than the p-mode wavepackets that might be overshooting granules or rising magnetic flux ropes. The events are too rare, however, to influence the global properties of the CO fundamental bands.

Seeing-selected frames of the off-limb CO emissions show a typical extension of 0".6 for the strongest lines, with little variation along the limb. The off-limb extensions indicate the presence of cool gas up to 350 km above the "Tmin" of popular reference models of the solar chromosphere.

We carried out two-dimensional model atmosphere simulations to study the effects of thermal inhomogeneities on the disk-center, extreme-limb, and off-limb behavior of the CO lines. The models are spherically symmetric, static, and in LTE. Our data favor a scenario in which the bulk of the low chromosphere below the base of the magnetic "canopy" is in reality a "COmosphere" dominated by gas colder than the minimum temperature in conventional models.

The moderate-scale (≍5"), mild thermal perturbations of the p-mode pattern have little influence on the CO Δυ = 1 spectra. Small-scale (≍1") hot regions embedded in a cool average atmosphere are strongly "shadowed" at the extreme limb. The shadowing is of little consequence, however, because the atmosphere already is dominated by the cool component. The opposite scenario-small-scale cold regions in a warm average produce effective shadowing at the limb for granule-size (≍1"-2") dark points only if the covering fraction is relatively large (f &#8819 0.2). That scenario is ruled out: it predicts high-contrast dark spots at disk center, contrary to our observations. We also argue against the possibility of shadowing by even smaller, subresolution (≍0"3) cold spots with f &#8819 0.1.

We show that multistep reactions, rather than direct radiative associations, dominate the gas-phase chemistry of CO molecules under conditions typical of the outer photosphere. The CO formation and radiative cooling timescales are fast enough that low-temperature plasma conditions can be restored following disruption by a localized heating event such as a Ca II K2v "flash." In cool giant stars, the chemical formation timescales are much longer than in dwarfs like the Sun. Nevertheless, the density dependence is such that the molecular cooling proceeds proportionately more rapidly than the gas dynamics, ensuring an even more important role for autocatalyzed "thermal bifurcation." Title: Evolution of the Solar EUV Radiation and Its Impact on Martian Exospheric Constituents Over Time Authors: Ayres, T. R. Bibcode: 1996emv..work....2A Altcode: 1995LPITR9504....2A No abstract at ADS Title: Hot Times in the Hertzsprung Gap Authors: Ayres, Thomas R. Bibcode: 1996aeu..conf..113A Altcode: 1996IAUCo.152..113A No abstract at ADS Title: Magnetic Structures and Giant Flares in HR1099 Authors: Foing, B. H.; Char, S.; Ayres, T.; Catala, C.; Zhai, D. S.; Jiang, S.; Huang, L.; Hao, J. X.; Houdebine, E.; Jankov, S.; Baudrand, J.; Czarny, J.; Donati, J. F.; Felenbok, P.; Catalano, S.; Cutispoto, G.; Frasca, A.; Rodono, M.; Neff, J. E.; Simon, T.; Collier-Cameron, A.; Butler, C. J.; MUSICOS 1989 Campaign Collaboration Bibcode: 1996mpsa.conf..283F Altcode: 1996IAUCo.153..283F No abstract at ADS Title: Stellar spectroscopy with HST Authors: Ayres, T. R. Bibcode: 1996ASPC..109..215A Altcode: 1996csss....9..215A No abstract at ADS Title: How Hot - and Variable - are the Coronae of Hertzsprung-Gap Giants? Authors: Ayres, Thomas Bibcode: 1996rxte.prop10001A Altcode: Hertzsprung-gap giants (F0-G1) are "hyperactive" late-type stars whose X-ray coronae are among the hottest known (>1 keV); reminiscent of flaring gas in solar active regions, or on RS CVn binaries and dMe stars. Yet, the H-gap giants as a class so far have shown no evidence for flare-like outbursts (at least in the UV or soft X-rays). The paradox - flare-temperature gas but lack of overt flaring behavior - bears on the nature of late-type magnetic activity and the elusive coronal heating mechanism. XTE can add crucial insight by directly detecting the highest excitation coronal gas, and possible transient variability of the multi-keV X-rays. 31 Comae (G0 III), a single star, and the nearby binary Capella (G8 III + G1 III) are the most promising targets. Title: Thermal bifurcation as a driver of stellar surface inhomogeneities (review) Authors: Ayres, T. R. Bibcode: 1996IAUS..176..371A Altcode: No abstract at ADS Title: Digging for Fossils in the Hertzsprung Gap Authors: Ayres, Thomas R. Bibcode: 1996euve.prop...37A Altcode: Something remarkable happens to moderate-mass giants during their post-MS evolution through the Hertzsprung gap (F-G5), on their way to the core helium burning Clump (G8-K0). The subcoronal fluxes of such stars (traced by Mg II and Si IV) appear normal for fast rotating giants, but their coronal X-rays are depressed an order of magnitude or more. The nearby binary Capella is the archetype: the G0 secondary has a Si IV flux ten times that of the G8 primary, and rotates faster by a similar margin. Yet, evidence suggests near equality of the coronal X-ray fluxes. I, and my colleagues, have been conducting a study of the dichotomy (and its implications for coronal heating, structure, and the evolution of magnetic dynamo action) through EUVE spectra of key stars on post-MS trajectories connecting the Hertzsprung gap and the Clump. Recent work points to a possibly pivotal role played by a fossil magnetosphere inherited from the upper-MS phase. We propose to pursue the idea further through observations of Beta Cassiopeia (F2 III) and Mu Velorum (G5 III), at the crucial blue and red edges of the gap. Title: Outer atmospheric structures of high-luminosity G/K stars Authors: Deeney, B. D.; Brown, A.; Ayres, T. R. Bibcode: 1996ASPC..109..519D Altcode: 1996csss....9..519D No abstract at ADS Title: The Transition Region, Corona, Chromosphere, and Wind of the K5 Giant gamma Draconis Authors: Brown, A.; Carpenter, K. G.; Robinson, R. D.; Harper, G. M.; Deeney, B. D.; Ayres, T. R. Bibcode: 1995AAS...18710303B Altcode: 1995BAAS...27.1430B Gamma Draconis (K5 III) is the first single, normal late K giant located on the red side of the coronal ``dividing line'' known to show conclusive evidence for both hot ( ~ 10(5) K) transition \ region (TR) and coronal (> 10(6) K) plasma. We present HST GHRS ultraviolet spectra of gamma Dra obtained on 1995 July 20 and 1991 April 6/18. These observations include spectra obtained at low, medium, and echelle resolution that provide a full set of chromospheric and TR emission line fluxes and profiles. These are combined with ROSAT PSPC observations to measure the TR and coronal properties, such as emission measure distribution, electron density, and nonthermal velocity fields, of this star. The high temperature emissions of gamma Dra are compared to those of a sample of hybrid-chromosphere bright giants and supergiants. This work is supported by Space Telescope Science Institute grant GO-06068.01-94A and NASA grants NAG5-1792 and NAGW-4529 to the University of Colorado. Title: A Semiempirical Determination of the Wind Velocity Structure for the Hybrid-Chromosphere Star alpha Trianguli Australis Authors: Harper, Graham M.; Wood, Brian E.; Linsky, Jeffrey L.; Bennett, Philip D.; Ayres, Thomas R.; Brown, Alexander Bibcode: 1995ApJ...452..407H Altcode: We have used the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope to study the wind of the hybrid-chromosphere star α TrA (K4 II). The stellar wind produces significant absorption at negative radial velocities in the chromospheric Mg II resonance lines (h and k). Spectra obtained with the GHRS echelle high-resolution grating (4A 85,000) on 1993 February 10 and 1994 May 1 reveal complex interstellar absorption in the Mg II emission lines and a high-velocity wind absorption feature centered near -95 km s-1. The 1993 February observation shows an asymmetry of the Mg II emission cores, corresponding to an apparent redshift of 6.0±1.5 km s-1. We construct a simple wind model that explains several of the key observational features. The scattering of the Mg II h and k photons in a geometrically extended region dominates the observed flux near line center, which supports the assignment of the low-velocity absorption components to interstellar absorption rather than to a chromospheric self-reversal. For the 1993 February observation, the parameters for our simple wind model are as follows: terminal velocity V(∞) = 100 km s-1, turbulent velocity Vturb = 24 km s-1, Mṡ ∼ 1.8 × 1010 Msun yr-1, for a fixed value of the velocity-law parameter β = 1 and fixed stellar radius of R* = 97 Rsun, assuming Mg II is the dominant ionization state in the flow. Our analysis of the 1994 May observation resulted in similar values for these parameters, and the mass-loss rate could be as small as Mṡ ∼ 1.6 × 10-10 Msun yr-1. The value of β is uncertain (≥ 0.3) and if β ∼ 3.5 as found from the recent analysis of the ζ Aurigae systems, Mṡ could be larger by a factor of 3-4. A comparison of our result with numerical solutions to the momentum and conservation equations reveals that the derived velocity distribution lies within a limited region of parameter space where there is a large nonthermal pressure on the plasma close to the base of the wind consistent with previous wind models for α TrA. Our best model fit to the two interstellar absorption components indicates a total hydrogen column density toward α TrA of NHI = 2 × 1019 cm-2. Title: Deuterium and the Local Interstellar Medium Properties for the Procyon and Capella Lines of Sight Authors: Linsky, Jeffrey L.; Diplas, Athanassios; Wood, Brian E.; Brown, Alexander; Ayres, Thomas R.; Savage, Blair D. Bibcode: 1995ApJ...451..335L Altcode: We present Goddard High-Resolution Spectrograph observations of the interstellar H I and D I Lyα lines and the Mg II and Fe II resonance lines formed along the lines of sight toward the nearby stars Procyon (3.5 pc, l = 214°, b = 13°) and Capella (12.5 pc, l = 163°, b = 5°). New observations of Capella were obtained at orbital phase 0.80, when the radial velocities of the intrinsic Lyα emission lines of each star were nearly reversed from those of the previous observations at phase 0.26 (analyzed by Linsky et al.). Since the intrinsic Lyα line of the Capella system the "continuum" against which the interstellar absorption is measured has different shapes at phases 0.26 and 0.80, we can derive both the intrinsic stellar profiles and the interstellar absorption lines more precisely by jointly analyzing the two data sets. We derive interstellar parameters from the simultaneous analysis of the two data sets as follows: (D/H)LISM = (1.60±0.09 [+0.05, - 0.10 systematic error]) × 10-5, temperature T = 7000±500 [±400 systematic error] K, and microturbulence ξ = 1.6±0.4 [and ±0.2 systematic error] km s-1. (All random errors determined in this paper are ±2 σ.)

For the analysis of the Procyon line of sight, we first assumed that the intrinsic Lyα line profile is a broadened solar profile, but this assumption does not lead to a good fit to the observed D I line profile for any value of D/H. We then assumed that (D/H)LISM = 1.6 × 10-5, the same value as for the Capella line of sight, and we modified the broadened solar profile to achieve agreement between the simulated and observed line profiles. The resulting asymmetric intrinsic stellar line profile is consistent with the shapes of the scaled Mg II line profiles. We believe therefore that the Procyon data are consistent with (D/H)LISM = 1.6 × 10-5, but the uncertainty in the intrinsic Lyα emission-line profile does not permit us to conclude that the D/H ratio is constant in the local interstellar medium (LISM). The temperature and turbulence in the Procyon line of sight are T = 6900±80 (±300 systematic error) K and ξ = 1.21±0.27 km s-1. These properties are similar to those of Capella, except that the gas toward Procyon is divided into two velocity components separated by 2.6 km s-1 and the Procyon line of sight has a mean neutral hydrogen density that is a factor of 2.4 larger than that of the Capella line of sight. This suggests that the first 5.3 pc along the Capella line of sight lies within the local cloud and the remaining 7.2 pc lies in the hot gas surrounding the local cloud.

We propose that nHI = 0.1065±0.0028 cm-2 be adopted for the neutral hydrogen density within the local cloud and that ξ = 1.21±0.27 km s-1 be adopted for the nonthermal motions. The existence of different second velocity components toward the nearby stars Procyon and Sirius provides the first glimpse of a turbulent cloudlet boundary layer between the local cloud and the surrounding hot interstellar gas. We speculate that what is often called "turbulence" may instead be velocity shear within the local cloud that is not a rigid comoving structure. We also derive gas phase abundances of iron and magnesium in the Procyon line of sight and the abundance of oxygen in the Capella line of sight.

Within the context of standard big bang nucleosynthesis, our observed value of (D/H)LISM leads to 0.042 ≤ ΩBh250 ≤ 0.09, depending on the assumed model for Galactic chemical evolution of deuterium. Our lower limit (D/H)LISM > 1.41 × 10-5 provides a hard lower limit to the primordial D abundance and thus a hard upper limit on ΩBh250 ≤ 0.125. These limits are independent of Galactic chemical evolution models and only assume that D is destroyed with time. Title: Hot Times in the Hertzsprung Gap Authors: Ayres, Thomas Bibcode: 1995hst..prop.6067A Altcode: 1995hst..prop.2540A I propose to explore the early evolution of magnetic activity in F-G0 giants crossing the Hertzsprung gap. The giant branch evolution of 2-4 solar mass stars provides a vital test of our understanding of magnetic Dynamo action, coronal heating, and winds. The ``X-ray deficiency'' of the F-G0 giants represents a clear distinction compared to cooler Main Sequence stars. Possibly connected with the deficiency is the newly recognized warm wind of the G0 secondary of Capella, as well as indications for a previously unrecognized ``broad component'' in its high excitation emissions like C IV 1548. The mass loss rate of the Capella wind is low, but could be quite important in braking the fast stellar rotation. The broad components might be associated with the wind, but more likely are due to highly dynamic phenomena in the subcoronal atmosphere; perhaps the stellar equivalent of solar ``transition zone explosive events.'' These new aspects of stellar activity warrant detailed consideration. My strategy is to use the HST/GHRS to record key FUV emissions -- spanning the broad temperature range 10,000 K - 200,000 K -- with high S/N in archetype Hertzsprung gap stars. The objective is to measure line widths, profile asymmetries, circumstellar absorptions, systematic Doppler shifts, and density sensitive line ratios. Such diagnostics will be used to constrain existing physical models, and develop new ones. The HST spectra will strongly complement ongoing ROSAT & EUVE work. Title: A Reanalysis of the SWP-HI IUE Observations of Capella Authors: Wood, Brian E.; Ayres, T. R. Bibcode: 1995ApJ...443..329W Altcode: We have reanalyzed the numerous high-resolution, far-ultraviolet observations of Capella made by the International Ultraviolet Explorer (IUE) in its 16 yr lifetime. Our purpose was to search for long-term profile variations in Capella's ultraviolet emission lines and to complement the analysis of Goddard High Resolution Spectrograph (GHRS) observations of Capella, discussed in a companion paper (Linsky et al. 1995). We implemented a state-of-the-art photometric correction and spectral extraction procedure to improve S/N and control potential sources for systematic errors. Nevertheless, we were unable to find compelling evidence for any significant long-term profile variations. Previous work has shown that the G8 primary star is only a minor contributor to the high-excitation transition region lines but is a significant contributor to the low-excitation chromospheric lines. We have found exceptions to this rule, however. We find that the G8 star is responsible for a significant portion of Capella's N V lambda lambda 1239, 1243 emission, but is not a large contributor to the S I lambda 1296, Cl I lambda 1352, and O lambda 1356 lines. We suggest possible explanations for these behaviors. We also find evidence that the He II lambda 1640 emission from the G1 star is from the transition region, while the He II lambda 1640 emission from the G8 star is chromospheric, consistent with the findings of Linsky et al. (1994). The C II lambda 1336 line shows a weak central reversal. It is blueshifted by about 9 km/s with respect to the centroid of the emission from the G1 star. While the central reversal of the C II line is blueshifted by about 9 km/s with respect to the centroid of the emission from the G1 star. While the central reversal of the C II line is blueshifted, the central reversal of the Si III lambda 1207 line discussed by Linsky et al. (1994) is not. Title: The Transition Regions of Capella Authors: Linsky, Jeffrey L.; Wood, Brian E.; Judge, Philip; Brown, Alexander; Andrulis, Catherine; Ayres, Thomas R. Bibcode: 1995ApJ...442..381L Altcode: We have used the Goddard High Resolution Spectrometer (GHRS) to observe the spectoscopic binary system Capella (G8 III + G1 III). Exposures with the G140L, G140M, G160M, G200M, and echelle gratings provide emission line profiles with unprecedented signal-to-noise and spectral resolving power (lambda/Delta-lambda) up to 92,000. Multi-Gaussin fits to the line profiles show that the hotter star contributes 60%-70% of the total flux in the chromospheric O I and Mg II resonance lines, but about 90% of the flux in the Si III, Si IV, and C IV lines formed in the transition region at T less than or = 105 K. We find clear evidence that the emission lines from the hotter star are systemtically redshifted relative to the photosphere with Doppler shifts of 5 +/- 1 km/s for the +9 +/- 3 km/s in the chromospheric Mg II and O I lines, respectively, increasing to +24 +/- 5 km/s for the transition region Si IV 1393.8A line. The multi-Gaussian fits to permitted transition region lines of SI III, Si IV, C IV, and N V indicate the presence of three components: moderately broad lines formed in the transition region of the hotter star (component H), narrow lines formed in the transition region of the cooler star (component C), and very broad lines that we think are formed in microflares on the hotter star (component B). The He II 1640.4 A feature has an broad profile, which indicates that it is formed by collisional excitation primarily from the hotter star, and a weak narrow component that we interpret as due to radiative recombination on the cooler star. We observed spin-forbidden emission lines of C III), O III), Si III), O IV), O V), and S IV) that are sensitive to electron density. Fainter members of the O IV) multiplet and all of the S IV) lines have never before been seen in any star than the Sun. We determine electron densities in the transition regions of the Capella stars using lines ratios of O IV) lines and emission measure analysis. The emission measures are self-consistent only when the fluxes from each emitting component are considered separately. In particular, the transition region abundance distributions appear to be different on the two stars, and the spin-forbidden lines were not detected in the B component. The emission measures for component H (the G1 star) are consistent with a constant electron pressure (or hydrostatic equilibrium) transition region with Pe = 1015 + 0.1/cu cm K and possibly solar 'coronal' abundances. Title: The Hydrogen Hole at the North Galactic Pole Authors: Ayres, T. R.; Linsky, J. L.; Diplas, A. Bibcode: 1995AAS...186.3508A Altcode: 1995BAAS...27..860A The yellow giant 31 Comae (HD111812: G0 III) lies near the North Galatic Pole (b(II) = +89{fdg }6; l(II) = 114{fdg }9). Although 80 pc distant in the Coma Berenices open cluster, 31 Com is a strong EUV source. Recent HST/GHRS spectra of the star show surprisingly weak Mg II lambda2800 and H I lambda1215 interstellar absorptions. The neutral hydrogen column in that direction must be quite low, reminiscent of the interstellar ``void'' toward epsilon CMa discovered by the EUVE. Indeed, previous EUVE observations have shown that the lines of sight to the hot white dwarfs HZ 43 (b(II) = +84deg ; l(II) = 54deg ) and GD 153 (b(II) = +85deg ; l(II) = 317deg ) have very low columns, NH < 1*E(18) cm(-2) , suggesting another ``tunnel'' near the NGP. We modeled the GHRS spectra of 31 Com to determine whether there is a further northward extension of the HZ 43/GD 153 void. [-3mm] The interstellar Mg II h and k absorptions in the 31 Com spectrum are quite sharp, suggesting only a single velocity component along the line of sight (compared with several distinct clouds in the direction of epsilon CMa). Our preliminary modeling of the Mg II, H I, and D I ISM features indicates that xi_t , T, and [D/H] are similar to the values measured previously for the lines of sight toward the nearby stars Capella and Procyon. Furthermore, the bulk velocity (-2 km s(-1) , heliocentric) is the same as predicted for the local cloud. The inferred neutral hydrogen column, NH ~ 8*E(17) cm(-2) , is one of the smallest ever measured directly from the Lyalpha absorption. We speculate that the majority of the neutral gas in the direction of 31 Com lies very close to the Sun in a few pc extension of the local ``fluff'', and that the remainder of the sightline is quite rarified and probably hot. In all likelihood the HZ 43/GD 153 void is considerably larger than suspected previously. [-2mm] This work was supported by NASA grants GO-5323.01-93A (HST), S-56460-D (HST), and NAG5-2274 (EUVE). Title: Hubble Observations of D/H in the Local ISM and Consequences for Authors: Linsky, J. L.; Diplas, A.; Ayres, T. R.; Wood, B.; Brown, A. Bibcode: 1995lea..conf..215L Altcode: No abstract at ADS Title: The RIASS Coronathon: Joint X-Ray and Ultraviolet Observations of Normal F--K Stars Authors: Ayres, Thomas R.; Fleming, T. A.; Simon, T.; Haisch, B. M.; Brown, A.; Lenz, D.; Wamsteker, W.; de Martino, D.; Gonzalez, C.; Bonnell, J.; Mas-Hesse, J. M.; Rosso, C.; Schmitt, J. H. M. M.; Truemper, J.; Voges, W.; Pye, J.; Dempsey, R. C.; Linsky, J. L.; Guinan, E. F.; Harper, G. M.; Jordan, C.; Montesinos, B. M.; Pagano, I.; Rodono, M. Bibcode: 1995ApJS...96..223A Altcode: Between 1990 August and 1991 January the ROSAT/IUE All Sky Survey (RIASS) coordinated pointings by the International Ultraviolet Explorer (IUE) with the continuous X-ray/EUV mapping by the Roentgensatellit (ROSAT). The campaign provided an unprecedented multiwavelength view of a wide variety of cosmic sources. We report findings for F-K stars, a large proportion of the RIASS targets. Forty-eight of our 91 'Coronathon' candidates were observed by the IUE during the campaign. For stars missed by the IUE, we supplemented the ROSAT survey fluxes with archival UV spectra and/or follow-on observations. Title: Surface structures and white-light flares on HR 1099: review of MUSICOS 1989 results. Authors: Foing, B. H.; Catala, C.; Baudrand, J.; Böhm, T.; Hubert, A. M.; Cuby, J. G.; Czarny, J.; Dreux, M.; Felenbok, P.; Zhai, D.; Jiang, S.; Huang, L.; Hao, J.; Char, S.; Jankov, S.; Ayres, T.; Neff, J. E.; Simon, T.; Houdebine, E. R.; Butler, C. J.; Beust, H.; Lagrange, A. -M.; Ferlet, R.; Vidal-Madjar, A.; Vitry, R.; Cutispoto, G.; Catalano, S.; Frasca, A.; Rodonò, M. Bibcode: 1995mscs.conf..131F Altcode: No abstract at ADS Title: Gappers and Clumpers: Finale Authors: Ayres, Thomas R. Bibcode: 1995euve.prop...45A Altcode: Something remarkable happens to moderate-mass giants during their post-MS evolution through the Hertzsprung gap (F-G1), on their way ultimately to the core-helium-burning Clump (G8-K0). The subcoronal emissions of such stars (traced by Mg II and C IV) appear to be normal for fast-rotating giants, but their coronal X-ray luminosities are depressed by an order of magnitude or more. The nearby binary Capella is the archetype: the G1 secondary has a C IV flux ten times that of the G8 primary, and rotates faster by a similar margin. Yet, evidence points to near equality of the coronal X-ray fluxes. I, and my colleagues, have been conducting a study of the dichotomy (and its implications for coronal heating, structure, and the evolution of Dynamo action) through EUVE spectroscopy of key stars along the post-MS trajectories connecting the Hertzsprung gap and the Clump. The remaining candidate for the program is the G5 giant, Mu Velorum. It is intermediate in its properties to the previous targets, and is a bright source in the 100A EUVE Survey band. Title: Thermal Bifurcation Revisited Authors: Ayres, T. R. Bibcode: 1995itsa.conf..289A Altcode: No abstract at ADS Title: EUVE guest investigator program Authors: Ayres, Thomas R. Bibcode: 1995cub..rept.....A Altcode: The purpose of the grant was to obtain and analyze data from the EUVE mission: specifically to investigate the 'coronal X-ray deficiency syndrome.' This refers to the fact that late-F/early-G giants in the Hertzsprung gap tend to show high levels of X-ray activity, but curiously depressed relative to their emissions of coronal proxies like C IV (lambda)1549. Later, when such stars have evolved through the red-giant branch to the post-flash 'Clump,' their X-ray levels decline dramatically, but their X-ray/C IV ratios return to 'normal' values. The origin of the dichotomy is thought to bear strongly on the nature of the elusive coronal heating mechanism, and its evolution in time. The observations undertaken here include: ROSAT and ASCA (specifically, 31 Com, a gap star; and beta Cet, an active Clump giant) to probe the high-temperature material; HST/GHRS spectroscopy to measure TZ flows and densities; and EUVE (31 Com observed in AO-1, re-observed in AO-3; beta Cet and v Peg (a gap giant) in AO-2). Title: HST/GHRS and EUVE Spectra of the Active Clump Giant beta Ceti (K0 III) Authors: Ayres, T. R.; Brown, A.; Drake, S.; Simon, T.; Stern, R. A.; Wood, B. E. Bibcode: 1994AAS...185.4510A Altcode: 1994BAAS...26.1381A The nearby red giant beta Ceti (HD 4128: K0 III; d= 16 pc) is in the postflash core helium burning phase. It is a member of a class of coronally active ``Clump'' giants that includes the G8 primary of Capella (alpha Aur: G8 III + G1 III) and the Hyad theta (1) Tauri (K0 III). Prior to the first ascent of the giant branch, such stars very likely were hyperactive Hertzsprung-gap giants, like the G0 secondary of Capella and 31 Comae (G0 III). HST/GHRS obtained spectra of beta Ceti on 1994 June 2, in five intervals using both the SSA and LSA. Exposure times ranged from 5.4 minutes (ECH-B/2800 Angstroms) to 43.5 minutes (G160M/1400 Angstroms). Strong emissions of H I, Mg II, Si III, Si IV, C IV, and N V were recorded with high S/N. Fainter lines of N I, C I, Si I, O IV], and O V] also were seen. After correction for systematic effects, we find that emissions which form below about 3*E(4) K are close to the rest frame of the star, but higher excitation species are systematically redshifted (as had been suggested previously on the basis of lower S/N IUE echelle spectra). The redshifts are 10+/-2 km s(-1) at N V/O IV temperatures (2*E(5) K); 16+/-1 at C IV (1*E(5) K); and 7+/-1 at Si IV (6*E(4) K). The strong high-excitation emissions have nearly uniform FWHM's (~ 90 km s(-1) ), but show evidence for ``broad components'' (FWHM ~ 150 km s(-1) ) at the bases of their profiles which are slightly more redshifted than the parent lines. We see no evidence for wind absorptions in the very