Author name code: saar ADS astronomy entries on 2022-09-14 author:"Saar, Steven H." ------------------------------------------------------------------------ Title: Unsigned Magnetic Flux as a Proxy for Radial-velocity Variations in Sun-like Stars Authors: Haywood, R. D.; Milbourne, T. W.; Saar, S. H.; Mortier, A.; Phillips, D.; Charbonneau, D.; Cameron, A. Collier; Cegla, H. M.; Meunier, N.; , M. L. Palumbo, III Bibcode: 2022ApJ...935....6H Altcode: 2020arXiv200513386H A major obstacle to detecting and characterizing long-period, low-mass exoplanets is the intrinsic radial-velocity (RV) variability of host stars. To better understand RV variability, we estimate disk-averaged RV variations of the Sun over its magnetic cycle, from the Fe I line observed by SDO/HMI, using a physical model for rotationally modulated magnetic activity that was previously validated against HARPS-N solar observations. We estimate the unsigned magnetic flux and show that a linear fit to it reduces the RMS of RV variations by 62%, i.e., a factor of 2.6. We additionally apply the FF' method, which predicts RV variations based on a star's photometric variations. At cycle maximum, we find that additional processes must be at play beyond suppression of convective blueshift and velocity imbalances resulting from brightness inhomogeneities, in agreement with recent studies of RV variations. By modeling RV variations over the magnetic cycle using a linear fit to the unsigned magnetic flux, we recover injected planets at a period of ≍300 days with RV semi-amplitudes down to 0.3 m s-1. To reach 0.1 m s-1, we will need to identify and model additional phenomena that are not well traced by $| {\hat{B}}_{\mathrm{obs}}| $ or FF'. This study motivates ongoing and future efforts to develop observation and analysis techniques to measure the unsigned magnetic flux at high precision in slowly rotating, relatively inactive stars like the Sun. We conclude that the unsigned magnetic flux is an excellent proxy for rotationally modulated, activity-induced RV variations, and could become key to confirming and characterizing Earth analogs. Title: HD 166620: Portrait of a Star Entering a Grand Magnetic Minimum Authors: Luhn, Jacob K.; Wright, Jason T.; Henry, Gregory W.; Saar, Steven H.; Baum, Anna C. Bibcode: 2022arXiv220700612L Altcode: HD 166620 was recently identified as a Maunder Minimum candidate based on nearly 50 years of Ca II H & K activity data from Mount Wilson and Keck-HIRES (Baum et al. 2022). These data showed clear cyclic behavior on a 17-year timescale during the Mount Wilson survey that became flat when picked up later with Keck-HIRES planet-search observations. Unfortunately, the transition between these two data sets -- and therefore the transition into the candidate Maunder Minimum phase -- contained little to no data. Here we present additional Mount Wilson data not present in Baum et al. (2022) along with photometry over a nearly 30-year baseline that definitively trace the transition from cyclic activity to a prolonged phase of flat activity. We present this as conclusive evidence of the star entering a grand magnetic minimum and therefore the first true Maunder Minimum analog. We further show that neither the overall brightness nor the chromospheric activity level (as measured by S$_{\mathrm{HK}}$) is significantly lower during the grand magnetic minimum than its activity cycle minimum, implying that anomalously low mean or instantaneous activity levels are not a good diagnostic or criterion for identifying additional Maunder Minimum candidates. Intraseasonal variability in S$_{\mathrm{HK}}$, however, is lower in the star's grand minimum; this may prove a useful symptom of the phenomenon. Title: VizieR Online Data Catalog: K2-79 and K2-222 photometry and radial velocity (Nava+, 2022) Authors: Nava, C.; Lopez-Morales, M.; Mortier, A.; Zeng, Li; Giles, H. A. C.; Bieryla, A.; Vanderburg, A.; Buchhave, L. A.; Poretti, E.; Saar, S. H.; Dumusque, X.; Latham, D. W.; Charbonneau, D.; Damasso, M.; Bonomo, A. S.; Lovis, C.; Collier, Cameron A.; Eastman, J. D.; Sozzetti, A.; Cosentino, R.; Pedani, M.; Pepe, F.; Molinari, E.; Sasselov, D.; Mayor, M.; Stalport, M.; Malavolta, L.; Rice, K.; Watson, C. A.; Martinez Fiorenzano, A. F.; di Fabrizio, L. Bibcode: 2022yCat..51630041N Altcode: We analyzed 3161 and 3424 photometric K2 observations of K2-79 and K2-222, respectively, collected in long-cadence (29.4minutes) mode. K2-79 was observed between 2015 February 10 and 2015 April 20 and K2-222 between 2016 January 6 and 2016 March 23.

We collected 79 spectra of K2-79 over four seasons between 2015 November 4 and 2019 December 29, and 63 spectra of K2-222 over three seasons between 2016 August 14 and 2019 December 23. All spectra were collected with HARPS-N, the high-precision spectrograph mounted on the Telescopio Nationale de Galileo at the Observatorio del Roque de los Muchachos in La Palma, Spain. The spectrograph covers wavelengths in the range 383-690nm, with average resolving power R=115000

(4 data files). Title: X-Ray Stellar Cycles at Low Rossby Numbers Authors: Irving, Zackery; Wargelin, Bradford; Do Nascimento, José-Dias; Saar, Steven Bibcode: 2022HEAD...1910102I Altcode: Stellar cycles, like that of our Sun, can be explained by dynamo theory, whereby kinetic energy is converted into magnetic energy via inductive effects of motions in an electrically conducting fluid. Unlike the Sun, however, Proxima Centauri (M5.5) is a fully convective star, and as such is not expected to be able to support a solar-like dynamo. Nonetheless, there is strong evidence in the optical, UV, and X-ray wavebands suggesting that Prox Cen possesses an 8-yr activity cycle. Analysis of this star could therefore provide key insights into the underlying mechanisms responsible for stellar cycles. We use Gaussian process regression (GPR) to model the rotational and cyclical variability of Prox Cen — and three other stars spanning a range of stellar type, rotation rate, and activity — and examine correlations (or their lack) among the different wavebands. GPR is preferred over traditional time-series analysis methods (e.g. fast Fourier transforms, Lomb-Scargle periodograms) as we are analysing quasi-periodic, unevenly sampled light curves, and GPR fits are better at following the data and interpolating over gaps. Title: VizieR Online Data Catalog: Ruprecht 147 members & rot. data for 5 other cl. (Curtis+, 2020) Authors: Curtis, J. L.; Agueros, M. A.; Matt, S. P.; Covey, K. R.; Douglas, S. T.; Angus, R.; Saar, S. H.; Cody, A. M.; Vanderburg, A.; Law, N. M.; Kraus, A. L.; Latham, D. W.; Baranec, C.; Riddle, R.; Ziegler, C.; Lund, M. N.; Torres, G.; Meibom, S.; Aguirre, V. S.; Wright, J. T. Bibcode: 2022yCat..19040140C Altcode: We have observed 130 cluster stars with Robo-AO in 2013 while it was on the Palomar 60-inch telescope (see Curtis 2016PhDT.......246C), of which 50 are dwarfs less massive than the 1.4Mȯ cutoff for this study. See Section 2.3.3.

Our team petitioned to adjust the pointing for K2's Campaign 7 so that it covered Ruprecht 147, which we then proposed to monitor (GO proposal 7035). Our GO program was allocated 1086 individual apertures for candidate members. A series of contiguous apertures, a "superstamp", was created to tile the inner cluster core in response to a different proposal and covered 96 additional candidates from our preliminary membership list (Cody+ 2018RNAAS...2Q..25C). See Section 3.1.

We monitored Ruprecht 147 from 2012 April 29 to 2012 October 7 as part of the PTF Open Cluster Survey. This survey used the robotic 48-inch Oschin (P48) telescope at Palomar Observatory, CA. See Section 3.2.

(2 data files). Title: K2-79b and K2-222b: Mass Measurements of Two Small Exoplanets with Periods beyond 10 days that Overlap with Periodic Magnetic Activity Signals Authors: Nava, Chantanelle; López-Morales, Mercedes; Mortier, Annelies; Zeng, Li; Giles, Helen A. C.; Bieryla, Allyson; Vanderburg, Andrew; Buchhave, Lars A.; Poretti, Ennio; Saar, Steven H.; Dumusque, Xavier; Latham, David W.; Charbonneau, David; Damasso, Mario; Bonomo, Aldo S.; Lovis, Christophe; Collier Cameron, Andrew; Eastman, Jason D.; Sozzetti, Alessandro; Cosentino, Rosario; Pedani, Marco; Pepe, Francesco; Molinari, Emilio; Sasselov, Dimitar; Mayor, Michel; Stalport, Manu; Malavolta, Luca; Rice, Ken; Watson, Christopher A.; Martinez Fiorenzano, A. F.; Di Fabrizio, Luca Bibcode: 2022AJ....163...41N Altcode: 2021arXiv211102608N We present mass and radius measurements of K2-79b and K2-222b, two transiting exoplanets orbiting active G-type stars observed with HARPS-N and K2. Their respective 10.99 day and 15.39 day orbital periods fall near periods of signals induced by stellar magnetic activity. The two signals might therefore interfere and lead to an inaccurate estimate of exoplanet mass. We present a method to mitigate these effects when radial velocity (RV) and activity-indicator observations are available over multiple observing seasons and the orbital period of the exoplanet is known. We perform correlation and periodogram analyses on subsets composed of each target's two observing seasons, in addition to the full data sets. For both targets, these analyses reveal an optimal season with little to no interference at the orbital period of the known exoplanet. We make a confident mass detection of each exoplanet by confirming agreement between fits to the full RV set and the optimal season. For K2-79b, we measure a mass of 11.8 ± 3.6 M ⊕ and a radius of 4.09 ± 0.17 R ⊕. For K2-222b, we measure a mass of 8.0 ± 1.8 M ⊕ and a radius of 2.35 ± 0.08 R ⊕. According to model predictions, K2-79b is a highly irradiated Uranus analog and K2-222b hosts significant amounts of water ice. We also present a RV solution for a candidate second companion orbiting K2-222 at 147.5 days. Title: VizieR Online Data Catalog: Solar analog rotations from Kepler & Gaia (Do Nascimento+, 2020) Authors: Do Nascimento, J. -D., Jr.; de Almeida, L.; Velloso, E. N.; Anthony, F.; Barnes, S. A.; Saar, S. H.; Meibom, S.; da Costa, J. S.; Castro, M.; Yana Galarza, J.; Lorenzo-Oliveira, D.; Beck, P. G.; Melendez, J. Bibcode: 2021yCat..18980173D Altcode: A major obstacle to interpreting the rotation period distribution for main-sequence stars from Kepler mission data has been the lack of a precise evolutionary status for these objects. We address this by investigating the evolutionary status based on Gaia Data Release 2 parallaxes and photometry for more than 30000 Kepler stars with rotation period measurements. Many of these are subgiants and should be excluded in future work on dwarfs. We particularly investigate a 193-star sample of solar analogs and report newly determined rotation periods for 125 of these. These include 54 stars from a prior sample, of which we can confirm the periods for 50. The remainder are new, and 10 of them longer than a solar rotation period, suggesting that Sun-like stars continue to spin down on the main sequence past solar age. Our sample of solar analogs could potentially serve as a benchmark for future missions, such as PLAnetary Transits and Oscillations of stars, and emphasizes the need for additional astrometric, photometric, and spectroscopic information before interpreting the stellar populations and results from time series surveys.

(1 data file). Title: Magnetic and Rotational Evolution of ρ CrB from Asteroseismology with TESS Authors: Metcalfe, Travis S.; van Saders, Jennifer L.; Basu, Sarbani; Buzasi, Derek; Drake, Jeremy J.; Egeland, Ricky; Huber, Daniel; Saar, Steven H.; Stassun, Keivan G.; Ball, Warrick H.; Campante, Tiago L.; Finley, Adam J.; Kochukhov, Oleg; Mathur, Savita; Reinhold, Timo; See, Victor; Baliunas, Sallie; Soon, Willie Bibcode: 2021ApJ...921..122M Altcode: 2021arXiv210801088M During the first half of main-sequence lifetimes, the evolution of rotation and magnetic activity in solar-type stars appears to be strongly coupled. Recent observations suggest that rotation rates evolve much more slowly beyond middle age, while stellar activity continues to decline. We aim to characterize this midlife transition by combining archival stellar activity data from the Mount Wilson Observatory with asteroseismology from the Transiting Exoplanet Survey Satellite (TESS). For two stars on opposite sides of the transition (88 Leo and ρ CrB), we independently assess the mean activity levels and rotation periods previously reported in the literature. For the less active star (ρ CrB), we detect solar-like oscillations from TESS photometry, and we obtain precise stellar properties from asteroseismic modeling. We derive updated X-ray luminosities for both stars to estimate their mass-loss rates, and we use previously published constraints on magnetic morphology to model the evolutionary change in magnetic braking torque. We then attempt to match the observations with rotational evolution models, assuming either standard spin-down or weakened magnetic braking. We conclude that the asteroseismic age of ρ CrB is consistent with the expected evolution of its mean activity level and that weakened braking models can more readily explain its relatively fast rotation rate. Future spectropolarimetric observations across a range of spectral types promise to further characterize the shift in magnetic morphology that apparently drives this midlife transition in solar-type stars. Title: Estimating Magnetic Filling Factors from Simultaneous Spectroscopy and Photometry: Disentangling Spots, Plage, and Network Authors: Milbourne, T. W.; Phillips, D. F.; Langellier, N.; Mortier, A.; Haywood, R. D.; Saar, S. H.; Cegla, H. M.; Collier Cameron, A.; Dumusque, X.; Latham, D. W.; Malavolta, L.; Maldonado, J.; Thompson, S.; Vanderburg, A.; Watson, C. A.; Buchhave, L. A.; Cecconi, M.; Cosentino, R.; Ghedina, A.; Gonzalez, M.; Lodi, M.; López-Morales, M.; Sozzetti, A.; Walsworth, R. L. Bibcode: 2021ApJ...920...21M Altcode: 2021arXiv210509113M State-of-the-art radial velocity (RV) exoplanet searches are limited by the effects of stellar magnetic activity. Magnetically active spots, plage, and network regions each have different impacts on the observed spectral lines and therefore on the apparent stellar RV. Differentiating the relative coverage, or filling factors, of these active regions is thus necessary to differentiate between activity-driven RV signatures and Doppler shifts due to planetary orbits. In this work, we develop a technique to estimate feature-specific magnetic filling factors on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our technique using observations from the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE. We then compare the results of each technique to direct observations by the Solar Dynamics Observatory. Both implementations yield filling factor estimates that are highly correlated with the observed values. Modeling the solar RVs using these filling factors reproduces the expected contributions of the suppression of convective blueshift and rotational imbalance due to brightness inhomogeneities. Both implementations of this technique reduce the overall activity-driven rms RVs from 1.64 to 1.02 m s-1, corresponding to a 1.28 m s-1 reduction in the rms variation. The technique provides an additional 0.41 m s-1 reduction in the rms variation compared to traditional activity indicators. Title: ALMA small-scale features in the quiet Sun and active regions Authors: Brajša, R.; Skokić, I.; Sudar, D.; Benz, A. O.; Krucker, S.; Ludwig, H. -G.; Saar, S. H.; Selhorst, C. L. Bibcode: 2021A&A...651A...6B Altcode: 2021arXiv210503644B
Aims: The main aim of the present analysis is to decipher (i) the small-scale bright features in solar images of the quiet Sun and active regions obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and (ii) the ALMA correspondence of various known chromospheric structures visible in the Hα images of the Sun.
Methods: Small-scale ALMA bright features in the quiet Sun region were analyzed using single-dish ALMA observations (1.21 mm, 248 GHz) and in an active region using interferometric ALMA measurements (3 mm, 100 GHz). With the single-dish observations, a full-disk solar image is produced, while interferometric measurements enable the high-resolution reconstruction of part of the solar disk, including the active region. The selected quiet Sun and active regions are compared with the Hα (core and wing sum), EUV, and soft X-ray images and with the magnetograms.
Results: In the quiet Sun region, enhanced emission seen in the ALMA is almost always associated with a strong line-of-sight magnetic field. Four coronal bright points were identified, while other small-scale ALMA bright features are most likely associated with magnetic network elements and plages. In the active region, in 14 small-scale ALMA bright features randomly selected and compared with other images, we found five good candidates for coronal bright points, two for plages, and five for fibrils. Two unclear cases remain: a fibril or a jet, and a coronal bright point or a plage. A comparison of the Hα core image and the 3 mm ALMA image of the analyzed active region showed that the sunspot appears dark in both images (with a local ALMA radiation enhancement in sunspot umbra), the four plage areas are bright in both images and dark small Hα filaments are clearly recognized as dark structures of the same shape also in ALMA. Title: Long-term stellar activity variations and their effect on radial-velocity measurements Authors: Costes, Jean C.; Watson, Christopher A.; de Mooij, Ernst; Saar, Steven H.; Dumusque, Xavier; Cameron, Collier; Phillips, David F.; Günther, Maximilian N.; Jenkins, James S.; Mortier, Annelies; Thompson, Andrew P. G. Bibcode: 2021MNRAS.505..830C Altcode: 2021MNRAS.tmp.1143C; 2021arXiv210501915C Long-term stellar activity variations can affect the detectability of long-period and Earth-analogue extrasolar planets. We have, for 54 stars, analysed the long-term trend of five activity indicators: log $R^{\prime }_\mathrm{{HK}}$, the cross-correlation function (CCF) bisector span, CCF full-width-at-half-maximum, CCF contrast, and the area of the Gaussian fit to the CCF; and studied their correlation with the RVs. The sign of the correlations appears to vary as a function of stellar spectral type, and the transition in sign signals a noteworthy change in the stellar activity properties where earlier type stars appear more plage dominated. These transitions become more clearly defined when considered as a function of the convective zone depth. Therefore, it is the convective zone depth (which can be altered by stellar metallicity) that appears to be the underlying fundamental parameter driving the observed activity correlations. In addition, for most of the stars, we find that the RVs become increasingly redshifted as activity levels increase, which can be explained by the increase in the suppression of convective blueshift. However, we also find a minority of stars where the RVs become increasingly blueshifted as activity levels increase. Finally, using the correlation found between activity indicators and RVs, we removed RV signals generated by long-term changes in stellar activity. We find that performing simple cleaning of such long-term signals enables improved planet detection at longer orbital periods. Title: Detection Limits of Low-mass, Long-period Exoplanets Using Gaussian Processes Applied to HARPS-N Solar Radial Velocities Authors: Langellier, N.; Milbourne, T. W.; Phillips, D. F.; Haywood, R. D.; Saar, S. H.; Mortier, A.; Malavolta, L.; Thompson, S.; Collier Cameron, A.; Dumusque, X.; Cegla, H. M.; Latham, D. W.; Maldonado, J.; Watson, C. A.; Buchschacher, N.; Cecconi, M.; Charbonneau, D.; Cosentino, R.; Ghedina, A.; Gonzalez, M.; Li, C. -H.; Lodi, M.; López-Morales, M.; Micela, G.; Molinari, E.; Pepe, F.; Poretti, E.; Rice, K.; Sasselov, D.; Sozzetti, A.; Udry, S.; Walsworth, R. L. Bibcode: 2021AJ....161..287L Altcode: 2020arXiv200805970L Radial velocity (RV) searches for Earth-mass exoplanets in the habitable zone around Sun-like stars are limited by the effects of stellar variability on the host star. In particular, suppression of convective blueshift and brightness inhomogeneities due to photospheric faculae/plage and starspots are the dominant contribution to the variability of such stellar RVs. Gaussian process (GP) regression is a powerful tool for statistically modeling these quasi-periodic variations. We investigate the limits of this technique using 800 days of RVs from the solar telescope on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. These data provide a well-sampled time series of stellar RV variations. Into this data set, we inject Keplerian signals with periods between 100 and 500 days and amplitudes between 0.6 and 2.4 m s-1. We use GP regression to fit the resulting RVs and determine the statistical significance of recovered periods and amplitudes. We then generate synthetic RVs with the same covariance properties as the solar data to determine a lower bound on the observational baseline necessary to detect low-mass planets in Venus-like orbits around a Sun-like star. Our simulations show that discovering planets with a larger mass (∼0.5 m s-1) using current-generation spectrographs and GP regression will require more than 12 yr of densely sampled RV observations. Furthermore, even with a perfect model of stellar variability, discovering a true exo-Venus (∼0.1 m s-1) with current instruments would take over 15 yr. Therefore, next-generation spectrographs and better models of stellar variability are required for detection of such planets. Title: Linear and Neural Network Estimates of Magnetic Filling Factors on Sun-Like Stars Authors: Milbourne, T.; Phillips, D.; Langellier, N.; Saar, S.; Walsworth, R. Bibcode: 2021csss.confE.308M Altcode: State of the art radial velocity (RV) searches for low-mass exoplanets are limited by the effects of stellar magnetic activity. Previously, we have shown that different types of active regions - spots, plage, and network - have different impacts on the apparent stellar RV. Differentiating the relative coverage of these active regions is thus necessary in order to successfully disentangle the RV signatures of stars from potential planetary signals. However, traditional activity indicators, such as the calcium S-index and photometry, only indicate the overall coverage by magnetized regions: more information is necessary to differentiate the different types of active regions. In this work, we outline techniques to estimate magnetic filling factors from spots, plage, and networks features on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our techniques using real solar observations taken by the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE, and compare the results of each technique to filling factors derived from full-disk images from the Solar Dynamics Observatory. We conclude by assessing the possibilities of applying these techniques to non-solar targets. Title: Synthetic Spectra of TiO Bands to Identify Diagnostics of Starspot Properties Authors: Cheng, K. P.; Neff, J. E.; Giacinto, A.; Johnson, D.; Saar, S. Bibcode: 2021AAS...23755003C Altcode: Magnetic activity similar to that of the Sun is observed on a variety of cool stars. Strong magnetic fields in stellar interiors and produce many magnetic phenomena, including starspots in the photosphere. These starspots are a major source limiting the precision of high-precision radial velocity measurements used to characterize exoplanets. In a previous series of papers, we demonstrated an empirical approach to measure starspot properties using observed spectra of active and inactive stars as proxies for the spotted and non-spotted photosphere. These empirical methods were successful for heavily spotted stars, but they are not sensitive enough to unravel the jitter caused by numerous small spots. To overcome these limitations, we have evaluated a wide range of model atmospheres and spectrum synthesis codes, and we have assimilated suitable line lists. By characterizing composite (spot+nonspot) synthetic spectra from the entire range of parameter space for G and K stars, we have developed new diagnostic indicators that can be used to measure starspot properties from observed high-resolution spectra of spotted stars, including spot temperatures, areas, and the effective decrease in gravity caused by strong magnetic fields within the spots. Title: A Study of Equatorial Coronal Holes and Active regions during the Maximum Phase of four Solar Cycles Authors: Karna, Nishu; DeLuca, Edward; Pesnell, William; Saar, Steven; Karna, Mahendra Bibcode: 2021cosp...43E.920K Altcode: The 11-year Solar Cycle (SC) is characterized by periodic changes in solar activity indicators such as number of sunspots, coronal holes, active regions (ARs), as well as the occurrence rate of solar energetic events such as filament eruptions, flares and coronal mass ejections (CMEs). In this work we performed a statistical study of the equatorial coronal holes (ECHs) and ARs during the maximum phase of the last four solar cycles: SC 21 (1979--1982), SC 22 (1989--1992), SC 23 (1999--2002) and SC 24 (2012--2015). We compared the number of ECHs and ARs, separations between their centroids, solar wind speed, pressure and the number of intense geomagnetic storms (IGS) data over these four cycles. We note a strong anticorrelation between the number of ARs and ECHs. We found that the number of close ARs and ECHs, solar wind speed, and the number of IGS increases with average sunspot maximum number for even cycles and decreases with average sunspot maximum for odd cycles. These odd-even trends largely (though not entirely) disappear in the relation between the wind properties and the numbers of close AR and ECH. This suggests a possible link between ECH-AR interactions and the solar wind phenomena, though residual odd-even trends point to the importance of other effects (e.g., Sun-earth magnetic alignment) as well. Title: When Do Stalled Stars Resume Spinning Down? Advancing Gyrochronology with Ruprecht 147 Authors: Curtis, Jason Lee; Agüeros, Marcel A.; Matt, Sean P.; Covey, Kevin R.; Douglas, Stephanie T.; Angus, Ruth; Saar, Steven H.; Cody, Ann Marie; Vanderburg, Andrew; Law, Nicholas M.; Kraus, Adam L.; Latham, David W.; Baranec, Christoph; Riddle, Reed; Ziegler, Carl; Lund, Mikkel N.; Torres, Guillermo; Meibom, Søren; Aguirre, Victor Silva; Wright, Jason T. Bibcode: 2020ApJ...904..140C Altcode: 2020arXiv201002272C Recent measurements of rotation periods ( ${P}_{\mathrm{rot}}$ ) in the benchmark open clusters Praesepe (670 Myr), NGC 6811 (1 Gyr), and NGC 752 (1.4 Gyr) demonstrate that, after converging onto a tight sequence of slowly rotating stars in mass-period space, stars temporarily stop spinning down. These data also show that the duration of this epoch of stalled spin-down increases toward lower masses. To determine when stalled stars resume spinning down, we use data from the K2 mission and the Palomar Transient Factory to measure ${P}_{\mathrm{rot}}$ for 58 dwarf members of the 2.7 Gyr old cluster Ruprecht 147, 39 of which satisfy our criteria designed to remove short-period or near-equal-mass binaries. Combined with the Kepler ${P}_{\mathrm{rot}}$ data for the approximately coeval cluster NGC 6819 (30 stars with M⋆ > 0.85 ${M}_{\odot }$ ), our new measurements more than double the number of ≍2.5 Gyr benchmark rotators and extend this sample down to ≍0.55 ${M}_{\odot }$ . The slowly rotating sequence for this joint sample appears relatively flat (22 ± 2 days) compared to sequences for younger clusters. This sequence also intersects the Kepler intermediate-period gap, demonstrating that this gap was not created by a lull in star formation. We calculate the time at which stars resume spinning down and find that 0.55 ${M}_{\odot }$ stars remain stalled for at least 1.3 Gyr. To accurately age-date low-mass stars in the field, gyrochronology formulae must be modified to account for this stalling timescale. Empirically tuning a core-envelope coupling model with open cluster data can account for most of the apparent stalling effect. However, alternative explanations, e.g., a temporary reduction in the magnetic braking torque, cannot yet be ruled out. Title: A Study of Equatorial Coronal Holes during the Maximum Phase of Four Solar Cycles Authors: Karna, Mahendra Lal; Karna, Nishu; Saar, Steven H.; Pesnell, W. Dean; DeLuca, Edward E. Bibcode: 2020ApJ...901..124K Altcode: The 11 yr solar cycle (SC) is characterized by periodic changes in solar activity indicators such as the number of sunspots, coronal holes, and active regions (ARs), as well as the occurrence rate of solar energetic events such as filament eruptions, flares, and coronal mass ejections. In this work we performed a statistical study of the equatorial coronal holes (ECHs) and ARs during the maximum phase of the last four SCs: SC 21 (1979-1982), SC 22 (1989-1992), SC 23 (1999-2002), and SC 24 (2012-2015). We compared the number of ECHs and ARs, separations between their centroids, solar wind speed, pressure, and the number of intense geomagnetic storm (IGS) data over these four cycles. We note a strong anticorrelation between the number of ARs and ECHs. We found that the number of close ARs and ECHs, solar wind speed, and the number of IGS increases with average sunspot maximum number for even cycles and decreases with average sunspot maximum for odd cycles. Also, we find strong odd-even trends in the relation between the wind properties and the numbers of close AR and ECH. These results obtained from the annual average data suggest a possible link between ECH and AR proximity and the solar wind phenomena, though odd-even trends point to the importance of other effects (e.g., Sun-Earth magnetic alignment) as well. Title: Long-term Periodicities in Kepler Photometry of Open Cluster NGC 6811 Authors: Velloso, E. N.; do Nascimento, J. -D., Jr.; Saar, S. H. Bibcode: 2020ApJ...900..173V Altcode: Long-term photometric variability can sometimes be related to the emergence of starspots in the photosphere following a quasi-periodic magnetic activity cycle. In order to investigate the existence and properties of magnetic cycles in a narrow range of fundamental parameters, we focused on solar-type stars in the intermediate-age open cluster NGC 6811 (1 Gyr). The cluster membership was analyzed both in terms of stellar kinematics and Gaia photometry. Rotation periods and photometric variability were analyzed for 138 stars from Kepler light curves and we discuss the existing trends and relationships. We also searched a sample of 11 solar-type stars for cycle-like periodicities and in each case classified the variability as either cyclic, multicyclic, flat, or acyclic. The results suggest a significant scatter, possibly due to sensitive nonlinearities in the dynamo process. This raises theoretical questions on whether these periodicities can be associated to activity cycles and what determines the stellar cycle presence or its period. Also, the lack of solar-twin flat activity stars in NGC 6811 combined with other recent results, suggests that the presence of magnetic grand minima in the Sun is a relatively recent phenomenon. Title: The Secrets of Stellar Siestas: the Magnetic Grand Minimum Candidate HD 4915 Authors: Saar, Steven Bibcode: 2020cxo..prop.5810S Altcode: Magnetic grand minima (MGM) are mysterious episodes when the Sun's magnetic dynamo cycle "takes a siesta" and goes into temporary quiescence. The phenomenon has never been observed in modern times; what was the Sun like then? Recently a star was observed to have a decaying cycle amplitude (in Ca HK), making it a strong candidate for an MGM episode. We propose to study the star with Chandra and HST, to explore magnetic heating throughout its outer atmosphere. Results will be compared with cycle minima and stars with "flat activity" (objects which may be in MGM or have "dead" dynamos) to explore similarities and differences, and reveal what may lie in store for our own Sun in the near future. Title: The Secrets of Stellar Siestas: the Magnetic Grand Minimum Candidate HD 4915 Authors: Saar, Steven H.; Drake, Jeremy J.; Kashyap, Vinay; Wargelin, Bradford; Wright, Jason T. Bibcode: 2020hst..prop16421S Altcode: Magnetic grand minima (MGM) are mysterious episodes when the Sun's magnetic dynamo cycle "takes a siesta" and goes into temporary quiescence. The phenomenon has never been observed in modern times; what was the Sun like then? Recently a star was observed to have a decaying cycle amplitude (in Ca HK), making it a strong candidate for an MGM episode. We propose to study the star with Chandra and HST, to explore magnetic heating throughout its outer atmosphere. Results will be compared with cycle minima and stars with "flat activity" (objects which may be in MGM or have "dead" dynamos) to explore similarities and differences, and reveal what may lie in store for our own Sun in the near future. Title: A Study of Equatorial Coronal Holes during the Maximum Phase of four Solar Cycles Authors: Karna, N.; Karna, M.; Saar, S.; Pesnell, W.; DeLuca, E. Bibcode: 2020SPD....5120903K Altcode: The 11-year Solar Cycle (SC) is characterized by periodic changes in solar activity indicators such as a number of sunspots, coronal holes, active regions (ARs), as well as the occurrence rate of solar energetic events such as filament eruptions, flares and coronal mass ejections (CMEs). In this work we performed a statistical study of the equatorial coronal holes (ECHs) and ARs during the maximum phase of the last four solar cycles: SC 21 (1979-1982), SC 22 (1989-1992), SC 23 (1999-2002) and SC 24 (2012-2015). We compared the number of ECHs and ARs, separations between their centroids, solar wind speed, pressure and the number of intense geomagnetic storms (IGS) data over these four cycles. We note a strong anticorrelation between the number of ARs and ECHs. We found that the number of close ARs and ECHs (which are potentially interacting), solar wind speed, and the number of IGS increases with average sunspot maximum number for even cycles and decreases with average sunspot maximum for odd cycles. Also, we find strong odd-even trends in the relation between the wind properties and the numbers of close AR and ECH. These results suggest a possible link between ECH-AR interactions and the solar wind phenomena, though odd-even trends point to the importance of other effects (e.g., Sun-earth magnetic alignment) as well. Title: VizieR Online Data Catalog: HARPS-N solar radial velocities and activity (Milbourne+, 2019) Authors: Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.; Saar, S. H.; Cegla, H. M.; Cameron, A. C.; Costes, J.; Dumusque, X.; Langellier, N.; Latham, D. W.; Maldonado, J.; Malavolta, L.; Mortier, A. M. L. P., III; Thompson, S.; Watson, C. A.; Bouchy, F.; Buchschacher, N.; Cecconi, M.; Charbonneau, D.; Cosentino, R.; Ghedina, A.; Glenday, A. G.; Gonzalez, M.; Li, C. -H.; Lodi, M.; Lopez-Morales, M.; Lovis, C.; Mayor, M.; Micela, G.; Molinari, E.; Pepe, F.; Piotto, G.; Rice, K.; Sasselov, D.; Segransan, D.; Sozzetti, A.; Szentgyorgyi, A.; Udry, S.; Walsworth, R. L. Bibcode: 2020yCat..18740107M Altcode: In this work, we analyze 3yr (Jul 2015-Sep 2017) of solar observations during the decline of Carrington Cycle 24 to test models of radial-velocity variations of Sun-like stars. We compare solar telescope/HARPS-N measurements of the solar RVs and logR'HK, SDO/HMI disk-resolved activity images, and SORCE/TIM measurements of the TSI.

The High Radial-velocity Planet Searcher for the Northern Hemisphere (HARPS-N) spectrograph at the Telescopio Nazionale Galileo (TNG) on La Palma is a cross-dispersed echelle spectrograph spanning the visible range (383-690nm with resolving power R=115000). See Section 2.1.

The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) captures full-disk images of the Sun with near single-granule resolution. We use six images each day, sampled evenly over the 2.5yr operational period of the solar telescope at HARPS-N. See Section 2.2.

The Total Irradiance Monitor (TIM) on board the SOlar Radiation and Climate Experiment (SORCE) measures the Total Solar Irradiance (TSI) using a set of four Electrical Substitution Radiometers. See Section 2.3.

(1 data file). Title: Rotation of Solar Analogs Crossmatching Kepler and Gaia DR2 Authors: do Nascimento, J. -D., Jr.; de Almeida, L.; Velloso, E. N.; Anthony, F.; Barnes, S. A.; Saar, S. H.; Meibom, S.; da Costa, J. S.; Castro, M.; Galarza, J. Y.; Lorenzo-Oliveira, D.; Beck, P. G.; Meléndez, J. Bibcode: 2020ApJ...898..173D Altcode: 2020arXiv200606204D A major obstacle to interpreting the rotation period distribution for main-sequence stars from Kepler mission data has been the lack of a precise evolutionary status for these objects. We address this by investigating the evolutionary status based on Gaia Data Release 2 parallaxes and photometry for more than 30,000 Kepler stars with rotation period measurements. Many of these are subgiants and should be excluded in future work on dwarfs. We particularly investigate a 193-star sample of solar analogs and report newly determined rotation periods for 125 of these. These include 54 stars from a prior sample, of which we can confirm the periods for 50. The remainder are new, and 10 of them longer than a solar rotation period, suggesting that Sun-like stars continue to spin down on the main sequence past solar age. Our sample of solar analogs could potentially serve as a benchmark for future missions, such as PLAnetary Transits and Oscillations of stars, and emphasizes the need for additional astrometric, photometric, and spectroscopic information before interpreting the stellar populations and results from time series surveys. Title: Synthetic Spectra of TiO Bands to Identify Diagnostics of Starspot Properties Authors: Neff, J. E.; Cheng, K.; Giacinto, A.; Johnson, D.; Saar, S. Bibcode: 2020AAS...23613004N Altcode: Magnetic activity similar to that of the Sun is observed on a variety of cool stars. Strong magnetic fields in stellar interiors and produce many magnetic phenomena, including starspots in the photosphere. These starspots are a major source limiting the precision of high-precision radial velocity measurements used to characterize exoplanets. In a previous series of papers, we demonstrated an empirical approach to measuring starspot properties using observed spectra of active and inactive stars as proxies for the spotted and non-spotted photosphere. These empirical methods were successful for heavily spotted stars, but they are not sensitive enough to unravel the jitter caused by numerous small spots. To overcome these limitations, we have evaluated a wide range of model atmospheres and spectrum synthesis codes, and we have assimilated suitable line lists. By characterizing composite (spot+nonspot) synthetic spectra from the entire range of parameter space for G and K stars, we have developed new diagnostic indicators that can be used to measure starspot properties from observed high-resolution spectra of spotted stars, including spot temperatures, areas, and the effective decrease in gravity caused by strong magnetic fields within the spots. Title: The spectral impact of magnetic activity on disc-integrated HARPS-N solar observations: exploring new activity indicators Authors: Thompson, A. P. G.; Watson, C. A.; Haywood, R. D.; Costes, J. C.; de Mooij, E.; Collier Cameron, A.; Dumusque, X.; Phillips, D. F.; Saar, S. H.; Mortier, A.; Milbourne, T. W.; Aigrain, S.; Cegla, H. M.; Charbonneau, D.; Cosentino, R.; Ghedina, A.; Latham, D. W.; López-Morales, M.; Micela, G.; Molinari, E.; Poretti, E.; Sozzetti, A.; Thompson, S.; Walsworth, R. Bibcode: 2020MNRAS.494.4279T Altcode: 2020arXiv200409830T; 2020MNRAS.tmp.1253T Stellar activity is the major roadblock on the path to finding true Earth-analogue planets with the Doppler technique. Thus, identifying new indicators that better trace magnetic activity (i.e. faculae and spots) is crucial to aid in disentangling these signals from that of a planet's Doppler wobble. In this work, we investigate activity related features as seen in disc-integrated spectra from the HARPS-N solar telescope. We divide high-activity spectral echelle orders by low-activity master templates (as defined using both log R'HK and images from the Solar Dynamics Observatory, SDO), creating 'relative spectra'. With resolved images of the surface of the Sun (via SDO), the faculae and spot filling factors can be calculated, giving a measure of activity independent of, and in addition to, log R'HK. We find pseudo-emission (and pseudo-absorption) features in the relative spectra that are similar to those reported in our previous work on α Cen B. In α Cen B, the features are shown to correlate better to changes in faculae filling factor than spot filling factor. In this work, we more confidently identify changes in faculae coverage of the visible hemisphere of the Sun as the source of features produced in the relative spectra. Finally, we produce trailed spectra to observe the radial velocity component of the features, which show that the features move in a redward direction as one would expect when tracking active regions rotating on the surface of a star. Title: Testing the Spectroscopic Extraction of Suppression of Convective Blueshift Authors: Miklos, M.; Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.; Saar, S. H.; Meunier, N.; Cegla, H. M.; Dumusque, X.; Langellier, N.; Maldonado, J.; Malavolta, L.; Mortier, A.; Thompson, S.; Watson, C. A.; Cecconi, M.; Cosentino, R.; Ghedina, A.; Li, C. -H.; López-Morales, M.; Molinari, E.; Poretti, Ennio; Sasselov, D.; Sozzetti, A.; Walsworth, R. L. Bibcode: 2020ApJ...888..117M Altcode: 2019arXiv191009038M Efforts to detect low-mass exoplanets using stellar radial velocities (RVs) are currently limited by magnetic photospheric activity. Suppression of convective blueshift is the dominant magnetic contribution to RV variability in low-activity Sun-like stars. Due to convective plasma motion, the magnitude of RV contributions from the suppression of convective blueshift is related to the depth of formation of photospheric spectral lines for a given species used to compute the RV time series. Meunier et al. used this relation to demonstrate a method for spectroscopic extraction of the suppression of convective blueshift in order to isolate RV contributions, including planetary RVs, that contribute equally to the time series for each spectral line. Here, we extract disk-integrated solar RVs from observations over a 2.5 yr time span made with the solar telescope integrated with the HARPS-N spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain). We apply the methods outlined by Meunier et al. We are not, however, able to isolate physically meaningful contributions due to the suppression of convective blueshift from this solar data set, potentially because our data set is taken during solar minimum when the suppression of convective blueshift may not sufficiently dominate activity contributions to RVs. This result indicates that, for low-activity Sun-like stars, one must include additional RV contributions from activity sources not considered in the Meunier et al. model at different timescales, as well as instrumental variation, in order to reach the submeter per second RV sensitivity necessary to detect low-mass planets in orbit around Sun-like stars. Title: Solar Flare Soft X-Ray Time Series Spectrum Reconstruction Authors: Goettlicher, C.; Moore, C. S.; Suarez, C.; Saar, S. Bibcode: 2020AAS...23521008G Altcode: Solar flares are magnetic reconnection events resulting in sudden bursts of electromagnetic energy, particle acceleration, and hot plasma heated to over 10 MK. Hot solar flare plasma generates copious soft X-rays. Hence, spectral soft X-ray measurements provide great constraints on flare plasma temperature and dynamics. Flare observations from Low-Earth orbiting satellites like the first Miniature X-ray Solar Spectrometer (MinXSS-1) CubeSat can be occulted for 30 minutes of the 90 minute orbit, missing vital portions of the temporal evolution of the spectrum and plasma. In this project, the eclipsed MinXSS-1 spatially integrated spectra from 0.8 - 15 keV is reconstructed using non-oculted data by fitting an empirical piecewise temporal-spectral function consisting of Gaussian, Lorentian, and polynomial components. This automated procedure fits the original data and adds synthetic data points to the eclipse period in the temporal profile, which can be used to reconstruct the spectral profile for energy range specified in the time series. At both points of egress and ingress there are larger decreases in the low energy (< 3 keV) soft X-ray flux due to absorption by nitrogen and oxygen in Earth's atmosphere. Results from this project could be used in future projects focusing on exoplanet atmospheres and models of flare plasma evolution. Title: Constructing A Physically Motivated Model of Activity-Driven Solar and Stellar Radial Velocities Authors: Iampietro, A.; Saar, S. H.; Haywood, R. D.; Milbourne, T. W. Bibcode: 2019AGUFMSH41F3321I Altcode: Analysing the periodic radial-velocity variations of a star caused by an orbiting planet is a highly successful way of inferring the masses of exoplanets around bright, nearby stars. A major limitation to this method comes from rotationally modulated stellar activity signals that hide orbits of small exoplanets by creating variations in radial-velocity measurements. We look to the Sun as a test of concept to understand the effects of solar and stellar activity on radial-velocity variations. We construct a physically grounded model for the suppression of convective blueshift and rotation of active regions across the solar/stellar disk. Additionally and for the first time, we model horizontal velocity flows in and around active regions (Evershed and moat flows directed radially outward from sun/starspots, inflows around plage regions). We use SORCE photometry and HARPS-N Ca II H&K line emission as proxies for these physical effects, and fit to measured radial-velocity variations of the Sun seen as a star from the HARPS-N spectrograph. We also model radial-velocity measurements of the rocky-planet host star CoRoT-7, using CoRoT photometry and HARPS Ca II H&K emission observations. We apply our model for stellar activity and compare to previous models that did not account for horizontal velocity flows. This work is an essential step towards modelling the physical effects of stellar activity on radial-velocity variations, which is crucial to uncovering Earth-like exoplanets orbiting Sun-like stars.