high S/N (>50:1) profiles of Mg II k or H I Lyalpha , although the former displays a clear chromospheric central reversal outside of the sharp ISM feature. We will compare the HST/GHRS spectra with a 140 ks pointing on beta Ceti by the EUVE, conducted during the six day period beginning 1994 September 30. This work was supported by NASA grants GO-5323.01-93A (HST) and NAG5-2274 (EUVE). Title: Multi-site continuous spectroscopy. II. Spectrophotometry and energy budget of exceptional white-light flares on HR1099 from the MUSICOS 89 campaign. Authors: Foing, B. H.; Char, S.; Ayres, T.; Catala, C.; Neff, J. E.; Zhai, D. S.; Catalano, S.; Cutispoto, G.; Jankov, S.; Rodono, M.; Simon, T.; Akan, C.; Aslanov, A.; Avellar, P.; Baudrand, J.; Beust, H.; Cao, H.; Chatzichristou, H.; Cuby, J. G.; Czarny, J.; de La Reza, R.; Dreux, M.; Felenbok, P.; Ferlet, R.; Frasca, A.; Floquet, M.; Ghosh, K.; Guo, Z.; Guerin, J.; Hao, J. X.; Houdebine, E. R.; Huang, L.; Hubert, A. M.; Hubert, H.; Huovelin, J.; Hron, J.; Ibanoglu, C.; Jiang, S.; Keskin, V.; Lagrange-Henri, A. M.; Lecontel, J. M.; Li, Q.; Mavridis, L.; Nolthenius, R.; Petrov, P.; Savanov, I.; Scherbakov, A.; Tuominen, I.; Vidal-Madjar, A.; Zhang, R.; Zhang, X. Bibcode: 1994A&A...292..543F Altcode: We report results from the December 89 multi-site continuous observing campaign (MUSICOS 89) dedicated to the study of surface active structures and flares on the RS CVn-type system HR1099 (=V711 Tau). This system has been observed by up to 17 telescopes around the globe during this campaign. We obtained complete phase coverage for Doppler imaging of photospheric spots. Quasi-simultaneously, we observed the modulation of Ca II K line profile due to chromospheric plage regions. At least two exceptional white-light flares on 14 Dec. 15:00 UT and 15 Dec. 1:00 UT (the largest such optical flare episode ever reported in a RS CVn system) were detected photometrically with typical rise and decay times of 60-90 min, and with remarkable spectral dynamic signatures in Hα, with longer decay time scale. Equivalent colours, temperature excesses and projected flare areas (0.55 and 0.89 solar disc areas) were derived for the two optical flares. We estimate the energy budget for these two events, with respective peak intensities of radiative losses of 1.65 and 1410^33^erg/s and integrated losses over the white-light event duration of a few hours of 8.10^36^ and 10^38^ergs (in the 3100-5900A range), indicating a total energy balance several times these values. The emission was also measured in the Hα and Hβ lines during these flares with a ratio of flare optical emission over Balmer emission 3-4 times larger compared to other flares on dwarfs. More than one day after the last white-light flare, part of the flare decay phase was also measured with IUE in UV lines of low and high excitation; the extrapolated transition region EUV losses are found similar to the derived Balmer line losses. Both flares were shown to occur near the limb. We derive their physical area, and estimate their densities, column mass, and penetration depth. From Balmer line broadening and flows, we derive a kinetic energy budget comparable to the radiative losses. We discuss a possible magnetic energy budget and the interpretation in terms of filament ejection occurring over a magnetic arcade. These observations bring a new understanding and questions about energy transport mechanisms in stellar flares. Title: A reanalysis of the IUE high resolution observations of Capella. Authors: Wood, B. E.; Ayres, T. R. Bibcode: 1994BAAS...26..864W Altcode: No abstract at ADS Title: The Flare-Ona of 31 Comae Authors: Ayres, T. R.; Brown, A. Bibcode: 1994AAS...184.0503A Altcode: 1994BAAS...26..863A 31 Comae (HD111812: G0 III) is a rapidly rotating moderate mass giant in the middle of the Hertzsprung gap. It is a luminous source of soft X-rays and C IV lambda 1549, although it is a member of the ``X-ray deficient'' class of F/G giants (and early-F dwarfs) identified by Simon & Drake (1989, ApJ, 346, 303). We discuss the nature of the corona of 31 Com based on an 80 ks pointing by the Extreme Ultraviolet Explorer (EUVE), and historical FUV and X-ray exposures from IUE and ROSAT, respectively. We provide a context for the 31 Com energy distribution by applying an identical analysis to archival EUVE, IUE, and ROSAT/PSPC spectra of the evolved stars alpha CMi (F5 IV), alpha Aur (G8 III + G0 III), and HR1099 (K0 IV [+ G5 V]). 31 Com shows a remarkably hot coronal energy distribution that rivals that of the hyperactive RS CVn system HR1099 (and the dMe flare star AU Mic). It is decidedly different from soft coronal sources like the Sun and alpha CMi. The hot coronal structure is reminiscent of a continuously flaring plasma. However, the overt signatures of impulsive outbursts -- common on RS CVn's and dMe flare stars -- are absent. We propose that the G0 III giants at the red edge of the Simon & Drake X-ray deficiency boundary are undergoing a transient evolutionary episode of intense magnetic activity. We believe that the surface manifestations include widespread compact flaring ``bright points'' commensurate with the shallow unstable envelopes of these newly convective stars. The ``flare-ona'' of 31 Com suggested by the EUVE allows us to interpret the peculiar 80--300 Angstroms spectrum of alpha Aur reported by Dupree and collaborators (1993, ApJL, 418, L41). The enhanced emission measure at and above 10(7) K very likely is from the active G0 III secondary, while the pronounced peak in EM near 5*E(6) K is from the more evolved (post helium flash) G8 III primary. Our work was supported by EUVE Guest Observer grants from NASA. Title: A Reanalysis of the IUE High Resolution Observations of Capella Authors: Wood, B. E.; Ayres, T. R. Bibcode: 1994AAS...184.0509W Altcode: 1994BAAS...26Q.864W We have reanalyzed the numerous high resolution observations of Capella (G8 III + G0 III) made by the SWP camera of the International Ultraviolet Explorer (IUE) in its 16 year lifetime. One of our goals was to search for long term profile variations in Capella's ultraviolet emission lines, but we were unable to find any compelling evidence for any significant variations. Another goal is to compare the line profiles observed by the IUE with those observed by the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope. Previous authors have shown that the G8 star is only a minor contributor to the high excitation transition region lines, but is a significant contributor to the low excitation chromospheric lines. We have found exceptions to this rule, however. We find that the G8 star is responsible for a large portion of Capella's N V lambda lambda 1238, 1242 emission, but is not a large contributor to the chromospheric S I lambda 1295, Cl I lambda 1351, and O I] lambda 1355 lines, and we suggest possible explanations for this. We also find evidence that the He II lambda 1640 emission from the G0 star is from the transition region, while the He II lambda 1640 emission from the G8 star is chromospheric. The C II lambda 1335 line shows a weak central reversal. We have modeled this line with Gaussians, and we find that the Gaussian representing the central reversal is blueshifted by about 9 km s(-1) with respect to the Gaussian representing the emission from the G0 star, similar to the central reversal observed in the solar C II lambda 1335 line. Title: Carbon Monoxide Fundamental Bands in Late-Type Stars. III. Chromosphere or CO-mosphere? Authors: Wiedemann, G.; Ayres, T. R.; Jennings, D. E.; Saar, S. H. Bibcode: 1994ApJ...423..806W Altcode: The strong vibration-rotation lines of CO at 4.6 microns (Δυ = 1) are unique diagnostics for the thermal conditions in the atmospheric altitude range of late-type stars near and above the temperature minimum in chromospheric models. Exploiting recent improvements in IR instrumentation, we observed a number of cool stars with high spectral resolution (R ≍ 100,000). The analysis of the spectra was based on an earlier theoretical study which had established CO Δυ = 1 non-LTE spectra as useful probes for stars of spectral type F, G, and K with log g ≥ 1.

No direct chromospheric indicators were detected in the CO spectra. Stellar boundary (CO) temperatures were determined for the program stars and temperature profiles were constructed for α Tau, α Boo, β Gem and β Dra. The CO-based models feature a steady decrease in temperature at the height where the temperature increases in chromospheric models. Further comparison with chromospheric indicators shows an increasing discrepancy between the temperatures determined from CO measurements and those predicted from radiative equilibrium models, respectively, with increasing chromospheric activity. Thermal bifurcation of the stellar surfaces is proposed to reconcile the contradicting scenarios derived based on different spectral diagnostics. Title: Sleuthing the Dynamo: HST/FOS Observations of UV Emissions of Solar-Type Stars in Young Clusters Authors: Ayres, T.; Basri, G.; Simon, T.; Stauffer, J.; Stern, R.; Antiochos, S.; Bookbinder, J.; Brown, A.; Doschek, G.; Linsky, J.; Ramsey, L.; Walter, F. Bibcode: 1994ASPC...64...53A Altcode: 1994csss....8...53A No abstract at ADS Title: The Corona of the K5 Giant γ Dra, and its Relation to the HybridChromosphere Stars Authors: Brown, A.; Linsky, J. L.; Ayres, T. R. Bibcode: 1994AIPC..313...36B Altcode: 1994sxrc.conf...36B Gamma Draconis is the first, normal, single late K giant located on the red side of the coronal ``dividing line'' known to show conclusive evidence for hot (∼105 K) transition region (TR) and coronal plasma. We present ROSAT PSPC data and HST GHRS spectra of γ Dra and describe the coronal and TR properties of this K5 III star. The high temperature emissions of γ Dra are compared to those of a sample of hybrid-chromosphere bright giants and supergiants. New PSPC detections of the K3 giant α Hya and the G supergiant β Aqr are presented. Upper limits are found for the hybrid-chromosphere stars θ Her and α Aqr. These new measurements extend the X-ray to C IV flux-flux relations to significantly lower activity levels. Title: A Far-Ultraviolet Flare on a Pleiades G Dwarf Authors: Ayres, T. R.; Stauffer, J. R.; Simon, Theodore; Stern, R. A.; Antiochos, S. K.; Basri, G. S.; Bookbinder, J. A.; Brown, A.; Doschek, G. A.; Linsky, J. L.; Ramsey, L. W.; Walter, F. M. Bibcode: 1994ApJ...420L..33A Altcode: The Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) recorded a remarkable transient brightening in the C IV lambda lambda 1548,50 emissions of the rapidly rotating Pleiades G dwarf H II 314. On the one hand the 'flare' might be a rare event luckily observed; on the other hand it might be a bellwether of the coronal heating in very young solar-mass stars. If the latter, flaring provides a natural spin-down mechanism through associated sporadic magnetospheric mass loss. Title: The Transition Regions of Capella Authors: Linsky, J. L.; Wood, B. E.; Brown, A.; Andrulis, C.; Judge, P.; Ayres, T. R. Bibcode: 1994ASPC...64...62L Altcode: 1994csss....8...62L No abstract at ADS Title: COmospheres and Coronae Authors: Ayres, T. R. Bibcode: 1994ASPC...57..124A Altcode: 1994scsa.conf..124A No abstract at ADS Title: New Light on the Heart of Darkness of the Solar Chromosphere Authors: Solanki, S. K.; Livingston, W.; Ayres, T. Bibcode: 1994Sci...263...64S Altcode: Solar carbon monoxide spectra indicate the existence of a cool (less than 4000 kelvin) component to the solar chromosphere coexisting with the hot, bright gas at 6000 to 7000 kelvin. However, both the existence and the location of the cool component have been controversial. New high-resolution spectra show that carbon monoxide goes into emission just beyond the limb, allowing it to be probed without photospheric contamination. The cool component has temperatures as low as 3000 to 3500 kelvin and appears to cover 50 to 85 percent of the quiet solar surface. There is a steep temperature rise to normal chromospheric temperatures at a height of 900 to 1100 kilometers. Large horizontal velocities are seen, suggesting that the cool component is maintained by the supersonic adiabatic expansion of upwelling gas in overshooting granules. Title: Gappers and Clumpers, Cont'd Authors: Ayres, Thomas R. Bibcode: 1994euve.prop...27A Altcode: Something remarkable happens to moderate mass stars during their post-MS evolution through the Hertzsprung gap (F-G0), on their way ultimately to the post-helium-flash Clump (G8-K0). The subcoronal emissions of the H-gap stars (traced by Mg II and C IV) appear to be normal for fast-rotating giants, but their coronal X-ray luminosities are depressed by an order of magnitude or more. The nearby binary Capella is the archetype: the G0 secondary has a C IV flux ten times that of the G8 primary, and rotates faster by a similar factor. Yet, evidence points to near equality of the coronal X-ray fluxes. I propose to continue a broad-reaching exploration of the dichotomy (and its implications for coronal heating, structure, and the evolution of Dynamo action) through EUVE spectroscopy of key stars along the post-Main-Sequence trajectories connecting the Hertzsprung gap and the Clump. Part of the program is a re-observation of the prime target from AO-1: 31 Comae (G0 III). The SW spectrum is faint but remarkable. It exhibits almost exclusively very hot (T = 1 keV) lines. A three times deeper exposure can almost triple the S/N owing to the reduced detector background in recent observations. Key coronal density diagnostic lines might then become accessible. Title: The Shocking Truth about Beta Cassiopeia Authors: Ayres, T. R. Bibcode: 1994ASPC...64..351A Altcode: 1994csss....8..351A No abstract at ADS Title: The Spectral Variability of BP Tauri Authors: Simon, Theodore; Imhoff, C. L.; Basri, G. S.; Ayres, T. R. Bibcode: 1994ASPC...64..729S Altcode: 1994csss....8..729S No abstract at ADS Title: The MUSICOS Network for Multi-Site Continuous Spectroscopy Authors: Foing, B. H.; MUSICOS Collaboration; Catala, C.; Baudrand, J.; Boehm, T.; Hubert, A. M.; Jankov, S.; Cutispoto, G.; Catalano, S.; Pagano, I.; Rodono, M.; Umana, G.; Zhai, D. S.; Jiang, S.; Huang, L.; Hao, J. X.; Char, S.; Houdebine, E. R.; Ayres, T.; Neff, J. E.; Simon, T.; Butler, C. J.; Collier-Cameron, A.; Kennelly, T.; Walker, G.; Talavera, A. Bibcode: 1994ASPC...64..699F Altcode: 1994csss....8..699F No abstract at ADS Title: The Relationship Between Radiative and Magnetic Fluxes on Three Active Solar-type Dwarfs Authors: Linsky, J. L.; Andrulis, C.; Saar, S. H.; Ayres, T. R.; Giampapa, M. S. Bibcode: 1994ASPC...64..438L Altcode: 1994csss....8..438L We present some preliminary results from our coordinated campaign of IUE and McMath Telescope magnetic field measurements of three active solar-type dwarf stars: 59 Vir, xi Boo A, and HD 131511. We observed the three stars nearly every day from May 9 to May 25, 1993, covering between 1 and 3 rotations. We explore the functional and spatial relationship between magnetic and radiative fluxes. Title: The upper photosphere and lower chromosphere of small-scale magnetic features Authors: Solanki, S. K.; Bruls, J. H. M. J.; Steiner, O.; Ayres, T.; Livingston, W.; Uitenbroek, H. Bibcode: 1994ASIC..433...91S Altcode: No abstract at ADS Title: Atmospheric Dynamics and Mass Loss in Gappers, Clumpers, and Hybrids CYC4 - Medium Authors: Ayres, Thomas Bibcode: 1994hst..prop.5323A Altcode: 1994hst..prop.1771A The giant branch evolution of moderate-mass stars provides a vital test of our understanding of magnetic dynamo action, coronal energization, and winds. The blatant``X-ray deficiency'' of the Hertzsprung-gap giants appears to be genuine, while that of many ``hybrid-chromosphere'' supergiants appears to be due to absorption by a previously unrecognized warm or hot component of their winds; not apparent in the Mg II circumstellar features but quite evident in the H I Lyman-alpha profile (of at least one case). There also is new evidence for a warm wind on the G0 secondary of Capella -- a ``gap'' star. The mass-loss rate is low, but dynamically quite significant in braking the fast stellar rotation. Outflows of some kind probably exist on post-helium-flash Clump giants, as well, although ``antiwinds'' are the hallmark of the archetype, Beta Ceti. I propose to clarify the subcoronal properties of the Hertzsprung-gap, active Clump, and Hybrid stars through a spectral dissection of one representative of each class. My strategy is to use the HST/GHRS to record key FUV emissions -- spanning the broad temperature range 10,000-250,000 K -- with high S/N to measure line widths, profile asymmetries, circumstellar absorptions, systematic Doppler shifts, and density-sensitive line ratios. Such diagnostics will be used to constrain existing physical models, and develop new ones. The HST spectra will strongly complement ongoing X-ray work with ROSAT and recent EUVE spectroscopy. Title: The Cold Heart of the Solar Chromosphere Authors: Ayres, T. R. Bibcode: 1994IAUS..154...11A Altcode: No abstract at ADS Title: Coronal Topology Authors: Ayres, Thomas Bibcode: 1994iue..prop.4749A Altcode: The coronal morphology of the RS Canum Venaticorum binaries has been the subject of considerable debate over the past decade. Are the UV and X-ray bright structures of the subgiant primaries relatively compact, surface-hugging features analogous to the magnetic arcades of solar active regions? Or, do they extend to great altitudes, possibly interacting with their counterparts from the MS secondary? Given the practical difficulties of directly resolving the high-excitation 'surface' of a distant star, one must resort to proxies: (1) spectral imaging; and (2) rotational modulations of inhomogeneous brightness distributions. The techniques are best suited to the fastest-rotating objects, which conveniently also are the most active owing to the catalyzing effect of rotation on the generation of magnetic flux in cool stars. We propose to obtain a unique one-month sampling of the UV emissions of three bright RS CVn variables in concert with the near-continuous record of coronal intensities provided by the ALEXIS EUV sky-monitor. We currently are undertaking such a campaign for the bright RS CVn II Peg and the distantly-related object alpha Aur (Capella: sometimes called a "long-period RS CVn"). Our objective is to study the 3-D structure of hyperactive atmospheres in their most favorable light. Title: Rapid Ultraviolet Variability in NGC 4151 Authors: Edelson, R.; Fenton, S.; Crenshaw, D. M.; Reichert, G. A.; Peterson, B. M.; Clavel, J.; Rodriguez-Pascual, P.; Warwick, R.; Smith, D.; Ayres, T.; Shull, J. M. Bibcode: 1994ASPC...69..171E Altcode: 1994rmbl.conf..171E No abstract at ADS Title: Coronal Winds from Giants and Supergiants Authors: Ayres, T. R.; Kashyap, V. Bibcode: 1994ASPC...64..681A Altcode: 1994csss....8..681A No abstract at ADS Title: A Reanalysis of the Interstellar Medium along the Capella Line of Sight Authors: Linsky, J. L.; Diplas, A.; Ayres, T.; Wood, B.; Brown, A. Bibcode: 1993AAS...18311413L Altcode: 1993BAAS...25.1464L We report on new GHRS/HST observations of the interstellar HI and DI Lyman-alpha lines and the FeII and MgII resonance lines along the line of sight toward the nearby (12.5 pc) star Capella. These observations were obtained at orbital phase 0.80 when the combined stellar emission lines had different shapes compared to those obtained in earlier observations at phase 0.26 and analyzed by Linsky et al. (ApJ 402, 694 (1993)). By reversing the radial velocities of the two stars we are better able to derive the intrinsic stellar profiles, especially for the Lyman alpha line, and therefore to determine the interstellar absorption lines more precisely. We compare the derived properties of the local interstellar medium (D/H ratio, temperature, turbulent velocity, hydrogen column density, and gas phase abundances) for Capella at the two phases with the properties derived for the line of sight to another nearby (3.5 pc) star Procyon. This work is supported by NASA grant S-56460-D to the National Institute of Standards and Technology. Title: Visualization techniques to aid in the analysis of multi-spectral astrophysical data sets Authors: Brugel, Edward W.; Domik, Gitta O.; Ayres, Thomas R. Bibcode: 1993colo.reptQ....B Altcode: The goal of this project was to support the scientific analysis of multi-spectral astrophysical data by means of scientific visualization. Scientific visualization offers its greatest value if it is not used as a method separate or alternative to other data analysis methods but rather in addition to these methods. Together with quantitative analysis of data, such as offered by statistical analysis, image or signal processing, visualization attempts to explore all information inherent in astrophysical data in the most effective way. Data visualization is one aspect of data analysis. Our taxonomy as developed in Section 2 includes identification and access to existing information, preprocessing and quantitative analysis of data, visual representation and the user interface as major components to the software environment of astrophysical data analysis. In pursuing our goal to provide methods and tools for scientific visualization of multi-spectral astrophysical data, we therefore looked at scientific data analysis as one whole process, adding visualization tools to an already existing environment and integrating the various components that define a scientific data analysis environment. As long as the software development process of each component is separate from all other components, users of data analysis software are constantly interrupted in their scientific work in order to convert from one data format to another, or to move from one storage medium to another, or to switch from one user interface to another. We also took an in-depth look at scientific visualization and its underlying concepts, current visualization systems, their contributions, and their shortcomings. The role of data visualization is to stimulate mental processes different from quantitative data analysis, such as the perception of spatial relationships or the discovery of patterns or anomalies while browsing through large data sets. Visualization often leads to an intuitive understanding of the meaning of data values and their relationships by sacrificing accuracy in interpreting the data values. In order to be accurate in the interpretation, data values need to be measured, computed on, and compared to theoretical or empirical models (quantitative analysis). If visualization software hampers quantitative analysis (which happens with some commercial visualization products), its use is greatly diminished for astrophysical data analysis. The software system STAR (Scientific Toolkit for Astrophysical Research) was developed as a prototype during the course of the project to better understand the pragmatic concerns raised in the project. STAR led to a better understanding on the importance of collaboration between astrophysicists and computer scientists. Title: Visualization techniques to aid in the analysis of multispectral astrophysical data sets Authors: Brugel, E. W.; Domik, Gitta O.; Ayres, T. R. Bibcode: 1993colo.reptS....B Altcode: The goal of this project was to support the scientific analysis of multi-spectral astrophysical data by means of scientific visualization. Scientific visualization offers its greatest value if it is not used as a method separate or alternative to other data analysis methods but rather in addition to these methods. Together with quantitative analysis of data, such as offered by statistical analysis, image or signal processing, visualization attempts to explore all information inherent in astrophysical data in the most effective way. Data visualization is one aspect of data analysis. Our taxonomy as developed in Section 2 includes identification and access to existing information, preprocessing and quantitative analysis of data, visual representation and the user interface as major components to the software environment of astrophysical data analysis. In pursuing our goal to provide methods and tools for scientific visualization of multi-spectral astrophysical data, we therefore looked at scientific data analysis as one whole process, adding visualization tools to an already existing environment and integrating the various components that define a scientific data analysis environment. As long as the software development process of each component is separate from all other components, users of data analysis software are constantly interrupted in their scientific work in order to convert from one data format to another, or to move from one storage medium to another, or to switch from one user interface to another. We also took an in-depth look at scientific visualization and its underlying concepts, current visualization systems, their contributions and their shortcomings. The role of data visualization is to stimulate mental processes different from quantitative data analysis, such as the perception of spatial relationships or the discovery of patterns or anomalies while browsing through large data sets. Visualization often leads to an intuitive understanding of the meaning of data values and their relationships by sacrificing accuracy in interpreting the data values. In order to be accurate in the interpretation, data values need to be measured, computed on, and compared to theoretical or empirical models (quantitative analysis). If visualization software hampers quantitative analysis (which happens with some commercial visualization products), its use is greatly diminished for astrophysical data analysis. The software system STAR (Scientific Toolkit for Astrophysical Research) was developed as a prototype during the course of the project to better understand the pragmatic concerns raised in the project. STAR led to a better understanding on the importance of collaboration between astrophysicists and computer scientists. Twenty-one examples of the use of visualization for astrophysical data are included with this report. Sixteen publications related to efforts performed during or initiated through work on this project are listed at the end of this report. Title: Signal-to-Noise Ratios in IUE Low-Dispersion Spectra. II. Photometrically-Corrected Images Authors: Ayres, Thomas R. Bibcode: 1993PASP..105..538A Altcode: The character of detector noise is explored in photometrically-corrected images from the shortwavelength and longwavelength prime intensified vidicon cameras of the International Ultraviolet Explorer. A protocol is proposed for deriving realistic "noise models"--crucial to the application of Optimal extraction algorithms like that of Kinney, Bohlin, and Neill (1991)--from the available collections of UV-Flood calibration images. The protocol includes evaluation of the "noise-filtering" properties of the SWP and LWP cameras through 2-D spatial power spectrum analysis. (SECTION: Instrumentation and Data Analysis) Title: The Hydrogen Lyman-Alpha Emission of Capella Authors: Ayres, Thomas R.; Brown, A.; Gayley, K. G.; Linsky, Jeffrey L. Bibcode: 1993ApJ...402..710A Altcode: We describe the hydrogen Ly-alpha emission of the spectroscopic binary Capella (G8 III + GO III) recorded at 0.1 A resolution by the International Ultraviolet Explorer. The overt changes in the composite line shape with orbital phase are controlled by the active GO III star and permit a dissection of the stellar components despite the obliteration of the central portion of the profile by atomic hydrogen and deuterium absorption along the 12.5 pc sightline. The Ly-alpha line shape of the active GO III star is surprisingly asymmetric and possibly is variable. Both characteristics suggest a stellar wind of moderate excitation (20,000-100,000 K), a key component of the coronal evolution scenario of Simon and Drake (1989) for the Hertzsprung-gap giants. Title: The Coronal X-ray Deficiency Syndrome Authors: Ayres, Thomas R. Bibcode: 1993euve.prop...38A Altcode: Something strange happens to M ~ 3 M(sun) stars during their post-MS evolution through the Hertzsprung gap (F--G0), on their way ultimately to the post-helium-flash ``Clump (G8--K0). The subcoronal emissions of the H-gap stars (traced by Mg II and C IV) appear to be normal for fast-rotating giants, but their coronal X-ray luminosities are depressed by an order of magnitude or more. The nearby binary Capella is the archetype: the G0 secondary has a C IV flux 10 times that of the G8 primary, and rotates faster by a similar factor. Yet, evidence points to near equality of the coronal X-ray fluxes. We propose to continue our broad-reaching exploration of the dichotomy (and its implications for coronal heating and the evolution of Dynamo action) through EUVE spectroscopy of key stars along the post-Main-Sequence trajectories connecting the Hertzsprung gap and the Clump. Title: Coronal Topology Authors: Ayres, Thomas R. Bibcode: 1993iue..prop.4481A Altcode: The coronal morphology of the RS Canum Venaticorum binaries has been the subject of considerable debate over the past decade. Are the UV and X-ray bright structures of the subgiant primaries relatively compact, surface-hugging features analogous to the magnetic arcades of solar active regions? Or, do they extend to great altitudes, possibly interacting with their counterparts from the MS secondary star? Given the practical difficulties of directly resolving the high-excitation 'surface' of a distant star, one must resort to proxies. The most useful are: (1) spectral imaging; and (2) "rotational modulations" of inhomogeneous brightness distributions. The techniques are best suited to the fastest-rotating objects, which conveniently also are the most "active" owing to the catalyzing effect of rotation on the generation of magnetic flux in cool stars. We propose to obtain a unique medium-term (months) sampling of the UV emissions of four bright RS CVn variables, and the related object alpha Aur, in concert with the near-continuous record of coronal intensities provided by the ALEXIS EUV sky-monitor. Our objective is to study the three-dimensional structure of hyperactive atmospheres in their most favorable light. [Our proposal is substantially identical to an approved 15th-Episode program of the same title. Our current target-of-opportunity program cannot, however, be implemented in the present episode because the launch of ALEXIS has slipped into spring 1993, and the five prime targets will not be available until the fall. Thus, we are renewing our request.] Title: The Cool-Star Spectral Catalog: A Uniform Collection of IUE SWP-LOs Authors: Ayres, T.; Lenz, D.; Burton, R.; Bennett, J. Bibcode: 1993ASPC...52...51A Altcode: 1993adass...2...51A We have assembled an extensive electronically-accessible catalog of low-dispersion far-ultraviolet spectra of chromospheric emission-line stars observed with the International Ultraviolet Explorer. Title: Goddard High-Resolution Spectrograph Observations of the Local Interstellar Medium and the Deuterium/Hydrogen Ratio along the Line of Sight toward Capella Authors: Linsky, Jeffrey L.; Brown, Alexander; Gayley, Ken; Diplas, Athanassios; Savage, Blair D.; Ayres, Thomas R.; Landsman, Wayne; Shore, Steven N.; Heap, Sara R. Bibcode: 1993ApJ...402..694L Altcode: HST Goddard High-Resolution Spectrograph observations of the 1216, 2600, and 2800 A spectral regions are analyzed for the spectroscopic binary system Capella, obtained at orbital phase 0.26 with 3.27-3.57 km/s resolution and high SNR. The column densities of H I, D I, Mg II, and Fe II for the local interstellar medium along this 12.5 pc line of sight, together with estimates of the temperature and turbulent velocity are inferred. It is inferred that the atomic deuterium/hydrogen ratio by number is 1.65(+0.07, -0.18) x 10 exp -5 for this line of sight. Galactic evolution calculations indicate that the primordial D/H ratio probably lies in the range of (1.5-3) x (D/H)LISM. If H0 = 80 km/s Mpc, as recent evidence suggests, then the baryonic density in units of the Einstein-de Sitter closure density is 0.023-0.031. Thus the universe is argued to expand forever, unless nonbaryonic matter greatly exceeds the amount of baryonic matter. Title: The Distant Future of Solar Activity: A Case Study of beta Hydri. III. Transition Region, Corona, and Stellar Wind Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Linsky, J. L.; Monsignori-Fossi, B.; Simon, T.; Wallinder, F. Bibcode: 1993ApJ...403..412D Altcode: The paper investigates the secular decay of solar-type activity through a detailed comparison of the present sun with the very old solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses of successive atmospheric layers are presented, with emphasis of the outermost parts. The FUV emission lines for the transition zone are among the faintest so far seen in any solar-type star. The coronal soft X-ray spectrum was measured through different filters on EXOSAT and compared to simulated X-ray observations of the sun seen as a star. The flux from Beta Hyi is weaker than that from the solar corona and has a different spectrum. It is inferred that a thermally driven stellar wind can no longer be supported, which removes the mechanism from further rotational braking of the star through a magnetic stellar wind. Title: Errors Associated with Fitting Gaussian Profiles to Noisy Emission-Line Spectra Authors: Lenz, Dawn D.; Ayres, Thomas R. Bibcode: 1992PASP..104.1104L Altcode: Landman, Roussel-Dupre, and Tanigawa developed prescriptions to predict profile fitting errors for Gaussian emission lines perturbed by white noise. We show that their scaling laws can be generalized to more complicated signal-dependent "noise models" of common astronomical detector systems. (SECTION: Instrumentation and Data Analysis) Title: Extreme Ultraviolet Spectroscopy of Capella Authors: Green, James C.; Wilkinson, Erik; Ayres, Thomas R.; Cash, Webster C. Bibcode: 1992ApJ...397L..99G Altcode: The X-ray active binary system Capella was observed with a moderate-resolution extreme ultraviolet spectrograph from 200 to 330 A. Two low-level emission features were detected. One most likely is geocoronal He II 304 A emission, while the other probably originates from the corona of Capella. The weak stellar emission at 304 A is in direct conflict with predictions of the intrinsic stellar He II flux based on standard scaling arguments but is consistent with the only previous observation of Capella in the EUV. The most plausible explanation for the lack of stellar 304 A emission is a warm wind from the active G0 III star. Title: The Capella Dichotomy: Paradigm Lost? Authors: Ayres, Thomas R. Bibcode: 1992euve.prop...82A Altcode: Recent studies of the soft X-ray and C IV emissions of M < 3 M(sun) giants have shown that those in the post helium flash Clump (near K0) sit on a R(X) ~ R(C IV)^3/2 power law like the F-K dwarfs, while the early-F/early-G Hertzsprung-gap giants tend to lie on a separate parallel relation. The nearby binary Capella (G8III + G0III) is the archtype: the G0 secondary has a C IV flux 10x that of the G8 primary, and rotates faster by a similar factor. Yet, evidence points to near equality of the coronal X-ray fluxes. The latter facet of the Capella dichotomy is at odds with the central paradigm of cool-star coronae: the rotation-activity connection. I propose to explore the differences between the coronal properties of the Hertzsprung-gap and active Clump giants through measurements of the T(cor)s and EM distributions of 3 representative members of each class. Title: The Shocking Truth About Beta Cassiopeiae Authors: Ayres, Thomas R. Bibcode: 1992iue..prop.4192A Altcode: No abstract at ADS Title: The distant future of solar activity: a case study of beta Hydri (abstract) Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.; Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, Å.; Simon, T.; Vandenberg, D.; Wallinder, F. Bibcode: 1992sccw.conf..105D Altcode: No abstract at ADS Title: The Colorado scale-model solar system Authors: Bennett, Jeffrey O.; Ayres, Thomas R.; Center, Kenneth B.; Carter, Matthew F.; Bass, Ronald S. Bibcode: 1991PhTea..29..371B Altcode: No abstract at ADS Title: Digging in the Coronal Graveyard: A ROSAT Observation of the Red Giant Arcturus Authors: Ayres, Thomas R.; Fleming, Thomas A.; Schmitt, Juergen H. M. M. Bibcode: 1991ApJ...376L..45A Altcode: A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream. Title: The Many Faces of F Stars: A Rotational Modulation Study of Capella, Procyon, and Caph with the International Ultraviolet Explorer Authors: Ayres, Thomas R. Bibcode: 1991ApJ...375..704A Altcode: Far-UV spectroscopy of the F stars Capella, Procyon, and Caph is reported. Although all three stars are regard as chromospherically 'active', none exhibited any sensible rotational modulations, indicating a smooth surface distribution of chromospheric emission. Balancing this nonsolar behavior are a variety of puzzling differences among the three stars. On the one hand, the C IV features of Procyon are narrow, while that of the Capella secondary and Caph are broad; differences in v sin i alone cannot explain the dichotomy. On the other hand, the high-excitation emissions of the Capella secondary and Procyon, but not Caph, exhibit statistically significant redshifts. The significance of these results is discussed in the light of the speculation by Simon and Drake (1989) that the X-ray deficient coronae of the early F dwarfs are produced by classical acoustic heating. Title: Sleuthing the Dynamo: Cycle 2 Continuation Authors: Ayres, Thomas Bibcode: 1991hst..prop.3908A Altcode: Innovative technologies of the 1990s will open new windows to the interior of the Sun and its hidden dynamics: the GONG project for helioseismology; rare-earth detectors for solar neutrinos; and SOLAR PROBE for high-order moments of the mass distribution. At the same time, newly-commissioned space observatories will provide unprecedented views of the vacuum-UV and X-ray emissions of stars in our Galactic neighborhood. These seemingly unrelated developments are in fact deeply connected. A central issue of solar-stellar physics is the nature and origin of magnetic activity: the profound link between the interior dynamics of a late-type star and the violent state of its outermost million-degree coronal layers. As solar physicists are unlocking the secrets of the hydromagnetic dynamo deep inside the Sun, we will apply one of the powerful new astronomical tools of the decade -- the HST -- to document the early evolution of the dynamo and its associated external gas-dynamic activity. In particular, we will obtain high-S/N FUV spectra of solar-type stars in young galactic clusters ranging in age from 1/10-th to 1/100-th that of the Sun. Title: IUE Far Ultraviolet Spectra of Capella and Gamma-Draconis for Comparison to Hst/ghrs / Hubble Space Telescope / Goddard High Resolution Spectroscopy GTO Observations Authors: Ayres, T. R. Bibcode: 1991fyho.conf..216A Altcode: No abstract at ADS Title: CO Fundamental Bands in Late-Type Stars. II. Spectrum Simulations for F--K Stars Authors: Wiedemann, Guenter; Ayres, Thomas R. Bibcode: 1991ApJ...366..277W Altcode: The procedure of Ayres and Wiedemann (1989) was applied to a range of stellar-atmosphere models to study the CO Delta-v = 1 spectrum and to establish its use as a remote sensor of thermal conditions in late-type stars. Spectra were computed to examine the sensitivity of the CO Delta-v = 1 to fundamental stellar parameters and to assess the errors introduced into the spectrum intepretation by uncertain input parameters and non-LTE effects. Results of the sensitivity study demonstrate that CO fundamental spectra are useful probes for the temperature structure of the outer layers of cool stellar atmospheres, but that their value is limited by the uncertainties introduced by non-LTE effects. However, in stars with surface gravities of log g of about 1.5 and greater, the values of these uncertainties are reasonably small. Title: An Infrared Perspective on Chromospheres (With 3 Figures) Authors: Ayres, T. R. Bibcode: 1991mcch.conf..228A Altcode: No abstract at ADS Title: Coronathon Follow-On Authors: Ayres, Thomas R. Bibcode: 1991iue..prop.3917A Altcode: RIASS is a campaign to coordinate IUE spectroscopy of selected high-excitation celestial sources with the ROSAT all-sky survey (8/90 - 1/91). 1 and collaborators responded to that unique opportunity in the 13th Episode with a carefully-chosen sample of approx 80 F-K stars. Studies of the magnetically-engendered chromospheres and coronae of such stars particularly benefit from joint observations of far-UV emission lines (Tex approx 10^4 - 10^5 K) and broad-band soft X-ray fluxes (0.1-2 keV: Tex > 101 K). Ultimately, half of our "Coronathon" targets were observed during RIASS. Here, I request additional IUE time to record far-UV spectra of two groups of stars from the original sample which were not observed during the campaign either: (1) because the target had not previously been observed by the IUE (thereby violating one of the central requirements of RIASS); or, (2) the star was too faint (at C IV 1549) given the limited observing time. Far-UV spectra of these two groups will complete (in a statistical sense) the IUE archival collection of specific key classes of late-type stars, thereby permitting a broad range of statistical studies of stellar coronae which heretofore have been frustrated by incomplete or highly-biased samples. Title: Signal-to-Noise Ratios in IUE SWP-LO Spectra of Chromospheric Emission-Line Sources Authors: Ayres, Thomas R. Bibcode: 1990PASP..102.1420A Altcode: The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the noise levels in flat-field images are several times higher. The exaggerated noise can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral image processing system. An empirical noise model for the current-epoch photometric linearization strategy and one for a hypothetical processing system that achieves complete flat fielding of the raw images are derived. A formula is then proposed to predict the signal-to-noise ratio in the measured flux of an emission line (possibly superimposed on a smooth continuum) in an IUE low-dispersion (5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded with the SWP camera. For illustration, the formula is specialized to the important C IV 1549 A feature of F-K stars. The S/N relation permits one to determine sensitivity limits, upper limits in faint exposures, and optimum exposure times. Title: Sleuthing the Dynamo: Cycle 1 Observations Authors: Ayres, Thomas Bibcode: 1990hst..prop.2485A Altcode: Innovative technologies of the 1990s will open new windows to the interior of the Sun and its hidden dynamics: the GONG project for helioseismology; rare-earth detectors for solar neutrinos; and SOLAR PROBE for high-order moments of the mass distribution. At the same time, newly-commissioned space observatories will provide unprecedented views of the vacuum-UV and X-ray emissions of stars in our Galactic neighborhood. These seemingly unrelated developments are in fact deeply connected. A central issue of solar-stellar physics is the nature and origin of magnetic activity: the profound link between the interior dynamics of a late-type star and the violent state of its outermost million-degree coronal layers. As solar physicists are unlocking the secrets of the hydromagnetic dynamo deep inside the Sun, we will apply one of the powerful new astronomical tools of the decade -- the HST -- to document the early evolution of the dynamo and its associated external gas-dynamic activity. In particular, we will obtain high-S/N FUV spectra of solar-type stars in young galactic clusters ranging in age from 1/10-th to 1/100-th that of the Sun. Title: Fourier Transform Spectrometer Observations of Solar Carbon Monoxide. III. Time-resolved Spectroscopy of the Delta V = 1 Bands Authors: Ayres, Thomas R.; Brault, James W. Bibcode: 1990ApJ...363..705A Altcode: Time series of the 2100/cm Delta v = 1 absorption bands of CO at the center of the solar disk and at the extreme limb have been recorded by Fourier transform spectrometer. The photospheric 5-min oscillation appears prominently at sun center. The peak-to-peak brightness temperature amplitude is roughly 300 K, and the peak-to-peak Doppler shift is roughly 1100 m/s. The 70 deg phase lag of maximum core intensity with respect to maximum redshift for the strongest Delta v = 1 absorptions is less than the 90 deg expected in the adiabatic limit. No dominant four-minute signal in the line intensity like that reported by Deming et al. (1984, 1986, and 1987) is found, nor is evidence for extreme fluctuations on short time scales like those proposed by Kalkofen et al. (1984). The strong Delta v = 1 lines exhibit systematic Doppler shifts of less than about 1 km/s, contrary to the predictions of transonic redshifts if the CO 'clouds' are associated with a dynamic cooling phase of the Ca II 'cell flashes.' Title: A Case Study: Multi-Sensor Data Analysis of HH Objects Via STAR: A Scientific Toolkit for Astrophysical Research Authors: Mickus, K. D.; Brugel, E. W.; Domik, G. O.; Ayres, T. R. Bibcode: 1990BAAS...22R1259M Altcode: No abstract at ADS Title: The distant future of solar activity - A case study of Beta Hydri Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.; Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, A.; Simon, T.; Vandenberg, D.; Wallinder, F. Bibcode: 1990ESASP.310..323D Altcode: 1990eaia.conf..323D No abstract at ADS Title: STAR - A Scientific Toolkit for Astrophysical Research Authors: Mickus, K. D.; Domik, G. O.; Brugel, E. W.; Ayres, T. R. Bibcode: 1990BAAS...22..828M Altcode: No abstract at ADS Title: Thermal Bifurcation of the Outer Photosphere Authors: Ayres, T. R. Bibcode: 1990IAUS..138...23A Altcode: No abstract at ADS Title: Sleuthing the Dynamo II Authors: Ayres, Thomas R. Bibcode: 1990iue..prop.3641A Altcode: A key puzzle in modern astrophysics is the nature of the solar hydromagnetic dynamo: the direct cause of the 11-year sunspot cycle, and indirect source of the ebb and flow of chromospheric and coronal activity. New clues have come with the discovery of analogous long-term cycles on a number of other late-type dwarfs through systematic monitoring-surveys of Ca II K. However, the low-excitation Ca II emission does not form exclusively in areas disturbed by magnetic flux, and thus provides an incomplete proxy view of the dynamogenerated fields. In contrast, high-excitation vacuum-ultraviolet emissions - like Si IV 1400 and C IV 1550 - form entirely in the regions most strongly affected by concentrated magnetic flux (spots, plage, and network). The modulations of these emissions over a stellar cycle directly mirror the changing face of the dynamo. We believe that the development of a complete theory of the dynamo requires a comprehensive database concerning the superficial manifestations of activity cycles, Particularly critical are far-UV spectra from the cycle maxima and minima of representative near-solar stars. We have received time in previous episodes to collect far-UV spectra of a small sample of key stars for that purpose. In addition, we calibrated and measured 2,500 SWP-LOs of late-type stars from the Archives, and published preliminary emission histories for 10 stars. Since the IUE continues to function well, it would be a tragic scientific oversight not to continue systematic monitoring of at least a few late-type stars for as long as the satellite remains healthy. Owing to the long-term nature of the program, we are requesting two-year status for it. Title: The distant future of solar activity - a case study of Beta Hydri. Authors: Dravins, D.; Linde, P.; Ayres, T. R.; Fredga, K.; Gahm, G.; Lindegren, L.; Linsky, J. L.; Monsignori-Fossi, B.; Nordlund, Å.; Simon, T.; Vandenberg, D.; Wallinder, F. Bibcode: 1990apsu.conf...17D Altcode: No abstract at ADS Title: The Chilling Truth about the Solar Chromosphere Authors: Ayres, Thomas R. Bibcode: 1990ASPC....9..106A Altcode: 1990csss....6..106A The notion that much of the solar gas in the low chromosphere is cool is discussed in terms of its validity. The dark CO absorption cores recorded at the extreme limb of the sun are described, including the 3-2 R14 line with a core-brightness temperature of 3620 K. A bifurcation in the plasma energy balance described to explain the high altitude cold gas is reviewed in terms of recent investigations. Spectral simulations of CO are described which examine the range of thermal profiles allowed by CO observations with low spatial resolution and limb darkening. Weak emission shoulders in the K line demonstrate that a cool chromosphere with Ca II emission is feasible, although the cold gas requires a surface coverage of as little as 20 percent to reproduce the limb darkening. To distinguish between the thermal bifurcation notion and the neophotosphere concept, observations of the high spatial resolution spectra of the CO bands are required. Title: CO Fundamental Lines - Indicators for Inhomogeneous Atmospheres in Cool Stars Authors: Wiedemann, Guenter; Ayres, Thomas R. Bibcode: 1990ASPC....9..158W Altcode: 1990csss....6..158W Carbon monoxide fundamental lines near 4.7 microns are employed to probe the thermal structure of the atmospheres of cool stars. A new non-LTE radiation transfer code is used to analyze high-resolution infrared CO line spectra and derive observation-based stellar atmosphere models. The main results are: (1) the CO-based models developed here deviate strongly from previously published models based on UV/visible observations; (2) varying degrees of agreement between the CO empirical models and predictions based on theoretical radiative-equilibrium atmosphere models are found; and (3) the parameter used to quantify this agreement is anticorrelated with the magnitude of chromospheric activity in the observed stars. These results suggest thermally bifurcated upper atmospheres as the standard case for cool stars. Title: How deep can one see into the Sun? Authors: Ayres, Thomas R. Bibcode: 1989SoPh..124...15A Altcode: Conventional wisdom dictates that the 1.642 μm H− `opacity minimum' is the best window to the depths of the solar photosphere. However, the violet continuum near 0.4 μm exhibits a larger intensity response to small thermal perturbations at depth, and thus might offer an even better view of the subsurface roots of granulation cells and magnetic flux tubes. Title: Non--LTE CO Revisited Authors: Ayres, Thomas R.; Wiedemann, Gunter R. Bibcode: 1989ApJ...338.1033A Altcode: A more extensive and detailed non-LTE simulation of the Delta v = 1 bands of CO than attempted previously is reported. The equations of statistical equilibrium are formulated for a model molecule containing 10 bound vibrational levels, each split into 121 rotational substates and connected by more than 1000 radiative transitions. Solutions are obtained for self-consistent populations and radiation fields by iterative application of the 'Lambda-operator' to an initial LTE distribution. The formalism is used to illustrate models of the sun and Arcturus. For the sun, negligible departures from LTE are found in either a theoretical radiative-equilibrium photosphere with outwardly falling temperatures in its highest layers or in a semiempirical hot chromosphere that reproduces the spatially averaged emission cores of Ca II H and K. The simulations demonstrate that the puzzling 'cool cores' of the CO Delta V = 1 bands observed in limb spectra of the sun and in flux spectra of Arcturus cannot be explained simply by non-LTE scattering effects. Title: FTS observation of CO fundamental bands in cool stellar atmospheres. Authors: Wiedemann, G.; Ayres, T. R.; Jennings, D. E. Bibcode: 1989hrft.conf...23W Altcode: CO fundamental lines are important diagnostics for cool star upper atmospheres. High resolution FTS observations at 4.7 μm provide an independent way to study inhomogeneous chromospheres. Title: Cool-Star Betathon Authors: Ayres, Thomas R. Bibcode: 1989iue..prop.3362A Altcode: As the IUE becomes firmly entrenched in the second decade of its mission, it is time to move away from the dominant focus of the first decade: broad-brush surveys of as many objects as possible regardless of how weak the resulting spectra might be. Continuing to add an increasing number of increasingly-marginal detections to the Archives is not the way to achieve fundamental understanding of, for example, physical processes in the high-excitation (10^4- 10^6 K) outer atmospheres of magnetically-active F-M stars. While such survey work was absolutely vital in the early years of the IUE, its continuation must fall to the next generation of instruments. The HST will will be capable of recording 1-A-resolution far-UV spectra of latetype stars a thousand times fainter than the IUE limit. Since the IUE cannot compete with the HST in faint-object spectroscopy, a better future course for the IUE lies in doing what it does best: taking diagnostic-quality SWP-HI spectra (0.15 A resolution; 1150-2000 A) of bright stars. The SWP echellograms represent a unique scientific resource that will not be duplicated by the HST spectrographs (owing to the minimal free spectral range of the HRS). The SWP-HIs have proved to be essential in exploring the properties of magnetic activity among late-type stars, particularly concerning the dynarnics and energy balance of the 10' K subcoronal transition zone. Unfortunately, the existing database of images is rather spotty, with only a few stars represented by more than one deep exposure. In the spirit of our exploratory SWP-HI work in the first decade of the IUE, we propose to invest a significant amount of observing time - both NASA and ESA - to acquire additional long-duration exposures of key stars. We will conduct the observations using newly-developed strategies designed to significantly enhance the quality of the spectra compared with previous work. The stars that will most benefit from new deep SWPIlls are betaAqr (G0 Ib), beta Cet (K0 III), beta Dra (G2 Ib-IIa), beta Gem (K0 III), and alpha Boo (K1 III). Owing to the nature of the targets, and the long durations of the proposed exposures, we call our project the "BETATHON" (with apologies to Arcturus). Title: Sleuthing the Dynamo II Authors: Ayres, Thomas R. Bibcode: 1989iue..prop.3359A Altcode: A key puzzle in modern astrophysics is the nature of the solar hydromagnetic dynamo: the direct cause of the 11-year sunspot cycle, and indirect source of the ebb and flow of chromospheric and coronal activity. New clues have come with the discovery of analogous long-term cycles on a number of other late-type dwarfs through systematic monitoringsurveys of Ca II K. However, the low-excitation Ca II emission does not form exclusively in areas disturbed by magnetic flux, and thus provides an incomplete proxy view of the dynamogenerated fields. In contrast, high-excitation vacuum-ultraviolet emissions - like Si IV 1400 and C IV 1550 - form entirely in the regions most strongly affected by concentrated magnetic flux (spots, plage, and network). The modulations of these emissions over a stellar cycle directly mirror the changing face of the dynamo. We believe that the development of a