This work is supported under the NSF-REU solar physics program at SAO, grant number AGS-1560313, performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute (R.D.H.), and supported in part by NASA award number NNX16AD42G, the Smithsonian Institution, NASA Heliophysics LWS grant NNX16AB79G (S.H.S.) and the HARPS-N project. Title: A Study of Equatorial Coronal Holes during the Maximum Phase of Four Solar Cycles Authors: Karna, N.; Karna, M. L.; Saar, S. H.; Pesnell, W. D.; DeLuca, E. Bibcode: 2019AGUFMSH44A..03K Altcode: The 11-year Solar Cycle (SC) is characterized by periodic changes in the solar activity such as sunspot numbers, coronal holes, active regions, eruptions such as prominence eruptions, flares and coronal mass ejections. In this work we performed a statistical study of the equatorial coronal holes and the active regions during the maximum phases of four solar cycles (SC 21 (1979, 1980, 1981 and 1982), SC 22 (1989, 1990, 1991 and 1992), SC 23 (1999, 2000, 2001 and 2002) and SC 24 (2012, 2013, 2014 and 2015)). We compared equatorial coronal hole and active region numbers, separations between equatorial coronal holes and active regions centroids, solar wind speed and the number of intense geomagnetic storms data over these four cycles. We found that the distance between equatorial coronal holes and active regions, the solar wind speed, and the the number of intense geomagnetic storms increases with average sunspot maximum number for even cycles and decreases with average sunspot maximum for odd cycles. We also noticed that the solar wind speeds, pressures, and the number of intense geomagnetic storms increase with the numbers of close equatorial coronal holes and active regions, suggesting a possible link between equatorial coronal holes--active regions interactions and the wind phenomena. Title: Stars at High Spatial Resolution Authors: Carpenter, Kenneth G.; van Belle, Gerard; Brown, Alexander; Cranmer, Steven R.; Drake, Jeremy; Dupree, Andrea K.; Creech-Eakman, Michelle; Evans, Nancy R.; Grady, Carol A.; Guinan, Edward F.; Harper, Graham; Karovska, Margarita; Kolenberg, Katrien; Labeyrie, Antoine; Linsky, Jeffrey; Peters, Geraldine J.; Rau, Gioia; Ridgway, Stephen; Roettenbacher, Rachael M.; Saar, Steven H.; Walter, Frederick M.; Wood, Brian Bibcode: 2019arXiv190805665C Altcode: We summarize some of the compelling new scientific opportunities for understanding stars and stellar systems that can be enabled by sub-milliarcsec (sub-mas) angular resolution, UV-Optical spectral imaging observations, which can reveal the details of the many dynamic processes (e.g., evolving magnetic fields, accretion, convection, shocks, pulsations, winds, and jets) that affect stellar formation, structure, and evolution. These observations can only be provided by long-baseline interferometers or sparse aperture telescopes in space, since the aperture diameters required are in excess of 500 m (a regime in which monolithic or segmented designs are not and will not be feasible) and since they require observations at wavelengths (UV) not accessible from the ground. Such observational capabilities would enable tremendous gains in our understanding of the individual stars and stellar systems that are the building blocks of our Universe and which serve as the hosts for life throughout the Cosmos. Title: The Deaths of Stellar Dynamos: Digging in the Magnetic Graveyard for Old Cold Coronae Authors: Metcalfe, Travis S.; Drake, Jeremy J.; Saar, Steven H. Bibcode: 2019hst..prop15991M Altcode: Sun-like stars exhibit three distinct phases of magnetic evolution. In the saturated regime, the X-ray luminosity is independent of the rapid rotation. For slightly older stars in the unsaturated regime, the X-ray luminosity declines in tandem with rotation. Recent observational evidence suggests that near the middle of their main-sequence lifetimes, stars may enter a third regime in which rotation remains nearly constant while magnetic activity continues to decline. We propose to measure X-ray luminosities for three stars with a range of spectral types and metallicities, to identify the signature of this third regime in the old cold coronae of stars that appear to have shut down their global dynamos. We will use previous observations to help constrain the coronal temperatures. Title: Temporal evolution and correlations of optical activity indicators measured in Sun-as-a-star observations Authors: Maldonado, J.; Phillips, D. F.; Dumusque, X.; Collier Cameron, A.; Haywood, R. D.; Lanza, A. F.; Micela, G.; Mortier, A.; Saar, S. H.; Sozzetti, A.; Rice, K.; Milbourne, T.; Cecconi, M.; Cegla, H. M.; Cosentino, R.; Costes, J.; Ghedina, A.; Gonzalez, M.; Guerra, J.; Hernández, N.; Li, C. -H.; Lodi, M.; Malavolta, L.; Molinari, E.; Pepe, F.; Piotto, G.; Poretti, E.; Sasselov, D.; San Juan, J.; Thompson, S.; Udry, S.; Watson, C. Bibcode: 2019A&A...627A.118M Altcode: 2019arXiv190603002M Context. Understanding stellar activity in solar-type stars is crucial for the physics of stellar atmospheres as well as for ongoing exoplanet programmes.
Aims: We aim to test how well we understand stellar activity using our own star, the Sun, as a test case.
Methods: We performed a detailed study of the main optical activity indicators (Ca II H & K, Balmer lines, Na I D1 D2, and He I D3) measured for the Sun using the data provided by the HARPS-N solar-telescope feed at the Telescopio Nazionale Galileo. We made use of periodogram analyses to study solar rotation, and we used the pool variance technique to study the temporal evolution of active regions. The correlations between the different activity indicators as well as the correlations between activity indexes and the derived parameters from the cross-correlation technique are analysed. We also study the temporal evolution of these correlations and their possible relationship with indicators of inhomogeneities in the solar photosphere like sunspot number or radio flux values.
Results: The value of the solar rotation period is found in all the activity indicators, with the only exception being Hδ. The derived values vary from 26.29 days (Hγ line) to 31.23 days (He I). From an analysis of sliding periodograms we find that in most of the activity indicators the spectral power is split into several "bands" of periods around 26 and 30 days. They might be explained by the migration of active regions between the equator and a latitude of ∼30°, spot evolution, or a combination of both effects. A typical lifetime of active regions of approximately ten rotation periods is inferred from the pooled variance diagrams, which is in agreement with previous works. We find that Hα, Hβ, Hγ, Hɛ, and He I show a significant correlation with the S index. Significant correlations between the contrast, bisector span, and the heliocentric radial velocity with the activity indexes are also found. We show that the full width at half maximum, the bisector, and the disc-integrated magnetic field correlate with the radial velocity variations. The correlation of the S index and Hα changes with time, increasing with larger sun spot numbers and solar irradiance. A similar tendency with the S index and radial velocity correlation is also present in the data.
Conclusions: Our results are consistent with a scenario in which higher activity favours the correlation between the S index and the Hα activity indicators and between the S index and radial velocity variations.

Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A118 Title: Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum Authors: Collier Cameron, A.; Mortier, A.; Phillips, D.; Dumusque, X.; Haywood, R. D.; Langellier, N.; Watson, C. A.; Cegla, H. M.; Costes, J.; Charbonneau, D.; Coffinet, A.; Latham, D. W.; Lopez-Morales, M.; Malavolta, L.; Maldonado, J.; Micela, G.; Milbourne, T.; Molinari, E.; Saar, S. H.; Thompson, S.; Buchschacher, N.; Cecconi, M.; Cosentino, R.; Ghedina, A.; Glenday, A.; Gonzalez, M.; Li, C. -H.; Lodi, M.; Lovis, C.; Pepe, F.; Poretti, E.; Rice, K.; Sasselov, D.; Sozzetti, A.; Szentgyorgyi, A.; Udry, S.; Walsworth, R. Bibcode: 2019MNRAS.487.1082C Altcode: 2019MNRAS.tmp.1180C; 2019arXiv190412186C The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of Earth twins. Since 2015 July, we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m s-1 per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s-1. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s-1 and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s-1 and is correlated with the line asymmetry, but leads it by 3 d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity. Title: Stellar Activity of Main Sequence Stars Authors: Larson, Alex; Miller, Brendan P.; Saar, Steven H.; Gallo, Elena; Wright, Jason; Hagen, Cedric Bibcode: 2019AAS...23432203L Altcode: Many main sequence stars have chromospheric activity levels that vary with time. These can be characterized based on their Ca II H and K line core emission. Using data obtained from the California Planet Search we fit a sinusoidal function to a sample of 244 stars to test for significant cyclic variability. We wrote a python program to analyze observations taken over timescales of up to 17 years to determine optimal sinusoidal parameters, with uncertainties estimated through a bootstrapping technique. We also identify some inactive stars with virtually no R'HK variability. We find that within our sample the less active cyclic stars tend to have longer periods. Ongoing work examines the potential impact of cyclic and flaring stellar activity on known exoplanets, including those orbiting within the habitable zone. Title: Turbulent Diffusion Derived from the Motions of SDO/AIA Coronal Bright Points Authors: Skokić, I.; Brajša, R.; Sudar, D.; Ruždjak, D.; Saar, S. H. Bibcode: 2019ApJ...877..142S Altcode: Diffusion of magnetic elements on the Sun has an important role in current solar dynamo models as a part of the mechanism for redistribution of the magnetic field and as an important part for maintaining the solar activity cycle. The main goal is to determine the character of solar magnetic diffusivity and a value of the diffusion coefficient by analyzing the motions of coronal bright points (CBPs) within the frame of the random walk model. We tracked positions of CBPs in Solar Dynamics Observatory/Atmospheric Imaging Assembly images for a period of 5 months and examined their displacement spectrum. We calculated spectral index and diffusion coefficient from the spectrum and investigated their variation with temporal and spatial scale. For the first time, variations of the spectral index with heliographic latitude and time were analyzed. Our results indicate subdiffusion with the spectral index γ = 0.70 ± 0.01 and the corresponding diffusion coefficient with a value decreasing from 400 to 100 km2 s-1 for temporal scales of 103-105 s and spatial scales of (1.5-7) × 103 km. Seemingly random variations around the mean value of spectral index were found, with peak-to-peak amplitudes <0.30 with time and <0.10 with latitude. The main conclusion is that CBP motions are consistent with a subdiffusion process. Title: VizieR Online Data Catalog: Optical activity indicators (Maldonado+, 2019) Authors: Maldonado, J.; Phillips, D. F.; Dumusque, X.; Collier, Cameron A.; Haywood, R. D.; Lanza, A. F.; Micela, G.; Mortier, A.; Saar, S. H.; Sozzetti, A.; Rice, K.; Milbourne, T.; Cecconi, M.; Cegla, H. M.; Cosentino, R.; Costes, J.; Ghedina, A.; Gonzalez, M.; Guerra, J.; Hernandez, N.; Li, C. -H.; Lodi, M.; Malavolta, L.; Molinari, E.; Pepe, F.; Piotto, G.; Poretti, E.; Sasselov, D.; San Juan, J.; Thompson, S.; Udry, S.; Watson, C. Bibcode: 2019yCat..36270118M Altcode: File tableA.1.dat lists the daily median activity indexes and their uncertainties as well as the daily median CCF parameters measured in the Sun-as-a-star observations.

(1 data file). Title: Stars at High Spatial Resolution Authors: Carpenter, Kenneth; van Belle, Gerard; Brown, Alexander; Cranmer, Steven R.; Drake, Jeremy; Dupree, Andrea K.; Creech-Eakman, Michelle; Evans, Nancy R.; Grady, Carol A.; Guinan, Edward F.; Harper, Graham; Karovska, Margarita; Kolenberg, Katrien; Labeyrie, Antoine; Linsky, Jeffrey; Peters, Geraldine J.; Rau, Gioia; Ridgway, Stephen; Roettenbacher, Rachael M.; Saar, Steven H.; Walter, Frederick M.; Wood, Brian Bibcode: 2019BAAS...51c..56C Altcode: 2019astro2020T..56C We summarize compelling new scientific opportunities for understanding stars and stellar systems that can be enabled by sub-milliarcsec angular resolution, UV/Optical spectral imaging observations. These can reveal details of many dynamic processes that affect stellar formation, structure, and evolution. Title: HARPS-N Solar RVs Are Dominated by Large, Bright Magnetic Regions Authors: Milbourne, T. W.; Haywood, R. D.; Phillips, D. F.; Saar, S. H.; Cegla, H. M.; Cameron, A. C.; Costes, J.; Dumusque, X.; Langellier, N.; Latham, D. W.; Maldonado, J.; Malavolta, L.; Mortier, A.; Palumbo, M. L., III; Thompson, S.; Watson, C. A.; Bouchy, F.; Buchschacher, N.; Cecconi, M.; Charbonneau, D.; Cosentino, R.; Ghedina, A.; Glenday, A. G.; Gonzalez, M.; Li, C. -H.; Lodi, M.; López-Morales, M.; Lovis, C.; Mayor, M.; Micela, G.; Molinari, E.; Pepe, F.; Piotto, G.; Rice, K.; Sasselov, D.; Ségransan, D.; Sozzetti, A.; Szentgyorgyi, A.; Udry, S.; Walsworth, R. L. Bibcode: 2019ApJ...874..107M Altcode: 2019arXiv190204184M State-of-the-art radial-velocity (RV) exoplanet searches are currently limited by RV signals arising from stellar magnetic activity. We analyze solar observations acquired over a 3 yr period during the decline of Carrington Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built solar telescope at the High Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) provides disk-integrated solar spectra, from which we extract RVs and {log}{R}HK}{\prime }. The Solar Dynamics Observatory (SDO) provides disk-resolved images of magnetic activity. The Solar Radiation and Climate Experiment (SORCE) provides near-continuous solar photometry, analogous to a Kepler light curve. We verify that the SORCE photometry and HARPS-N {log}{R}HK}{\prime } correlate strongly with the SDO-derived magnetic filling factor, while the HARPS-N RV variations do not. To explain this discrepancy, we test existing models of RV variations. We estimate the contributions of the suppression of convective blueshift and the rotational imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We investigate the time variation of these contributions over several rotation periods, and how these contributions depend on the area of active regions. We find that magnetic active regions smaller than 60 Mm2 do not significantly suppress convective blueshift. Our area-dependent model reduces the amplitude of activity-induced RV variations by a factor of two. The present study highlights the need to identify a proxy that correlates specifically with large, bright magnetic regions on the surfaces of exoplanet-hosting stars. Title: Where's That Flare: A Comprehensive Hard X-Ray Solar Flare Catalog Authors: Merhi, Maya; Loftus, Kaitlyn; Saar, Steven Bibcode: 2019AAS...23335901M Altcode: We have created a hard x-ray solar flare catalog using short channel wavelength bands of 0.5 to 4 Å from NOAA's Geostationary Operational Environmental Satellites (GOES) X-Ray Sensor (XRS) data for 2003 to 2018. The Where's That Flare (WTF) catalog was developed using an automated algorithm designed to use changes in the derivative of the hard X-ray flux to identify flares. Intended to provide a complete archive of all hard X-ray solar flare events in GOES XRS data, the WTF catalog (novelly for the hard X-ray) distinguishes between "simple" single peak flare events and "complex" multi-peak flare events and is sensitive to small flares near the background level. To account for the varying background level of the hard X-ray flux, the detection algorithm dynamically adapts to the local background to detect flares of all sizes and complexities. A statistical analysis of flare characteristics was performed on the WTF catalog investigating correlations between total energy, flare duration, peak flux, peak time, rise time, decay time, as well as characteristics of complex events such as number of peaks per complex event. Frequency distributions of total energy, flare duration, and number of peaks per complex event were also investigated and fit with power laws where applicable. Our catalog is complete to approximately 10-7.5 W/m2 peak flux. In the future, we will run our algorithm on all available GOES data and use this catalog in conjunction with NOAA GOES SXI data and NASA Hinode image data to give spatial locations of solar flares in our catalog. This work is supported by NSF-REU Solar Physics program at SAO, grant number AGS-1560313. Keywords: Catalogs, Solar flares, X-ray flares Title: Instrument Calibration of the Interface Region Imaging Spectrograph (IRIS) Mission Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell, T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.; Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.; Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M. Bibcode: 2018SoPh..293..149W Altcode: The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer mission that provides high-resolution spectra and images of the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The IRIS data are archived in calibrated form and made available to the public within seven days of observing. The calibrations applied to the data include dark correction, scattered light and background correction, flat fielding, geometric distortion correction, and wavelength calibration. In addition, the IRIS team has calibrated the IRIS absolute throughput as a function of wavelength and has been tracking throughput changes over the course of the mission. As a resource for the IRIS data user, this article describes the details of these calibrations as they have evolved over the first few years of the mission. References to online documentation provide access to additional information and future updates. Title: Stellar Surface Magneto-convection as a Source of Astrophysical Noise. II. Center-to-limb Parameterization of Absorption Line Profiles and Comparison to Observations Authors: Cegla, H. M.; Watson, C. A.; Shelyag, S.; Chaplin, W. J.; Davies, G. R.; Mathioudakis, M.; Palumbo, M. L., III; Saar, S. H.; Haywood, R. D. Bibcode: 2018ApJ...866...55C Altcode: 2018arXiv180711423C Manifestations of stellar activity (such as star-spots, plage/faculae, and convective flows) are well-known to induce spectroscopic signals often referred to as astrophysical noise by exoplanet hunters. For example, setting an ultimate goal of detecting true Earth analogs demands reaching radial velocity (RV) precisions of ∼9 cm s-1. While this is becoming technically feasible with the latest generation of highly stabilized spectrographs, it is astrophysical noise that sets the true fundamental barrier on attainable RV precisions. In this paper, we parameterize the impact of solar surface magneto-convection on absorption line profiles, and extend the analysis from the solar disk center (Paper I) to the solar limb. Off disk-center, the plasma flows orthogonal to the granule tops begin to lie along the line of sight, and those parallel to the granule tops are no longer completely aligned with the observer. Moreover, the granulation is corrugated and the granules can block other granules, as well as the intergranular lane components. Overall, the visible plasma flows and geometry of the corrugated surface significantly impact the resultant line profiles and induce center-to-limb variations in shape and net position. We detail these herein, and compare to various solar observations. We find our granulation parameterization can recreate realistic line profiles and induced radial velocity shifts, across the stellar disk, indicative of both those found in computationally heavy radiative 3D magnetohydrodynamical simulations and empirical solar observations. Title: How Cool is That? Taking the Temperature of the Coldest Coronae: the Magnetic Grand Minimum Candidate Tau Ceti Authors: Saar, Steven Bibcode: 2018cxo..prop.5338S Altcode: The Sun sporadically has "naps", called magnetic grand minima (MGM), when its cyclic dynamo sputters into a fitful state with few spots. As the last of these happened long ago, we know little about this phase of solar life. There are hints that the Sun will soon enter a new MGM, raising the question: what happens then? We propose to study the brightest candidate MGM star, tau Ceti, to explore a proxy for the solar MGM corona. Previous data show its corona is cold (log T < 6.1) but T is poorly constrained. We will reobserve it using HRC-S with an enlarged dither pattern, through thick and thin filters. This yields high T sensitivity at cool T, enabling us to find tau Ceti's coronal T. We use this to estimate the mix of coronal holes and quiet areas on the star, and thus the MGM Sun. Title: A First Look at the Effect of Flares on Radial Velocity Jitter in G Dwarfs: A Punch and a Splash? Authors: Saar, Steven H.; Palumbo, Michael L., III; Haywood, Raphaelle D.; Dupree, Andrea K. Bibcode: 2018csss.confE..86S Altcode: conference poster Title: Magnetic activity cycles in the open cluster NGC 6811? Authors: Velloso, Eduardo N.; do Nascimento, José-Dias, Jr.; Saar, Steven H.; Meibom, Søren Bibcode: 2018csss.confE..43V Altcode: The sun shows a magnetic activity cycle related to the occurrence of spots on its surface with a strong periodicity of 11 years. With the advent of space missions like CoRoT and Kepler, astronomers began to try and find ways to associate the photometric variability of the star with its intrinsic magnetic activity. Photometric proxies for activity appear to be correlated with the chromospheric mathcal{S} index and p-modes from asteroseismology. In order to investigate the existence and properties of magnetic cycles in a narrow range of fundamental parameters, we studied solar-type stars in the intermediate-age open cluster NGC 6811. We searched our sample for cycle-like periodicities and in each case classified the variability as either cyclic, multicyclic, flat or acyclic. We checked the usual correlations between P_cyc, P_rot and Rossby number and we find a high degree of dispersion among them, which casts doubt on the existence of the Active branch. We introduce theoretical questions about what determines the activity cycle period and whether there is some sort of fundamental difference between cyclic and acyclic stars. The comparison between stars with the same mass, age and chemistry suggests that neither of these properties is truly decisive. Title: Observations of the solar chromosphere with ALMA and comparison with theoretical models Authors: Brajsa, Roman; Sudar, Davor; Skokic, Ivica; Benz, Arnold O.; Kuhar, Matej; Kobelski, Adam; Wedemeyer, Sven; White, Stephen M.; Ludwig, Hans-G.; Temmer, Manuela; Saar, Steven H.; Selhorst, Caius L. Bibcode: 2018csss.confE..37B Altcode: 2018arXiv181207293B In this work we use solar observations with the ALMA radio telescope at the wavelength of 1.21 mm. The aim of the analysisis to improve understanding of the solar chromosphere, a dynamic layer in the solar atmosphere between the photosphere andcorona. The study has an observational and a modeling part. In the observational part full-disc solar images are analyzed.Based on a modied FAL atmospheric model, radiation models for various observed solar structures are developed. Finally, theobservational and modeling results are compared and discussed. Title: A comparison of solar ALMA observations and model based predictions of the brightness temperature Authors: Brajša, R.; Kuhar, M.; Benz, A. O.; Skokić, I.; Sudar, D.; Wedemeyer, S.; Báarta, M.; De Pontieu, B.; Kim, S.; Kobelski, A.; Shimojo, M.; White, S.; Yagoubov, P.; Yan, Y.; Ludwig, H. G.; Temmer, M.; Saar, S. H.; Selhorst, C. L.; Beuc, R. Bibcode: 2018CEAB...42....1B Altcode: The new facility Atacama Large Millimeter/submillimeter Array (ALMA) is capable of observing the Sun in the wavelength range from 0.3 mm to 10 mm with an unprecedented spatial, temporal and spectral resolution. The first aim of the present work is to identify different structures in the solar atmosphere (quiet Sun, active regions, filaments on the disc, and coronal holes) in a full disc solar ALMA image at 1.21 mm obtained on December 18, 2015 during a CSV-EOC campaign. It is compared with full disc solar images from the same day in the Hα line (Cerro Tololo Observatory, NISP), and at three EUV wavelengths (30.4 nm, 21.1 nm, 17.1 nm; a composite SDO image). Positions of the quiet Sun areas, active regions, filaments on the disc, and coronal holes are identified in the ALMA image. To interpret solar observations with ALMA it is important to compare the measured and calculated intensities of various solar structures. So, the second aim of this work is to calculate the intensity (brightness temperature) for those structures (quiet Sun, active regions, filaments on the disc, and coronal holes) for a broad wavelength range (from 0.3 mm to 10 mm), closely related to that of the ALMA, and to compare the results with available ALMA observations. Thermal bremsstrahlung is the dominant radiation mechanism for explanation of the observed phenomena. A procedure for calculating the brightness temperature for a given wavelength and model atmosphere, which integrates the radiative transfer equation for thermal bremsstrahlung, is used. At the wavelength of 1.21 mm active regions appear as bright areas, while filaments on the disc and coronal holes are not discernible from the quiet Sun background. The models generally agree with the observed results: Active regions are bright primarily due to higher densities, filaments can appear bright, dark or not at all and coronal holes cannot be easily identified. Title: Rotational Modulation and Activity Cycles at Rotational Extremes: 25 yrs of NURO Photometry for HII 1883 Authors: Milingo, Jackie; Saar, Steven; Marschall, Laurence Bibcode: 2018AAS...23134928M Altcode: We present a 25 yr compilation of V-band differential photometry for the Pleiades K dwarf HII 1883 (V660 Tau). HII 1883 has a rotational period <P_rot> of ~ 0.24 d and displays significant rotational modulation due to non-uniform surface brightness or "starspots". Preliminary work yields a cycle period of ~ 9 yrs and rotational shear (ΔP_rot/<P_rot>) considerably less than solar. HII 1883 is one of the fastest rotating single stars with a known cycle. With additional data available we compare newly determined P_cyc and ΔP_rot/<P_rot> values with those of other stars, putting HII 1883 into the broader context of dynamo properties in single cool dwarfs. Title: Radial-Velocity Signatures of Magnetic Features on the Sun Observed as a Star Authors: Palumbo, M. L., III; Haywood, R. D.; Saar, S. H.; Dupree, A. K.; Milbourne, T. W. Bibcode: 2017AGUFM.P53B2651P Altcode: In recent years, the search for Earth-mass planets using radial-velocity measurements has become increasingly limited by signals arising from stellar activity. Individual magnetic features induce localized changes in intensity and velocity, which combine to change the apparent radial velocity of the star. Therefore it is critical to identify an indicator of activity-driven radial-velocity variations on the timescale of stellar rotation periods. We use 617.3 nm photospheric filtergrams, magnetograms, and dopplergrams from SDO/HMI and 170.0 nm chromospheric filtergrams from AIA to identify magnetically-driven solar features and reconstruct the integrated solar radial velocity with six samples per day over the course of 2014. Breaking the solar image up into regions of umbrae, penumbrae, quiet Sun, network, and plages, we find a distinct variation in the center-to-limb intensity-weighted velocity for each region. In agreement with past studies, we find that the suppression of convective blueshift is dominated by plages and network, rather than dark photospheric features. In the future, this work will be highly useful for identifying indicators which correlate with rotationally modulated radial-velocity variations. This will allow us to break the activity barrier that currently precludes the precise characterization of exoplanet properties at the lowest masses. This work was supported by the NSF-REU solar physics program at SAO, grant number AGS-1560313. This work was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Title: Steps Towards Detecting Coronal Mass Ejections on Stars: Tests Using Solar Data Authors: Saar, S.; Cressman, A. Bibcode: 2017AGUFM.P53E2680S Altcode: One important parameter affecting exoplanet habitability is the frequency and energy spectrum of coronal mass ejections (CMEs) and their associated energetic particle fluences. Estimates of CME rates have been made based on magnetic fluxes, and the frequency of strong flares, but actual detections have been sparse and debated. We propose a new way to detect stellar CMEs by watching for their effect on the He I 1083 nm line with high cadence, high S/N data. Filaments are dark against the background chromosphere in He I, and a filament eruption (FE) or CME should lead to a sudden, small step function increase in total emission, provided the rest of the star was unchanging. He I disk integrated velocity should show a similar change, depending on the relative velocity of the newly uncovered underlying material. We test this idea using CRISP data from the Mauna Loa Solar Observatory compared to the AIA FE list of MacCauley et al. Though hampered by the typically short observing window each day, which is not always well matched to the solar events, we identify several FE with the distinctive expected He I signatures in integrated light. We compare our "detections" with the He I signatures of flares (with and without CMEs), and with randomly selected days of data to better understand the detection success rate, and the number of false positives. We note that the signature of flares typically evolves more quickly, and exhibits more complex intensity and velocity changes (often with positive and negative excursions). We conclude that He I observations hold promise for obtaining statistics on stellar CMEs. We plan test stellar observations in the near future. This work was supported by NASA Heliophysics grant NNX16AB79G. Title: Automated X-ray Flare Detection with GOES, 2003-2017: The Where of the Flare Catalog and Early Statistical Analysis Authors: Loftus, K.; Saar, S. H. Bibcode: 2017AGUFMSH52B..05L Altcode: NOAA's Space Weather Prediction Center publishes the current definitive public soft X-ray flare catalog, derived using data from the X-ray Sensor (XRS) on the Geostationary Operational Environmental Satellites (GOES) series. However, this flare list has shortcomings for use in scientific analysis. Its detection algorithm has drawbacks (missing smaller flux events and poorly characterizing complex ones), and its event timing is imprecise (peak and end times are frequently marked incorrectly, and hence peak fluxes are underestimated). It also lacks explicit and regular spatial location data. We present a new database, "The Where of the Flare" catalog, which improves upon the precision of NOAA's current version, with more consistent and accurate spatial locations, timings, and peak fluxes. Our catalog also offers several new parameters per flare (e.g. background flux, integrated flux). We use data from the GOES Solar X-ray Imager (SXI) for spatial flare locating. Our detection algorithm is more sensitive to smaller flux events close to the background level and more precisely marks flare start/peak/end times so that integrated flux can be accurately calculated. It also decomposes complex events (with multiple overlapping flares) by constituent peaks. The catalog dates from the operation of the first SXI instrument in 2003 until the present. We give an overview of the detection algorithm's design, review the catalog's features, and discuss preliminary statistical analyses of light curve morphology, complex event decomposition, and integrated flux distribution. The Where of the Flare catalog will be useful in studying X-ray flare statistics and correlating X-ray flare properties with other observations. This work was supported by Contract #8100002705 from Lockheed-Martin to SAO in support of the science of NASA's IRIS mission. Title: The Flares of Proxima Cen Authors: Kashyap, Vinay; Wargelin, Bradford J.; Drake, Jeremy J.; Saar, Steven H. Bibcode: 2017AAS...23030104K Altcode: The corona of Proxima Cen has been observed with a variety of high-energy instruments (ASCA/SIS, XMM/MOS, XMM/pn, Swift/XRT, Swift/UVOT, Chandra/HRC-I, Chandra/ACIS-S) covering different levels of activity as the star goes through a stellar cycle. The data exhibit numerous strong flares as well as lower level flaring activity. In analogy with the solar case, flare intensities are expected to be scale-free and distributed as a power-law. We have modeled the flare distributions separately for each observation in order to explore their dependence on the energy environment defined by the stellar activity. We find that the flare distribution indices differ considerably, ranging from ≈1.4-2, and discuss the causes of such variations, including dependences on spectral hardness and activity levels. Title: Optical, UV, and X-ray evidence for a 7-yr stellar cycle in Proxima Centauri Authors: Wargelin, B. J.; Saar, S. H.; Pojmański, G.; Drake, J. J.; Kashyap, V. L. Bibcode: 2017MNRAS.464.3281W Altcode: 2016arXiv161003447W Stars of stellar type later than about M3.5 are believed to be fully convective and therefore unable to support magnetic dynamos like the one that produces the 11-yr solar cycle. Because of their intrinsic faintness, very few late M stars have undergone long-term monitoring to test this prediction, which is critical to our understanding of magnetic field generation in such stars. Magnetic activity is also of interest as the driver of UV and X-ray radiation, as well as energetic particles and stellar winds, that affects the atmospheres of close-in planets that lie within habitable zones, such as the recently discovered Proxima b. We report here on several years of optical, UV, and X-ray observations of Proxima Centauri (GJ 551; dM5.5e): 15 yr of All Sky Automated Survey photometry in the V band (1085 nights) and 3 yr in the I band (196 nights), 4 yr of Swift X-Ray Telescope and UV/Optical Telescope observations (more than 120 exposures), and nine sets of X-ray observations from other X-ray missions (ASCA, XMM-Newton, and three Chandra instruments) spanning 22 yr. We confirm previous reports of an 83-d rotational period and find strong evidence for a 7-yr stellar cycle, along with indications of differential rotation at about the solar level. X-ray/UV intensity is anticorrelated with optical V-band brightness for both rotational and cyclical variations. From comparison with other stars observed to have X-ray cycles, we deduce a simple empirical relationship between X-ray cyclic modulation and Rossby number, and we also present Swift UV grism spectra covering 2300-6000 Å. Title: Giant Coronal Loops Dominate the Quiescent X-Ray Emission in Rapidly Rotating M Stars Authors: Cohen, O.; Yadav, R.; Garraffo, C.; Saar, S. H.; Wolk, S. J.; Kashyap, V. L.; Drake, J. J.; Pillitteri, I. Bibcode: 2017ApJ...834...14C Altcode: 2016arXiv161102141C Observations indicate that magnetic fields in rapidly rotating stars are very strong, on both small and large scales. What is the nature of the resulting corona? Here we seek to shed some light on this question. We use the results of an anelastic dynamo simulation of a rapidly rotating fully convective M star to drive a physics-based model for the stellar corona. We find that due to the several kilo Gauss large-scale magnetic fields at high latitudes, the corona, and its X-ray emission are dominated by star-size large hot loops, while the smaller, underlying colder loops are not visible much in the X-ray. Based on this result, we propose that, in rapidly rotating stars, emission from such coronal structures dominates the quiescent, cooler but saturated X-ray emission. Title: Data Mining Solar X-Ray Flares Triggered by Emerging Magnetic Flux Authors: Loftus, Kaitlyn; Saar, Steven H.; Schanche, Nicole Bibcode: 2017AAS...22933906L Altcode: We investigate the association between emerging magnetic flux and solar X-ray flares to identify, and if possible quantify, distinguishing physical properties of flares triggered by flux emergence versus those triggered by other sources. Our study uses as its basis GOES-classified solar flares from March 2011 through June 2016 that have been identified by the Space Weather Prediction Center’s flare detection algorithm. The basic X-ray flare data is then enriched with data about related EUV-spectrum flares, emerging fluxes, active regions, eruptions, and sigmoids, which are all characterized by event-specific keywords, identified via SDO feature finding tools, and archived in the Heliophysics Events Knowledgebase (HEK). Using appropriate spatial and temporal parameters for each event type to determine association, we create a catalogue of solar events associated with each GOES-classified flare. After accounting for the primitive state of many of these event detection algorithms, we statistically analyze the compiled dataset to determine the effects of an emerging flux trigger on flare properties. A two-sample Kolmogorov-Smirnov test confirms with 99.9% confidence that flares triggered by emerging flux have a different peak flux distribution than non-emerging-flux-associated flares. We observe no linear or logarithmic correlations between flares’ and their associated emerging fluxes’ individual properties and find flares triggered by emerging flux are ~ 10% more likely to cause an eruption inside an active region while outside of an active region, the flare’s association with emerging flux has no effect on its likeliness to cause an eruption. We also compare the morphologies of the flares triggered by emerging flux and flares not via a superposed epoch analysis of lightcurves. Our results will be of interest for predicting flare behavior as a function of magnetic activity (where we can use enhanced rates of emerging flux as a proxy for heightened stellar magnetic activity). Title: Estimates Of Magnetic Plage Filling Factors Using The Cn Band Authors: Saar, Steven H.; Judge, Philip Bibcode: 2016csss.confE.151S Altcode: The 388nm CN band (like the better known "G band" of CH) is used in the Sun to locate strong magnetic concentrations. Magnetic network and plage are bright in these molecular bands, since the enhanced chromospheric heating there destroys the molecule, erasing its absorption and allowing the continuum to shine through. We take advantage of this to estimate the filling factor of strong fields in active dwarf stars. CN band depths in active stars can be compared with those of inactive stars of very similar temperature and metallicity, and after an adjustment for line-blanketing, used to estimate a magnetic plage filling factor. We estimate filling factors for a two stars, and compare them to direct Stokes I line-broadening measurements. Limitations, caveats, and future directions are briefly considered. 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: Meridional motions and Reynolds stress from SDO/AIA coronal bright points data Authors: Sudar, D.; Saar, S. H.; Skokić, I.; Poljančić Beljan, I.; Brajša, R. Bibcode: 2016A&A...587A..29S Altcode: 2016arXiv160102406S Context. It is possible to detect and track coronal bright points (CBPs) in Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) images. A combination of high resolution and high cadence provides a wealth of data that can be used to determine velocity flows on the solar surface with very high accuracy.
Aims: We derived a very accurate solar rotation profile and investigated meridional flows, torsional oscillations, and horizontal Reynolds stress based on ≈6 months of SDO/AIA data.
Methods: We used a segmentation algorithm to detect CBPs in SDO/AIA images. We also used invariance of the solar rotation profile with central meridian distance (CMD) to determine the height of CBPs in the 19.3 nm channel.
Results: The best fit solar rotation profile is given by ω(b) = (14.4060 ± 0.0051 + (-1.662 ± 0.050)sin2b + (-2.742 ± 0.081)sin4b)° day-1. The height of CBPs in the SDO/AIA 19.3 nm channel was found to be ≈6500 km. Meridional motion is predominantly poleward for all latitudes, while solar velocity residuals show signs of torsional oscillations. Horizontal Reynolds stress was found to be smaller than in similar works, but still showed transfer of angular momentum towards the solar equator.
Conclusions: Most of the results are consistent with Doppler measurements rather than tracer measurements. The fairly small calculated value of horizontal Reynolds stress might be due to the particular phase of the solar cycle. Accuracy of the calculated rotation profile indicates that it is possible to measure changes in the profile as the solar cycle evolves. Analysis of further SDO/AIA CBP data will also provide a better understanding of the temporal behaviour of the rotation velocity residuals, meridional motions, and Reynolds stress.

Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A29 Title: An Application of the Random Walk Model to Proper Motions of Coronal Bright Points from SDO Data Authors: Skokić, I.; Sudar, D.; Saar, S. H.; Brajša, R.; Poljančić-Beljan, I. Bibcode: 2016CEAB...40...23S Altcode: Atmospheric Imaging Assembly (AIA) images from the Solar Dynamics Observatory (SDO) were used to follow the motions of coronal bright points (CBPs) in the period 1 January - 19 May 2011 with a cadence of 10 minutes. This resulted in a data set of 80966 CBPs with measured lifetimes and mean velocities which were used in a random walk model to calculate the diffusion coefficient, D. The results show that D has a value of ≈260 km^2 s^{-1} for CBPs with lifetime below 6 hours, decreasing to ≈170 km^2 s^{-1} for lifetimes above 12 hours, with a mean value of ≈230 km^2 s^{-1}. Title: VizieR Online Data Catalog: Granulation model for 508 KIC stars (Cranmer+, 2014) Authors: Cranmer, S. R.; Bastien, F. A.; Stassun, K. G.; Saar, S. H. Bibcode: 2016yCat..17810124C Altcode: A goal of this work is to find self-consistent and accurate ways to predict the properties of stellar light-curve variability, and to use this variability to calibrate against other methods of determining their fundamental parameters. Thus, it may be possible to develop the analysis of granular flicker measurements in a way that augments the results of asteroseismology and improves the accuracy of, e.g., stellar mass and radius measurements.

To assist in this process, we provide tabulated data for 508 stars with photometric light curves measured by the Kepler mission, which also includes their derived masses and predicted values of the turbulent Mach number (Ma), the root-mean-square (rms) granulation intensity amplitude σ, and the flicker amplitude F8. These data are also hosted, with updates as needed, on the first author's Web site (http://www.cfa.harvard.edu/~scranmer/). With the data is a short code written in the Interactive Data Language (IDL) that reads the data and reproduces two of the three panels of Figure4 in the paper.

(3 data files). Title: The Hinode/XRT Full-Sun Image Corrections and the Improved Synoptic Composite Image Archive Authors: Takeda, Aki; Yoshimura, Keiji; Saar, Steven H. Bibcode: 2016SoPh..291..317T Altcode: 2015SoPh..tmp..176T The XRT Synoptic Composite Image Archive (SCIA) is a storage and gallery of X-ray full-Sun images obtained through the synoptic program of the X-Ray Telescope (XRT) onboard the Hinode satellite. The archived images provide a quick history of solar activity through the daily and monthly layout pages and long-term data for morphological and quantitative studies of the X-ray corona. This article serves as an introduction to the SCIA, i.e., to the structure of the archive and specification of the data products included therein. We also describe a number of techniques used to improve the quality of the archived images: preparation of composite images to increase intensity dynamic range, removal of dark spots that are due to contaminants on the CCD, and correction of the visible stray light contamination that has been detected on the Ti-poly and C-poly filter images since May 2012. Title: VizieR Online Data Catalog: Time and positions of coronal bright points (Sudar+, 2016) Authors: Sudar, D.; Saar, S. H.; Skokic, I.; Poljancic Beljan, I.; Brajsa, R. Bibcode: 2016yCat..35870029S Altcode: Positional information about CBPs detected by the segmentation algorithm are presented. For each CBP time in Julian days (JD) and x and y coordinates in pixels are given.