complete theory of the dynamo requires a comprehensive database concerning the superficial manifestations of activity cycles. Particularly critical are far-UV spectra from the cycle maxima and minima of representative near-solar stars. We have received time in previous episodes to collect far-UV spectra of a small sample of key stars for that purpose. In addition, we calibrated and measured 2,500 SWP-LOs of late-type stars from the Archives, and published preliminary emission histories for 10 stars. Since the IUE continues to function well, it would be a tragic scientific oversight not to continue systematic monitoring of at least a few late-type stars for as long as the satellite remains healthy. Owing to the long-term nature of the program, we are requesting two-year status for it. Title: Sleuthing the Dynamo Authors: Ayres, Thomas R. Bibcode: 1989iue..prop.3358A Altcode: Long-term cycles of "activity", analogous to the 11-year sunspot cycle, have been discovered on a number of late-type dwarf stars through systematic groundbased surveys of the Ca II HK "S-index". The Ca II emission forms over a diverse range of chromospheric structures, and thus provides a broad view of the areas of the stellar surface disturbed by magnetic activity. In contrast, spectral signatures of activity in the vacuum ultraviolet - like Si IV 1400 and C IV 1550 - form exclusively in the high-excitation layers of the stellar outer atmosphere: the modulation of these emissions over a stellar cycle mirror the changing area of the regions most strongly affected by concentrated fields. Thus, comparisons between low-excitation, chromospheric diagnostics - like Ca II and high-excitation, transition-zone emissions - like Si IV and C IV - provide insight into the relative surface distributions of large scale plage and network compared with small-scale, concentrated active regions. We believe that the development of a complete theory of the stellar magnetic "dynamo" requires a comprehensive understanding of the surface distributions of magnetic regions throughout activity cycles. Thus, we propose to continue a program we began in the Ninth Episode to study the properties of far-UV spectra of representative late-type stars over their cycles. Our objective is not to measure the cycle periods, themselves; that is better done with Ca II photometry from the ground. Instead, we wish to record representative emission levels of each star throughout at least one complete cycle: our goal is to compare chromospheric and transition-zone emissions in flux-flux diagrams; in particular, the trajectory followed by a star over its cycle relative to the slope defined by the broad behavior of many stars of different mean activity levels. Differences in the slopes are signatures of 'nonlinear' behavior in the dynamo; important clues to confront theoretical models of dynamo action. Title: CO Fundamental Bands: Diagnostic for Inhomogeneities in Cool Stellar Atmospheres Authors: Wiedemann, G.; Ayres, T. R. Bibcode: 1988BAAS...20..998W Altcode: No abstract at ADS Title: Empirical Continuum Modeling for IUE Low-Dispersion Spectra Authors: Bennett, Jeffrey O.; Ayres, Thomas R. Bibcode: 1988PASP..100.1129B Altcode: The authors describe a numerical procedure for empirically determining a "continuum" level in low-dispersion spectra from the International Ultraviolet Explorer. They developed the technique for the automated fitting of SWP-LO (1150 Å - 2000 Å) spectra of stars of late spectral type, but it is more widely applicable. Title: A Spectral Dissection of the Ultraviolet Emissions of Capella Authors: Ayres, Thomas R. Bibcode: 1988ApJ...331..467A Altcode: Phase-resolved observations of Capella (α Aurigae A: G5 III+G0 III) were conducted with the IUE in order to separate the spectrum of the core-helium-burning (CHeB) primary (Aa) from that of the fast-rotating, chromospherically active secondary (Ab). The ultraviolet emissions of the primary were compared to those of the four K0 giants of the Hyades and the field K giants β Cet and β Gem. In terms of C IV emission, the six reference CHeB giants fall into two distinct groups: the more active β Cet type; and the less active β Gem type. Capella Aa clearly belongs in the β Cet group. The similarity between the Capella primary and the two active Hyads - γ Tauri and θ1 Tauri - is striking. If Capella truly is coeval with the Hyades nucleus, then the age of the cluster might be less than half that commonly assumed. The UV spectra of the Capella secondary show evidence of mass outflow in the upper chromosphere, although the flow very likely is part of a circulation system like that thought to operate in magnetic active regions on the Sun. Title: Ultraviolet emission lines and optical photometry of the flare star AT Microscopii. Authors: Elgaroy, O.; Joras, P.; Engvold, O.; Jensen, E.; Pettersen, B. R.; Ayres, T. R.; Ambruster, C.; Linsky, J. L.; Clark, M.; Kunkel, W.; Marang, F. Bibcode: 1988A&A...193..211E Altcode: Ultraviolet spectra of the dwarf flare star binary AT Mic (dM 4.5e+dM 4.5e) were obtained with the IUE spacecraft on three days in September 1985. A high-resolution short-wavelength spectrum was exposed for 25 hours. Simultaneous optical monitoring in the U-band was performed during part of the IUE observations. At the time of observation AT Mic was flaring at an average rate of 1.3 flares per hour. On the average 9% of the energy in the U-band was due to the detected flare activity. From the observed high resolution spectra, line wavelengths, widths and fluxes were derived, and the effects of the binary structure of AT Mic on the spectral lines were evaluated. The ultraviolet emission line spectrum is similar in character to that of flare regions on the Sun and other stars. Title: Far-ultraviolet and X-ray emission of the long period RS CVn star sigma Geminorum. Authors: Engvold, O.; Ayres, T. R.; Elgaroy, O.; Jensen, E.; Joras, P. B.; Kjeldseth-Moe, O.; Linsky, J. L.; Schnopper, H. W.; Westergaard, N. J. Bibcode: 1988A&A...192..234E Altcode: The new UV and X-ray observations of σ Gem support the theory that large active regions associated with starspots are responsible for the enhanced line emission commonly seen in RS CVn systems. The rotational modulation of the UV line fluxes increases with temperature of the line-forming region. The X-ray emission from the stellar corona, on the other hand, shows only a barely detectable variation with rotational phase. One may infer that the coronal active regions of the system are not co-spatial with the activity in the transition region below, and/or occupy a significantly larger surface area. An equally probable explanation, however, is that the X-ray emission is emitted from huge, stellar sized loops. Title: Redshifts of High Temperature Emission Lines in the Far-Ultraviolet Spectra of Late-Type Stars. II. New, Precise Measurements of Dwarfs and Giants Authors: Ayres, Thomas R.; Jensen, Eberhard; Engvold, Oddbjorn Bibcode: 1988ApJS...66...51A Altcode: Results are presented from an IUE SWP camera investigation of the occurrence of gasdynamic flows, analogous to the downdrafts of 10 to the 5th K material observed over magnetic active regions of the sun, among stars of late spectral type. The SWP calibration spectra study conducted documents the existence of local, small, persistent distortions of the echelle wavelength scales that are of unknown origin. Attention is given to the enormous widths of the stellar high-excitation emission lines in both the dwarfs and the giants, with respect to the comparatively small, subsonic Doppler shifts; the widths are typically an order of magnitude greater than the redshifts. Title: Doppler-Dissection of UX Arietis Authors: Ayres, Thomas R. Bibcode: 1988iue..prop.3041A Altcode: UX Arietis (K0 IV+G5 V) is a 6.4-day period RS CVn binary - near the peak of magnetic "activity" among stars of late spectral type - that recently was subjected to intense scrutiny with the IUE, including a very-deep (1265-min exposure) SWP-HI spectrum. We wish to continue our study of this hyperactive system by conducting a unique series of LWP-HI measurements of Mg II A2800 at ten phases near consecutive orbital velocity extrema. We intend to subject the spectra to "Doppler dissection", a powerful technique to extract information concerning spatial nonuniformities on the surfaces of rapidly-rotating stars from recurring distortions in chromospheric emission profiles. Our objective is to understand why the "hyperactive" chromospheres still exhibit substantial spatial irregularities, instead of being completely covered by intense, uniform magnetic plage as the solar analogy would suggest. We will approach this question by identifying the typical sizes and surface fluxes of chromospheric nonuniformities on UX Ari (in addition to other representative close binaries we have observed previously); and attempt to deduce, through numerical modelling, the physical properties and total heating rates of the enhanced regions. The derived physical quantities, in turn, can guide the development of theories of the heating processes and thermal-instability mechanisms that might lead to the natural formation of chromospheric inhomogeneities. In order to take advantage of specialized algorithms to filter camera defects from IUE spectrograms, we propose to acquire a graded sequence, of echellograms at independent locations on the LWP camera (by placing the target image at offcenter positions in the large aperture). The scheme not only extends the dynamic range and improves S/N, but it also mitigates the influence of any persistent artifacts of the vidicon images that are not eliminated in the nominal IUESIPS processing or by our spike- removal procedures. Title: Very-Deep SWP-HI of Aldebaran Authors: Ayres, Thomas R. Bibcode: 1988iue..prop.3039A Altcode: We propose to conduct the longest exposure ever attempted with the IUE (>25 hours) in order to obtain a high-quality recording of the far-ultraviolet (1150-2000 A) emission line spectrum of the bright red giant Aldebaran (alpha Tauri: K5 III), in high dispersion (0.15 A). Our objectives include: the study of fluorescent phenomena; the measurement of tracers of temperature and density in the possibly highly-inhomogeous chromosphere; and the search for faint emissions of high-excitation species, like Si IV and C IV, which are signatures of hotter gas (101 K) usually not found in the low-gravity, evolved stars. In addition, preceding and during the very long SWP exposure, we propose to monitor the chromosphere and wind of Aldebaran, with LWP echellograms exposed for the Mg II 2800 doublet. Our objective is to document possible short-term variability like that identified in optical studies of the redgiant Arcturus. Our proposal is intended to carry forward a program - to explore the ultraviolet spectra of stars of late spectral type - that we, and our collaborators at Oxford, have been conducting since the early years of the IUE. Title: The Debit Side of the Chromospheric Energy Budget Authors: Ayres, Thomas R. Bibcode: 1988iue..prop.3032A Altcode: The chromosphere is a thick, hot (< 10' K), nonradiatively heated layer of the stellar outer atmosphere, immediately above the photosphere, which is found in virtually all stars of late spectral type. Despite considerable observational and theoretical effort in the particularly favorable case of the Sun, the origin of the chromosphere - and its wealth of fine structure largely remains a mystery. Small-scale magnetic "flux tubes" are thought to play a significant role in imposing physical structure on the chromosphere, and the heating of the gas is believed to be associated with the deposition of wave energy - acoustic or various magnetic modes propagating up from the deep convection zone; however, there is considerably more speculation in the field than hard facts, despite literally decades of work (in the solar case, at least). A fundamental question in this regard is the relative importance of various atomic and ionic species in cooling the chromospheric gas. Not only is an understanding of the detailed constituents of the plasma cooling function important to theoretical modelling efforts, but also to observational efforts to measure the radiative losses of stellar chromospheres across the HR diagram: identification of the most important species, and their relative contributions, permits observers to concentrate on a few critical spectral intervals, and correct their measurements for the additional species that are not directly detected. The present proposal seeks to assess the relative importance of several species in the chromospheric energy budget by numerically comparing the vacuumultraviolet energy distributions of pairs of stars of similar spectral type and luminosity class, but widely different "activity" levels. The ultimate goal is to examine the gross properties of chromospheres as a function of fundamental stellar attributes like spectral type and luminosity class: by moving away from the perhaps too-familiar solar example, one might be able to develop new clues into the nature of the elusive chromospheric heating processes. Title: Short-Term Variability of Arcturus Authors: Ayres, Thomas R. Bibcode: 1988iue..prop.3036A Altcode: Arcturus is the nearest and brightest of the low-mass red giants; a paradigm of the "inactive" stars in the cool-half of the Hertzsprung-Russell diagram. Nevertheless, recent optical studies have reported unexpected periodicities in the global velocity of the red giant on timescales of hours to days: the envelope pulsations share some similarities with those of the RR Lyrae variables. Furthermore, the B-band polarization and the Ca II "S-index" exhibit erratic variability from day to day, as well as evidence for a 45-day periodicity. Finally, a time-series of the 4.7 micron bands of CO has suggested significant global changes in the coolest layers of the Arcturan chromosphere on timescales of hours. The recent variability studies have raised important questions concerning the structure and dynamics of the outer atmosphere of Arcturus, and their relationship to the mass-loss process. We, therefore, propose a program, in collaboration with our colleagues at Oxford, to study the short-term (hours to days) variability of important ultraviolet emission features that form in the chromosphere and wind of the archetype red giant. Title: The Age of the Hyades Authors: Ayres, Thomas R. Bibcode: 1988iue..prop.3038A Altcode: Based on recent evidence, it is very likely that Capella (alpha Aurigae: G6 III+F9 III) is the same age as the nucleus of the nearby Hyades open cluster. Further, the evolutionary status of the fast-rotating F9 secondary star is well-established (it is one of the rare "HertzsprungGap" giants, in a transient, magnetically-active phase of the first-crossing to the red giant branch). Thus, if one can measure the mass of Capella "F", the age of the Hyades follows directly. Unfortunately, previous attempts to record the diffuse, rotationally-broadened absorption lines of the secondary spectrum in the optical and near-IR have met with mixed success, presumably owing to the confusing influence of the rich, sharp-line spectrum of the cooler, more slowly-rotating primary. One study finds the secondary about 7% less massive than the primary; and the inferred age is nearly a factor of three less than commonly assumed for the Hyades based on the cluster turnoff method. If that mass estimate is correct - and Capella and the Hyades nucleus truly are coeval - then there is a curious, inexplicable deficit of early-A main-sequence stars in the cluster. A second study - based on extensive observations with a CORAVEL-type radial velocity spectrometer - finds that the secondary is less massive than the primary by almost 20%; an amount large enough to stretch the credence of existing models of stellar evolution. Therefore, I propose to apply a carefully-designed observing strategy to obtain the highest SIN, highest-wavelength-precision observations ever attempted with the IUE in order to: (1) establish, unambiguously, the radial velocity semiamplitude of the secondary of Capella - by observing in the 1800-2000 A region where the F9 photosphere is seen in its most favorable light; and (2) record the faint emissions of the far-UV spectra of the primary and secondary in order to study questions of gas-dynamics, line-broadening, and densitysensitive line ratios at the limits of the capabilities of the IUE. Title: The chromospheres and coronae of five G-K main-sequence stars. Authors: Jordan, C.; Ayres, T. R.; Brown, A.; Linsky, J. L.; Simon, T. Bibcode: 1987MNRAS.225..903J Altcode: Five main-sequence stars, χ1 Ori (G0 V), α Cen A (G2 V), ξ Boo A (G8 V), α Cen B (K0 V) and ɛ Eri (K2 V) have been observed at low and high dispersion with the International Ultraviolet Explorer (IUE) satellite. The data obtained and X-ray observations reported in the literature are used to make models of the structure of the atmospheres of these stars, from the high chromosphere to the corona. The electron pressures and coronal temperatures in these stars range from being similar to those in the quiet solar atmosphere (α Cen A) to the higher values found more typically in solar active regions (e.g. χ1 Ori, ξ Boo A). The models are used to examine the energy lost by radiation and transferred by thermal conduction, in order to establish the heating requirements. The results are similar to those found for the solar atmosphere. Title: A Deep, Doppler-Compensated IUE SWP Echellogram of the KO Primary of HR 1099 Authors: Bennett, J. O.; Ayres, T. R.; Jensen, E.; Engvold, O. Bibcode: 1987BAAS...19R.706B Altcode: 1987BAAS...19Z.706B No abstract at ADS Title: The Colorado Scale Model Solar System Authors: Bennett, J. O.; Ayres, T. R.; Center, K.; Bass, R.; Carter, M. Bibcode: 1987BAAS...19Q.750B Altcode: No abstract at ADS Title: Deep SWP-HI of Lux Arietis Authors: Ayres, Thomas R. Bibcode: 1987iue..prop.2725A Altcode: In the Ninth Episode of the IUE, I and my collaborators applied a novel observing technique to the 2.8-day RS CVn binary HR 1099 (KO IV+G5 V) the paradigm of magnetic activity among the nearby stars of late spectral type - to record high S/N profiles of a diverse range of chromospheric (6,000 K) and transition-zone (10^5 K) emissions. The program involved a 19.5-hour highdispersion exposure of the far-ultraviolet (1150-2000 A) spectrum in which the image of the target periodically was stepped in the large aperture to compensate for the changing orbital Doppler shifts of the active K0 primary. The success of the observation has encouraged us to attempt the same technique on another prototype RS CVn: the 6.4-day system UX Arietis (K0 IV+G5 V), which is very similar in its properties to HR 1099, aside from the longer orbital period (and hence slower synchronous rotational velocities). The major objectives of the program are to: search for evidence of gasdynamic flows in the high-excitation emissions like C IV 1548; measure the profiles of weak, but important, emissions like Si IV 1394 and O I 1305; evaluate the high-pressure limit of chromospheric density diagnostics like C II] 2325; and measure the relative "activity" of the G-type secondary star. A detailed comparison of the high-dispersion spectra of UX Ari and HR 1099 should reveal, through any differences, important properties of the magneticallydisturbed outer atmospheres of the "classical" RS CVn stars. Title: Further Studies of Beta Cassiopeiae Authors: Ayres, Thomas R. Bibcode: 1987iue..prop.2721A Altcode: In an exploratory IUE program two years ago, one of us (TRA) obtained an intriguing series of far-ultraviolet spectra of beta Cassiopeiae: the nearest and brightest of the delta Scuti variables. On the one hand, a sequence of low-dispersion spectra recorded an abrupt, factorof-two increase in the chromospheric Ly-alpha (1216 A) emission on a timescale comparable to the 2.4-hour pulsation period. This behavior favors a "pulsational" origin for the chromospheric heating as Schmidt and Parsons have suggested for the more luminous Cepheids. On the other hand, the C IV 1548 emission profile, though noisy, exhibits one of the largest velocity widths known among "normal" stars of late spectral type. The enhanced broadening, if due to the rapid rotation of the star, implies that the atmospheric structures which are bright in the C IV emission must reach to considerable heights above the limb of the star. This behavior is more compatible with a conventional magnetic origin for the high excitation emission. In the magnetic picture, the abrupt brightening of the Ly-alpha emission might be due to a stellar "flare", or to the rotation onto the visible hemisphere of a bright "activity center". The purpose of the present proposal is to collect additional low-dispersion SWP spectra, in conjunction with ground-based Stromgren photometry and high-precision radial-velocity spectroscopy, to monitor beta Cas on both rotational (few days) and pulsational (few hours) timescales. Our objective is to to distinguish among the possible chromospheric energization mechanisms at the important juncture in the H-R diagram represented by early-F stars like beta Cas. We also propose to take a deep high-dispersion SWP exposure to improve the profiles of the C IV features and reach down to weaker emissions like the Si IV doublet near 1400 A, in an effort to study gas-dynamic phenomena in the outer atmosphere of this intensely active delta Sct variable. Title: Far-ultraviolet observations of the Delti-Scuti variable Beta Cassiopeiae Authors: Ayres, Thomas R.; Bennett, Jeffrey O. Bibcode: 1987LNP...274..127A Altcode: 1987stpu.conf..127A FUV (115-200-nm) observations of Beta Cas, obtained at resolutions 5 and 0.15 A by the IUE during September 1984, are reported and analyzed. The data are presented graphically and compared with results for Procyon, a sharp-lined F star similar in temperature to Beta Cas. A sharp factor-of-two increase in H I Ly-alpha flux on a time scale comparable to its Delta Sct pulsation period was observed, but the data were insufficient to determine whether the increase was flarelike or pulsation-related. The outer edges of the Beta Cas emission are shown to be significantly wider than those of Procyon. Title: Carbon Monoxide Fundamental Bands in Late Type Stars Authors: Wiedemann, G.; Ayres, T.; Jennings, D.; Saar, S. Bibcode: 1987LNP...291..374W Altcode: 1987csss....5..374W; 1987LNP87.291..374W No abstract at ADS Title: High-Dispersion Observations of Alpha Bootis (K1 III) with the International Ultraviolet Explorer Authors: Ayres, T. R.; Judge, P.; Jordan, C.; Brown, A.; Linsky, J. L. Bibcode: 1986ApJ...311..947A Altcode: The authors have obtained very deeply exposed IUE echelle spectrograms of the bright, early-K giant Arcturus. They did not detect significant flux in the most prominent high-excitation species of a solar-like transition zone, C IV λ1548.2. The presence of a weak feature of Si III] λ1892.0, and possibly also Si IV λ1393.8, indicates the existence of a small amount of plasma at temperatures as hot as 6×104K. Measurements of C II] multiplet UV0.01 near 2325 Å provide a lower limit of about 5×109cm-3 for the electron density in the chromospheric layers. C II UV1 (1335 Å) emission is very weak. These results confirm that the "coronal" activity of the old red giants is considerably diminished from that of even the "quietest" of their main-sequence predecessors, stars like the Sun. Title: Exploration of the CO Fundamental Bands in Late Type Stars Authors: Wiedemann, G.; Ayres, T.; Jennings, D.; Saar, S. Bibcode: 1986BAAS...18..982W Altcode: No abstract at ADS Title: Far-Ultraviolet Fluorescence of Carbon Monoxide in the Red Giant Arcturus. II. Analysis of High-Dispersion IUE Spectra Authors: Ayres, T. R. Bibcode: 1986ApJ...308..246A Altcode: Faint, diffuse emissions near 1380 A in deeply exposed IUE spectrograms of the red giant Arcturus very likely are associated with bands of the A-X fourth-positive system of carbon monoxide, fluoresced by multiplet UV2 of neutral oxygen near 1305 A. Numerical simulations indicate that the strength of the CO bands is exceedingly sensitive, in the best available one-dimensional model of the chromosphere of Arcturus, to a delicate balance between the rapid inward attenuation of the oxygen radiation field and the rapid outward decline of the molecular absorptivity. The fortuitous character of the overlap region in the single-component model argues that one should also consider the possibility that the pumping occurs in a highly inhomogeneous chromosphere, of the type proposed in previous studies of Arcturus based on observations of the infrared absorption bands of CO. Title: UV and optical observations of AT Mic Authors: Ayres, T. R.; Elgaroy, O.; Joras, P. Bibcode: 1986ESASP.263...91A Altcode: 1986NIA86.......91A; 1986niia.conf...91A The red dwarf binary AT Mic was observed in 1985 by IUE in the UV and optical wavelength regions. In the U-band flares were observed at a rate of 1 per hour. In the UV region surface line fluxes are enhanced compared to those of the quiet Sun and show closer relation to values which are characteristic of very active regions on the Sun. Hot lines (C IV, Si IV) show larger broadening and negative frequency shifts whereas cooler lines (Fe II, Mg II) are less broadened and reveal small negative or positive line shifts. Improved radial velocity determinations of AT Mic are essential for the interpretation of the results. Title: Tz-Fornacis - an Eclipsing Capella-Like System Observed with IUE Authors: Eriksson, K.; Saxner, M.; Gustafsson, B.; Ayres, T. R.; Linsky, J. L.; Anderson, J. Bibcode: 1986ESASP.263..225E Altcode: 1986niia.conf..225E; 1986NIA86......225E The IUE observed TZ Fornacis at orbital phases 0.0, 0.25 and 0.79 in 1986. Most of the exposures were LWP-HI or SWP-LO. Results show that: the surface fluxes for transition region emission lines are similar to those for the Capella system while that of the Mg II emission is smaller; the total flux in the Mg II emission lines is constant with phase, whereas the flux in the C IV emission lines decreases by 1/3 during primary eclipse, indicating that most of the activity is due to the hotter giant (F7 III), which is also the case for Capella. Title: Fourier Transform Spectrometer Observations of Solar Carbon Monoxide. II. Simultaneous Cospatial Measurements of the Fundamental and First-Overtone Bands, and CA II K, in Quiet and Active Regions Authors: Ayres, T. R.; Testerman, L.; Brault, J. W. Bibcode: 1986ApJ...304..542A Altcode: Fourier transform spectrometry has yielded simultaneous cospatial measurements of important diagnostics of thermal structure in the high solar photosphere and low chromosphere. It is noted that the anomalous behavior of the fundamental bands of CO in quiet areas near the limb is accentuated in an active region plage observed close to the limb. The difference between the core temperatures of the CO fundamental bands in a plage and a nearby quiet region at the limb is larger than the corresponding brightness temperature differences in the inner wings of the Ca II line measured in a quiet region and several plages closer to the disk center. Numerical simulations indicate that the disparate behavior of the CO bands with respect to Ca II K cannot be reconciled with existing single component thermal structure models; a two-component atmosphere is required. Title: Ultraviolet, Optical, Infrared, and Microwave Observations of HR 5110 Authors: Little-Marenin, I. R.; Simon, Theodore; Ayres, T. R.; Cohen, N. L.; Feldman, P. A.; Linsky, J. L.; Little, S. J.; Lyons, R. Bibcode: 