(1 data file). Title: Simulating Starspot Properties as a Function of Stellar Properties When Emergence Rates are High Authors: Hotton, Kate; Saar, Steven H. Bibcode: 2016AAS...22714513H Altcode: We wish to explore, under various stellar conditions, how aggregate starspot properties change when spot emergence rates are high. We use a Sun-based model to simulate the emergence, motion and decay of starspots on active stars. The spots are generated with a solar log-normal distribution of areas, and the emergence rate scaled according to the stellar rotation rate. The initial longitude of each spot is generated randomly, and initial latitude is generated with a normal distribution about a changing average, equivalent to the solar butterfly diagram. The spots are then allowed to decay at a rate dependent on the stars' surface turbulence, with a motion determined by the differential rotation and meridional flow. At high emergence rates spots can erupt into old ones, where we will either experience a merger or (partial) destruction, depending on their polarity. We follow this evolution over a magnetic cycle, logging the resulting distribution of spot sizes, latitudes, decay rates and destruction (flare) rates, for varying input parameters and stellar conditions. We compare our results with both stellar observations (including light curves, apparent spot distributions, measured differential rotation and flare rates) and theoretical estimates such as magnetic diffusivities. Title: Ultra-luminous X-Ray Sources in HARO II and the Role of X-Ray Binaries in Feedback in Lyα Emitting Galaxies Authors: Prestwich, A. H.; Jackson, F.; Kaaret, P.; Brorby, M.; Roberts, T. P.; Saar, S. H.; Yukita, M. Bibcode: 2015ApJ...812..166P Altcode: 2015arXiv150707900P Lyman Break Analogs (LBAs) are local proxies of high-redshift Lyman Break Galaxies. Spatially resolved studies of nearby starbursts have shown that Lyman continuum and line emission are absorbed by dust and that the Lyα is resonantly scattered by neutral hydrogen. In order to observe Lyα emission from star-forming regions, some source of feedback is required to blow the neutral gas away from the starburst to prevent scattering and allow the Lyα emission to escape. We show that there are two X-ray point sources embedded in the diffuse emission of the LBA galaxy Haro 11. CXOU J003652.4-333316 (abbreviated to Haro 11 X-1) is an extremely luminous (L{}{{X}}∼ {10}41 erg s-1), spatially compact source with a hard-X-ray spectrum. We suggest that the X-ray emission from Haro 11 X-1 is dominated by a single accretion source. This might be an active galactic nucleus or a source similar to the extreme black hole binary (BHB) M82 X-1. The hard X-ray spectrum indicates that Haro 11 X-1 may be a BHB in a low accretion state. In this case, the very high X-ray luminosity suggests an intermediate mass black hole that could be the seed for formation of a supermassive black hole. Source CXOU J003652.7-33331619.5 (abbreviated Haro 11 X-2) has an X-ray luminosity of {L}{{X}}∼ 5× {10}40 erg s-1 and a soft X-ray spectrum (power-law photon index Γ ∼ 2.2). This strongly suggests that Haro 11 X-2 is an X-ray binary in the ultra luminous state (i.e., an Ultra Luminous X-ray source, ULX). Haro 11 X-2 is coincident with the star-forming knot that is the source of the Lyα emission. The association of a ULX with Lyα emission raises the possibility that strong winds from X-ray binaries play an important role in injecting mechanical power into the interstellar medium, thus blowing away neutral material from the starburst region and allowing the Lyα to escape. We suggest that feedback from X-ray binaries may play a significant role in allowing Lyα emission to escape from galaxies in the early universe. Title: Differential rotation of young solar analogs from NGC 6811 Authors: do Nascimento, José-Dias; Meibom, Soren; Saar, Steven H. Bibcode: 2015IAUGA..2258562D Altcode: NGC 6811 and is an intermediate-age open cluster in the constellation of Cygnus and one of the four open clusters observed by Kepler spacecraft. This fact, make NGC 6811 ideal target for probing the differential rotation of early-G type main-sequence stars around 1 Gyr. Applying a carefully process we compare results from the periodogram and wavelet analyses of Kepler light curves for stars with membership probability estimated from photometric and spectroscopic campaigns. Here, we present our progress toward the diagnostic and detection of surface differential rotation (DR) on G-type stars in the open cluster NGC 6811. We also explore the time dependence by comparing our results with one solar mass stars from NGC 6819. This temporal analysis can provide essential observational constraint for theoretical understanding of DR and dynamo. Title: Rotational Modulation and Activity Cycles at Rotational Extremes: HII 1883 Authors: Milingo, Jacquelynne; Saar, Steven H.; Marschall, Laurence A. Bibcode: 2015IAUGA..2255707M Altcode: We present a 23 yr compilation of V-band differential photometry for the Pleiades K dwarf HII 1883 (V660 Tau). HII 1883 has a rotational period <Prot> of ~ 0.235 d and displays significant rotational modulation due to non-uniform surface brightness or "starspots". Preliminary work with 17 years of data yields a cycle period (Pcyc) of ~ 8 years and rotational shear (ΔProt/<Prot>) considerably less than solar. With additional data available we compare newly determined Pcyc and ΔProt/<Prot> values with those of other stars, including HII 1883 in a larger study of magnetic activity in single cool dwarfs. Title: Linking Stellar Coronal Activity and Rotation at 500 Myr: A Deep Chandra Observation of M37 Authors: Núñez, Alejandro; Agüeros, Marcel A.; Covey, Kevin R.; Hartman, Joel D.; Kraus, Adam L.; Bowsher, Emily C.; Douglas, Stephanie T.; López-Morales, Mercedes; Pooley, David A.; Posselt, Bettina; Saar, Steven H.; West, Andrew A. Bibcode: 2015ApJ...809..161N Altcode: 2015arXiv150702333N Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods ({P}{rot}). M37 was observed almost continuously for five days, for a total of 440.5 ks, to measure stellar X-ray luminosities ({L}{{X}}), a proxy for coronal activity, across a wide range of masses. The cluster’s membership catalog was revisited to calculate updated membership probabilities from photometric data and each star’s distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with {P}{rot}, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, {R}o= {P}{rot}/τ , where τ is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, {L}{{X}}/{L}{bol}, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500 Myr. We find that fast rotators, for which {R}o\lt 0.09+/- 0.01, show saturated levels of activity, with log({L}{{X}}/{L}{bol})=\-3.06+/- 0.04. For {R}o≥slant 0.09+/- 0.01, activity is unsaturated and follows a power law of the form {R}oβ , where β = -{2.03}-0.14+0.17. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3 {M}⊙ , {P}{rot} in the range 0.4-12.8 days, and {L}{{X}} in the range {10}28.4-30.5 {erg} {{{s}}}-1. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ≈ 500 Myr. Title: Differential Rotation as a Function of Mass and Age in Kepler Clusters Authors: Saar, Steven; Meibom, Soren; do Nascimento, Jose Bibcode: 2015IAUGA..2258556S Altcode: We present an update on our ongoing analysis of solar-type stars in Kepler clusters. We explore the mass, rotation, and age dependence of surface differential rotation using data from stars in three Kepler clusters, spanning ages from 0.5 to 2.5 Gyr. We discuss these in the context of previous measurments. Title: Superflare Rates as a Function of Mass and Age in Kepler Clusters Authors: Saar, Steven; Meibom, Soren; Wright, Paul Bibcode: 2015IAUGA..2258518S Altcode: The rate of very powerful, so-called superflares (log E > 33 ergs) is of great interest for space weather and planetary habitability. We identify flares in three Kepler clusters and explore trends in superflare rates as a function of mass, rotation, and age. Title: How typical is the Sun's magnetic cycle ? Authors: do Nascimento, José-Dias; Saar, Steven H.; Dumusque, Xavier; Meibom, Soren Bibcode: 2015IAUGA..2250017D Altcode: Solar analogs refer to main-sequence stars with 0.8 Msun < mass < 1.2 Msun. Solar twins are stars with Teff, [Fe/H], mass and rotation indistinguishable from the Sun. These solar twins shed a new light on the question of how typical the Sun is within the class of solar-type stars. From the magnetic activity point of view, some previous work has suggested that the Sun's magnetic cycle period Pcyc is unusual compared with similar stars, falling between sequences of active and inactive stars. Combining a sample from HARPS planet-search program with high-precision Ca II H & K chromospheric activity measurements we selected a large number of new reliable Pcyc, and we revisit the relation between rotation periods Prot and Pcyc. Our preliminary analysis shows that the Sun does not has a special position between the active and inactive sequences, but instead follows a new solar-analog-twin sequence proposed here. Title: Grand Minima in the Sun and Sun-like Stars Authors: Saar, Steven Bibcode: 2015IAUGA..2258484S Altcode: The Maunder minimum (about 1645 - 1715), when the numbers of sunspots dropped precipitously (<2 year-1 during one 30 year interval), raises the question of the long-term stability of the solar dynamo. While it now appears that some aspects of the cycle continued during the minimum, it is also clear that the Sun's dynamo underwent major short-term changes, and that these grand minima are not uncommon. I review what is known, and not known, about solar grand minima. One way to fill in the gaps in our understanding of solar grand minima is to turn to solar-like stars. I review efforts to find stars which may be in grand minima, properties of these candidates, and the light this may shed on the state of the Sun in grand minima. Title: The Radial Velocity Signature and Line Diagnostics Arising from Realistic, Rotating Stellar Plage Models Authors: Saar, Steven; Dumusque, Xavier Bibcode: 2015IAUGA..2258500S Altcode: The radial velocity (RV) signature of starspots has been well-studied and methods to mitigate for them have been developed. The RV signature of magnetic plage is smaller, but more complex (since plage differs from its surroundings more by velocity than intensity) and less well understood. There are reasons however to expect that RV jitter from plage may be important, especially in low to moderate activity stars. We explore the RV effects of stellar plage by taking spatially resolved solar line bisectors in and out of plage at various limb angles to construct semi-empirical stellar intensity profiles profiles of different strengths. These lines are placed on model stars with various plage configurations, rotated, and disk-integrated. The resulting spectra are analyzed to yield the RV and various line and cross-correlation profile diagnostics as a function of rotational phase. We discuss the results and some ideas for mitigating the inferred RV signatures. Title: Internetwork Chromospheric Bright Grains Observed With IRIS and SST Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson, Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt, Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan; Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli, Sarah; Kankelborg, Charles Bibcode: 2015ApJ...803...44M Altcode: 2015arXiv150203490M The Interface Region Imaging Spectrograph (IRIS) reveals small-scale rapid brightenings in the form of bright grains all over coronal holes and the quiet Sun. These bright grains are seen with the IRIS 1330, 1400, and 2796 Å slit-jaw filters. We combine coordinated observations with IRIS and from the ground with the Swedish 1 m Solar Telescope (SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H 3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å, Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.} 33), temporal, and spectral resolution. We conclude that the IRIS slit-jaw grains are the counterpart of so-called acoustic grains, i.e., resulting from chromospheric acoustic waves in a non-magnetic environment. We compare slit-jaw images (SJIs) with spectra from the IRIS spectrograph. We conclude that the grain intensity in the 2796 Å slit-jaw filter comes from both the Mg ii k core and wings. The signal in the C ii and Si iv lines is too weak to explain the presence of grains in the 1300 and 1400 Å SJIs and we conclude that the grain signal in these passbands comes mostly from the continuum. Although weak, the characteristic shock signatures of acoustic grains can often be detected in IRIS C ii spectra. For some grains, a spectral signature can be found in IRIS Si iv. This suggests that upward propagating acoustic waves sometimes reach all the way up to the transition region. Title: Stellar activity and coronal heating: an overview of recent results Authors: Testa, Paola; Saar, Steven H.; Drake, Jeremy J. Bibcode: 2015RSPTA.37340259T Altcode: 2015arXiv150207401T Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars. Title: Steps towards a high precision solar rotation profile: Results from SDO/AIA coronal bright point data Authors: Sudar, D.; Skokić, I.; Brajša, R.; Saar, S. H. Bibcode: 2015A&A...575A..63S Altcode: 2015arXiv150101285S Context. Coronal bright points (CBP) are ubiquitous small brightenings in the solar corona associated with small magnetic bipoles.
Aims: We derive the solar differential rotation profile by tracing the motions of CBPs detected by the Atmospheric Imaging Assembly (AIA) instrument aboard the Solar Dynamics Observatory (SDO). We also investigate problems related to the detection of CBPs resulting from instrument and detection algorithm limitations.
Methods: To determine the positions and identification of CBPs we used a segmentation algorithm. A linear fit of their central meridian distance and latitude vs time was used to derive velocities.
Results: We obtained 906 velocity measurements in a time interval of only 2 days. The differential rotation profile can be expressed as ωrot = (14.47° ± 0.10° + (0.6° ± 1.0°) sin2(b) = (-4.7° ± 1.7°) sin4(b)) d-1. Our result is in agreement with other work and it comes with reasonable errors in spite of the very short time interval used. This was made possible by the higher sensitivity and resolution of the AIA instrument compared to similar equipment as well as high cadence. The segmentation algorithm also played a crucial role by detecting so many CBPs, which reduced the errors to a reasonable level.
Conclusions: Data and methods presented in this paper show a great potential for obtaining very accurate velocity profiles, both for rotation and meridional motion and, consequently, Reynolds stresses. The amount of CBP data that could be obtained from this instrument should also provide a great opportunity to study changes of velocity patterns with a temporal resolution of only a few months. Other possibilities are studies of evolution of CBPs and proper motions of magnetic elements on the Sun. Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode and Magnetic Modeling With Data-Driven Simulations Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.; Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner, P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint, L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.; Carlsson, M.; Hansteen, V. Bibcode: 2015ApJ...801...83C Altcode: 2015arXiv150101593C We report on observations of recurrent jets by instruments on board the Interface Region Imaging Spectrograph, Solar Dynamics Observatory (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21, recurrent coronal jets were observed to emanate from NOAA Active Region 11793. Far-ultraviolet spectra probing plasma at transition region temperatures show evidence of oppositely directed flows with components reaching Doppler velocities of ±100 km s-1. Raster Doppler maps using a Si iv transition region line show all four jets to have helical motion of the same sense. Simultaneous observations of the region by SDO and Hinode show that the jets emanate from a source region comprising a pore embedded in the interior of a supergranule. The parasitic pore has opposite polarity flux compared to the surrounding network field. This leads to a spine-fan magnetic topology in the coronal field that is amenable to jet formation. Time-dependent data-driven simulations are used to investigate the underlying drivers for the jets. These numerical experiments show that the emergence of current-carrying magnetic field in the vicinity of the pore supplies the magnetic twist needed for recurrent helical jet formation. 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: A New Light on the Relation Between Rotation Periods and Cycle Lengths of Stellar Activity Authors: do Nascimento, Jose-Dias, Jr.; Saar, Steven H.; Anthony, Francys Bibcode: 2015csss...18...59D Altcode: Solar analogs and twins shed a new light on the relation between rotation period and cycle length of stellar activity . The question of how typical the Sun is within the class of solar-type stars has been the subject of active investigation over the past three decades. Some previous work has suggested that the Sun's magnetic cycle period Pcyc is unusual compared with similar stars, falling between sequences of active and inactive stars. The HARPS planet-search has been gathering high-precision Ca II H&K chromospheric activity measurements for many years, and has measured a large number of new Pcyc. We collect the most robust cycles among these for stars which are solar analogs (main-sequence stars with 0.8M_{⊙} < mass < 1.2M_{⊙}) or solar twins twins (stars with T_{eff}, [Fe/H] and mass indistinguishable from the Sun). Combining this new sample with older data, we revisit the relation between rotation periods Prot and Pcyc. Our preliminary analysis shows that the Sun does not have a special position between the active and inactive sequences, but instead follows the a new solar-analog sequence proposed here. Title: A First Look at Differential Rotation in Kepler Open Clusters NGC 6811 (1 Gyr) and NGC 6819 (2.5 Gyr) Authors: Saar, Steven H.; Meibom, Soren; do Nascimento, Jose-Dias, Jr. Bibcode: 2015csss...18..125S Altcode: Open clusters are ideal targets for controlled studies of stellar properties, since members are coeval and have the same abundances. We present the first results of measurements of surface differential rotation (SDR) in two clusters of different ages in the Kepler field. We compare results for single stars over a range of masses and rotation rates, and compare and contrast these with previous results for single and binary stars. All of these properties are found to have an effect on the average SDR rate. Title: Solar velocity field determined tracking coronal bright points Authors: Brajša, R.; Sudar, D.; Skokić, I.; Saar, S. H.; Žic, T. Bibcode: 2015CEAB...39...21B Altcode: Preliminary data from Atmospheric Imaging Assembly (AIA) instrumenton board Solar Dynamics Observatory (SDO) satellite were used to determine solar differential rotation and related phenomena. A segmentation algorithm, which uses multiple AIA channels in search for intensity enhancements in EUV and X-ray parts of the spectrum compared to the background intensity, was applied to obtain positional information of coronal bright points (CBPs). More than 60000 position measurements of more than 10000 identified CBPs from the period 1 - 2 January 2011 were analyzed. Rotational and meridional velocities were determined by tracking identified CBPs and various filters were used to exclude erroneous results. Also, proper motions of CBPs were calculated from rotation velocity residuals and meridional velocities. Proper motions of CBPs were investigated using a random walk model and the diffusion constant was calculated. These results were compared with the previous ones obtained by other instruments and methods (especially with the SOHO-EIT and Hinode data) and a striking agreement of the obtained diffusion constant with results from other studies was found. Title: Cool Stars and Space Weather Authors: Vidotto, A. A.; Jardine, M.; Cameron, A. C.; Morin, J.; Villadsen, J.; Saar, S. H.; Alvarado, J.; Cohen, Ofer; Holzwarth, V.; Poppenhaeger, K.; Reville, V. Bibcode: 2015csss...18...65V Altcode: 2014arXiv1408.3943V Stellar flares, winds and coronal mass ejections form the ``space weather''. They are signatures of the magnetic activity of cool stars and, since activity varies with age, mass and rotation, the space weather that extra-solar planets experience can be very different from the one encountered by the solar system planets. How do stellar activity and magnetism influence the space weather of exoplanets orbiting main-sequence stars? How do the environments surrounding exoplanets differ from those around the planets in our own solar system? How can the detailed knowledge acquired by the solar system community be applied in exoplanetary systems? How does space weather affect habitability? These were questions that were addressed in the splinter session ``Cool stars and Space Weather'', that took place on 9 Jun 2014, during the Cool Stars 18 meeting. In this paper, we present a summary of the contributions made to this session. Title: Hot explosions in the cool atmosphere of the Sun Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.; De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint, L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V. Bibcode: 2014Sci...346C.315P Altcode: 2014arXiv1410.5842P The solar atmosphere was traditionally represented with a simple one-dimensional model. Over the past few decades, this paradigm shifted for the chromosphere and corona that constitute the outer atmosphere, which is now considered a dynamic structured envelope. Recent observations by the Interface Region Imaging Spectrograph (IRIS) reveal that it is difficult to determine what is up and down, even in the cool 6000-kelvin photosphere just above the solar surface: This region hosts pockets of hot plasma transiently heated to almost 100,000 kelvin. The energy to heat and accelerate the plasma requires a considerable fraction of the energy from flares, the largest solar disruptions. These IRIS observations not only confirm that the photosphere is more complex than conventionally thought, but also provide insight into the energy conversion in the process of magnetic reconnection. Title: The unresolved fine structure resolved: IRIS observations of the solar transition region Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira, T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.; Martínez-Sykora, J. Bibcode: 2014Sci...346E.315H Altcode: 2014arXiv1412.3611H The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long-standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low-lying loops or loop segments at transition-region temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a long-standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle. Title: Evidence of nonthermal particles in coronal loops heated impulsively by nanoflares Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale, F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli, S. Bibcode: 2014Sci...346B.315T Altcode: 2014arXiv1410.6130T The physical processes causing energy exchange between the Sun’s hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High-resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60 seconds) of intensity and velocity on small spatial scales (≲500 kilometers) at the footpoints of hot and dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of nonthermal electrons, which are generated in small impulsive (≲30 seconds) heating events called “coronal nanoflares.” The accelerated electrons deposit a sizable fraction of their energy (≲1025 erg) in the chromosphere and TR. Our analysis provides tight constraints on the properties of such electron beams and new diagnostics for their presence in the nonflaring corona. Title: Prevalence of small-scale jets from the networks of the solar transition region and chromosphere Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.; Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves, K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber, M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W. Bibcode: 2014Sci...346A.315T Altcode: 2014arXiv1410.6143T As the interface between the Sun’s photosphere and corona, the chromosphere and transition region play a key role in the formation and acceleration of the solar wind. Observations from the Interface Region Imaging Spectrograph reveal the prevalence of intermittent small-scale jets with speeds of 80 to 250 kilometers per second from the narrow bright network lanes of this interface region. These jets have lifetimes of 20 to 80 seconds and widths of ≤300 kilometers. They originate from small-scale bright regions, often preceded by footpoint brightenings and accompanied by transverse waves with amplitudes of ~20 kilometers per second. Many jets reach temperatures of at least ~105 kelvin and constitute an important element of the transition region structures. They are likely an intermittent but persistent source of mass and energy for the solar wind. Title: On the prevalence of small-scale twist in the solar chromosphere and transition region Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.; Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.; Martinez-Sykora, J. Bibcode: 2014Sci...346D.315D Altcode: 2014arXiv1410.6862D The solar chromosphere and transition region (TR) form an interface between the Sun’s surface and its hot outer atmosphere. There, most of the nonthermal energy that powers the solar atmosphere is transformed into heat, although the detailed mechanism remains elusive. High-resolution (0.33-arc second) observations with NASA’s Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere and TR that are replete with twist or torsional motions on sub-arc second scales, occurring in active regions, quiet Sun regions, and coronal holes alike. We coordinated observations with the Swedish 1-meter Solar Telescope (SST) to quantify these twisting motions and their association with rapid heating to at least TR temperatures. This view of the interface region provides insight into what heats the low solar atmosphere. Title: An Interface Region Imaging Spectrograph First View on Solar Spicules Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen, V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli, S.; Kankelborg, C. Bibcode: 2014ApJ...792L..15P Altcode: 2014arXiv1407.6360P Solar spicules have eluded modelers and observers for decades. Since the discovery of the more energetic type II, spicules have become a heated topic but their contribution to the energy balance of the low solar atmosphere remains unknown. Here we give a first glimpse of what quiet-Sun spicules look like when observed with NASA's recently launched Interface Region Imaging Spectrograph (IRIS). Using IRIS spectra and filtergrams that sample the chromosphere and transition region, we compare the properties and evolution of spicules as observed in a coordinated campaign with Hinode and the Atmospheric Imaging Assembly. Our IRIS observations allow us to follow the thermal evolution of type II spicules and finally confirm that the fading of Ca II H spicules appears to be caused by rapid heating to higher temperatures. The IRIS spicules do not fade but continue evolving, reaching higher and falling back down after 500-800 s. Ca II H type II spicules are thus the initial stages of violent and hotter events that mostly remain invisible in Ca II H filtergrams. These events have very different properties from type I spicules, which show lower velocities and no fading from chromospheric passbands. The IRIS spectra of spicules show the same signature as their proposed disk counterparts, reinforcing earlier work. Spectroheliograms from spectral rasters also confirm that quiet-Sun spicules originate in bushes from the magnetic network. Our results suggest that type II spicules are indeed the site of vigorous heating (to at least transition region temperatures) along extensive parts of the upward moving spicular plasma. Title: Tanagra: Timing Analysis of Grating Data Authors: Kashyap, Vinay; Posson-Brown, Jennifer; Drake, Jeremy J.; Saar, Steven H.; Scargle, Jeffrey D; Connors, Alanna Bibcode: 2014HEAD...1411905K Altcode: We describe the Tanagra dataset, which now contains the complete set of cool stars observed with the Chandra gratings thus far. We have analyzed the datasets to produce a catalog of light curves, flare-like events, measures of spectral variability, evaluations of variability for strong spectral lines, correlations of intensity between high- and low-temperature lines, and other useful observational summaries. We will describe the analysis methods used and the data products obtained, and highlight some special cases.This work has been supported by the Chandra archival grant AR0-11001X. Title: Swift Observations of Proxima Cen Authors: Wargelin, Bradford J.; Saar, Steven H.; Drake, Jeremy J.; Kashyap, Vinay Bibcode: 2014HEAD...1411901W Altcode: Swift observed Proxima Cen (dM5.5e) for more than 40 segments (roughly 100 separate exposures) from 2009 to 2012, including several UV grism observations. We present analyses of variability in the optical, UV, and X-ray bands on time scales covering individual flares to a possible multiyear stellar cycle, and show moderate-resolution spectra covering 2300-6000 Angstroms. Title: Calibrating Data from the Hinode/X-Ray Telescope and Associated Uncertainties Authors: Kobelski, Adam R.; Saar, Steven H.; Weber, Mark A.; McKenzie, David E.; Reeves, Katharine K. Bibcode: 2014SoPh..289.2781K Altcode: 2013arXiv1312.4850K; 2014SoPh..tmp...27K The X-Ray Telescope (XRT) onboard the Hinode satellite, launched 23 September 2006 by the Japan Aerospace Exploration Agency (JAXA), is a joint mission of Japan, the United States, and the United Kingdom to study the solar corona. In particular, XRT was designed to study solar plasmas with temperatures between 1 and 10 MK with ≈ 1″ pixels (≈ 2″ resolution). Prior to analysis, the data product from this instrument must be properly calibrated and data values quantified to accurately assess the information contained within. We present here the standard methods of calibration for these data. The calibration was performed on an empirical basis that uses the least complicated correction that accurately describes the data while suppressing spurious features. By analyzing the uncertainties remaining in the data after calibration, we conclude that the procedure is successful, because the remaining uncertainty after calibration is dominated by photon noise. This calibration software is available in the SolarSoft software library. Title: The Interface Region Imaging Spectrograph (IRIS) Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.; Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou, C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman, C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish, D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.; Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons, R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.; Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.; Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.; Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski, W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.; Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.; Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.; Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson, M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu, K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora, J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.; Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N. Bibcode: 2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 - 0.4 arcsec spatial resolution, two-second temporal resolution, and 1 km s−1 velocity resolution over a field-of-view of up to 175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å, 1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec × 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation. Title: Detection of Supersonic Downflows and Associated Heating Events in the Transition Region above Sunspots Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.; De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.; McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen, J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.; Kankelborg, C. Bibcode: 2014ApJ...789L..42K Altcode: 2014arXiv1406.6816K Interface Region Imaging Spectrograph data allow us to study the solar transition region (TR) with an unprecedented spatial resolution of 0.''33. On 2013 August 30, we observed bursts of high Doppler shifts suggesting strong supersonic downflows of up to 200 km s-1 and weaker, slightly slower upflows in the spectral lines Mg II h and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated with brightenings in the slitjaw images (SJIs). The bursty behavior lasts throughout the 2 hr observation, with average burst durations of about 20 s. The locations of these short-lived events appear to be the umbral and penumbral footpoints of EUV loops. Fast apparent downflows are observed along these loops in the SJIs and in the Atmospheric Imaging Assembly, suggesting that the loops are thermally unstable. We interpret the observations as cool material falling from coronal heights, and especially coronal rain produced along the thermally unstable loops, which leads to an increase of intensity at the loop footpoints, probably indicating an increase of density and temperature in the TR. The rain speeds are on the higher end of previously reported speeds for this phenomenon, and possibly higher than the free-fall velocity along the loops. On other observing days, similar bright dots are sometimes aligned into ribbons, resembling small flare ribbons. These observations provide a first insight into small-scale heating events in sunspots in the TR. Title: Investigating Molecular Hydrogen in Active Regions with IRIS Authors: Jaeggli, Sarah A.; Saar, Steven H.; Daw, Adrian N.; Innes, Davina Bibcode: 2014AAS...22432306J Altcode: Molecular hydrogen should be the most abundant molecular species in sunspots, but recent observations with IRIS show that its florescent signature is absent from above the sunspot umbra, but appears brightly during flares. In this poster we continue the analysis of FUV observations of H2 in active regions, examining the correlation between the intensity of the H2 lines and the lines of C II and Si IV which are responsible for their excitation. We particularly focus on differentiating places where H2 is abundant, holes in the chromospheric opacity where FUV photons can enter more deeply into the solar atmosphere, and places where the FUV radiation field is intense, as in flares. Title: Rates of Large Flares in Old Solar-like Stars in Kepler Clusters NGC 6811 and 6819 With Implications for the Sun Authors: Saar, Steven H.; Wright, Paul J.; Meibom, Soren; Kashyap, Vinay; Drake, Jeremy J. Bibcode: 2014AAS...22412343S Altcode: We hope to better estimate the rate of very strong (Carrington event-type) flares in the Sun by studying flares of stars in several open clusters with well determined ages using Kepler data. Here we derive white light flare distributions for a sample of near-solar-mass (G0-G5) dwarfs in NGC 6811 (age ~ 1 Gyr) and NGC 6819 2.5 Gyr). We compare these with solar white light flare rates and, by estimating X-ray emission from the same flares using a solar-based relationship, we compare the Kepler results to other solar and stellar X-ray flare data. We explore implications of our results for the rates of large solar flares. This research was supported by Kepler grant NNX13AC29G. Title: SOLAR ANALOGS AND TWINS SHED A NEW LIGHT ON THE RELATION BETWEEN ROTATION PERIODS AND CYCLE LENGTHS OF STELLAR ACTIVITY Authors: Do Nascimento, José-Dias; Saar, Steven H.; Anthony, Francys Bibcode: 2014AAS...22432208D Altcode: The question of how typical the Sun is within the class of solar-type stars has been the subject of active investigation over the past three decades. Some previous work has suggested that the Sun's magnetic cycle period Pcyc is unusual compared with similar stars,falling between sequences of active and inactive stars. The HARPS planet-search has been gathering high-precision Ca II H&K chromospheric activity measurements for about 7 years, and has measured a large number of new Pcyc. We collect the most robust cycles among these for stars which are solar analogs (main-sequence stars with 0.8 Msun < mass < 1.2 Msun) or solar twins twins (stars with Teff, [Fe/H] and mass indistinguishable from the Sun). Combining this new sample with older data, we revisit the relation between rotationperiods Prot and Pcyc. Our preliminary analysis shows that the Sun does not has a special position between the active and inactive sequences, but instead follows the a new solar-analog sequence proposed here. Title: H2 Emission in the Sun and Stars: A New Window on Spots and Flares Authors: Saar, Steven H.; Jaeggli, Sarah A. Bibcode: 2014AAS...22412344S Altcode: Molecular H2 is likely important for the formation of sun and starspots, but has been difficult to observe in the past. H2 emission has been seen in solar FUV spectra of sunspots and flares, where it produced by fluorescent excitation driven (primarily) by Si IV and O IV. New observations with IRIS show that the emission is strong in flares, and in loops connected to pores or the boundaries of umbrae. We find evidence for H2 emission in the HST spectra of several magnetically active, flaring, spotted stars. Once the excitation process is better understood, observations of H2 emission should permit new insight into spot formation on the Sun and active stars. Title: Coronae at 3 Gyr: First Results from a Chandra Observation of the Open Cluster Ruprecht 147 Authors: Saar, Steven H.; Curtis, Jason L.; Wright, Jason Bibcode: 2014AAS...22432203S Altcode: Ruprecht 147 is the oldest nearby star cluster, with an age of 3 Gyr and a distance of 300 pc. This makes it an important benchmark in exploring activity-age-rotation relationships, bridging the gap between the Hyades and M67. We present the first results from a deep 250 ksec ACIS-I observation of the cluster. Analysis of the longest (81 ksec) pointing detects more than half of the known members in the field, with spectral types ranging from F6 to K5. The star most like the Sun in our sample, a G2V, has an X-ray luminosity (0.2-7 keV) of L_X ~ 1.1e28 ergs/s, which suggests a scaling with age t of log L_X ~ -b log t where 1.25 < b < 4, possibly steeper than seen at younger ages. This research was supported by Chandra grant G02-13022X. Title: High-resolution Observations of the Shock Wave Behavior for Sunspot Oscillations with the Interface Region Imaging Spectrograph Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu, B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.; Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Kankelborg, C.; Jaeggli, S.; McIntosh, S. W. Bibcode: 2014ApJ...786..137T Altcode: 2014arXiv1404.6291T We present the first results of sunspot oscillations from observations by the Interface Region Imaging Spectrograph. The strongly nonlinear oscillation is identified in both the slit-jaw images and the spectra of several emission lines formed in the transition region and chromosphere. We first apply a single Gaussian fit to the profiles of the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the sunspot. The intensity change is ~30%. The Doppler shift oscillation reveals a sawtooth pattern with an amplitude of ~10 km s-1 in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and ~12 s, respectively. The line width suddenly increases as the Doppler shift changes from redshift to blueshift. However, we demonstrate that this increase is caused by the superposition of two emission components. We then perform detailed analysis of the line profiles at a few selected locations on the slit. The temporal evolution of the line core is dominated by the following behavior: a rapid excursion to the blue side, accompanied by an intensity increase, followed by a linear decrease of the velocity to the red side. The maximum intensity slightly lags the maximum blueshift in Si IV, whereas the intensity enhancement slightly precedes the maximum blueshift in Mg II. We find a positive correlation between the maximum velocity and deceleration, a result that is consistent with numerical simulations of upward propagating magnetoacoustic shock waves. Title: Stellar Granulation as the Source of High-frequency Flicker in Kepler Light Curves Authors: Cranmer, Steven R.; Bastien, Fabienne A.; Stassun, Keivan G.; Saar, Steven H. Bibcode: 2014ApJ...781..124C Altcode: 2013arXiv1312.5928C A large fraction of cool, low-mass stars exhibit brightness fluctuations that arise from a combination of convective granulation, acoustic oscillations, magnetic activity, and stellar rotation. Much of the short-timescale variability takes the form of stochastic noise, whose presence may limit the progress of extrasolar planet detection and characterization. In order to lay the groundwork for extracting useful information from these quasi-random signals, we focus on the origin of the granulation-driven component of the variability. We apply existing theoretical scaling relations to predict the star-integrated variability amplitudes for 508 stars with photometric light curves measured by the Kepler mission. We also derive an empirical correction factor that aims to account for the suppression of convection in F-dwarf stars with magnetic activity and shallow convection zones. So that we can make predictions of specific observational quantities, we performed Monte Carlo simulations of granulation light curves using a Lorentzian power spectrum. These simulations allowed us to reproduce the so-called flicker floor (i.e., a lower bound in the relationship between the full light-curve range and power in short-timescale fluctuations) that was found in the Kepler data. The Monte Carlo model also enabled us to convert the modeled fluctuation variance into a flicker amplitude directly comparable with observations. When the magnetic suppression factor described above is applied, the model reproduces the observed correlation between stellar surface gravity and flicker amplitude. Observationally validated models like these provide new and complementary evidence for a possible impact of magnetic activity on the properties of near-surface convection. Title: Preliminary results on the solar rotation determined tracing SDO/AIA coronal bright points Authors: Brajša, R.; Sudar, D.; Skokič, I.; Saar, S. H. Bibcode: 2014CEAB...38..105B Altcode: In this paper we present preliminary results on the solar differential rotation measured tracing coronal bright points in SDO/AIA images. An automatic recognition method was applied to the series of images taken in the test period, 1-2 January 2011. Coronal bright points are suitable tracers for the determination of the solar differential rotation, because they are localized objects which are very well distributed over solar disc. Results presented in this paper show that the SDO/AIA data are very useful for that aim, due to the high spatial and temporal resolution of the images. Title: Strong-Flare Rates of Solar-Like Stars in Kepler Cluster NGC 6811 Authors: Wright, Paul J.; Saar, S. H.; Meibom, S.; Kashyap, V.; Drake, J. J. Bibcode: 2014AAS...22315108W Altcode: Strong flares on the Sun are accompanied by intense ionizing radiation (X-rays, far UV) and are often associated with coronal mass ejections (CMEs), which can be hazardous to astronauts, and infrastructure such as satellites and electrical systems. The rates of the largest flare events are, however, poorly known. By taking advantage of the exquisite precision of Kepler photometry, we derive white light flare distributions for a sample of near-solar-mass (G1-G5) dwarfs in NGC 6811 (age ~ 1 Gyr). Using a solar-based relationship, we estimate the X-ray emission from these flares in order to compare the results to other solar and stellar X-ray flare data. We also take a first look at some stars of different masses, to study the mass dependence of flaring at fixed age, and explore the implications of our results for the rates of the largest flaring events on the Sun. This work was supported by Kepler grants NNX11AC82G and NNX13AC29G and NASA HGI grant NNX10AF29G. 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: X-ray Binaries and Feedback in Lyman-α Galaxies Authors: Prestwich, Andrea H.; Jackson, F.; Kaaret, P.; Brorby, M.; Roberts, T. P.; Saar, S. H. Bibcode: 2014AAS...22342807P Altcode: We describe evidence for a compact, extremely luminous (LX ≈ 1041 ergs s-1) X-ray source in the Lyman Break Analog (LBA) galaxy Haro 11. The X-ray spectrum is hard with a power-law photon index γ≈1.2. This source is most likely dominated by an extreme ULX with LX ≧ 5 × 1040 ergs s-1, possibly with a contribution of other X-ray binaries and Inverse Compton emission. If this source is a Black Hole Binary (BHB) in the low state, as suggested by the hard X-ray spectrum, the compact object is almost certainly an Intermediate Mass Black Hole (IMBH). Discovery of an IMBH in a low metallicity star bursting dwarf would be significant because (1) such objects may be accreted into larger galaxies to form HLX such as ESO 243-49 HLX-1 and (2) Haro 11 X-1 may be a ``seed'' black hole which is currently growing rapidly to form a supermassive black hole. This source is also coincident with the center of the Lyman-α emission. Outflow from the ULX may occur very early in the life of the starburst and inject enough mechanical power into the Interstellar Medium (ISM) to accelerate it and thus reduce resonant scattering. ULX may be critical to allow Lyman-α photons to escape. Haro 11 and other LBAs are important for understanding the role X-ray binaries play in the evolution of young galaxies. Title: Extreme Ultraviolet and X-Ray Observations of Comet Lovejoy (C/2011 W3) in the Lower Corona Authors: McCauley, P.; Saar, S.; Raymond, J. C.; Ko, Y.; Saint-Hilaire, P. Bibcode: 2013AGUFM.P31A1784M Altcode: On December 16, 2011, Comet Lovejoy (C/2011 W3) came to within 140,000 km of the solar photosphere and survived its perihelion passage to the surprise of many. We present observations recorded by two solar observatories, the X-Ray Telescope (XRT) aboard Hinode and the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory. We explore a time series of post-perihelion observations in eight wavelength bands between 22 and 1600 Å. As material sublimates from the nucleus and is immersed in coronal plasma, it rapidly ionizes through charge states that are seldom seen in this environment. O III through O VII, along with C IV, are observed, and we derive outgassing rates from these data where applicable. We estimate peak rates of 10^32.5 oxygen atoms per second and a total mass loss of ~10^13 g during the egress, assuming that all neutral oxygen comes from sublimated water molecules. From this, we expect that the nucleus was on the order of 600 m in diameter on approach to perihelion. Our data show distinct spikes in the observed intensity, which we attribute to outbursts triggered by explosions of interior water ice. AIA is also poised to observe Comet ISON (C/2012 S1) as it makes its perihelion passage on November 28, 2013. ISON will pass much further from the Sun, but is thought to be considerably larger, than Lovejoy, so it is uncertain whether or not a signature will be detected by AIA. We will present these observations, along with some very preliminary analysis, if they are successful. Title: Fixing the Leak: Empirical Corrections for the Small Light Leak in Hinode XRT Authors: Saar, Steven H.; DeLuca, E. E.; McCauley, P.; Kobelski, A. Bibcode: 2013SPD....44...93S Altcode: On May 9, 2012, the the straylight level of XRT on Hinode suddenly increased, consistent with the appearance of a pinhole in the entrance filter (possibly a micrometeorite breach). The effect of this event is most noticeable in the optical G band data, which shows an average light excess of ~30%. However, data in several of the X-ray filters is also affected, due to low sensitivity "tails" of their filter responses into the visible. Observations taken with the G band filter but with the visible light shutter (VLS) closed show a weak, slightly shifted, out-of-focus image, revealing the leaked light. The intensity of the leak depends on telescope pointing, dropping strongly for images taken off-disk. By monitoring light levels in the corners of full-Sun Ti-poly filter images, we determine the approximate time of the event: ~13:30 UT. We use pairs of images taken just-before and after the filter breach to directly measure the leakage in two affected X-ray filters. We then develop a model using a scaled, shifted, and smoothed versions of the VLS closed images to remove the contamination. We estimate the uncertainties involved in our proposed correction procedure. This research was supported under NASA contract NNM07AB07C for Hinode XRT. Title: Exploring Low-State Accretion in Polars with a Solar Flux Rope Model Authors: Saar, Steven H.; Reeves, K. Bibcode: 2013SPD....44...78S Altcode: Polars are cataclysmic variables, close binaries consisting of a strongly magnetic white dwarf (WD) and a cool solar-like secondary star. They tend to have high and low photometric states, corresponding to times of high accretion (due to Roche lobe overflow from the secondary) and low accretion (where the accretion source is under debate). Since tidal spin-up forces the secondary to rotate at the orbital period, typically < 1 day, it should be very magnetically active. We use a solar flux rope/CME model with field strength Bsec, placed in a strong external field (BWD), to explore the stability of magnetic loops on the secondary in the presence of the megagauss WD field. We find that for low ratios BWD/Bsec, loops confining a prominence separated by more than a certain distance are stable, but as the ratio is increased, a second regime of instability for widely separated loops appears. The two instability regimes grow with BWD/Bsec, until above a certain value, no loops are stable. We find that for reasonable masses of loop confined material, the BWD induced instability may be able to explain much of the accretion seen in polar low states, as well as several other observed properties. Implications for polar evolution are discussed. This research was supported by several NSF grants. Title: Extreme-ultraviolet and X-Ray Observations of Comet Lovejoy (C/2011 W3) in the Lower Corona Authors: McCauley, Patrick I.; Saar, Steven H.; Raymond, John C.; Ko, Yuan-Kuen; Saint-Hilaire, Pascal Bibcode: 2013ApJ...768..161M Altcode: 2013arXiv1304.1544M We present an analysis of extreme-ultraviolet and soft X-ray emission detected toward Comet Lovejoy (C/2011 W3) during its post-perihelion traverse of the solar corona on 2011 December 16. Observations were recorded by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory and the X-Ray Telescope (XRT) aboard Hinode. A single set of contemporaneous images is explored in detail, along with prefatory consideration for time evolution using only the 171 Å data. For each of the eight passbands, we characterize the emission and derive outgassing rates where applicable. As material sublimates from the nucleus and is immersed in coronal plasma, it rapidly ionizes through charge states seldom seen in this environment. The AIA data show four stages of oxygen ionization (O III-O VI) along with C IV, while XRT likely captured emission from O VII, a line typical of the corona. With a nucleus of at least several hundred meters upon approach to a perihelion that brought the comet to within 0.2 R ⊙ of the photosphere, Lovejoy was the most significant sungrazer in recent history. Correspondingly high outgassing rates on the order of 1032.5 oxygen atoms per second are estimated. Assuming that the neutral oxygen comes from water, this translates to a mass-loss rate of ~9.5 × 109 g s-1, and based only on the 171 Å observations, we find a total mass loss of ~1013 g over the AIA egress. Additional and supporting analyses include a differential emission measure to characterize the coronal environment, consideration for the opening angle, and a comparison of the emission's leading edge with the expected position of the nucleus. Title: MMT Hectochelle Spectral Variability of Active Late-type Stars in the Kepler Field (2013A) Authors: Brown, Alexander; Walkowicz, Lucianne; Saar, Steven; Hawley, Suzanne; Kowalski, Adam; Furesz, Gabor; Piskunov, Nikolai Bibcode: 2013noao.prop..286B Altcode: We have on-going it Kepler photometric monitoring of over 300 active late-type (mid-A - K) stars as part of our Cycles 1/2/3/4 Guest Observer (GO) programs with the aim of studying starspot evolution, differential rotation, activity cycles, and flares. We propose to use the MMT Hectochelle multiobject spectrograph to observe over 140 of these stars to determine a range of basic physical properties for the stars, such as radial velocity variations due to binarity, chromospheric activity levels from Ca II H+K and H(alpha), projected rotational velocities for comparison to the rotational periods measured directly by it Kepler, age/youth as indicated by Li I, and better effective temperature and luminosity estimates. In addition, to provide a superior sample for statistical studies another 800 GKM dwarf stars showing either starspot modulation from the it Kepler Team's data or from our deep XMM X-ray survey will be observed using the unassigned fibers in each field. These measurements require the 32,000 spectral resolution provided by Hectochelle, which is hard to obtain efficiently for 13-15th magnitude stars any other way. Title: Deep Imaging of M37, A Better Hyades Authors: Bowsher, Emily C.; Agueros, M. A.; Covey, K. R.; Hartman, J. D.; Lopez-Morales, M.; Pooley, D. A.; Saar, S.; West, A. A. Bibcode: 2013AAS...22125207B Altcode: X-ray emission traces the strength of a star's magnetic dynamo and is tightly linked to age and stellar rotation. Early studies found that X-ray luminosity decreases steadily as stars age. However, recent studies suggest that the picture of X-ray luminosity decaying from 10 Myr to 5 Gyr as a single power-law, and independently of mass, is too simplistic. Open clusters, with their homogeneous, coeval populations, provide an ideal environment for calibrating empirically how stellar activity depends on age and rotation. M37, a Hyades analog, has been carefully surveyed in the optical, and we have obtained complementary deep (450 ksec) Chandra ACIS-I imaging of this open cluster. M37's rich membership, good match to Chandra's field-of-view, and large number of measured periods 700) make it ideal for examining the evolution of coronal X-ray emission. Here we report the first results from our analysis of the combined X-ray and optical data. These data will enable determinations of X-ray luminosity as a function of rotation period, tests of whether magnetic effects produce anomalous optical colors/luminosities for high X-ray luminosity sources, and theta characterization of M37's interacting binaries. 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: A Preliminary Study of Active Region Canopies With AIA Authors: Lucchini, Scott; Saar, S.; Muglach, K. Bibcode: 2013AAS...22115905L Altcode: Active region canopies are areas frequently accompanying active regions which have extensive horizontal magnetic fields. The large-scale canopy fields have a significant effect on the kinds of structures which can exist beneath them, and how they evolve. Using data from the Atmospheric Imaging Assembly (AIA), we developed methods to automatically identify these regions. A Differential Emission Measure (DEM) analysis is consistent with the idea that the long, hotter active region loops overlie quite cool, small-scale features ("fibrils"). We suggest that the overlying loops restrict the growth of underlying structures to mostly very short, cool features. We also studied evolution of canopy regions over time. In several cases, a large quiescent filament formed out of the former canopy region over the course of a few solar rotations, confirming previous suggestions. The canopy remains visible for several rotations after its active regions have begun to decay; in this time, the fibril magnetic fields gradually align in such a way as to form a filament channel. Further analysis of our large canopy database should uncover more information on the frequency and characteristics of these canopy-to-filament evolutions, as well as other canopy properties. This work is supported by the NSF REU program at SAO (grant ATM-0851866) and contract SP02H1701R from Lockheed Martin to SAO for SDO research. Title: Fearsome Flashes: A Study Of The Evolution Of Flaring Rates In Cool Stars Using Kepler Cluster Data Authors: Saar, Steven Bibcode: 2013adap.prop..242S Altcode: Strong solar flares can damage power grids, satellites, interrupt communications and GPS information, and threaten astronauts and high latitude air travelers. Despite the potential cost, their frequency is poorly determined. Beyond purely current terrestrial concerns, how the rate of large flares (and associated coronal mass ejections [CMEs], high-energy particle fluxes and far UV emission) varies over the stellar lifetime holds considerable astrophysical interest. These include: the contributions of flares to coronal energy budgets; the importance of flares and CMEs to terrestrial and exoplanet atmospheric and biological evolution; and importance of CME mass loss for angular momentum evolution. We will explore the rate of strong flares and its variation with stellar age, mass and rotation by studying Kepler data of cool stars in two open clusters NGC 6811 (age ~ 1 Gyr) and NGC 6819 (~2.5 Gyr). We will use two flare analysis methods to build white-light flare distributions for cluster stars. One subtracts a low-pass filtered version of the data and analyzes the residue for positive flux deviations, the other does a statistical analysis of the flux deviations vs. time lags compared with a model. For near- solar stars, a known solar relation can then be used to estimate X-ray production by the white-light flares. For stars much hotter or cooler or with significantly different chromospheric density, we will use particle code flare models including bombardment effects to estimate how the X-ray to white light scaling changes. With the X-ray values, we can estimate far UV fluxes and CME rates, building a picture of the flare effects; with the two cluster ages, we can make a first estimate of the solar rate (by projecting to the Sun's age) and begin to build up an understanding of flare rate evolution with mass and age. Our proposal falls squarely in the "Stellar Astrophysics and Exoplanets" research area, and is relevant to NASA astrophysics goals in promoting better understanding the evolution of stars and their exoplanets, and better understanding the environment in which life evolved, and threats to it, both on Earth and in the wider cosmos. 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: Differential Emission Measure Analysis of Multiple Structural Components of Coronal Mass Ejections in the Inner Corona Authors: Cheng, X.; Zhang, J.; Saar, S. H.; Ding, M. D. Bibcode: 2012ApJ...761...62C Altcode: 2012arXiv1210.7287C In this paper, we study the temperature and density properties of multiple structural components of coronal mass ejections (CMEs) using differential emission measure (DEM) analysis. The DEM analysis is based on the six-passband EUV observations of solar corona from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The structural components studied include the hot channel in the core region (presumably the magnetic flux rope of the CME), the bright loop-like leading front (LF), and coronal dimming in the wake of the CME. We find that the presumed flux rope has the highest average temperature (>8 MK) and density (~1.0 × 109 cm-3), resulting in an enhanced emission measure over a broad temperature range (3 <= T(MK) <= 20). On the other hand, the CME LF has a relatively cool temperature (~2 MK) and a narrow temperature distribution similar to the pre-eruption coronal temperature (1 <= T(MK) <= 3). The density in the LF, however, is increased by 2%-32% compared with that of the pre-eruption corona, depending on the event and location. In coronal dimmings, the temperature is more broadly distributed (1 <= T(MK) <= 4), but the density decreases by ~35%-~40%. These observational results show that: (1) CME core regions are significantly heated, presumably through magnetic reconnection; (2) CME LFs are a consequence of compression of ambient plasma caused by the expansion of the CME core region; and (3) the dimmings are largely caused by the plasma rarefaction associated with the eruption. Title: The thermal and spatial structure of the solar corona over the cycle and its implication for the coronae of inactive stars Authors: Testa, P.; Landi, E.; Saar, S. Bibcode: 2012AGUFMSH42A..05T Altcode: We use spectral (SOHO/SUMER and Hinode/EIS) and imaging (Hinode/XRT and SDO/AIA) solar coronal data to systematically measure the thermal structure of different types of solar features (coronal hole, quiet Sun, X-ray bright points, active regions...), and how they vary over the solar cycle. We use a combination of these structures to construct a model for the quiet corona of the inactive G8V star tau Ceti, which is a candidate stellar analog of a solar magnetic minimum. Since tau Ceti is significantly metal-poor relative to the Sun, we reconstruct the solar results with corresponding lower metallicities to generate more appropriate coronal structures. Title: Evolution of Coronal Bright Points and Photospheric Magnetic Fields Authors: Lamb, D. A.; Saar, S.; DeForest, C. Bibcode: 2012AGUFMSH33A2227L Altcode: Coronal bright points are excellent probes of the connection between the photosphere and corona, and occur in sufficiently larger numbers all over the Sun to make statistical or ensemble studies necessary and useful. We present initial results on the evolution of coronal bright points and the state of the associated photospheric magnetic field. Using an automated bright point detection algorithm that has found thousands of bright points in multiple SDO/AIA passbands, combined with an automated magnetic feature tracking algorithm on SDO/HMI magnetograms, we explore the magnetic conditions necessary for bright point formation and destruction. Title: Secretive Solar Waves Stimulate X-ray Bright Points Authors: Saar, S. H.; Attrill, G. D. Bibcode: 2012ASPC..454..395S Altcode: We discuss Hinode XRT observations of temporally-related emission enhancements in solar X-ray bright points (XBPs) consistent with excitation by an otherwise unseen wave. In one case, the wave source is unclear (out of the field of view), in the other which we report here, the wave seems to be excited by a flaring/erupting XBP. In this latter case, the wave velocity averaged ∼340 km s-1 in areas of quiet Sun emission, but was reduced by ∼1/3 in areas of higher emission and magnetic flux density. Larger loops were mostly unaffected by the wave's passage, while XBPs could still be excited at distances of 105 km and more from the apparent origin. Small coronal dimming regions (displaying characteristic evolution properties in EUV intensity) are seen next to the flaring XBP, suggesting a small CME may have been associated with the event. We speculate on the origin and properties of these mysterious waves, which may prove useful tools for studying the media through which they travel. These events are inconspicuous, showing low intensity enhancements of only selected small regions, and require high cadence, high spatial resolution data to be detected. Since they are easily overlooked and/or confused with stochastic variability, these waves may be a fairly common, but under-recognized component of the flare/CME phenomenon at small energies and spatial scales. SDO's AIA should be very useful in further study of these waves. Title: Cooler and Hotter X-ray Bright Points from Hinode/XRT Observations Authors: Kariyappa, R.; DeLuca, E. E.; Saar, S. H.; Golub, L.; Damé, L.; Varghese, B. A. Bibcode: 2012ASPC..454..149K Altcode: We use a 7-hour (17:00 UT - 24:00 UT) time sequence of soft X-ray images observed almost simultaneously in two filters (Ti_poly and Al_mesh) on April 14, 2007 with X-Ray Telescope (XRT) on-board the Hinode mission to determine the temperature of X-ray bright points (XBPs). A sample of 14 XBPs and 2 background coronal regions have been identified and selected on both the images for detailed analysis. The temperature of XBPs is determined by filter ratio method. We find that the XBPs show temperature fluctuations and that the average temperature ranges from 1.1 MK to 3.4 MK which may correspond to different X-ray fluxes. These results suggest the existence of cooler and hotter XBPs and that the heating rate of XBPs is highly variable on short time scales. Title: Spatial and Thermal Study of an Isolated Loop with XRT and EIS Authors: Saar, S. H.; Schmelz, J. T.; Kashyap, V. L. Bibcode: 2012ASPC..454..241S Altcode: We use multi-filter contemporaneous XRT and EIS observations of a small active region to study the spatial and thermal properties of an isolated quiescent loop. We study the loop as a whole, in segments, in transverse cuts, and point-by-point, always with some form of "background" subtraction. We find the loop DEM is not-isothermal, but is also not extremely broad, with ≍96% of the EM between 6.2 ≤ log T ≤ 6.7, and an EM-weighted average temperature of log T = 6.48 ± 0.16. There is some evidence for a gradual change in temperature along the loop, with log T increasing by ≍0.1 from the foot points to the peak. Including EIS data helps better constrain the EM at low T. Future work includes combining the analysis with contemporaneous RHESSI data and to explore XRT-EIS-RHESSI cross-calibration at AR temperatures. Title: Stars in magnetic grand minima: where are they and what are they like? Authors: Saar, Steven H.; Testa, Paola Bibcode: 2012IAUS..286..335S Altcode: We explore various ideas of what a star in a Maunder-like magnetic minimum would look like, and ways of finding stars in such a state, and make some estimates of their physical and magnetic activity properties. We discuss new X-ray observations of a small selection of candidates for being in magnetic grand minima. These are then compared with the Sun and other low activity stars. Title: The Journey of Sungrazing Comet Lovejoy Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.; Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson, H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse, C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.; Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson, W.; Weissman, P.; Comet Lovejoy Collaboration Team Bibcode: 2012AAS...22052507B Altcode: Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed by space-based instruments, to survive perihelion passage. First observed by ground-based telescopes several weeks prior to perihelion, its journey towards the Sun was subsequently recorded by several solar observatories, before being observed in the weeks after perihelion by a further array of space- and ground-based instruments. Such a surfeit of wide-ranging observations provides an unprecedented insight into both sungrazing comets themselves, and the solar atmosphere through which they pass. This paper will summarize what we have learnt from the observations thus far and offer some thoughts on what future sungrazing comets may reveal about comets, the Sun, and their interaction. Title: Rotational Modulation, Shear, And Cyclic Activity In HII 2927 Authors: Milingo, Jackie; Saar, S. H.; Lehman, S. L.; Marschall, L. A.; Stauffer, J. R. Bibcode: 2012AAS...22032806M Altcode: We present a 15 yr compilation of V-band differential photometry for the Pleiades K4 dwarf HII 2927 (V378 Tau). HII 2927 has a rotational period (P_rot) of 0.26 d and displays significant rotational modulation due to non-uniform surface brightness or "starspots". With the long timeline of data available we can explore many aspects of the star's photometric variability, with the goal of including them in a larger study of magnetic activity in single cool dwarfs. Preliminary work yields a cycle period (P_cyc) of 14.5 +/- 1.9 yrs. We also present preliminary work on the rotational shear for this star (ΔP_rot/<P_rot>). Measurements of P_cyc and rotational shear contribute to our understanding of the magnetic dynamo at the source of stellar activity. We compare our P_cyc and ΔP_rot/<P_rot> estimates with those of other stars, including our measurements of fellow Pleaid HII 1883 (V660 Tau). Title: Photometric Uncertainties within Hinode XRT Authors: Kobelski, Adam; Saar, S. H.; Weber, M. A.; McKenzie, D. E.; Reeves, K. K. Bibcode: 2012AAS...22020126K Altcode: We have developed estimates of the systematic uncertainties for the X-Ray Telescope (XRT) on Hinode. These estimates are included as optional returns from the standard XRT data reduction software, xrt_prep.pro. Included in these software estimates are uncertainties from instrument vignetting, dark current subtraction, split bias leveling, Fourier filtering and JPEG compression. Sources of uncertainty that rely heavily on models of plasma radiation or assumptions of elemental abundances, such as photon noise, are discussed, but not included in the software. It will be shown that the photon noise is much larger than the systematic uncertainty.