1986ApJ...303..780L Altcode: HR 5110 is a close binary system (P = 2d.6) with the characteristics of an Algol system. Because the primary star is relatively cool (F2 IV) and there is no apparent emission from an accretion disk, the authors were able to detect in IUE spectra the emission of an active chromosphere and transition region of the cooler (K0 IV) secondary. The surface fluxes of the UV emission lines of the K star are similar to those of active RS CVn binaries. The line fluxes appear to vary with orbital phase and are interpreted as emission from an active region on the K star. Two large radio flares were detected. VLBI observations during one of these flares indicated that half the emission came from a region more than 4 times the binary separation. Title: A Deep, Doppler-Compensated, SWP Echellogram of HR 1099 Authors: Ayres, Thomas R. Bibcode: 1986iue..prop.2399A Altcode: I, and my ESA collaborators, propose to apply a novel observing technique to the classical shortperiod (2.8 d) RS CVn binary HR 1099 (K0 IV + G5 V) - the paradigm of magnetic activity among the nearby stars of late spectral type. The program involves a long-duration exposure (25 hours or more) of the far-ultraviolet (1150-2000 A) spectrum in high dispersion (0.15 A resolution) in which the image of the target is periodically stepped in the large aperture along the dispersion axis in order to compensate for the orbital Doppler shifts of the K0 primary, which largely by virtue of its size completely dominates the ultraviolet emission of the system. We also propose to obtain very high-quality maps of the middle-ultraviolet (2000-3200 A) spectrum using graded sequences of LWP exposures obtained at nonstandard positions in the large aperture, and combined by means of a filtering technique that largely eliminates defects like reseau marks and cosmic-ray hits. The major objectives of the program are to: Search for persistent redshifts of the high-excitation (105 K) emissions, above the smoothed background of "Doppler-imaged" surface structure; identify weak blends near important diagnostic lines, which otherwise might be misconstrued as Dopplerimaged features; measure the profiles of weak, but important, emissions like the N V doublet (1240 A), 0 V] (1218 A), and the O I triplet near 1305 A; attempt to detect coronal forbidden lines like [Fe XII]; and evaluate the high-pressure limit of chromospheric density diagnostics like C II] (2325 A). The observations of HR 1099 also will be valuable for long-term monitoring programs and efforts to construct a high-dispersion atlas of late type stars. Title: Activity on Both Components of HR 1099 Authors: Bennett, J. O.; Ayres, T. R. Bibcode: 1986LNP...254...37B Altcode: 1986csss....4...37B No abstract at ADS Title: An IUE High-Dispersion Cool-Star Atlas Authors: Ayres, T. R.; Brugel, E. W.; Linskyl, J. L.; Brown, A.; Carpenter, K. G. Bibcode: 1986LNP...254..106A Altcode: 1986csss....4..106A We are planning to compile a spectral atlas based on high-dispersion images of representative late-type stars recorded by the International Ultraviolet Explorer. We solicit advice from the ultraviolet community concerning how best to present the spectral material. Title: The dichotomy between co absorptions and CA II emissions in the sun and stars: an indirect diagnostic for gas disturbed by magnetic fields?1 Authors: Ayres, T. Bibcode: 1986LNP...254..336A Altcode: 1986csss....4..336A Spectra of the 4.7 um bands of carbon monoxide in absorption, and spectra of the cores of the 0.4 um resonance lines of ionized calcium in emission, might be used to diagnose the presence of atmospheric inhomogeneities, caused by the action of surface magnetic fields, on stars as diverse as the Sun and the red giant Arcturus. Title: The dichotomy between CO absorption and CA II emissions in the sun and stars - an indirect diagnostic for gas disturbed by magnetic fields? Authors: Ayres, T. Bibcode: 1986HiA.....7..425A Altcode: It has been found that the cores of the strongest of the CO transitions in the solar disk do not exhibit limb-brightening, but continue to darken toward the limb. The results of research are reviewed which show that, to the extent that the hot regions of the solar atmosphere are manifestations of magnetic 'activity' and the cool zones represent the undisturbed state of the gas, simultaneous cospatial measurements of the 4.7 micron absorption bands of CO and 0.4 micron emission cores of the H and K lines of Ca(+) can be used to diagnose indirectly the presence and scale of such activity on the solar surface. The finding of a similar dichotomy between the absorptions of the fundamental CO bands in the red giant Arcturus and chromospheric models based on the prominent emission reversals of the Ca II lines is also discussed. Title: Long-Term Cycles in the Magnetic Active Regions of Cool Stars Authors: Ayres, Thomas R. Bibcode: 1986iue..prop.2398A Altcode: Long-term activity cycles, believed to be analogous to the 11 year solar cycle, have been discovered on numerous late-type stars through ground-based Ca II observations. The most valuable activity diagnostics, however, are emission features found in the ultraviolet: UV emission features available in IUE spectra are formed over a wide range of physical conditions in the active layers of stellar atmospheres, and are free of the photospheric contamination suffered by Ca II. We therefore propose to search for and study stellar activity cycles using data collected by the IUE. We have chosen a set of program stars which are well-represented in the Archives, and propose a multiyear program of continued monitoring of these stars. We believe that the development of a complete theory of stellar activity will ultimately require the compilation of a large data base concerning empirical properties of activity cycles. Our proposed program will provide the first extensive, ultraviolet data set of this type. The key to the success of our project will be to analyze all data in a systematic and consistent fashion. We therefore intend to reprocess relevant Archive images using the latest calibrations and ITFs, and to measure line fluxes in all new and existing images using automated software in order to ensure homogeneity of the data analysis procedures. Title: Progress Report: Precise Measurements of Radial Velocities of Far-Ultraviolet Emission Lines in Stars of Late Spectral Type Authors: Ayres, T.; Engvold, O.; Jensen, E.; Linsky, J. Bibcode: 1986LNP...254...94A Altcode: 1986csss....4...94A Recent high-dispersion, far-ultraviolet IUE spectra of the G-type supergiant β Draconis contain evidence for organized, persistent downflows of gas, apparently confined to a high-density component of the stellar transition zone. Title: Hydrogen Lyman Alpha Fluxes for Late-Type Dwarf Stars Authors: Neff, J. E.; Carpenter, K. G.; Ayres, T. R. Bibcode: 1985BAAS...17..879N Altcode: No abstract at ADS Title: A physically realistic approximate form for the redistribution function R(II-A) Authors: Ayres, T. R. Bibcode: 1985ApJ...294..153A Altcode: An approximation is proposed to the redistribution function R(II-A) (coherent, isotropic scattering in the rest frame of the atom) which is fast to compute and attains much higher accuracy than previous approximations for the astrophysically important case of small Voigt parameters. Further, the new approximation permits the diffusion in frequency of wing photons ('Doppler drifting') which is lost in one of the widely-used versions of the R(II-A) approximation schemes: Kneer's normalization of the Jefferies-White formulation. Title: Alpha Trianguli Australis (K2 II-III) : hybrid or composite ? Authors: Ayres, T. R. Bibcode: 1985ApJ...291L...7A Altcode: The prototype "hybrid-spectrum" giant, α Trianguli Australis, exhibits a far-ultraviolet continuum which is considerably bluer than would be expected of a star of its optical colors, suggesting the presence of a previously unrecognized companion. If the K type primary is as luminous as indicated by the widths of its Ca II and Hα lines, the companion could be an early F type dwarf that only recently has arrived on the main sequence. Indeed, the flux of C IV from α TrA - an important measure of "hybridness" - would not be inconsistent with that expected from a very young, chromospherically active F star. Title: Cool plasma at the base of the solar chromosphere revealed by infrared bands of carbon monoxide. Authors: Ayres, T. R. Bibcode: 1985cdm..proc..259A Altcode: The author describes empirical evidence - cool cores in strong, middle-infrared carbon monoxide (CO) lines - for the existence of low-temperature plasma (T < 4000K) at the levels of the solar outer atmosphere where conventional models place the chromosphere proper (T ≈ 6000K). He also reports recent observational and interpretative studies of CO, and Ca II K, in magnetic active regions which further support the hypothesis of a highly inhomogeneous, thermally "bifurcated" chromosphere. Title: A Deep SWP Echelle Exposure of a Red Dwarf Flare Star: At Microscopii Authors: Ayres, Thomas R. Bibcode: 1985iue..prop.2101A Altcode: Among the late-type stars that exhibit prominent chromospheric and coronal activity, the H-alpha emission-line red dwarfs (dMe) fall at the extreme high end of Xray and C IV intensity levels. The extraordinary emission strengths of the dMe stars almost certainly are related to high rates of magnetic field production by the "dynamo" mechanism owing to the extensive convective zones of the low-mass, main-sequence stars. Despite the large intrinsic surface fluxes of the dMe stars in high-excitation emissions like C IV, the observed fluxes at Earth are too small for these objects to be studied with the high dispersion mode of IUE, at least using conventional observing strategies. Nevertheless, high-dispersion observations of other late-type single stars and binary systems have provided a wealth of information concerning the physical conditions and dynamics of the important "transition zone" between the lowexcitation chromospheric layers and the overlying, multimillion degree corona. We therefore propose an IUE observing program to attempt high-dispersion, far-ultraviolet spectroscopy of a prototype flare-star binary, AT Mic AR (dM4.5e + dM4.5e), using a novel observing strategy. The goals of our program are threefold: - To measure at high dispersion the line profiles of prominent emissions in the far-ultraviolet spectrum of the main-sequence, M-type flare star AT Mic B inside and outside of flares. - To separately determine the emission levels of the two nearly identical components of the AT Mic binary. - Test whether a novel observing technique can extend IUE exposures to as long as 30 hours. Our program is designed to push IUE to its observational limits, and, if successful, will pave the way for much deeper IUE exposures than heretofore have been considered practical. Furthermore, the program will provide high quality UV line profile information for the latest-type main-sequence star(s) that are accessible to the IUE in high dispersion, and will thereby fill an important gap in the existing data base of echelle observations of cool stars. Title: A Far-Ultraviolet Echelle Survey of Young F Stars in the URSa Major Cluster Authors: Ayres, Thomas R. Bibcode: 1985iue..prop.2099A Altcode: Late-type stars nearly universally exhibit the spectroscopic symptoms of solarlike chromospheric and coronal activity, while the early-type stars are decidedly non-solar in their outer atmospheric properties. The boundary between the solar-like and non-solar behavior occurs among the F-type stars, where shallow convective envelopes first develop. Within this critical boundary, the very young, fast-rotating F-type stars are an important sub-class of their own: It is among the fast rotating late-type stars that the most intense chromospheric and coronal phenomena are observed, presumably related to extremes of magnetic dynamo action. It is our intent, therefore, to carry previous high-dispersion, farultraviolet studies of late-type stars to the important sub-class represented by the very young F-types. The region of the stellar outer atmosphere that is perhaps most sensitive to the transition from non-solar to solar-like behavior is the chromosphere-corona 'transition zone' (TZ), with characteristic temperatures between 2XJ04 and a few x lO^5 K. High-dispersion observations of TZ lines in the far-UV spectra of active G and K stars have revealed the existence of important dynamical phenomena--systematic downflows and supersonic 'turbulence'-as well as providing detailed information concerning TZ densities. However, even the brightest of the young F stars (which are in the nearby Ursa Major Cluster and Stream) are too faint to observe with high S/N at the most prominent TZ emission -- C IV 1548 -- in high dispersion. Therefore, we will focus our attention on the longwavelength end of the farultraviolet spectrum: The SWP camera is most sensitive near 1900A, and the region contains important emissions of Si III] and C III], as well as Si II at somewhat shorter wavelengths, all of which are superimposed on a bright photospheric continuum. Title: How Steady are the Far-Ultraviolet Emissions of the F Stars? Authors: Ayres, Thomas R. Bibcode: 1985iue..prop.2100A Altcode: A detailed monitoring of the ultraviolet spectrum of the active F-type giant of Capella ( alpha Aur A: G6 III + F9 III) over the course of two months in the Spring of 1981 revealed that fluctuations in the high-excitation emissions like C IV 1548 were remarkably small, in fact below the sensitivity limit of the IUE echelle images taken during the program. The steadiness of the C IV flux of Capella was quite surprising, given the rather dramatic variations of highexcitation emissions seen in other stars of comparable C IV and X-ray intensity levels, particularly the cool K0 subgiants of the RS CVn-type binaries. Recently, M. Giampapa and R. Rosner have argued that the F-stars should he comparatively steady in their chromospheric and coronal emissions compared with the cooler late-type stars, because the shallow convective envelopes of the Ftypes are not conducive to the development of large, spatially-coherent structures of the internal magnetic field. It is the eruption of the subsurface fields into large, organized, long-lived active regions which is thought to be responsible for the substantial "rotational modulations" of the ultraviolet emissions of the cooler stars. If the Giampapa-Rosner mechanism is correct, then steady far-ultraviolet emissions should be a trade-mark of the F-stars. I propose to test that hypothesis by a very sensitive monitoring of the C IV emission of three prototype F-stars: Procyon (F5 IV-V), the secondary of Capella (F9 III), and a Cassiopeia (F2 IV). Title: A Critical Test of the SWP Wavelenght Scale Authors: Ayres, Thomas R. Bibcode: 1985iue..prop.2102A Altcode: Calibrations using the onboard platinum hollow-cathode lamps of the IUE provide a high degree of internal consistency in the derived wavelengths of SWP echelle images. However, it has been recognized recently that SWP images suffer small, stable wavelength distortions on spatial scales comparable to, or larger than, the size of the calibration 'spots'. Although the distortions are small enough that routine observations are not appreciably affected, there are several programs involving high-precision measurements of late-type chromospheric emission-line stars where the presence of the wavelength distortions might seriously compromise the scientific objectives. I propose, therefore, to undertake a detailed study of small-scale wavelength distortions in SWP echelle-mode images. The study will consist of two parallel parts: - A detailed analysis of existing images of the onboard calibration lamp based on very recent laboratory measurements of the lamp spectrum. The new measurements increase by a factor of about three the number of emission spots in the calibration images for which reliable laboratory wavelengths are available. Accordingly, the spatial extents of the wavelength distortions can be mapped significantly more accurately than previously. - A critical empirical test of the fidelity of the IUE wavelength scales for a typical chromospheric emission-line star based on observations of the target at different locations in the large aperture. By positioning the target at one end of the large aperture, parallel to the dispersion direction, one should obtain the same wavelength scale as for an aperture-center observation, aside from the easily calculated shift owing to the physical translation of the 'image'. Any differences between relative line positions in apertureedge and aperture-center observations therefore should reveal the extent of the wavelength distortions. The chromospheric emission-line stars are important for such a test because their high-excitation, far-ultraviolet emission lines are much broader than the calibration lines, but are narrow enough that comparatively subtle dynamical phenomena--like the 10-20 km s^-1 redshifts of the C IV and Si IV doublets of Capella--can be measured at a significant level. Therefore, the broad lines of the stellar sources might respond differently to the wavelength distortions than the narrow lines of the calibration lamps: Gauging of the magnitude of the effect is critically important to the study of the dynamics of high-excitation plasma in the outer atmospheres of late-type stars. Title: Summary report for working group on line synthesis and atmospheric modeling. Authors: Ayres, T. R. Bibcode: 1985cdm..proc....3A Altcode: Obstacles encountered in the fields of atmospheric modeling and line synthesis are discussed with attention focused on the following: (1) velocity fields, (2) thermal inhomogeneities, (3) geometry, and (4) finite computing resources. It is noted that in some cases, such as global P-mode oscillations, the velocity fields are indicative of fundamental solar properties; in others, such as turbulence in the upper chromosphere and lower transition zone, these fields signify the operation of energy transport and dissipation mechanisms. With regard to geometry, particular emphasis is placed on the vertical spreading of magnetic flux tubes. It is concluded that in order to solve the current problems in this field, high-quality ultraviolet, optical and infrared observations of the sun from space must be obtained. Title: The solar stellar connection in the far ultraviolet. Authors: Bennett, J. O.; Ayres, T. R.; Rottman, G. J. Bibcode: 1984NASCP2349..437B Altcode: 1984IUE84......437B; 1984fiue.rept..437B The authors compare the far-ultraviolet "activity" of solar-type stars, as measured with the IUE, to that of the Sun, as measured by the Solar Irradiance Monitor of the Solar Mesosphere Explorer. The goal of the study is to explore the relationships between the "ultraviolet activity" at different levels of the atmospheres of solar type stars. Secondary goals are to establish the strength of the solar ultraviolet activity within the class of solar-type stars, and to examine the amplitudes of rotational modulations of the solar emission lines during the declining portion of the current sunspot cycle. A unique aspect of the study is that the spectral resolution of the SME instrument (7.5 Å) compares very favorably with that of the low dispersion model of the IUE (5 Å). Title: Three short-period binaries seen at high-dispersion: UX Ari, Iota Triand HR 5110. Authors: Little-Marenin, I. R.; Ayres, T. R.; Simon, T. Bibcode: 1984NASCP2349..404L Altcode: 1984IUE84......404L; 1984fiue.rept..404L The three short-period binary systems UX Ari (P=6.43791 days), iota Tri (P=14.732 days) and RH5110 (P=2.61328 days) represent three different evolutionary stages: (1) an evolved subgiant primary with a secondary still on the main sequence (UX Ari); (2) two evolved G giants that appear to be crossing the Hertzsprung gap for the first time together (iota Tri); and (3) an evolved subgiant that fills its Roche lobe and has lost mass to the secondary to the point where the original secondary is now about 3.5 times as massive as its evolved KOIV companion (HR5110). All three systems show strong UV emission lines indicative of plasmas ranging in temperature from 6000K to 20,000K. X-ray emission was detected from UX Ari and HR5110 indicating hot coronae. The chromospheric, transition region and coronal activity appears to be related primarily to the rotational velocity of the stars (but also to other parameters such as the depth of the convection zone). High-dispersion short-wavelength as well as long-wavelength IUE spectra of all three systems were analyzed. Title: A progress report on the analysis of long exposure SWP high resolution spectra of cool stars. Authors: Linsky, J. L.; Ayres, T. R.; Brown, A.; Carpenter, K.; Jordan, C.; Judge, P.; Gustafsson, B.; Eriksson, K.; Saxner, M.; Engvold, O.; Jensen, E.; Moe, O. K.; Simon, T. Bibcode: 1984NASCP2349..445L Altcode: 1984fiue.rept..445L; 1984IUE84......445L The IUE is the first experiment with sufficient sensitivity to obtain high resolution spectra (lambda/delta lambda is approximately 10,000) of many cool stars in the vitally important 1200 to 2000 A spectral region. These data provide qualitatively new information with which to understand the properties of and structures in the outer atmospheres of these stars. Also, these cool star spectra will be extremely useful in planning for the Space Telescope High Resolution Spectrograph, which will be 1000 times more sensitive than IUE but will be hampered by limited observing time and limited spectral bandwidth in each exposure. Very long exposure, high disperson SWP spectra of many stars located throughout the cool half of the HR diagram were obtained. These 12 to 21 hour exposures were obtained by combining NASA and Vilspa shifts so as to obtain the longest possible exposures at times of low background. Included are dwarf stars of spectral type G0 V to M2 V, G9.5 III to M5 II giants, G2 Ib to M2 Iab supergiants, a number of RS CVn-type systems, and Barium stars. Title: Precise measurements of radial velocities of emission lines in the far-ultraviolet spectra of late-type stars. Authors: Ayres, T. R.; Engvold, O.; Moe, D. K.; Simon, T.; Jordan, C.; Judge, P.; Brown, A.; Linsky, J. L. Bibcode: 1984NASCP2349..468A Altcode: 1984fiue.rept..468A; 1984IUE84......468A The radial velocities of emission lines in deep short wave prime camera echelle exposures of several late-type dwarf and giant stars were measured. The goal was to search for absolute and differential Doppler shifts of emission lines formed at different temperatures in the stellar outer atmospheres analogous to the redshifts of C IV lambda 1548 (10 to the 5th power K) which occur in the solar transition zone. Existing images, taken without the precise radial velocity precautions, of five dwarf stars, four giant stars, and three supergiants are reanalyzed. Title: Calibrations of wavelengths in SWP echelle spectra Authors: Delapana, M. D.; Ayres, T. R. Bibcode: 1984NASCP2349..521D Altcode: 1984fiue.rept..521D Sources of random and systematic errors in the echelle wavelength scales that must be minimized in order to obtain high quality radial velocity measurements of emission lines in the far UV with IUE are reviewed. The problem of overexposure of the strongest Pt II emission lines at the long wavelength end of the spectrum and the faintness of the remaining Pt II emission features is also examined. Wavelength calibration spectra from IUE archives were analyzed using an interactive procedure incorporating a least squares Gaussian fitting algorithm. The standard deviation of the PHCAL wavecals (+/- 1.1 km/sec using 1982 data only) is less than was found for the 6 wavecals (+/- 3.1 km/sec) obtained on consecutive days in December of 1982 in a previous study nearly contemporaneous wavecals to register velocity scales of stellar high dispersion observations. The standard deviation of the mean residuals of the orders averaged over 1982 is 2.2 km/sec, which can be interpreted as the internal consistency of the IUE SW wavelength scales. Title: IUE Observations of the RS CVn Binary - TZ Tri Authors: Little-Marenin, I. R.; Ayres, T. R.; Young, A. Bibcode: 1984BAAS...16..912L Altcode: 1984BAAS...16S.912L No abstract at ADS Title: New Insights into the Solar-Stellar Connection Authors: Ayres, T. R. Bibcode: 1984BAAS...16.1011A Altcode: No abstract at ADS Title: The many faces of Capella : a search for rotational modulations and astudy of systematic velocities of emission lines in the ultraviolet. Authors: Ayres, T. R. Bibcode: 1984ApJ...284..784A Altcode: The ultraviolet emission of the spectroscopic binary Capella has been monitored with IUE over the course of half an orbital cycle (2 months). The first objective was to detect changes in the fluxes or shapes of ultraviolet emission lines in response to the evolution of large-scale active regions or their rotation onto and off the visible hemisphere of the active F-type secondary star. Capella proved to be surprisingly steady in its ultraviolet emissions. The second objective was to investigate systematic velocities of the low-excitation and high-excitation emission lines. It is found that the latter are significantly redshifted with respect to the former. The author concludes that the redshifts indicate true downflows of 105K plasma in the stellar "transition zone", rather than the operation of a "P Cygni" effect in an optically thick outflow. Title: The Many Faces of HR 1099 Authors: Ayres, T. R.; Bennett, J. O.; Linsky, J. L.; Simon, T. Bibcode: 1984BAAS...16..893A Altcode: No abstract at ADS Title: High-resolution, far-ultraviolet study of beta Draconis (G2 Ib-II) : transition region structure and energy balance. Authors: Brown, A.; Jordan, C.; Stencel, R. E.; Linsky, J. L.; Ayres, T. R. Bibcode: 1984ApJ...283..731B Altcode: High-resolution far ultraviolet spectra of the star Beta Draconis have been obtained with the IUE satellite. The observations and emission line data from the spectra are presented, the interpretation of the emission line widths and shifts is discussed, and the implications are given in terms of atmospheric properties. The emission measure distribution is derived, and density diagnostics involving both line ratios and line opacity arguments is investigated. The methods for calculating spherically symmetric models of the atmospheric structure are outlined, and several such models are presented. The extension of these models to log T(e) greater than 5.3 using the observed X-ray flux is addressed, the energy balance of an 'optimum' model is investigated, and possible models of energy transport and deposition are discussed. Title: A Far-Ultraviolet Study of the Bright Delta Scuti Variable Beta Cassiopeia Authors: Ayres, Thomas R. Bibcode: 1984iue..prop.1747A Altcode: Beta Cassiopeiae is a fast rotating early-F subgiant that exhibits smallamplitude pulsations in optical light and radial velocity of the delta Scuti class, and is a bright far-ultraviolet emission-line source having surface fluxes in excess of thirty times those of the quiet Sun. It is plausible that the fast rotation of a Cas, and the recent development of a shallow convection zone as the star has evolved into the blue edge of the Hertzsprung gap, have conspired to produce substantial amounts of surface magnetic activity by means of the dynamo mechanism. The strong chromospheric and higher temperature emissions might then arise from processes analogous to those operating in magnetic "active regions" on the Sun. However, it certainly also is possible that the strong ultraviolet emissions are a byproduct of the delta Sct phenomenon, itself, as in fact has been suggested recently in the case of the Cepheids, which are similar in temperature but more luminous than the delta Scuti stars. Accordingly, I feel that beta Cas is a worthwhile subject for a detailed study with IUE in order to investigate the properties of its chromospheric and higher -temperature emission lines: High-dispersion, far-ultraviolet measurements of beta Cas would extend previous studies of F-M dwarfs, giants, and supergiants into the earliest spectral types where solar-like chromospheric phenomena have been identified; and IUE is sufficiently sensitive to test the hypothesis of pulsationinduced chromospheric heating, through monitoring of the lowdispersion SWP spectrum of beta Cas over several of the 2^h.4 cycles for evidence of periodic behavior in the far-ultraviolet emissions. Title: Wind or Antiwinds Authors: Ayres, Thomas R. Bibcode: 1984iue..prop.1752A Altcode: One of the surprising discoveries by IUE is that of redshifted emission lines of Si IV and C IV in the farultraviolet spectra of several late-type giants and supergiants. In the solar atmosphere, redshifts of high excitation emissions frequently are observed over magnetic active regions, and are thought to be associated with downflows of 10^5 K plasma in magnetic filaments. Nevertheless, the giants and supergiants that exhibit redshifted Si IV and C IV emissions differ substantially from dwarf stars like the Sun in terms of their fundamental stellar properties. It is possible, therefore, that the redshifts of the giants and supergiants have an entirely different origin than suggested by the solar analogy. For example, the appearance of a redshifted emission profile could result from an expanding, optically thick wind owing to the "P-Cygni" mechanism. We propose to continue, in the 7th year of IUE, the exploration of redshifts of high excitation emissions by addressing the question of whether the phenomenon in the supergiants is produced by an outflow of optically thick plasma (a "wind") or by a downflow of material (an "antiwind"). The test requires observations, using a precise radial velocity technique, of the intersystem lines of Si III (1892) and C III (1909) in the spectrum of the most luminous star, beta Draconis (G2 Ib-II), for which redshifts have been detected previously. In particular, the intersystem lines are optically thin, and therefore cannot exhibit a P-Cygni effect, whereas the Si IV and C IV doublets might be optically thick and therefore susceptible to the P-Cygni phenomenon. Furthermore, owing to different sensitivities to density, the C III] emission will be more heavily weighted towards a low-density, extended wind, while the Si III] emission will tend to be formed in the higher density structures from which the permitted lines of Si IV and C IV arise. Accordingly, the absolute velocity of Si III] 1892, and the difference in the velocities of 1892 and C III] 1909, can be used to test the wind and antiwind hypotheses. The highest precision in the measurement of the velocity differences can be achieved by taking a minimum of four separate spectra of the 1900A region of Beta Dra. The optimum exposures of the 1900 A region of Beta Ori are 7 hours, but the precise measurement of radial velocities requires that the satellite be thermally stable prior to the observations. The necessary stability can be attained, and maintained, only by coordinating US2, Vilspa, and US1 shifts on consecutive days. An important practical byproduct of the requirement for thermal stability is the opportunity to take Intensity Transfer Function calibrations in the LWR or LWP cameras during the long SWP exposures. Title: Ultraviolet Observations of the Limb-Crossing of an Active Region on Sigma Geminorum Authors: Ayres, Thomas R. Bibcode: 1984iue..prop.1755A Altcode: We propose to study, at high dispersion, the behavior of the ultraviolet emission line spectrum of the RS CVn-type binary Sigma Geminorum (KI III + ?) as an optically identified starspot group rotates over the limb of the K giant and onto the visible hemisphere. The scientific goal is to distinguish between the two most promising hypotheses to explain the significant changes that were observed in a pair of IUE SWP echelle images of Sigma Gem taken over consecutive days in May 1982: (1) a flare which occurred near the receding limb of the giant (or near disk center but accompanied by significant downflows of 10^5 K material); or (2) the rotation off of the visible hemisphere of a small-scale, but bright, active region associated with a previously identified optical starspot group. We feel that the behavior of similar systems, like II Peg, favors the second hypothesis. If so, a mechanism must operate in the cool, fast rotating giants to produce a significant spatial concentration of the decaying magnetic fields that are thought to be responsible for the enormously enhanced far-ultraviolet emissions of the RS CVn-type binaries. We believe that it is essential to understand why the "activity" on the cool giants can become so concentrated and intense. An important way to explore in detail the physical association of high excitation active regions with photospheric starspot groups is to use the technique of "Doppler, Imaging", developed by Vogt and collaborators to study the changing profiles of absorption features in the spectra of fast rotating late-type stars. We have applied the emission-line analog of the approach previously to the shortperiod RS CVn system, HR 1099, and propose to continue our work in the 7th-year of IUE with a study of Sigma Gem. In addition, we intend to search for the occurrence of flare activity in Si IV and C IV by monitoring the farultraviolet spectrum of a Gem at low dispersion. As a novel twist to the program, we intend to arrange simultaneous coverage with the Very Large Array to explore the association of the microwave corona of a Gem with the farultraviolet emission regions and optical starspots. [Note: this program could be easily integrated into an ITF recalibration effort for the LWP, LWR and SWP cameras: The optimum observing window is in late February or early March, before Spring shadow season.] Title: Sigma Geminorum (K1 III + ?) : variability of the ultraviolet emission lines near conjunction. Authors: Ayres, T. R.; Simon, T.; Linsky, J. L. Bibcode: 1984ApJ...279..197A Altcode: Far-ultraviolet IUE echelle spectra are reported of the moderate-period RS CVn system σ Geminorum. Despite the location of the red giant primary of σ Gem in a portion of the H-R diagram where cool stellar winds are common, no evidence is found for circumstellar absorption features or blueward asymmetries in the chromospheric O I emission cores. However, observations on two consecutive days indicate significant changes in the profiles of high-excitation species, such as Si IV and C IV which probably were produced by the rotation off of the visible hemisphere of the primary of a large-scale magnetic active region identified in a previous photometric study. Title: Observing the Sun as a Star; Observing Stars as Suns Authors: Ayres, T. R. Bibcode: 1984stp..conf....1A Altcode: No abstract at ADS Title: Capella HL Authors: Ayres, Thomas R. Bibcode: 1984LNP...193..202A Altcode: 1984csss....3..202A No abstract at ADS Title: Outer atmospheres of cool stars. XV. High-dispersion ultraviolet studies of active chromospheric G-K dwarfs. Authors: Ayres, T. R.; Linsky, J. L.; Simon, T.; Jordan, C.; Brown, A. Bibcode: 1983ApJ...274..784A Altcode: The authors have obtained IUE ultraviolet echelle spectra of the three late-type active-chromosphere dwarf stars χ1 Ori, ξ Boo A and ɛ Eri. These are compared with previously published observations of the quiet chromosphere dwarfs α Cen A and α Cen B. The spectra indicate a gross strengthening of chromospheric and transition-region line fluxes from quiet to active dwarf stars without a fundamental change in the line shapes. Qualitatively the same spectroscopic behavior is seen in detail on the solar surface between regions of strong and weak magnetic fields. They believe that the correspondence between the stellar and solar behavior is not accidental, but instead affirms that enhanced chromospheric and coronal emission on late-type main sequence stars is a result of increased surface coverage of magnetic active regions. Title: Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars. Authors: Ayres, T. R.; Stencel, R. E.; Linsky, J. L.; Simon, T.; Jordan, C.; Brown, A.; Engvold, O. Bibcode: 1983ApJ...274..801A Altcode: High-dispersion IUE spectra of six late-type stars exhibit small but statistically significant differential redshifts of high-temperature emission lines, like Si IV and C IV, with respect to low-temperature lines like S I and O I. A well-exposed, small-aperture spectrum of the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9 III) establishes that the high-temperature lines are redshifted in an absolute sense with respect to the accurately determined photospheric velocity of the system at single-line phase 0.50. Several possible explanations for the stellar redshifts are discused, including a warm wind (100,000 K) in which aparent redshifts are produced in optically thick lines by an accelerating outfow, and the downflowing component of a vertical circulation system for which the up-leg portion of the flow is too cool, too hot, or too tenuous to be visible in Si IV and C IV. If the second scenario is true, the stellar redshifts may provide an important phenomenological link to the downflows observed in 100,000 K species over magnetic active regions in the sun. Title: Outer atmospheres of cool stars. XIII. Capella at critical phases. Authors: Ayres, T. R.; Schiffer, F. H., III; Linsky, J. L. Bibcode: 1983ApJ...272..223A Altcode: The results are presented of a program of high-dispersion spectroscopy of Capella at critical orbital phases utilizing the International Ultraviolet Explorer. The considered program had the objective to establish as carefully as possible the relative ultraviolet emission levels of the Capella primary and secondary in order to obtain an understanding regarding the nature of their chromospheres and coronae. The results of the program confirm the earlier study of the Capella by Ayres and Linsky (1980), which was limited to orbital phases 0.50 and 0.75. Both programs found that the Capella secondary is considerably brighter than the primary, in surface flux, in all of the prominent far-ultraviolet emissions, particularly the high-excitation CII-CIV lines. In addition, the present study has revealed several puzzling aspects of the system. It is concluded that the Capella primary is comparatively bright, for a yellow giant, in far-ultraviolet and perhaps also in soft X-ray normalized fluxes. The implications of this conclusion are evaluated. Title: The narrow ultraviolet emission lines of the red dwarf AU Microscopii(dM1.6e). Authors: Ayres, T. R.; Eriksson, K.; Linsky, J. L.; Stencel, R. E. Bibcode: 1983ApJ...270L..17A Altcode: It is pointed out that the red dwarfs are the smallest, coolest, faintest, least massive, but most common of normal main-sequence stars. The dMe (H-alpha emission) subclass of the red dwarfs exhibits the largest median soft X-ray to bolometric luminosity ratio of any group of late-type stars. In connection with the present investigation, attention is given to the first high-dispersion spectra of the chromospheric (6000 K) and higher temperature (up to 100,000 K) emissions of a dMe star, AU Microscopii in the far-ultraviolet (1150-2000 A) and middle-ultraviolet (2000-3000 A) bands accessible to the International Ultraviolet Explorer (IUE). AU Mic is one of the most luminous of lower main-sequence stars in C IV and soft X-ray emission. Title: High-Dispersion Observations of Alpha Bootis Authors: Ayres, Thomas R. Bibcode: 1983iue..prop.1394A Altcode: Investigating the late phases of the life of a star is central to an understanding of stellar structure and evolution, and the aping of stellar magnetic activity. For yellow dwarf stars like the Sun, the advanced stages of their life cycle are represented by old red giants like Arcturus (alpha Bootis, K2 III). I propose, therefore, to undertake the most detailed spectroscopic study of Arcturus yet attempted with the International Ultraviolet Explorer. The study includes a 24-hour superexposure of the farultraviolet (1150-2000 A) region, obtained with collaborators in the U.K., and a uniformly high signalto-noise map of the 2750-2900 A region of the middle ultraviolet. The IUE observations will be coordinated with ground-based high-resolution spectroscopy of the Ca I, Ca II and H-alpha lines of the optical region. The SWP superexposure will be utilized to search for bands of the carbon monoxide 4th positive system, which have been identified in low dispersion spectra but are not seen in the existing 8-hour SWP echelle exposure, and to detect, or set harder upper limits on, highexcitation emission lines like C II 1336, Si IV 1394, and C IV 1548, which are diagnostics for the presence of hot plasma (T>2_10^4 K) in the outer atmosphere of the red giant. The strength of the farultraviolet ionic emission lines can be used to constrain the competing models to explain the structure of red giant chromospheres, coronae and winds, while the fluoresced molecular features can be used to probe the coolest layers of the red giant photosphere, which are radiatively pumped from above by the strong chromospheric emissions of O I 1305 triplet) and C I (1657 multiplet). The high quality map of the middle ultraviolet region can be utilized to study the strong chromospheric emission cores and faint inner damping wings of the Mg II resonance lines, and the weak emission core of the neutral magnesium resonance line at 2852 A. These spectra can he applied to a number of problems ranging from the properties of the circumstellar envelope and wind of Arcturus, to the surface gravity and mass of the archetype red giant. Title: Capella HL Authors: Ayres, Thomas R. Bibcode: 1983iue..prop.1393A Altcode: The main component of the a Aurigae system, alpha Aurigae A (also known simply as Capella), is a 104 day spectroscopic binary of evolved yellow giants which is extraordinarily bright in the far-ultraviolet region and accordingly has been the subject of a number of detailed studies with IUE. These studies have revealed that the evolutionarily less advanced F-type secondary of Capella is the dominant source of highexcitation emissions from the system, and reinforce the notion that evolutionary "youth" and enhanced chromospheric activity are strongly associated. Capella HL is a faint binary of red dwarfs which is an outlying member of the a Aurigae system. Although the dM stars as a class are quite common in the solar neighborhood, Capella HL is quite unusual among the red dwarfs since it is one of the very few for which a reliable age is available. In particular, the well-determined masses of Capella Aa and Ab and their evolutionary status imply that the spectroscopic binary is about half the age of the Hyades cluster. Since Capella HL is gravitationally bound to the main pair, it very likely is coeval and therefore as young. There are surprisingly few other dM stars whose ages are known as unambiguously as that of Capella HL, an important exception being Proxima Centauri which is bound to the solar-age alpha Centauri system. Accordingly, Capella HL provides a unique opportunity to study the youthactivity connection among stars of the lower main sequence. I therefore am requesting a US1 low radiation shift to obtain wellexposed low-dispersion spectra of the red dwarf pair in the farultraviolet and middle-ultraviolet hands accessible to IUE. The objective of the program is to study the strength of chromospheric and higher temperature emissions in one of the very few red dwarfs whose age is known. The study is intended to advance our understanding of the evolution of magnetic activity in the cool half of the Hertzsprung-Russell diagram. Title: The Hydrogen Emission of Active Red Dwarfs Authors: Ayres, Thomas R. Bibcode: 1983iue..prop.1390A Altcode: A number of low-dispersion studies of the emission-line dwarf M stars with IUE have revealed that their ultraviolet emissions share the enormous enhancement over quiet Sun levels typical of their coronal soft X-ray intensities. In fact, the visually very faint red dwarf AU Mic (M1.6e) is so bright in the far-ultraviolet region that highdispersion IUE spectra have been obtained successfully. These measurements further corroborate the notion that the dMe stars are heavily covered by intense magnetic activity, although the most pronounced effects appear to be confined to the multi-million degree corona. Indeed, an important new model for the lower atmospheres of the dMe stars proposed by L. Cram suggests that the 6,000 K chromospheric layers in fact are heated largely by XUV emission from the overlying corona, rather than by hydrodynamical effects. If this model is correct, the red dwarfs provide an opportunity to study a significant physical phenomenon that is thought to operate on the Sun only during the most intense flares. In this regard, the previous studies of the red dwarfs with IUE have overlooked the most important feature of the far-ultraviolet spectrum for elucidating the X-ray heating scenario: the Ly-alpha resonance line of neutral hydrogen. Owing to the substantial recombination of hydrogen throughout the XUV irradiated layers of the dMe chromosphere, the Ly-alpha emission is anticipated to be considerably brighter than ordinarily would be expected from a more solar-like star, where the H I emission is governed largely by collisional excitation at conductive interfaces between the chromosphere and corona. I therefore propose a program to obtain short exposures of the farultraviolet Ly-alpha emission of a representative sample of dMe stars in order to test the Cram X-ray heating hypothesis. In fact, the predicted Ly-alpha exposure times are so short that the program is suitable for NASA high radiation time. Furthermore, I intend to coordinate the IUE observations with ground-based measurements of Ca II, the H I Balmer series and other chromospheric emission lines in the optical region. The main objective is to obtain a complete set of chromospheric diagnostics to constrain the numerical models that will he utilized to test the Cram hypothesis or other possible mechanisms for energizing the red dwarf chromospheres. Title: Determination of Absolute Velocities for Emission Lines of Late-Type Stars Authors: Ayres, Thomas R. Bibcode: 1983iue..prop.1391A Altcode: The recent discovery of redshifted emission lines like Si IV and C IV in the far-ultraviolet spectra of active-chromosphere stars may be an important link with the downflows of 10^5 K material seen commonly in the magnetic loon structures of solar active regions. On the Sun, the net redshifts of the hiqh-excitation species almost certainly result from a continual exchange of plasma between the chromosphere and corona, in which the upleg portion of the circulation is too cool (spicules, for example) or too hot (explosive evaporation, for example) to be visible in the intermediate temperature emissions. However, the differential redshifts measured in the spectra of other late-type stars may result from a net blueshift of the weak, lowexcitation emission features that are used to provide -an ad hoc zero velocity reference. Furthermore, even if the 10^5 K lines are redshifted in an absolute sense, an outflowing wind at that temperature could absorb some of the emission on the short-wavelength side of the line profile, and thereby give the appearance of a net redshifted feature. According to the importance of the redshift phenomenon with regard to winds and "antiwinds" in late-type chromospheric emission-line stars, we propose to undertake an extensive observational program with IUE to (1) establish whether the high-excitation lines indeed are redshifted in an absolute sense, (2) distinguish among the several competing hypotheses to explain the redshifts, and (3) study the flow structure in a number of red giants that are known to possess winds of moderate terminal velocity but comparatively low excitation. The observational objectives of the program can be met by obtaining long exposures in the SWP and LWR regions of prototype bright stars whose spectra contain optically thin forbidden and intersystem lines as well as strong permitted transitions that probably are optically thick. The spectra will he taken according to simple procedures that permit the assignment of a sufficiently reliable absolute velocity scale. Finally, the absolute velocity spectra that result from this program will be analyzed in the context of detailed numerical simulations of geometrically extended, expanding chromospheres, in order to elucidate the mechanisms responsible for the winds and/or downflows. Title: The structure and energy balance in main sequence stars Authors: Jordan, C.; Ayres, T. R.; Brown, A. Bibcode: 1983ASSL..102...61J Altcode: 1983ards.proc...61J; 1983IAUCo..71...61J High-resolution spectra obtained with the IUE satellite have been used to study the structure and energy balance in the main sequence stars ξ Boo A, α Cen A, α Cen B and ɛ Eri. The EUV observations are combined with X-ray fluxes to predict the coronal temperatures, the electron pressures and energy lost or transferred by radiation and thermal conduction. Title: Evolution of chromospheres and coronae in solar mass stars : a far-ultraviolet and soft X-ray comparison of Arcturus (K2III) and alf CEN A (G2V). Authors: Ayres, T. R.; Simon, T.; Linsky, J. L. Bibcode: 1982ApJ...263..791A Altcode: IUE far-UV and Einstein Observatory soft X-ray observations for the red giant Arcturus and the nearby yellow dwarf Alpha-Centauri A, which are archetypes of solar mass stars in different stages of evolution, are compared. Evidence is found for neither coronal soft X-ray emission from the red giant, at surface flux levels of only 0.0006 that detected previously for the yellow dwarf, nor C II and IV resonance line emission at surface flux levels of only 0.02 those of the yellow dwarf. The resonance line upper limits and previous detections of the C II intersystem UV multiplet 0.01 near 2325 A provide evidence for an Arcturus outer atmosphere that is geometrically extended, tenuous and cool. The red giant has, in addition, a prominent cool stellar wind. An extensive tabulation of line identifications, widths and fluxes for the IUE far-UV echelle spectra of the two stars is given, and two competing explanations for the Wilson-Bappu effect are discussed. Title: Prospects for the Solar-Stellar Connection Outside the Optical Band: A Matter of Resolution Authors: Ayres, T. R. Bibcode: 1982BAAS...14..946A Altcode: No abstract at ADS Title: The Narrow Ultraviolet Emission Lines of the Red Dwarf AU Microscopii (dM1.6e) Authors: Ayres, T. R.; Eriksson, K.; Gustafsson, B.; Linsky, J. L.; Saxner, M.; Stencel, R. E. Bibcode: 1982BAAS...14Q.865A Altcode: No abstract at ADS Title: Appendix - Empirical Estimates of Noise Levels in IUE Low-Dispersion Spectra Authors: Ayres, T. R. Bibcode: 1982ApJ...257..243A Altcode: No abstract at ADS Title: Outer atmospheric properties of beta Draconis (G2 Ib-II) Authors: Brown, A.; Jordan, C.; Ayres, T. R.; Linsky, J. L.; Stencel, R. E. Bibcode: 1982ESASP.176..142B Altcode: 1982IUE3r......142B; 1982iue..conf..142B Observations of the supergiant Beta Draconis made by IUE are discussed. Electron pressure is comparable with that found in the quiet solar atmosphere. The X-ray fluxes from previous observations suggest T = 10 to 20 million k, when combined with the analysis of the IUE spectra; this would be greater than the proton escape velocity. The radiation losses between 10,000 and 100,000 K exceed those from the Sun by an order of magnitude, but in the absence of a stellar wind the energy losses from the corona would be lower than in the Sun. The line profile widths indicate substantial (M=2) nonthermal broadening. If interpreted as energy associated with a wave flux, they would imply more coronal energy than required by radiation and conduction losses, suggesting an energetic mass loss. However, line asymmetries can also be interpreted as motions within the atmosphere. Title: High resolution EUV spectroscopy of 56 Pegasi (K0II P + wd). Authors: Jordan, C.; Brown, A.; Ayres, T. R.; Linsky, J. L.; Stencel, R. E. Bibcode: 1982ESASP.176..161J Altcode: 1982iue..conf..161J; 1982IUE3r......161J The hypothesis that X-ray and UV emission by 56 Pegasi (K0II p + wd) originates in a conventional chromosphere, transition region and corona, as opposed to Schindler's hypothesis of accretion of the cool stellar wind onto the white dwarf companion, is discussed. Analysis of IUE data indicates that within the uncertainties associated with determining the stellar radius and abundances, the chromosphere, transition region, and corona of 56 Peg are similar to that of Beta Draconis both in structure and energy balance. The accretion hypothesis is not a unique explanation of the observed spectral properties and the white dwarf companion may not play a direct role. Furthermore, 56 Peg, according to current values of V-R and luminosity class, is on the nonsolar side of the Linsky-Haisch dividing line whereas Beta Draconis is on the solar side. Title: Outer atmospheres of cool stars. XI. High-dispersion IUE spectra of five late-type dwarfs and giants. Authors: Ayres, T. R.; Linsky, J. L.; Basri, G. S.; Landsman, W.; Henry, R. C.; Moos, H. W.; Stencel, R. E. Bibcode: 1982ApJ...256..550A Altcode: We present high-dispersion, far-ultraviolet (1150-2000 Å) spectra of five late-type dwarfs and giants obtained with the International Ultraviolet Explorer. The chromospheric (T ≲104K) emission lines in the giants tend to be about twice as broad as the corresponding features of the dwarf star spectra, suggesting a width-luminosity relation similar to the Wilson-Bappu effect for Ca II H and K. The Si III λ1892 and C III λ1909 intercombination lines formed in hotter layers (T ≍ 5 × 104K) also broaden by a factor of 2 from the main-sequence stars to the evolved stars, and the permitted resonance doublets of C II(3 × 104 K), Si IV (6 × 104 K), and C IV (105 K) are as much as a factor of 4 broader in the giants than in the dwarfs. However, we find no evidence for asymmetric or shifted emission profiles that might indicate the presence of warm (T≪105K) stellar winds. We conclude that broad C iv profiles, in particular, are typical of active chromosphere giant stars and are unlikely to be a unique signature of an extended, expanding warm wind. Since the resonance lines tend to be wider than the intersystem lines formed at similar temperatures in the chromosphere and in hotter layers, we conclude that opacity must be an important broadening enhancement mechanism in active chromosphere giant stars. Nevertheless, the intercombination line widths do indicate a general increase in the outer atmosphere Doppler motions from the dwarfs to the giants.

Application of the density sensitive line ratio C III λ1909/Si III λ1892 suggests that the outer atmosphere pressures (T ≍ 5 × 104K) are similar in the active chromosphere subgiant λ And and the quiet chromosphere dwarfs, α Cen A and B. However, the pressures derived for the Capella secondary and β Dra are factors of 3 or more lower than the dwarfs, suggesting geometrically extended, low-density outer atmosphere structures qualitatively different from the high-pressure, compact structures typical of solar magnetic active regions.