This work is supported by NASA under contract NNM07AB07C with the Harvard-Smithsonian Astrophysical Observatory Title: An Exploration of the Emission Properties of X-ray Bright Points Seen With SDO Authors: Saar, Steven H.; Elsden, T.; Muglach, K. Bibcode: 2012AAS...22020713S Altcode: We present preliminary results of a study of X-ray Bright Point (XBP) EUV emission and its dependence on other properties. The XBPs were located using a new, automated XBP finder for AIA developed

as part of the Feature Finding Team for SDO Computer Vision. We analyze XBPs near disk center, comparing AIA EUV fluxes, HMI LOS

magnetic fields, and photospheric flow fields (derived from HMI data) to look for relationships between XBP emission, magnetic flux, velocity fields, and XBP local environment. We find some evidence for differences in the mean XBP temperature with environment.

Unsigned magnetic flux is correlated with XBP emission, though other parameters play a role. The majority of XBP footpoints are approaching

each other, though at a slight angle from head-on on average. We discuss the results in the context of XBP heating. Title: Combined XRT and AIA Differential Emission Measure Analysis of Active Region Loops and Weak Flares Authors: Saar, S. H.; Schmelz, J. T. Bibcode: 2012ASPC..455..353S Altcode: The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) provides excellent new tools for exploring the thermal properties of active regions at high cadence. The thick filters of the Hinode X-ray Telescope (XRT), however, can add important additional constraints on high temperature plasma, particularly in flares. We demonstrate the power of combined AIA and XRT studies by conducting a joint AIA+XRT differential emission measure analysis of an active region loop and a weak flare. Title: Differential Emission Measure Analysis for AIA and XRT Observations of Comet Lovejoy (C/2011 W3) Authors: McCauley, Patrick; Saar, S. H.; Raymond, J.; Golub, L. E. Bibcode: 2012AAS...22020115M Altcode: We present observations of Comet Lovejoy (C/2011 W3) recorded by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) and the X-Ray Telescope (XRT) aboard the Hinode satellite. Lovejoy, a member of the Kreutz family of sungrazing comets, came to within 1.2 solar radii during its perihelion approach and escaped, despite expectations to the contrary, on December 6, 2011. The most significant sungrazer since the launch of SDO, Lovejoy provides an unprecedented opportunity to examine the effects of a comet traversing the solar corona. Both the ingress and egress were detected in seven AIA passbands (131, 171, 193, 211, 304, 335, and 1600 Angstroms), with XRT successfully imaging the outbound trip using its Al-mesh filter. We estimate the temperature structure of the emitting plasma using a differential emission measure analysis and explore interactions with the solar magnetic field. In several cases, secondary lines in a given channel appear to be the dominant comet-related emitters. Use of a radial filter for improved contrast of the faint cometary emission is also discussed. Title: Measuring Uncertainties in the Hinode X-Ray Telescope Authors: Kobelski, A.; Saar, S.; McKenzie, D. E.; Weber, M.; Reeves, K.; DeLuca, E. Bibcode: 2012ASPC..456..241K Altcode: We have developed estimates of the systematic photometric uncertainties the X-Ray Telescope (Kano et al. (2008)) on Hinode (Kosugi et al.(2007)). These estimates are included as optional returns from the standard XRT data reduction software, xrt_prep.pro. Included in the software estimates are uncertainties from instrument vignetting, dark current subtraction, split bias leveling, fourier filtering and JPEG compression. We show that these uncertainties are generally smaller than the photon counting uncertainty. However, due to the reliance on assumptions of plasma radiation models and elemental abundances, photon counting is not included in the software. Title: Long-term magnetic field monitoring of the Sun-like star ξ Bootis A Authors: Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin, J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.; Théado, S.; Van Grootel, V. Bibcode: 2012A&A...540A.138M Altcode: 2011arXiv1109.5066M
Aims: We aim to investigate the long-term temporal evolution of the magnetic field of the solar-type star ξ Bootis A, both from direct magnetic field measurements and from the simultaneous estimate of indirect activity indicators.
Methods: We obtained seven epochs of high-resolution, circularly-polarized spectra from the NARVAL spectropolarimeter between 2007 and 2011, for a total of 76 spectra. Using approximately 6100 photospheric spectral lines covering the visible domain, we employed a cross-correlation procedure to compute a mean polarized line profile from each spectrum. The large-scale photospheric magnetic field of the star was then modelled by means of Zeeman-Doppler Imaging, allowing us to follow the year-to-year evolution of the reconstructed magnetic topology. Simultaneously, we monitored the width of several magnetically sensitive spectral lines, the radial velocity, the line asymmetry of intensity line profiles, and the chromospheric emission in the cores of the Ca II H and Hα lines.
Results: During the highest observed activity states, in 2007 and 2011, the large-scale field of ξ Bootis A is almost completely axisymmetric and is dominated by its toroidal component. The toroidal component persists with a constant polarity, containing a significant fraction of the magnetic energy of the large-scale surface field through all observing epochs. The magnetic topologies reconstructed for these activity maxima are very similar, suggesting a form of short cyclicity in the large-scale field distribution. The mean unsigned large-scale magnetic flux derived from the magnetic maps varies by a factor of about 2 between the lowest and highest observed magnetic states. The chromospheric flux is less affected and varies by a factor of 1.2. Correlated temporal evolution, due to both rotational modulation and seasonal variability, is observed between the Ca II emission, the Hα emission and the width of magnetically sensitive lines. The rotational dependence of polarimetric magnetic measurements displays a weak correlation with other activity proxies, presumably due to the different spatial scales and centre-to-limb darkening associated with polarimetric signatures, as compared to non-polarized activity indicators. Better agreement is observed on the longer term. When measurable, the differential rotation reveals a strong latitudinal shear in excess of 0.2 rad d-1.

Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France.Tables 3-6 are available in electronic form at http://www.aanda.org Title: MMT Hectochelle Spectral Variability of Active Late-type Stars in the Kepler Field (2012A) Authors: Brown, Alexander; Walkowicz, Lucianne; Hawley, Suzanne; Kowalski, Adam; Saar, Steven; Furesz, Gabor Bibcode: 2012noao.prop..332B Altcode: We have on-going Kepler photometric monitoring of over 200 active late-type (mid-A - K) stars as part of our Cycles 1/2/3 Guest Observer (GO) programs with the aim of studying starspot evolution, differential rotation, activity cycles, and flares. We propose to use the MMT Hectochelle multiobject spectrograph to observe over 120 of these stars to determine a range of basic physical properties for the stars, such as radial velocity variations due to binarity, chromospheric activity levels from Ca II H+K and H(alpha), projected rotational velocities for comparison to the rotational periods measured directly by Kepler, age/youth as indicated by Li I, and better effective temperature and luminosity estimates. In addition, to provide a superior sample for statistical studies another ~1,000 GKM dwarf stars showing either starspot modulation from the Kepler Team's data or from our on-going deep XMM X-ray survey will be observed using the unassigned fibers in each field. These measurements require the 32,000 spectral resolution provided by Hectochelle, which is hard to obtain efficiently for 13-15th magnitude stars any other way. Title: Computer Vision for the Solar Dynamics Observatory (SDO) Authors: Martens, P. C. H.; Attrill, G. D. R.; Davey, A. R.; Engell, A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.; Savcheva, A.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P. N.; Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F.; Cirtain, J. W.; DeForest, C. E.; Angryk, R. A.; De Moortel, I.; Wiegelmann, T.; Georgoulis, M. K.; McAteer, R. T. J.; Timmons, R. P. Bibcode: 2012SoPh..275...79M Altcode: 2011SoPh..tmp..144M; 2011SoPh..tmp..213M; 2011SoPh..tmp....8M In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre-Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO). Title: Properties of Candidate Magnetic Grand Minimum Stars Authors: Saar, S. H. Bibcode: 2011ASPC..448.1239S Altcode: 2011csss...16.1239S Using a large database of Ca II HK measurements from exoplanet search candidates, I explore properties of stars with the lowest activity levels. The minimum R'HK level (using the traditional calibration) seen in bona-fide dwarfs (as determined spectroscopically) is a strong function of metallicity: log RHK(min) ≍ -5.1 - 0.2 log M/H. Dwarf stars with a small Δ R'HK above this boundary uniformly show fractional rms Ca II HK index SHK variation of σS /<SHK> ≤ 2%. I propose stars which show this low-variability, low RHK behavior on timescales of several years (longer than a typical solar minimum) are candidates for being in magnetic grand minima (MM). These candidate MM stars span a wide range in M/H and Teff, but show a sharp cutoff at higher masses. Their v sin i distribution is consistent with their being drawn from a mostly older (≥ 2 Gyr) stellar population. Title: Long-term Magnetic Field Monitoring of the Sun-like Star ζ Bootis A Authors: Morgenthaler, A.; Petit, P.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Morin, J.; Ramirez, J.; Saar, S.; Solanki, S. K.; Théado, S.; Van Grootel V., V. Bibcode: 2011ASPC..448.1203M Altcode: 2011csss...16.1203M Phase-resolved observations of the solar-type star ζ Bootis A were obtained using the NARVAL spectropolarimeter at the Telescope Bernard Lyot (Pic du Midi, France) during years 2007, 2008, 2009 and 2010. The data sets enable us to study both the rotational modulation and the long-term evolution of various magnetic and activity tracers. Here, we focus on the large-scale photospheric magnetic field (reconstructed by Zeeman-Doppler Imaging), the Zeeman broadening of the FeI 846.84 nm magnetic line, and the chromospheric CaII H and Hα emission. Title: Testing a Predictive Theoretical Model for the Mass Loss Rates of Cool Stars Authors: Cranmer, Steven R.; Saar, Steven H. Bibcode: 2011ApJ...741...54C Altcode: 2011arXiv1108.4369C The basic mechanisms responsible for producing winds from cool, late-type stars are still largely unknown. We take inspiration from recent progress in understanding solar wind acceleration to develop a physically motivated model of the time-steady mass loss rates of cool main-sequence stars and evolved giants. This model follows the energy flux of magnetohydrodynamic turbulence from a subsurface convection zone to its eventual dissipation and escape through open magnetic flux tubes. We show how Alfvén waves and turbulence can produce winds in either a hot corona or a cool extended chromosphere, and we specify the conditions that determine whether or not coronal heating occurs. These models do not utilize arbitrary normalization factors, but instead predict the mass loss rate directly from a star's fundamental properties. We take account of stellar magnetic activity by extending standard age-activity-rotation indicators to include the evolution of the filling factor of strong photospheric magnetic fields. We compared the predicted mass loss rates with observed values for 47 stars and found significantly better agreement than was obtained from the popular scaling laws of Reimers, Schröder, and Cuntz. The algorithm used to compute cool-star mass loss rates is provided as a self-contained and efficient computer code. We anticipate that the results from this kind of model can be incorporated straightforwardly into stellar evolution calculations and population synthesis techniques. Title: Isothermal and Multithermal Analysis of Coronal Loops Observed with Atmospheric Imaging Assembly. II. 211 Å Selected Loops Authors: Schmelz, J. T.; Worley, B. T.; Anderson, D. J.; Pathak, S.; Kimble, J. A.; Jenkins, B. S.; Saar, S. H. Bibcode: 2011ApJ...739...33S Altcode: An important component of coronal loop analysis involves conflicting results on the cross-field temperature distribution. Are loops isothermal or multithermal? The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory was designed in part to answer this question. AIA has a series of coronal filters that peak at different temperatures and cover the entire active region temperature range. These properties should make AIA ideal for multithermal analysis, but recent results have shown that the response functions of two of the filters, AIA 94 and 131 Å, are missing a significant number of low-temperature emission lines. Here we analyze coronal loops from several active regions that were chosen in the 211 Å channel of AIA, which has a peak response temperature of log T = 6.3. The differential emission measure (DEM) analysis of the 12 loops in our sample reveals that using data from the 131 Å AIA filter distorts the results, and we have no choice but to do the analysis without these data. The 94 Å data do not appear to be as important, simply because the chosen loops are not visible in this channel. If we eliminate the 131 Å data, however, we find that our DEM analysis is not well constrained on the cool temperature end of six of our loops. The information revealed by our 211 selected loops indicates that additional atomic data are required in order to pin down the cross-field temperature distribution. Title: Warm and Fuzzy: Temperature and Density Analysis of an Fe XV EUV Imaging Spectrometer Loop Authors: Schmelz, J. T.; Rightmire, L. A.; Saar, S. H.; Kimble, J. A.; Worley, B. T.; Pathak, S. Bibcode: 2011ApJ...738..146S Altcode: The Hinode EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) were designed in part to work together. They have the same spatial resolution and cover different but overlapping coronal temperature ranges. These properties make a combined data set ideal for multithermal analysis, where EIS provides the best information on the cooler corona (log T < 6.5) and XRT provides the best information on the hotter corona (log T > 6.5). Here, we analyze a warm non-flaring loop detected in images made in a strong EIS Fe XV emission line with a wavelength of 284.16 Å and peak formation temperature of log T = 6.3. We perform differential emission measure (DEM) analysis in three pixels at different heights above the footpoint and find multithermal results with the bulk of the emission measure in the range 6.0 < log T < 6.6. Analysis with the EIS lines alone gave a DEM with huge amounts of emission measure at very high temperatures (log T >7.2) analysis with XRT data alone resulted in a DEM that was missing most of the cooler emission measure required to produce many of the EIS lines. Thus, both results were misleading and unphysical. It was only by combining the EIS and XRT data that we were able to produce a reasonable result, one without ad hoc assumptions on the shape and range of the DEM itself. Title: A Close Look At Middle-Aged Coronae: The Nearby 2.5 Gyr Old Cluster Ruprecht 147 Authors: Saar, Steven Bibcode: 2011cxo..prop.3327S Altcode: Just six years ago Kharchenko (2005) used catalog data to identify Ruprecht 147 (R147) as the 15th closest stellar cluster to the Solar System. At a distance of only 250 pc, and an age estimated to be 2.5 Gyr, R147 is by far the closest old cluster: the next closest with an age > 1 Gyr is nearly twice as distant. We request a 240 ksec observation with ACIS-S near the cluster core to characterize the coronal emission in cool stars at an unexplored age: ~half solar. The data will close a large age gap in our understanding of coronal evolution, improve age-rotation-activity calibration and explore the coronal consequences of significant magnetic dynamo/activity changes which appear around this time. Title: A Unified Analysis of Time Variability in Chandra Grating Observations of Low-Mass Stars Authors: Posson-Brown, Jennifer; Kashyap, V.; Saar, S.; Drake, J. Bibcode: 2011HEAD...12.1005P Altcode: We are carrying out a unified study of archival Chandra grating observations of active low-mass coronal stars and present preliminary results here. We include ACIS-S/HETG, ACIS-S/LETG, and HRC-S/LETG observations. Gratings data are optimal for timing analysis since they are free from pile-up and allow for joint spectro-temporal analysis. We discuss techniques for timing analysis of gratings data and explore the distribution of stellar flare energies and the time variability of individual lines fluxes. This work is supported by CXC NASA contract NAS8-39073 and Chandra grant AR0-11001X. 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: Starspots, cycles, and magnetic fields Authors: Saar, Steven H. Bibcode: 2011IAUS..273...61S Altcode: I make a perhaps slightly foolhardy attempt to synthesize a semi-coherent scenario relating cycle characteristics, starspots, and the underlying magnetic fields with stellar properties such as mass and rotation. Key to this attempt is to first study single dwarfs; differential rotation plays a surprising role. Title: The dependence of maximum starspot amplitude and the amplitude distribution on stellar properties Authors: Saar, Steven H.; Dyke, Michelle; Meibom, Søren; Barnes, Sydney A. Bibcode: 2011IAUS..273..469S Altcode: We combine photometric data from field stars, plus over a dozen open clusters and associations, to explore how the maximum photometric amplitude (Amax) and the distribution of amplitudes varies with stellar properties. We find a complex variation of Amax with inverse Rossby number Ro-1, which nevertheless can be modeled well with a simple model including an increase in Amax with rotation for low Ro-1, and a maximum level. Amax may then be further affected by differential rotation and a decline at the highest Ro-1. The distribution of Aspot below Amax varies with Ro-1 : it peaks at low Aspot with a long tail towards Amax for low Ro-1, but is more uniformly distributed at higher Ro-1. We investigate further dependences of the Aspot distributions on stellar properties, and speculate on the source of these variations. Title: BOREAS: Mass Loss Rate of a Cool, Late-type Star Authors: Cranmer, Steven R.; Saar, Steven H. Bibcode: 2011ascl.soft08019C Altcode: The basic mechanisms responsible for producing winds from cool, late-type stars are still largely unknown. We take inspiration from recent progress in understanding solar wind acceleration to develop a physically motivated model of the time-steady mass loss rates of cool main-sequence stars and evolved giants. This model follows the energy flux of magnetohydrodynamic turbulence from a subsurface convection zone to its eventual dissipation and escape through open magnetic flux tubes. We show how Alfven waves and turbulence can produce winds in either a hot corona or a cool extended chromosphere, and we specify the conditions that determine whether or not coronal heating occurs. These models do not utilize arbitrary normalization factors, but instead predict the mass loss rate directly from a star's fundamental properties. We take account of stellar magnetic activity by extending standard age-activity-rotation indicators to include the evolution of the filling factor of strong photospheric magnetic fields. We compared the predicted mass loss rates with observed values for 47 stars and found significantly better agreement than was obtained from the popular scaling laws of Reimers, Schroeder, and Cuntz. The algorithm used to compute cool-star mass loss rates is provided as a self-contained and efficient IDL computer code. We anticipate that the results from this kind of model can be incorporated straightforwardly into stellar evolution calculations and population synthesis techniques. Title: Rotational modulation, shear, and cyclic activity in HII 1883 Authors: Milingo, J. B.; Saar, S. H.; Marschall, L. A.; Stauffer, J. R. Bibcode: 2011IAUS..273...74M Altcode: We present a 30 year compilation of V-band differential photometry for the Pleiades K dwarf HII 1883. HII 1883 has an average rotational period <Prot> of ~0.235d and displays rotational modulation due to non-uniform surface brightness as large as 0.2 magnitudes in V. Preliminary work yields a cycle period of ~9yrs and rotational shear δProt/<Prot> considerably less than solar. With such a long baseline of data available we can explore many aspects of the star's photometric variability. We present studies of the variation of the rotational modulation amplitude, <V>, and Prot over the cycle. Title: The Color-period Diagram and Stellar Rotational Evolution—New Rotation Period Measurements in the Open Cluster M34 Authors: Meibom, Søren; Mathieu, Robert D.; Stassun, Keivan G.; Liebesny, Paul; Saar, Steven H. Bibcode: 2011ApJ...733..115M Altcode: 2011arXiv1103.5171M We present the results of a 5 month photometric time-series survey for stellar rotation periods combined with a 4 year radial-velocity survey for membership and binarity in the 220 Myr open cluster M34. We report surface rotation periods for 120 stars, 83 of which are kinematic and photometric late-type cluster members. A comparison to previous work serves to illustrate the importance of high-cadence long baseline photometric observations and membership information. The new M34 periods are less biased against slow rotation and cleaned for non-members. The rotation periods of the cluster members span over more than an order of magnitude from 0.5 days up to 11.5 days, and trace two distinct rotational sequences—fast (C) and moderate-to-slow (I)—in the color-period diagram. The sequences represent two different states (fast and slow) in the rotational evolution of the late-type cluster members. We use the color-period diagrams for M34 and for younger and older clusters to estimate the timescale for the transition from the C to the I sequence and find lsim150 Myr, ~150-300 Myr, and ~300-600 Myr for G, early-mid K, and late K dwarfs, respectively. The small number of stars in the gap between C and I suggests a quick transition. We estimate a lower limit on the maximum spin-down rate (dP/dt) during this transition to be ~0.06 days Myr-1 and ~0.08 days Myr-1 for early and late K dwarfs, respectively. We compare the I sequence rotation periods in M34 and the Hyades for G and K dwarfs and find that K dwarfs spin down slower than the Skumanich \sqrt{t} rate. We determine a gyrochronology age of 240 Myr for M34. The gyro-age has a small formal uncertainty of 2% which reflects the tight I sequence in the M34 color-period diagram. We measure the effect of cluster age uncertainties on the gyrochronology age for M34 and find the resulting error on the gyro-age to be consistent with the ~15% error estimate for the technique in general. We use the M34 I sequence to redetermine the coefficients in the expression for rotational dependence on color used in gyrochronology. Finally, we propose that stability in the phase, shape, and amplitude of the photometric variability for the 120 rotators over the ~5 month duration of our survey is due to spot generation at active stellar longitudes.