Finally, we have isolated the He II λ1640 emission component from contaminant blends, and we find that the line strength is well correlated with soft X-ray fluxes of the sample stars, as predicted by photoionization-recombination models of the He II Bα formation. Title: Outer atmospheres of cool stars. X. HR 1099 at quadrature. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1982ApJ...254..168A Altcode: IUE high-dispersion, far-UV spectra of the active-chromosphere RS CVn binary HR 1099 are reported. The emission features produced by such high-temperature species as C II and C IV are found to be very bright, to exhibit structure, change significantly in the one-week interval separating the two exposures, and generally follow the radial velocity motion of the K subgiant primary, while the less massive G dwarf secondary appears only weakly in the composite spectrum. It is concluded that chromospheric and transition region emission in RS CVn binaries is a stellar rather than system phenomenon, and the structure evident in some of the emission line shapes is interpreted as a patchy brightness distribution on and above the K star surface that is spread out in velocity by the rapid rotation. Title: High dispersion IUE spectra of active chromosphere G and K dwarfs. Authors: Ayres, T. R.; Linsky, J. L.; Brown, A.; Jordan, C.; Simon, T. Bibcode: 1982NASCP2238..281A Altcode: 1982auva.nasa..281A; 1982NASCP2338..281A; 1982IUE82......281A IUE far ultraviolet echelle spectra of three active chromosphere dwarf stars X1 Orionis (GO V), Bootis A (G8 V), and Eridani (K2 V), are analyzed utilizing spectra of Alpha Cen A (G2 V) and Alpha Cen B (K1 V) as quiet chromosphere comparisons. Title: The Many Faces of HR 1099 Authors: Ayres, Thomas R. Bibcode: 1982iue..prop.1045A Altcode: We propose to monitor, in high-dispersion, the far-ultraviolet emission of the archetype short-period RS Canum Venaticorum binary system, HR 1099 = V711 Tauri (K0 IV + G5 V) through two complete orbital revolutions. The tidally-locked RS CVn binaries have among the brightest chromospheres (T = 6000 K) and coronae (T ~ 10^6 K) known, and are thought to suffer intense magnetic activity in their surface layers. Accordingly, RS CVn binaries, as a class, are valuable prototypes for investigating how magnetic flux is generated in rapidly-rotating convective stars; the spatial scales associated with structural expressions of the surface fields (magnetic active regions, for example); and general questions concerning the physical response of atmospheric plasma to embedded, intense magnetic activity. Our objective in monitoring HR 1099 throughout its orbit is to study the spatial distribution of far-ultraviolet emission on all faces of the active K0 subgiant in that system. Previous exploratory spectra obtained at critical orbital phases, namely the opposite quadratures, indicate that the cool subgiant is quite variable in its far-ultraviolet output, and suggests that the emission has a rather patchy surface distribution. We propose to obtain further observations in order to characterize the spatial scales and brightness levels of large, coherent active regions on the stellar surface. Central to our study is the issue of whether the dark "starspots", thought responsible for the low-amplitude, periodic photometric fluctuations in such systems, are sites of enhanced farultraviolet emission, as the solar analogs--active regions--might tend to suggest. Since the emission features from any large-scale activity center will be spread out in velocity by the rapid rotation of the tidally synchronized subgiant, high-dispersion spectroscopy can be utilized to diagnose what fraction of the stellar surface is involved. Furthermore, a sequence of IUE high-dispersion images with the long- and shortwavelength echelles over the binary orbit can help establish more firmly the contribution of the main-sequence component of HR 1099 to the composite emission spectrum. The former observation is relevant to the mechanisms that amplify magnetic fields in the stellar convection zone and impress large-scale spatial coherence on emerging flux ropes. The latter observation is relevant to the mechanisms that generate magnetic flux (dynamo action for example), since the primary and secondary of HR 1099 have somewhat different stellar properties and linear rotation rates. An investigation of these issues is central to understanding the extremely energetic phenomena associated with the intense surface magnetic activity of the RS CVn subgiants. Title: The Wilson-Bappu Effect & Beyond Authors: Ayres, Thomas R. Bibcode: 1982iue..prop.1043A Altcode: The broad photospheric damping wings and bright chromospheric emission cores of the resonance lines of ionized Magnesium (h and k) and Calcium (H and K) contain an extraordinarily detailed picture of the temperature-height profile of the stellar outer atmosphere. When combined with the wing shapes of the neutral species resonance lines, Mg I 2852 A and Ca I 4227 A, the Mg II h and k and Ca II H and K wings provide an empirical measure of the stellar surface gravity. Furthermore, the core intensities of the six resonance lines indicate the overall rates of plasma radiative cooling at different, but adjacent, levels of the chromosphere. Finally, the emission cores of Mg II k and Ca II K are known to exhibit a remarkable systematic broadening with increasing stellar luminosity--the Wilson-Bappu effect--whose origin remains controversial despite several decades of study. Further fueling that controversy are recent highresolution, ground-based studies of the absorption profile of H I Balmer alpha (6562 A), that demonstrate a general broadening of the chromospheric core with increasing luminosity, although not in a one-to-one correspondence with the Ca II K behavior. We propose below an observing program to address these several issues by means of coordinated IUE and ground-based observations of a small sample of representative G-K dwarfs and giants. The ground-based side of the study, in collaboration with the Australian National University, will consist of high-resolution spectrograms of Ca II H and K, Ca I 4227 A, H-alpha, and other Balmer lines utilizing the Coude echelle and PCA detector of the Mt. Stromlo 74". supplemented with Cassegrain echelle spectra from the Siding Spring 40". The IUE side of the study will consist of graded sequences of long-wavelength echellograms to optimally expose the bright emission features of Mg II (2800 A) as well as the faint damping wings of Mg II h and k and the chromospheric absorption core of Mg I 2852 A. Previous observational work in this region has tended to concentrate on the Mg II k core itself. Consequently, the low contrast wings are usually recorded at poor signal-to-noise and thereby are useless for theoretical interpretations. Our proposed program is novel in that we will obtain analogous high-resolution, high signal-tonoise profiles of Ca II H and K, Ca I 4227 A and H-alpha as close in time to the IUE spectra as is practical. Near simultaneity is an important consideration since late-type stars are known to exhibit profile changes in their chromospheric emission cores on time scales as short as hours. We intend to provide, by our coordinated investigation, a high-quality set of calibrated chromospheric emission and absorption line profiles of representative G-K dwarfs and giants to serve as a basis for subsequent detailed numerical simulation studies of radiative cooling, gravity-sensitive wing ratios, and the Wilson-Bappu effect. Title: Far-Ultraviolet Echelle Spectra of RS CVN Giants Authors: Ayres, Thomas R. Bibcode: 1982iue..prop.1049A Altcode: RS Canum Venaticorum systems, containing late-type main-sequence and subgiant stars, are tidally-synchronized binaries that are among the brightest far-ultraviolet and x-ray sources known. Such systems very likely owe their enhanced chromospheric and coronal emission to intense surface magnetic activity driven, in turn, by the interaction of rapid rotation with strong subsurface convection. The RS CVn binaries are valuable prototypes for investigating how magnetic -flux is generated in stars, how the surface magnetic fields are expressed structurally, and how the atmospheres of cool stars respond physically to intense magnetic activity. Of special importance among the RS CVn binaries are the moderateperiod (P ~ 20 day) subclass containing evolved giant stars. Such systems represent the extreme of low surface gravities, and consequently are critically important in any effort to understand how chromospheric activity might be modified by gross stellar parameters. The RS CVn giants also are pivotal in the question of how the development of strong stellar winds among the later giants might affect the expression of magnetic activity: Does the wind directly smother the formation of high-temperature coronal magnetic loops? Does the wind, instead, merely play a secondary role, for example shortcircuiting magnetic activity by spinning down the star and thereby quenching dynamo action? We propose to extend our previous studies of the classical shortperiod RS CVn systems HR 1099 and UX Arietis, and that of the long period Capella system, to an investigation of moderate period (20 day) RS CVn binaries that contain evolved giant stars. We intend to search for the as yet unseen secondary stars, by observing the systems at critical orbital phases; for massive stellar winds, by detecting Doppler shifts of far-ultraviolet emission features or absorption components in Mg II h and k; and for opacity broadening of the hightemperature lines caused by significant geometrical extension of the emitting structures. Such studies are central to understanding the exotic and energetic phenomena associated with chromospheric and coronal magnetic activity among late-type stars in the solar neighborhood. Title: High dispersion far ultraviolet spectra of cool stars. Authors: Stencel, R. E.; Linsky, J. L.; Ayres, T. R.; Jordan, C.; Brown, A.; Engvold, O. Bibcode: 1982NASCP2238..259S Altcode: 1982auva.nasa..259S; 1982IUE82......259S; 1982NASCP2338..259S Recent far ultraviolet high dispersion spectra of two cool supergiant stars, Beta Dra (G2 Ib) and Alpha Ori (M2 Iab) are examined in the context of current questions regarding stellar chromospheres, coronae and mass loss. These stars show very different outer atmosphere structure. Beta Dra has a geometrically thin transition region with bright emission lines of 100,000 K plasma that are red-shifted, indicating downflow in magnetic flux tubes. By contrast, Alpha Ori has a cool extended chromosphere and circumstellar envelope with large mass loss. Title: Capella revisited. Authors: Ayres, T. R. Bibcode: 1982NASCP2238..251A Altcode: 1982auva.nasa..251A; 1982NASCP2338..251A; 1982IUE82......251A The highlights of two studies of Capella, a spectroscopic binary, undertaken during the third and fourth years of the IUE are given. The first program consists of high dispersion spectroscopy at critical phases of the Capella orbit. The second program is a two month monitoring effort to search for ultraviolet modulations induced by the rotation of magnetic active regions onto and off of the visible hemisphere of the Capella secondary. Title: The cool Half of the H-R diagram in soft X-rays. Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.; Rosner, R. Bibcode: 1981ApJ...250..293A Altcode: The results of an Einstein Observatory program to map the occurrence of hot coronae (T greater than 1 million K) in the cool half of the Hertzsprung-Russell diagram are reported. F-M dwarfs, and late F through early K star giants characterized by 10,000 K chromospheric and 20,000-200,000 K FUV emission lines were studied in one region, while a second region study included red giants later than K2 III and supergiants later than G5 Ib with weaker chromospheric emission and no high temperature species. Program goals comprised determination of the C IV division as seen in soft X-rays, and identification of stellar parameters which distinguish strong from weak coronal X-ray sources. A summary of target stars, X-ray fluxes, and UV emission profiles is provided, and coronal emissions, comparisons of C IV and wind boundaries, hybrid-spectrum supergiants, the energy balance of stellar outer atmospheres, stellar rotation and coronae, and evolutionary considerations are discussed, along with lines of future research. Title: Far-ultraviolet fluorenscence of carbon monoxide in the red giant Arcturus. Authors: Ayres, T. R.; Moos, H. W.; Linsky, J. L. Bibcode: 1981ApJ...248L.137A Altcode: Evidence is presented that many of the weak features observed with International Ultraviolet Explorer (IUE) in the far-ultraviolet (1150-2000 A) spectrum of the archetype red giant Arcturus (K2 III) are A-X fourth positive bands of carbon monoxide excited by chromospheric emissions of O I, C I, and H I. The appearance of fluorescent CO bands near the wavelength of commonly used indicators of high-temperature (T greater than 20,000 K) plasma, such as C II at wavelength 1335 and C IV at wavelength 1548, introduces a serious ambiguity in diagnosing the presence of hot material in the outer atmospheres of the cool giants by means of low-dispersion IUE spectra. Title: Relations among stellar X-ray emission observed from Einstein, stellar rotation and bolometric luminosity. Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. S.; Ayres, T.; Linsky, J. L. Bibcode: 1981ApJ...248..279P Altcode: The correlation between observed stellar X-ray luminosities, bolometric luminosities, and projected rotational velocities for stars of various spectral types and luminosity classes are determined. Early type stars (O3 to A5) have X-ray luminosities independent of rotational velocities, and correlating with bolometric luminosities. Late type stars of spectral type G to M have luminosities well correlated to equatorial rotational velocities, and are independent of luminosity class. The dependence of late type stars is found to be equivalent to a relation between the X-ray surface flux and the stellar angular velocity. F stars are intermediate with X-ray luminosities higher than would be predicted on the basis of the early type star relation, although lower than expected from the late type velocity dependence. The location of RS CVn stars as a class is also discussed, and it is found that the heating of late type stellar coronas does not result from direct conversion of ratational energy. Title: Outer atmospheres of cool stars. IX. A survey of ultraviolet emission from F-K dwarfs and giants with the IUE. Authors: Ayres, T. R.; Marstad, N. C.; Linsky, J. L. Bibcode: 1981ApJ...247..545A Altcode: Low-dispersion ultraviolet spectra (1150-2000 A) of a representative sample of cool stars, including dwarfs and giants of spectral types F-K, obtained with the IUE, are examined. The observation and the absolute calibration procedures are described. Correlation diagrams are constructed that compare chromospheric and transition-region emission line strengths and broadband coronal soft X-ray fluxes. The transition-region and coronal emission in the G-K dwarfs and G giants is well correlated with the Mg II (wavelength 2800) doublet emission strength, which is symptomatic of chromospheric energy losses. The power-law slopes are steeper than unity, particularly for soft X-rays. The implications of the correlations are discussed with respect to the weakening or disappearance of transition regions and hot coronae in the cool half of the red-giant branch and possible chromospheric and coronal heating mechanisms. It is proposed that the weakness of outer atmospheres in the red giants compared with the yellow giants can be understood as a consequence of stellar evolution, since it is possible that stars of slightly different spectral type in the giant branch have very different main-sequence progenitors. Title: Fourier Transform Spectrometer observations of solar carbon monoxide. I - The fundamental and first overtone bands in the quiet sun Authors: Ayres, T. R.; Testerman, L. Bibcode: 1981ApJ...245.1124A Altcode: Measurements of the 2200/cm fundamental and 4300/cm first overtone vibration-rotation band systems of solar carbon monoxide, were obtained with the Fourier Transform Spectrometer of the McMath telescope at Kitt Peak. The overtone measurements were taken at the east, north, and west heliocentric limbs, and at disk center. Observations of the strong fundamental bands were obtained at disk center and near the north limb. The low core brightness temperatures of the strongest fundamental carbon monoxide lines near the limb, reported previously by Noyes (1972) and Hall (1974), are confirmed. The possibility that thermal inhomogeneities might be responsible for the unusual behavior of the fundamental carbon dioxide lines have been examined. The somewhat discordant behavior of the fundamental lines at disk center compared with the north limb seems to favor a limb shadowing effect. The first overtone limb equivalent widths and the best-fit thermal and microvelocity models indicate a solar carbon abundance of 0.004 (on the scale with AH = 1) for an oxygen-to-carbon abundance ratio of 2. Title: The stars that do not obey the Wilson-Bappu relationship. Authors: Ayres, T. R. Bibcode: 1981Obs...101...38A Altcode: No abstract at ADS Title: High-resolution spectra of five late-type dwarfs and giants obtained with the IUE satellite. Authors: Ayres, T. R.; Basri, G. S.; Henry, R. C.; Landsman, W.; Linsky, J. L.; Moos, H. W.; Stencel, R. E. Bibcode: 1981BAAS...13..546A Altcode: No abstract at ADS Title: Thermal Bifurcation in Solar Calcium Plages Authors: Ayres, T. R.; Linsky, J. L.; Testerman, L.; Brault, J. Bibcode: 1981BAAS...13..915A Altcode: No abstract at ADS Title: Excitation of the Chlorine I Line at 1351Å Authors: Shine, R. A.; Woodgate, B. E.; Ayres, T. R. Bibcode: 1981BAAS...13Q.830S Altcode: No abstract at ADS Title: Far-Ultraviolet Fluorescence of Carbon Monoxide in the Red Giant Arcturus Authors: Ayres, T. R.; Moos, H. W.; Linsky, J. L. Bibcode: 1981BAAS...13..515A Altcode: No abstract at ADS Title: High-Resolution Studies of Arcturus with IUE &Einstein: A Sensitive Search for High-Temperature Emission Authors: Ayres, T. R.; Simon, T.; Linsky, J. L. Bibcode: 1981BAAS...13..811A Altcode: No abstract at ADS Title: Thermal bifurcation in the solar outer atmosphere Authors: Ayres, T. R. Bibcode: 1981ApJ...244.1064A Altcode: It is suggested that two distinct plasma thermal states are possible in the solar outer atmosphere because of the bifurcated character of the low-temperature cooling function at small optical depths. In radiative equilibrium, the plasma is strongly cooled to temperatures well below 4000 K by surface emission in the Delta V = 1 fundamental vibration-rotation bands of CO. However, when significant mechanical energy deposition is present in addition to the radiative heating component, the only effective cooling channel available to stabilize the plasma is optically thin emission in the recombination continuum of H(-). Consequently, thermal equilibrium in a mechanically heated atmospheric zone can be attained only for temperatures above the critical temperature of 4900 K because H(-) is itself a net radiative heating agent for temperatures cooler than the critical temperature. Title: High-Resolution Spectra of Five Late-Type Dwarfs and Giants Obtained with the IUE Satellite Authors: Ayres, T. R.; Basri, G. S.; Henry, R. C.; Landsman, W.; Linsky, J. L.; Moos, H. W.; Stencel, R. E. Bibcode: 1981BAAS...13R.545A Altcode: No abstract at ADS Title: The Mg II h and k lines in a sample of dMe and dM stars. Authors: Giampapa, M. S.; Pornmann, P. L.; Ayres, T. R.; Linsky, J. L.; Worden, S. P. Bibcode: 1981NASCP2171..279G Altcode: 1981uviu.nasa..279G; 1981NASCP3171..279G; 1980IUE80......279G Both Mg II h and k line fluxes are presented for a sample of 4 dMe and 3 dM stars obtained with the IUE satellite in the long wavelength, low dispersion mode. The observed fluxes are converted to stellar surface flux units and the importance of chromospheric non radiative heating in this sample of M dwarf stars is intercompared. In addition, the net chromospheric radiative losses due to the Ca II H and K lines in those stars in the sample for which calibrated Ca II H and K line data exist are compared. Active region filling factors which likely give rise to the observed optical and ultraviolet chromospheric emission are estimated. The implications of the results for homogeneous, single component stellar model chromospheres analyses are discussed. Title: Timing Capella in the Ultraviolet Authors: Ayres, Thomas R. Bibcode: 1981iue..prop..719A Altcode: The long-period RS CVn-type spectroscopic binary system Capella (alpha Aur A: G6 III and F9 III) presents a unique opportunity to study the medium-term time evolution of chromospheric activity on a star that is considerably more active than our Sun. (Note: The rapidly rotating Ftype secondary is responsible for virtually all of the line emission from the Capella system in high excitation species, such as C IV 1548 A and Si IV 1394 A, and for most of the emission in chromospheric species, such as H I L-alpha and Si II 1808 A.) In particular, a recent study of Capella at critical orbital phases has revealed that the ultraviolet output of the system is comparatively steady over timescales of ~hours, but appears to decline somewhat over the three observing sessions, which were separated 26^d apart. Because ultraviolet changes are apparent over month-long timescales, but not over hour-long intervals, it would be extremely valuable to explore the intermediate timescales, namely days, of variability in the Capella secondary's chromospheric output. One expects, for instance, to see modulations of the ultraviolet emission lines in the Capella spectrum owing to the ~10^d rotational period of the secondary. One might also expect to find longer term modulations (~l month) owing to the birth, evolution and decay of large, bright activity centers. In fact, the amplitude of the rotational modulation provides an indication of how patchy the brightness distribution might be. The patchiness of the chromospheric emission in turn provides an indication of the size-scale spectrum of the emerging magnetic flux elements that are likely ultimately responsible for the chromospheric activity itself. Finally, a monitoring program extending from one quadrature in the Capella orbit to the othe (54 degrees) would be quite valuable in searching for and characterizing weak interstellar components in the prominent chromospheric emission features, the O I triplet near 1305 A and Si II 1808 A for example. I outline below an observing program to obtain a timing record, at high dispersion, of the ultraviolet output of an active chromosphere star the Capella secondary - that is very different from the better studied, but more mundane, solar example. Such a comparison should prove invaluable in exploring the mechanisms responsible for magnetic flux generation in stars, and the ultimate expression of the magnetic fields in chromospheric activity. Title: Calibration of the SWP Echelle Mode for Chromospheric Emission Sources Authors: Ayres, Thomas R. Bibcode: 1981iue..prop..716A Altcode: I propose to establish an absolute calibration for the SWP echelle mode of IUE that would be useful for chromospheric emission-line stars. In addition propose to study and characterize apparent vidicon artifacts that appear in and near some of the prominent emission features of the 1150-2000 A region, particularly C IV 1548 A. The calibration would be accomplished by a graded sequence of alternating echelle-mode and low-dispersion exposures of the bright, chromospheric emission-line source Capella (alpha Aurigae A). Such a calibration is straightforward, and quite timely in view of the increasing number of long-exposure, SWP echelle-mode observations of cool-star chromospheres that have been attempted in the past, and are contemplated for the future. For aesthetic reasons, the calibration should be obtained during a single, low-noise shift. However, for expediency, many of the objectives could be accomplished satisfactorily during a US #2 shift. Title: The IUE's eye view of cool-star outer atmospheres. Authors: Ayres, T. R. Bibcode: 1981NASCP2171..237A Altcode: 1981uviu.nasa..237A; 1980IUE80......237A; 1981NASCP3171..237A Three topics are discussed which together demonstrate the power of the IUE to probe the occurrences of chromospheres and coronas in the cool half of the HR diagram. These are: (1) the complementary low dispersion and echelle observing modes; (2) Mg II h and k: chromospheric cooling and width luminosity correlation; and (3) empirical correlations among chromospheric, transition region, and coronal emission. The spectra of alpha Centauri (G2 V + K1 V) and Capella (G6 III + F9 III) are compared with that of the Sun and recent low dispersion surveys of cool star emission in the 1150 A to 2000 A short wavelength region are summarized. Title: SWP Echelle Spectra of Chromospherically Active Dwarf Stars Authors: Ayres, Thomas R. Bibcode: 1981iue..prop..715A Altcode: High resolution spectra of the 1150-2000 A region are enormously valuable for probing outer- atmosphere structure in cool stars. For example, such data can be used to separate blends, identify individual emission components in short-period binary systems, determine intensity ratios in close multiplets, estimate reliable emission strengths of lines superimposed on bright stellar continua, and test for the presence or absence of stellar winds at 105 K temperatures. These possibilities are not practical with IUE low-dispersion spectra. However, one must pay a steep-price to obtain useable high-dispersion IUE spectra and the additional dimension of diagnostic information, namely only a handful of the brightest UV sources are accessible even with shift-long exposures. We propose below an observing program to obtain echelle spectra of chromospherically active dwarf stars in the 1150-2000 A shortwavelength region. This program is intended to explore a particular class of objects that heretofore have not been observed at high dispersion with the SWP camera. Futhermore, this program complements previous SWP echelle studies by our group at the University of Colorado of quiet-chromosphere dwarf stars (alpha Cen A, alpha Cen B), active giants (alpha Aur A, lambda And, beta Dra), and the extreme case of the very active RS CVn-type system HR 1099. As described below, highdispersion spectra of these targets have provided a critical interpretive dimension that was lacking in previous low-dispersion studies. However, several fundamental questions have been raised in the course of our exploratory SWP work on what, in practice, are two distinct classes of chromospheric stars: the quiet dwarfs and the active giants. We feel that many of these questions can be answered by bridging the interpretive gap with a careful study of the active dwarfs. Our recent experience with shift-long SWP echelle exposures of chromospheric emission stars has suggested that our previous estimates of feasibility were too pessimistic, and that a larger sample of chromospherically bright stars is in fact accessible to IUE. Accordingly, we propose five candidate stars that we believe can be observed successfully with deep SWP echelle-mode exposures. If our proposal is accepted, we intend to collaborate with the Oxford (U-K) cool-star group to attempt a joint 14^h exposure of one of the brighter targets -- xi Boo A -- to provide an active-dwarf spectrum that is well exposed even at the weaker diagnostic features of the short-wavelength region. Title: Does H− truly cool the solar chromosphere? Authors: Ayres, T. R. Bibcode: 1980SoPh...68..125A Altcode: I examine the controversial problem of H− radiative cooling in the solar chromosphere. I find, in agreement with Praderie and Thomas, that H− is a substantial source of radiative heating in the outer atmosphere, especially when departures from LTE are important. The role of H− as a chromospheric heating agent must be considered carefully before net radiative cooling rates can be assessed from empirical chromospheric models, or calculations of nonradiative heating, for example by acoustic waves, can be pursued meaningfully. Title: Outer atmospheres of cool stars. V. IUE observations of Capella: the rotation-activity connection. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1980ApJ...241..279A Altcode: UV spectra of Capella (G6 III + F9 III) obtained with the IUE are analyzed. High-resolution emission-line profiles taken near the elongation at phase 78 days suggest that virtually all of the emission in transition-region lines and most of the emission in chromospheric lines comes from the late-F secondary of the system. It is suggested that the origin of the extraordinary activity levels on these otherwise very similar stars can be traced to the one property that is obviously different, i.e., rotation. The Capella primary is a normal sharp-line slow rotating giant, whereas the secondary has broader lines and is a rapid rotator for a late-type giant. Title: The Cool Half of the HR Diagram in Soft X-Rays Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.; Rosner, R. Bibcode: 1980BAAS...12..870A Altcode: No abstract at ADS Title: Coronal Dichotomies Authors: Ayres, T. Bibcode: 1980SAOSR.389...65A Altcode: 1980csss....1...65A No abstract at ADS Title: Outer atmospheres of cool stars. III. IUE spectra and transition region models for alf CEN A and B. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1980ApJ...235...76A Altcode: We describe lUE ultraviolet spectra of two nearby dwarf stars, α Centauri A (G2 V) and B (K1 V). These data include high-resolution profiles of the Mg II h and k features and lower- resolution integrated fluxes of lines from the following species: H I, C I-IV, N V, O I, A1 II, Si II-IV, and Fe II. We find that surface fluxes in chromospheric and transition-region lines of α Cen A and B are nearly identical to those of the quiet Sun. In addition, the measured stellar line fluxes are in good agreement with predictions of a transition-region scaling law based on conductive heating and pressures estimated from chromospheric models of α Cen A and B. While this agreement does not verify the conductive heating hypothesis, it does suggest that the basic physical processes that control the structure and energy balance in the chromospheres and transition regions of α Cen A and B and the Sun are, on a gross scale, very likely the same. Title: Effects of Flux Tubes on Conventional Chromospheric Diagnostics Authors: Ayres, T. R. Bibcode: 1980LNP...114..299A Altcode: 1980sttu.coll..299A; 1980IAUCo..51..299A No abstract at ADS Title: A search for coronal soft X-ray emission from cool stars with HEAO 1. Authors: Ayres, T. R.; Linsky, J. L.; Garmire, G. P.; Cordova, F. Bibcode: 1979ApJ...232L.117A Altcode: A search of the HEAO 1 A-2 experiment all-sky survey for coronal soft X-ray emission from a sample of active chromosphere G-M stars including six dwarfs, eight giants, four supergiants, and 10 dMe flare stars is summarized. Point sources were detected near the positions of several of the stars considered. However, of these, only the flare stars BY Draconis (dM0e) and AD Leonis (dM3.5e) appear to be likely candidates for the detected X-rays. Title: Discovery of X-rays from the 40 Eridani system. Authors: Cash, W.; Charles, P.; Bowyer, S.; Walter, F.; Ayres, T. R.; Linsky, J. L. Bibcode: 1979ApJ...231L.137C Altcode: The detection of a point source of soft X-rays (H0405-08) consistent with the position of the nearby triple star system 40 Eridani is reported. The source, which has a temperature near 10 million K, has a flux of 3 x 10 to the -11th erg/sqcm-sec at earth, implying a luminosity of 9(+ or -3) x 10 to the 28th erg/s at the distance of 40 Eridani. The likely source of the bulk of the X-rays is considered, including the K1 dwarf, the DA white dwarf, the dwarf M4 flare star, or accretion onto the white dwarf. Title: Chromospheric scaling laws, width-luminosity correlations, and the Wilson-Bappu effect. Authors: Ayres, T. R. Bibcode: 1979ApJ...228..509A Altcode: Simple scaling laws for the thickness and mean electron density of stellar chromospheres as functions of surface gravity and chromospheric heating are proposed. These scaling laws are shown to be a consequence of hydrostatic equilibrium, the influence of gas ionization on plasma cooling functions, and the assumption that chromospheric heating is relatively constant with height. It is argued that line width-luminosity correlations similar to those observed in the Ca II K and Mg II k resonance lines are implied by the chromospheric scaling laws if the outer edges of the K and k emission cores are formed in the Lorentzian wings of the absorption profile. The results are compared with the Wilson-Bappu effect, empirical width-luminosity correlations for Ca II K1 minimum features, and solar-plage profiles of the Ca II K and Mg II k resonance lines. Title: Capella: 1/2 of an RS CVn? Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1979BAAS...11..472A Altcode: No abstract at ADS Title: The center-to-limb behavior of Ca i λ6573 and [Ca ii] λ7324 Authors: Ayres, T. R.; Testerman, L. Bibcode: 1978SoPh...60...19A Altcode: 1978SoPh...60...19. Center-to-limb measurements of the Ca I λ6573 intercombination line and the Ca II λ7324 forbidden line are compared with synthetic profiles based on a simple representation of the non-LTE Ca-Ca+ ionization equilibrium. The effects of photoionizations from low lying excited states of neutral calcium are found to reduce the sensitivity of the λ6573 center-to-limb behavior as a thermal structure diagnostic. The synthetic center-to-limb behavior is also sensitive to uncertainties in the nonthermal broadening. Nevertheless, the measured center-to-limb behavior of λ6573 favors a `cool' photospheric model similar to the Vernazza, Avrett, and Loeser model M over hotter models based on the Ca II K wings. The non-LTE calcium abundance obtained from the disk center equivalent widths of λ6573 and λ7324 using the best fit model is ACa≅2.1±0.2 × 10-6 (by number relative to hydrogen). Applications of these lines as diagnostics of the Ca-Ca+ ionization equilibrium in other stars are briefly discussed. Title: Upper limits on extreme ultraviolet radiation from nearby main sequence and subgiant stars. Authors: Ayres, T. R.; Linsky, J. L.; Margon, B.; Bowyer, S. Bibcode: 1978A&A....70..431A Altcode: Flux upper limits for 44-800 A radiation were measured in a sample of nearby main sequence stars and one subgiant star with the aid of the Apollo-Soyuz grazing incidence telescope. Comparisons of emission measure upper limits with three different methods for predicting coronal properties cannot yet determine which, if any, are valid. Data for Alpha Centauri A and B are consistent with recent HEAO-1 soft X-ray measurements which suggest that the surface flux of coronal emission from the Alpha Cen system is comparable to that of the 'normal' sun. Title: Center-to-limb behavior of first-overtone vibration-rotation transitions of solar carbon monoxide. Authors: Ayres, T. R. Bibcode: 1978ApJ...225..665A Altcode: High-spectral-resolution measurements of the center-to-limb behavior of weak transitions in the carbon monoxide first-overtone (A V = 2) vibration-rotation bands (w 4300 cm -`) are compared with synthetic line widths and equivalent widths for a range of single-component and multicomponent models of the solar photosphere. The single-component thermal structure in best quantitative agreement with the observed properties of the solar CO spectrum is similar to the Vernazza, Avrett, and Loeser model M. Multicomponent models consisting of Gaussian- distributed temperature perturbations around the best-fit model do not significantly affect the computed center-to-limb behavior of CO lines or the solar carbon abundance derived from measured disk-center equivalent widths. The equivalent width ratios of low- and high-excitation lines within a given vibration-rotation band are found to be inconsistent with "hot" upperphotosphere models, such as the Linsky and Ayres and Holweger and semiempirical single-component models, as well as with the two-stream thermal structure proposed by Tsuji. Excitation ratios and center-to-limb behavior of CO lines require a solar carbon abundance near 3 x 10- for an assumed oxygen abundance of 7 x 10- . This value is consistent with carbon abundances obtained by Tsuji (CO) and Mount and Linsky (CN), but is much smaller than the revised solar carbon abundance recommended recently by Lambert. Subject headings: molecular processes - Sun: abundances - Sun: atmosphere - Sun: spectra Title: IUE observations of cool stars : alf Aur, HR 1099, lam and EPS Eri. Authors: Linsky, J. L.; Ayres, T. R.; Basri, G. S.; Morrison, N. D.; Boggess, A.; Schiffer, F. H., III; Holm, A.; Cassatella, A.; Heck, A.; Macchetto, F.; Stickland, D.; Wilson, R.; Blanco, C.; Dupree, A. K.; Jordan, C.; Wing, R. F. Bibcode: 1978Natur.275..389L Altcode: Initial IUE observations of four cool stars are reported. Observed fluxes and surface fluxes are given for several UV emission lines in the spectral range 1175-2000 A, obtained at low and high dispersion with the short-wavelength spectrograph and camera. These lines are formed in the outer atmospheres of these stars, in regions presumably analogous to the solar chromosphere and transition region. The surface fluxes in the lines increase along the sequence: quiet sun, Epsilon Eri, Lambda And, Alpha Aur, and HR1099. The 2.8-d RS CVn-type binary HR1099, observed on 1 March 1978 near the end of a major flaring episode, has line surface fluxes roughly 100 times that of the quiet sun, similar to those seen in solar flares. Line profiles and flux ratios in multiplets for Capella are presented, and comments given on the opacity of the lines and on a tendency of line width to increase with temperature of formation. Title: Evolution of the alpha Centauri system. Authors: Flannery, B. P.; Ayres, T. R. Bibcode: 1978ApJ...221..175F Altcode: Available astrometric and photometric data are examined and in some cases reanalyzed in order to derive accurate estimates for the stellar masses, luminosities, temperatures, and chemical compositions of the A and B components of Alpha Centauri. Theoretical evolutionary sequences for the A and B components are computed for two values of metallicity, Z = 0.02 and 0.04; a reference solar model with Z = 0.02 is also calculated. The observed abundances are partially reanalyzed on the basis of the equivalent measurements of French and Powell (1971), which provide a consistency check on the evolutionary models. The results indicate that: (1) the system is partially evolved since component A is 30% brighter with respect to B than would be expected for an unevolved system; (2) the system is somewhat metal-rich with respect to the sun; (3) the age of Alpha Cen is 6 billion years and the helium abundance is essentially solar for an evolutionary sequence with twice the solar metals; and (4) the components of Alpha Cen are also similar to the sun in terms of galactic orbits. The difference in Z between the sun and Alpha Cen is shown to be consistent with the idea that there is a substantial dispersion in the metallicity of the interstellar medium at any one time. Title: IUE Observations of the RS CVn Stars HR 1099 and λ And Authors: Ayres, T. R.; Linsky, J. L.; Morrison, N. D. Bibcode: 1978BAAS...10R.444A Altcode: No abstract at ADS Title: A comparison of synthetic and measured solar continuum intensities and limb darkening coefficients. Authors: Ayres, T. R. Bibcode: 1978SoPh...57...19A Altcode: Absolute continuum intensities and wavelength-dependent low-order polynomial fits to optical and infrared continuum limb darkening provide useful discriminants among single-component models of the solar photosphere. The thermal structure in best quantitative agreement with the recent center-limb measurements by Pierce and Slaughter (1977) and by Pierce et. al. (1977) is the semi-empirical model by Vernazza, Avrett and Loeser (VAL). However, the VAL model M temperatures must be scaled upward by a factor of 1.015 ±0.005 to be consistent with the Labs and Neckel absolute calibration of continuum high points in the optical region 0.40-0.65 μm. Title: Stellar model chromospheres. VI. Empirical estimates of the chromospheric radiative losses of late-type stars. Authors: Linsky, J. L.; Ayres, T. R. Bibcode: 1978ApJ...220..619L Altcode: A method is developed for estimating the nonradiative heating of stellar chromospheres by measuring the net radiative losses in strong Fraunhofer line cores. This method is applied to observations of the Mg II resonance lines in a sample of 32 stars including the sun. At most a small dependence of chromospheric nonradiative heating on stellar surface gravity is found, which is contrary to the large effect predicted by recent calculations based on acoustic-heating theories. Title: High Resolution IUE Observations of α AUR: Is the Outer Atmosphere of Capella Similar to a Sunspot? Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1978BAAS...10Q.444A Altcode: No abstract at ADS Title: A Search for Solar Global Oscillations in the CA Ii K-Line Authors: Beckers, Jacques M.; Ayres, Thomas R. Bibcode: 1977ApJ...217L..69B Altcode: No abstract at ADS Title: Evolution of the α Centauri System. Authors: Flannery, B. P.; Ayres, T. R. Bibcode: 1977BAAS....9..638F Altcode: No abstract at ADS Title: Nonthermal broadening in the solar photosphere derived from widths of weak absorption features in the Ca II H and K wings. Authors: Ayres, T. R. Bibcode: 1977ApJ...214..905A Altcode: The depth dependence of nonthermal broadening in the solar photosphere is estimated using the widths of weak absorption features in spatially averaged profiles of the Ca II H and K wings. The inferred vertical component of the photospheric total-motion field does not show a significant depth dependence in constrast to previously proposed models which have sharply inward increasing velocities in the deep photosphere. The mean Gaussian nonthermal broadening obtained is 1.6 + or - 0.1 km/s (one-half full e-folding width). In addition, the inferred nonthermal broadening is used to estimate thermal widths, and therefore also atomic weights, for several weak features in the H and K wings which are unidentified or have uncertain identifications. It is found that the majority of these are consistent with rare-earth absorption. Title: The surface gravity and mass of Arcturus. Authors: Ayres, T. R.; Johnson, H. R. Bibcode: 1977ApJ...214..410A Altcode: The surface gravity of the K giant Arcturus is estimated by comparing synthetic spectra based on model atmospheres with measured wing shapes of the Ca I and Ca II resonance lines calibrated by absolute photometry. The result, log g of approximately 1.6 cm/sec per sec, is consistent with previous spectroscopic estimates based on weak-line ionization ratios, with the exception of a recent determination by Maeckle et al. (1975). A stellar mass of 1.1(+1.7, -0.7) solar masses is obtained for a radius of 27 solar radii. This estimate suggests that Arcturus has not suffered substantial mass loss during its post-main-sequence evolution on the 'ascending red-giant branch'. Title: A reexamination of solar upper photosphere models, the calcium abundance, and empirical damping parameters. Authors: Ayres, T. R. Bibcode: 1977ApJ...213..296A Altcode: A general iterative method is described for constructing thermal models of the solar photosphere consistent with observed strong and weak lines of Ca I and Ca II. Calibrations of the solar calcium abundance and the van der Waals parameter for important Ca I and Ca II lines are obtained using plane-parallel largely LTE model atmospheres, and these thermal models are modified for better fits to the measured Ca II H and K inner wing shapes. Possible sources of error in this semiempirical approach are evaluated. The derived hydrogen van der Waals broadening is compared with theoretical estimates of that broadening as well as with experimental measurements of the helium broadening Title: Stellar model chromospheres. V. Alpha Centauri A (G2 V) and Alpha Centauri B (K1 V). Authors: Ayres, T. R.; Linsky, J. L.; Rodgers, A. W.; Kurucz, R. L. Bibcode: 1976ApJ...210..199A Altcode: Models for the upper photospheres and lower chromospheres of Alpha Centauri A and B are derived from high-dispersion spectrograms of the Ca II K-line emission cores and damping wings. Effective temperatures, surface gravities, and ages consistent with the measured broadband colors, metallicities, and absolute magnitudes are estimated for the two stars. The spectrograms are calibrated by fitting the far-wing K profiles with synthetic fluxes based on radiative-equilibrium models, and the model atmospheres are obtained through a partial-redistribution analysis of the line cores and damping wings. These models are compared with those previously proposed for Procyon, Arcturus, and the sun. Many features in all the models are found to be quite similar, and some evidence suggests that Alpha Cen A may be significantly older and more evolved than the sun, even though both stars exhibit similar chromospheric properties. Title: The MG II h and k lines. II. Comparison with synthesized profiles and Ca II K. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1976ApJ...205..874A Altcode: Measured high-dispersion center and limb profiles of the solar Mg II h and k resonance lines are compared with synthetic spectra computed with a partial-redistribution formalism and based on several upper-photosphere and lower-chromosphere temperature distributions. Profiles of the analogously formed Ca II K resonance line are also synthesized for the same atmospheric models. The spectrum-synthesis approach is outlined, and the collisional and fixed radiative rates appropriate to the adopted model atoms and solar atmosphere are discussed. It is found that the HSRA and VAL models predict systematically lower intensities in the h, k, and K inner wings than observed and that models with a somewhat higher minimum temperature (about 4450 K) can reproduce the measured inner wings and limb darkening. A 'Ca II' solar model with a minimum temperature of 4450 K is proposed as an alternative to the class of models based on continuum observations. Title: The Mass of Arcturus Authors: Ayres, T. R.; Johnson, H. R. Bibcode: 1976BAAS....8..303A Altcode: No abstract at ADS Title: Semiempirical upper photosphere models: the sun (G2 V) and Procyon (F5 IV-V). Authors: Ayres, T. R. Bibcode: 1975ApJ...201..799A Altcode: A description is presented of an approach for developing a model of the average upper photosphere temperature structure of a late-type star. The approach makes use of the frequency dependence of the damping wing opacity of a strong resonance line. Difficulties related to a dependence on uncertain constant and parameter values are to be overcome with the aid of a 'calibration' relative to a solar photosphere model obtained by an independent method. Title: Stellar model chromospheres. IV. The formation of the Hepsilon feature in the sun (G2 V) and Arcturus (K2 III). Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1975ApJ...201..212A Altcode: The formation of the Balmer-series member H-epsilon in the near-red wing of the Ca II H line is discussed for two cases: the sun (H-epsilon absorption profile) and Arcturus (H-epsilon emission profile). It is shown that although the H-epsilon source functions in both stars are dominated by the Balmer-continuum radiation field through photoionizations, the line-formation problems in the two stars are quantitatively different, owing to a substantial difference in the relative importance of the stellar chromosphere temperature inversion as compared with the stellar photosphere. Title: Stellar model chromospheres. III. Arcturus (K2 III). Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1975ApJ...200..660A Altcode: Models are constructed for the upper photosphere and chromosphere of Arcturus based on the H, K, and IR triplet lines of Ca II and the h and k lines of Mg II. The chromosphere model is derived from complete redistribution solutions for a five-level Ca II ion and a two-level Mg II ion. A photospheric model is derived from the Ca II wings using first the 'traditional' complete-redistribution limit and then the more realistic partial-redistribution approximation. The temperature and mass column densities for the temperature-minimum region and the chromosphere-transition region boundary are computed, and the pressure in the transition region and corona are estimated. It is found that the ratio of minimum temperature to effective temperature is approximately 0.77 for Arcturus, Procyon, and the sun, and that mass tends to increase at the temperature minimum with decreasing gravity. The pressure is found to be about 1 percent of the solar value, and the surface brightness of the Arcturus transition region and coronal spectrum is estimated to be much less than for the sun. The partial-redistribution calculation for the Ca II K line indicates that the emission width is at least partially determined by damping rather than Doppler broadening, suggesting a reexamination of previous explanations for the Wilson-Bappu effect. Title: A non-LTE analysis of the CN 3883 Å band head in the upper photosphere of Arcturus. Authors: Mount, G. H.; Ayres, T. R.; Linsky, J. L. Bibcode: 1975ApJ...200..383M Altcode: A detailed non-LTE study of the CN(0,0) 3883 A band-head spectrum of Arcturus (K2 iii) provides an accurate determination of the carbon, nitrogen, and oxygen abundances in Arcturus. Non-LTE effects are significant, and we find that the Ayres-Linsky model provides an adequate fit to the observations for [C,N]* = 13[C,N]0 and [O]* = 0.60[0]o, or for [C,N,O]* = 16[C,N,O]0, but the latter abundances are unlikely. The upper photospheric microturbulence is found to be 2.5 + . Subject headings: abundances, stellar - atmospheres, stellar - late-type stars - molecules - stars, individual (alpha Boo) Title: The MG II H and K lines. II. Comparison with synthesized profiles and CA II K Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1975STIN...7722038A Altcode: The Mg II h and k resonance line data and profiles of the Ca II K line are compared with synthetic profiles computed using a partial redistribution formalism and several single-component solar upper photosphere and lower chromosphere models. It is found that second models predict systematically lower intensities in the h, k, and K inner wings than are observed, but that models with a somewhat larger minimum temperature (T(min) about 4450 K) can reproduce the measured inner wing intensities and limb darkening of these resonance lines. A 'hot' T(min) solar model, which is reasonably consistent with the empirical emission cores and wing intensities of the Ca II and Mg II resonance lines is proposed to serve as an alternative to the class of models, such as the HSRA and VAL, based on continuum observations. Title: Resonance line transfer with partial redistribution. III. Mg II resonance lines in solar-type stars. Authors: Milkey, R. W.; Ayres, T. R.; Shine, R. A. Bibcode: 1975ApJ...197..143M Altcode: We discuss the gravity dependence of the Mg II resonance lines calculated with inclusion of effects of partial redistribution in frequency. Using chromospheric models scaled from a solar model, we demonstrate the increased decoupling of the radiation temperature of the k1 feature from the minimum electron temperature in lower-gravity models. The limb darkening of the k-line in the main-sequence model is also discussed. Title: Stellar Upper Photosphere Models Based on the Ca II K-wing. II. The Coherent Scattering Approximation Authors: Ayres, T. R.; Linsky, J. L.; Shine, R. A. Bibcode: 1975BAAS....7..359A Altcode: No abstract at ADS Title: A possible width-luminosity correlation of the Ca II K1 and Mg II k1 features. Authors: Ayres, T. R.; Linsky, J. L.; Shine, R. A. Bibcode: 1975ApJ...195L.121A Altcode: Existing high resolution stellar profiles of the Ca II and Mg II resonance lines suggest a possible width-luminosity correlation of the K1 minimum features. It is shown that such a correlation can be simply understood if the continuum optical depth of the stellar temperature minimum is relatively independent of surface gravity as suggested by three stars studied in detail. Title: The lower chromospheres and upper chromospheres of late-type stars Authors: Ayres, Thomas Russell Tom Bibcode: 1975PhDT........99A Altcode: No abstract at ADS Title: The Lower Chromospheres and Upper Photospheres of Late-Type Stars. Authors: Ayres, T. R. Bibcode: 1975PhDT.........3A Altcode: High dispersion, well calibrated profiles of Ca 2 K, Mg 2 h and k, and H are interpreted in five late-type stars, including the sun, by constructing plane-parallel, hydrostatic atmospheric models and synthesizing spectra using a partial redistribution formalism. In the empirical data there is a strong correlation between the widths of the K1 inner wing minimum features and luminosity, analogous to the Wilson-Bappu effect obeyed by the Ca 2 and Mg 2 emission half-widths. It is shown qualitatively that this behavior of the K1 features would be expected if the continuum optical depth of the stellar temperature minimum is relatively independent of surface gravity, and support this conjecture by detailed modeling of the temperature minimum regions of the five program stars. Title: Stellar Model Chromospheres. H. Procyon (F5 Iv/v) Authors: Ayres, Thomas R.; Linsky, Jeffrey L.; Shine, Richard A. Bibcode: 1974ApJ...192...93A Altcode: 1974ApJ...192...95A No abstract at ADS Title: The Formation of the Hɛ Emission Feature in Late-Type Stars. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1974BAAS....6..226A Altcode: No abstract at ADS Title: A Model for the Chromosphere of Arcturus. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1973BAAS....5Q.454A Altcode: No abstract at ADS Title: Photospheric Models Based on the Wings of the Ca II Lines. Authors: Shine, R. A.; Ayres, T. R. Bibcode: 1973BAAS....5..453S Altcode: No abstract at ADS Title: A model for the chromosphere of Arcturus. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1973BAAS....5..336A Altcode: No abstract at ADS Title: A simple explanation of the Wilson-Bappu effect. Authors: Ayres, T. R.; Linsky, J. L.; Shine, R. A.; Chipman, E. Bibcode: 1973BAAS....5..364A Altcode: No abstract at ADS Title: A Model for the Chromosphere of Arcturus. Authors: Ayres, T. R.; Linsky, J. L. Bibcode: 1973BAAS....5R.336A Altcode: No abstract at ADS Title: Stellar model chromospheres. I. On the temperature minima of F,G, and K stars. Authors: Linsky, J. L.; Ayres, T. Bibcode: 1973ApJ...180..473L Altcode: Brightness temperatures are deduced for the Hiv and Kiv features of the Ca ii resonance lines in Procyon (F5 IV-V), Arcturus (K2 IlIp), and the Sun (G2 V). The brightness temperatures of Procyon and the Sun are in the same ratio as their effective temperatures, suggesting a simple scaling law for the temperature minima of F and early G stars. Arcturus departs from this law in a way that can be explained by CO line blanketing. Subject headings: Ca ii emission - chromosphere, solar chromospheres, stellar - late-type stars Title: Equator-Pole Temperature Difference and the Solar Oblateness Authors: Noyes, R. W.; Ayres, T. R.; Hall, D. N. B. Bibcode: 1973SoPh...28..343N Altcode: No abstract at ADS Title: Discovery of upper photospheric temperature inversions or chromospheres in early A stars. Authors: Linsky, J. L.; Shine, R. A.; Ayres, T. R.; Praderie, F. Bibcode: 1973BAAS....5....3L Altcode: No abstract at ADS Title: Discovery of Chromospheres in Early A Stars. Authors: Linsky, J. L.; Shine, R. A.; Ayres, T. R.; Praderie, F. Bibcode: 1973BAAS....5R...3L Altcode: No abstract at ADS Title: A Model for the Chromosphere of Procyon. Authors: Linsky, J. L.; Ayres, T. R. Bibcode: 1972BAAS....4..334L Altcode: No abstract at ADS Title: The Identification of ^{13}C^{16}O in the Infrared Sunspot Spectrum and the Determination of the Solar ^{12}C/^{13}C Abundance Ratio Authors: Hall, Donald N. B.; Noyes, Robert W.; Ayres, Thomas R. Bibcode: 1972ApJ...171..615H Altcode: The presence of the first-overtone vibration-rotation bands of 13C16O in the infrared sunspot spectrum has been established on the basis of wavenumber and relative intensity consistency of 30 weak lines. Nine particularly clean lines have been used to obtain a solar 12C/13C abundance ratio of 90 with a probable error of 15 percent.