WIYN Open Cluster Study XLV. Title: Chandra Observations of the Well-Studied 180 Myr Old Open Cluster M35 Authors: Meibom, Soren; Saar, S. H.; Barnes, S. A. Bibcode: 2011AAS...21813303M Altcode: 2011BAAS..43G13303M M35 is a relatively close ( 800 pc), rich, young ( 180 Myr) open cluster which has been the focus of extensive multi-epoch spectroscopic and photometric study. Some 250 single and 100 binary stars ( 50 with orbits) are confirmed members and 310 have measured rotation periods. This detailed information about membership, binarity, and rotation, makes M35 an ideal target for studying not only the rotation-activity-age relation for cool stars, but also for the effect of a stellar companion on this relationship. We present preliminary results of a 130 ksec ACIS-I observation near the core of the M35, containing 180 cluster members. We explore how the coronal flux and temperature change across the cluster's color-period diagram, how binarity affects these results, and compare our findings with other clusters.

This work was funded by Chandra Award No. GO0-11041A. Title: Testing a Predictive Theoretical Model for the Mass Loss Rates of Cool Stars Authors: Cranmer, Steven R.; Saar, S. H. Bibcode: 2011AAS...21820503C Altcode: 2011BAAS..43G20503C All stars are believed to possess expanding outer atmospheres known as stellar winds. The continual evaporation of gas from stars has a significant impact on stellar and planetary evolution, and also on the larger-scale evolution of gas and dust in galaxies. Despite more than a half-century of study, though, the basic mechanisms responsible for producing stellar winds are still largely unknown. Fortunately, there has been a great deal of recent progress toward identifying and characterizing the processes that produce our own Sun's mass outflow. Based on this progress, we have developed a new generation of physically motivated models of stellar wind acceleration for cool main-sequence stars and evolved giants. These models follow the production of magnetohydrodynamic turbulent motions from subsurface convection zones to their eventual dissipation and escape through the stellar wind. The magnetic activity of these stars is taken into account by extending standard age/rotation/activity indicators to include the evolution of the filling factor of strong magnetic fields in stellar photospheres. We will present tests of these models based on a large database of observationally determined mass loss rates, in combination with accurate measurements of the basic properties of these stars (e.g., masses, radii, luminosities, metallicities, and rotation rates) on which the mass loss rates must depend. The eventual goal of this project is to provide a simple stand-alone algorithm for predicting the mass loss rates of cool stars for use in stellar atmosphere and population synthesis calculations. Title: Many Flares Make a Corona Authors: Saar, Steven H.; Kashyap, V.; Drake, J.; Reeves, K.; Connors, A. Bibcode: 2011AAS...21832202S Altcode: 2011BAAS..43G32202S It is well known that solar flare energies have a self-similar distribution. The number of flares, N, of any given energy, E, follows a power-law distribution, dN/dE E^(-alpha), over many orders of magnitude, with alpha 1.8. A similar distribution holds for stellar coronae, but in this case, typically alpha > 2. The value alpha=2 is important because it represents a threshold beyond which it is possible to ascribe all of the coronal luminosity to increasingly weaker, but more numerous, flares.

Current methods to evaluate the flare distribution index alpha for stars are limited by two factors: they either depend on explicit detections of flares, or if the flare distribution itself is being modeled, then they are highly computation intensive and are thus slow. We have developed analytical methodology that substitutes for Monte Carlo simulations over a majority of the latter calculations. This causes improvements in computational speed of over 100x. We describe these methods below, and apply it to some simulated and observed data.

This work was supported by CXC NASA contract NAS8-39073 and Chandra grant AR0-11001X. 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: Kepler Observations of Pulsations In A Sample of Magnetically-Active Stars Authors: Neff, James E.; Brown, A.; Hawley, S.; Kowalski, A.; Walkowicz, L.; Saar, S. Bibcode: 2011AAS...21822704N Altcode: 2011BAAS..43G22704N We have observed about 200 targets in Kepler Cycle 1/2 Guest Observer programs. The sample of active star candidates was selected primarily using GALEX colors, and the Kepler light curves have revealed a rich variety of variability. Rotational modulation (typical periods a few days) due to starspots over the multi-year timeline of the Kepler observations will permit us to measure surface differential rotation and stellar magnetic cycles. On shorter timescales, the Kepler data show dramatic evidence of stellar pulsations across much of the HR diagram. Our selection criteria yielded a sample of magnetically active G and K dwarfs, which might show solar-like pulsations. It also yielded subsamples of several well-known pulsators (e.g., Delta Scuti stars) as well as pulsators that currently defy easy classification. We are systematically classifying and analyzing the pulsating stars in the our Kepler GO program. We are particularly interested in using pulsations to probe the interior properties of active G and K dwarfs, while the starspots serve as a probe of the convection zone and surface layers. We will present summary results for several different types of pulsation, and we will provide a detailed asteroseismic analysis of those stars in our sample that were observed to have both pulsations and magnetic activity.

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: Preliminary Results From An Automated X-ray Bright Point Detector for AIA Authors: Saar, Steven H.; Farid, S. Bibcode: 2011SPD....42.2121S Altcode: 2011BAAS..43S.2121S We present preliminary results of X-ray Bright Point (XBP) properties derived from a new, automated XBP finder for AIA developed as part of the Feature Finding Team for SDO Computer Vision. We analyze several days of data and explore the size, location, intensity, local environment, and lifetime of the XBPs, and the relationships between these properties.

This work was supported by NASA Grant NNX09AB03G to the Smithsonian Astrophysical Observatory and contract SP02H1701R from Lockheed-Martin to SAO. Title: Temperature variability in X-ray bright points observed with Hinode/XRT Authors: Kariyappa, R.; Deluca, E. E.; Saar, S. H.; Golub, L.; Damé, L.; Pevtsov, A. A.; Varghese, B. A. Bibcode: 2011A&A...526A..78K Altcode:
Aims: We investigate the variability in temperature as a function of time among a sample of coronal X-ray bright points (XBPs).
Methods: We analysed a 7-h (17:00-24:00 UT) long time sequence of soft X-ray images observed almost simultaneously in two filters (Ti_poly and Al_mesh) on April 14, 2007 with X-ray telescope (XRT) onboard the Hinode mission. We identified and selected 14 XBPs for a detailed analysis. The light curves of XBPs were derived using the SolarSoft library in IDL. The temperature of XBPs was determined using the calibrated temperature response curves of the two filters by means of the intensity ratio method.
Results: We find that the XBPs show a high variability in their temperature and that the average temperature ranges from 1.1 MK to 3.4 MK. The variations in temperature are often correlated with changes in average X-ray emission. It is evident from the results of time series that the XBP heating rate can be highly variable on short timescales, suggesting that it has a reconnection origin. Title: Beyond the Limb: A Narrow Band EUV Search for Background Objects with the AIA Authors: Schonfeld, Sam; Testa, P.; Saar, S. Bibcode: 2011AAS...21715505S Altcode: 2011BAAS...4315505S As the star closest to Earth, the Sun provides us with the opportunity to study up close and test models for X-ray stellar activity. Its close proximity (and consequent brightness), however, makes it challenging to observe the Sun and other celestial objects with the same instrument; thus instrumental cross-calibration difficulties have complicated comparison of the Sun with other stars. The new Solar Dynamics Observatory (SDO) launched in February 2010 may at last allow for direct comparison of the Sun and other stars. The Atmospheric Imaging Assembly (AIA) onboard the SDO, a series of telescopes taking images of the full Sun at high spatial and temporal resolution in seven extreme ultraviolet (EUV) pass bands, can potentially observe background objects passing within the field of view of the telescopes off the limb of the Sun. Young stars, active galactic nuclei and other strong X-ray and EUV emitters may be bright enough to observe after careful background subtraction. Using technical specifications of the telescopes and measured X-ray fluxes of various background sources, we determined that with exposure times of the order of minutes, significantly longer than the standard 3s exposure, we should be able to observe the brightest background sources when they pass in the AIA field of view. We also determined what kinds of instrumental limitations we need to overcome and how best to make observations of these dim background sources. Title: Atmospheric Imaging Assembly Multithermal Loop Analysis: First Results Authors: Schmelz, J. T.; Kimble, J. A.; Jenkins, B. S.; Worley, B. T.; Anderson, D. J.; Pathak, S.; Saar, S. H. Bibcode: 2010ApJ...725L..34S Altcode: The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory has state-of-the-art spatial resolution and shows the most detailed images of coronal loops ever observed. The series of coronal filters peak at different temperatures, which span the range of active regions. These features represent a significant improvement over earlier coronal imagers and make AIA ideal for multithermal analysis. Here, we targeted a 171 Å coronal loop in AR 11092 observed by AIA on 2010 August 3. Isothermal analysis using the 171-to-193 ratio gave a temperature of log T ≈ 6.1, similar to the results of Extreme ultraviolet Imaging Spectrograph (EIT) and TRACE. Differential emission measure analysis, however, showed that the plasma was multithermal, not isothermal, with the bulk of the emission measure at log T > 6.1. The result from the isothermal analysis, which is the average of the true plasma distribution weighted by the instrument response functions, appears to be deceptively low. These results have potentially serious implications: EIT and TRACE results, which use the same isothermal method, show substantially smaller temperature gradients than predicted by standard models for loops in hydrodynamic equilibrium and have been used as strong evidence in support of footpoint heating models. These implications may have to be re-examined in the wake of new results from AIA. Title: Multi-stranded and Multi-thermal Solar Coronal Loops: Evidence from Hinode X-ray Telescope and EUV Imaging Spectrometer Data Authors: Schmelz, J. T.; Saar, S. H.; Nasraoui, K.; Kashyap, V. L.; Weber, M. A.; DeLuca, E. E.; Golub, L. Bibcode: 2010ApJ...723.1180S Altcode: Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS) on the Japanese/USA/UK Hinode spacecraft were used to investigate the spatial and thermal properties of an isolated quiescent coronal loop. We constructed differential emission measure (DEM) curves using Monte Carlo based, iterative forward fitting algorithms. We studied the loop as a whole, in segments, in transverse cuts, and point-by-point, always with some form of background subtraction, and find that the loop DEM is neither isothermal nor extremely broad, with approximately 96% of the EM between 6.2 <=log T<= 6.7, and an EM-weighted temperature of log T = 6.48 ± 0.16. We find evidence for a gradual change in temperature along the loop, with log T increasing only by ≈0.1 from the footpoints to the peak. The combine XRT-EIS data set does a good job of constraining the temperature distribution for coronal loop plasma. Our studies show that the strong constraints at high and low temperatures provided by the combined data set are crucial for obtaining reasonable solutions. These results confirm that the observations of at least some loops are not consistent with isothermal plasma, and therefore cannot be modeled with a single flux tube and must be multi-stranded. Title: Low-state Magnetic Structures in Polars: Nature or Nurture? Authors: Kafka, S.; Tappert, C.; Ribeiro, T.; Honeycutt, R. K.; Hoard, D. W.; Saar, S. Bibcode: 2010ApJ...721.1714K Altcode: We present an orbit-resolved study of the magnetic cataclysmic variable (MCV) BL Hyi in its low state, and we explore the origin of its Hα emission line components, their properties, and their possible formation mechanism. We tentatively associate one of the line components with a high-velocity component also seen in the high state. We propose a scenario in which streaming prominence-like magnetic loops (super-prominences) are kept in place by magnetic field interactions between the white dwarf and the donor star and are responsible for the high-velocity line components in the Balmer lines. We also discuss how this is in accord with the standard scenario of the secular evolution for MCVs. Finally, we offer an observational test of our ideas and present challenges for future theoretical studies. Title: Magnetically Sleepy Stars: An X-ray Survey of Candidate Stars in Extended Magnetic Minima Authors: Saar, Steven Bibcode: 2010cxo..prop.3071S Altcode: The Sun occasionally slips into periods of extended magnetic quiescence where the normal magnetic cycle largely ceases (e.g., the Maunder minimum). Understanding these episodes is important for understanding non-linear magnetic dynamos and the Earth's radiation budget. We have developed a new method for determining which stars may be in the stellar analog of these magnetic minima. We propose to study five such stars with Chandra ACIS-S. Combined with archival spectra of more stars, we can 1) explore (by proxy) properties of the solar corona in a Maunder-like minimum, 2) determine what stellar properties affect this state, and 3) investigate the coronal product of the residual turbulent dynamo in a solar mass star. Title: Numerical MHD Simulation of Star-Planet Interaction Authors: Cohen, O.; Kashyap, V. L.; Drake, J. J.; Saar, S. H.; Sokolov, I. V. Bibcode: 2010epsc.conf..804C Altcode: No abstract at ADS Title: X-ray coronae and stellar magnetospheres Authors: Hussain, G. A. J.; Brickhouse, N. S.; Dupree, A. K.; Saar, S. H.; Jardine, M. Bibcode: 2010AIPC.1248...19H Altcode: Chandra's spectroscopic resolving power allows us to measure velocity shifts down to ~30 km/s in line profiles. Observations covering >2Prot are needed to disentangle flaring and quiescent coronal emission. The rotational modulation in X-ray lightcurves and spectra enable us to estimate the size and location of non-flaring X-ray emitting regions stellar coronae. We probe the coronal structure in systems covering a range of parameters (e.g., spectral type and rotation rate), and summarise results from new studies. Title: Steady Heating Model of an Active Region Core Authors: Winebarger, Amy R.; Schmelz, J. T.; Saar, S. H.; Kashyap, V. L.; Warren, H. P. Bibcode: 2010AAS...21640711W Altcode: 2010BAAS...41R.861W If the heating in an active region core is steady, the base pressure of loop as well as its loop length determines exactly the apex temperature, density and required heating rate. In this research, we analyze data of an active region core that is observed with both Hinode XRT and EIS instruments. We use the density sensitve Fe XII line ratios to determine the base pressure of the loops and geometrical constraints to determine the loop lengths. We use the hotter spectral lines coupled with the XRT filter intensities to determine the differential emission measure (DEM) of the core plasma. Using the base pressures and loop lengths, we populate loops in a model active region to determine a model DEM. We then compare this emission measure distribution to the observed distribution. Title: Computer Vision for SDO: First Results from the SDO Feature Finding Algorithms Authors: Martens, Petrus C.; Attrill, G.; Davey, A.; Engell, A.; Farid, S.; Grigis, P.; Kasper, J.; Korreck, K.; Saar, S.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P.; Raouafi, N.; Georgoulis, M.; Deforest, C.; Peterson, J.; Berghoff, T.; Delouille, V.; Hochedez, J.; Mampaey, B.; Verbeek, C.; Cirtain, J.; Green, S.; Timmons, R.; Savcheva, A.; Angryk, R.; Wiegelmann, T.; McAteer, R. Bibcode: 2010AAS...21630804M Altcode: The SDO Feature Finding Team produces robust and very efficient software modules that can keep up with the relentless SDO data stream, and detect, trace, and analyze a large number of phenomena including: flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, CME's, coronal oscillations, and jets. In addition we track the emergence and evolution of magnetic elements down to the smallest features that are detectable, and we will also provide at least four full disk nonlinear force-free magnetic field extrapolations per day.

During SDO commissioning we will install in the near-real time data pipeline the modules that provide alerts for flares, coronal dimmings, and emerging flux, as well as those that trace filaments, sigmoids, polarity inversion lines, and active regions. We will demonstrate the performance of these modules and illustrate their use for science investigations. Title: Stellar Coronae at 250 Myr: Chandra Observations of NGC 3532 Authors: Saar, Steven H.; Barnes, S.; Meibom, S. Bibcode: 2010AAS...21642104S Altcode: 2010BAAS...41R.833S We present preliminary results of a Chandra observation of the 250 Myr open cluster NGC 3532, one of the best studied clusters for rotation periods between Pleiades and Hyades ages. We detect over 30 stars spanning a wide range in rotation period. We discuss the cluster's X-ray distribution function, rotation-activity relationship, and how X-ray flux and temperature vary along the cluster's rotational sequences. We compare the results with other clusters, and draw implications for the evolution of rotation and activity in young stars. Title: Hinode XRT and EIS Multithermal Analysis of a Coronal Loop Authors: Schmelz, Joan T.; Saar, S.; Kashyap, V. Bibcode: 2010AAS...21640713S Altcode: 2010BAAS...41..861S Data from the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS) on Hinode were used to investigate the spatial and thermal properties of an isolated quiescent coronal loop. We constructed Differential Emission Measure (DEM) curves using Monte Carlo based reconstruction algorithms. We studied the loop as a whole, in segments, in transverse cuts, and point-by-point, always with some form of background subtraction, and find that the loop DEM is neither isothermal nor extremely broad, with 96% of the EM between 6.2 < log T < 6.7, and an EM weighted average temperature of log T = 6.48 +/- 0.16. We find evidence for a gradual change in temperature along the loop, with log T increasing by 0.1 from the footpoints to the peak. The combined XRT-EIS data can do a good job of constraining the temperature distribution for coronal loop plasma, but strong high- and low- temperature constraints are crucial. Solar physics research at the University of Memphis is supported by a Hinode subcontract from NASA/SAO as well as NSF ATM-0402729. Title: Cool Star Photometry: Insight Into Temporal and Spatial Activity Variation Authors: Saar, Steven H. Bibcode: 2010AAS...21631303S Altcode: 2010BAAS...41R.888S I briefly review selected significant results from stellar photometry (broadband and Ca II HK) related to magnetic phenomena in cool stars, with particular focus on what these results may be telling us about stellar surface structures, dynamos, and the Sun's place in the broad scope of stellar activity. Title: Searching for a Stellar Cycle and Spin in Proxima Cen Authors: Wargelin, Bradford J.; Saar, S. H.; Kashyap, V. L.; Drake, J. J. Bibcode: 2010HEAD...11.1706W Altcode: 2010BAAS...42R.683W Although hundreds of stars have been optically monitored to look for analogs of the solar 11-year activity cycle, almost no M stars have been examined because of their optical faintness, particularly in the CaII H and K lines that are the basis of most studies. Proxima Cen (dM5.5e) has been monitored somewhat regularly in the optical and UV and there have have been tentative reports of stellar periods ranging from 1.2 to 7 years. Any cyclicity would be surprising since Prox Cen is fully convective and should not have an αΩ dynamo. Several rotation periods have also been suggested, with 83 days currently favored. We present preliminary results on variability and rotation period after monitoring Prox Cen for nearly a year using Swift.

Support for this work was provided by NASA through Swift Grant Number NNX09AR09G. Title: Sunspot cycles and Grand Minima Authors: Sokoloff, Dmitry; Arlt, Rainer; Moss, David; Saar, Steven H.; Usoskin, Ilya Bibcode: 2010IAUS..264..111S Altcode: Observational data concerning the long-term history of cyclic solar activity as recorded in sunspot and isotopic data are discussed in the context of solar dynamo theory. In particular, a simple dynamo model based on differential rotation and the mirror asymmetry of convection with random fluctuations of dynamo governing parameters is shown to reproduce some basic features of the solar magnetic activity evolution. Title: Solar Mystery Waves Excite X-ray Bright Points Authors: Saar, Steven H.; Attrill, G. D. R. Bibcode: 2010AAS...21542205S Altcode: 2010BAAS...42..292S We report on Hinode XRT observations of sequential emission enhancements in solar X-ray bright points (XBPs) consistent with excitation by an (otherwise undetected) wave. In one case, the wave appears to have been excited by a flaring/erupting XBP. The wave velocity averaged about 350 km/s in areas of weak magnetic field and quiet Sun emission, but was reduced by about 1/3 in areas of higher magnetic flux density. Larger loops were mostly unaffected by the wave disturbance, which could still excite XBPs at distances of 4e5 km and more from their apparent starting point. We speculate on the origin and properties of these mystery waves, which may be useful as diagnostics of the medium in which they travel. We suspect these waves may be relatively common, but heretofore under-recognized due to their low level, enhancement selectivity, need for high cadence data, and confusion from stochastic variability. SDO's AIA should aid considerably in further study of this intriguing phenomenon.

This work was supported by NASA contract NNM07AB07C to SAO. Title: Automated Feature and Event Detection with SDO AIA and HMI Data Authors: Davey, Alisdair; Martens, P. C. H.; Attrill, G. D. R.; Engell, A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.; Su, Y.; Testa, P.; Wills-Davey, M.; Savcheva, A.; Bernasconi, P. N.; Raouafi, N. -E.; Delouille, V. A.; Hochedez, J. F. .; Cirtain, J. W.; Deforest, C. E.; Angryk, R. A.; de Moortel, I.; Wiegelmann, T.; Georgouli, M. K.; McAteer, R. T. J.; Hurlburt, N.; Timmons, R. Bibcode: 2010cosp...38.2878D Altcode: 2010cosp.meet.2878D The Solar Dynamics Observatory (SDO) represents a new frontier in quantity and quality of solar data. At about 1.5 TB/day, the data will not be easily digestible by solar physicists using the same methods that have been employed for images from previous missions. In order for solar scientists to use the SDO data effectively they need meta-data that will allow them to identify and retrieve data sets that address their particular science questions. We are building a comprehensive computer vision pipeline for SDO, abstracting complete metadata on many of the features and events detectable on the Sun without human intervention. Our project unites more than a dozen individual, existing codes into a systematic tool that can be used by the entire solar community. The feature finding codes will run as part of the SDO Event Detection System (EDS) at the Joint Science Operations Center (JSOC; joint between Stanford and LMSAL). The metadata produced will be stored in the Heliophysics Event Knowledgebase (HEK), which will be accessible on-line for the rest of the world directly or via the Virtual Solar Observatory (VSO) . Solar scientists will be able to use the HEK to select event and feature data to download for science studies. Title: Towards accurate cross-calibration of Hinode XRT with other X-ray observatories: tentative detection of the F star HD199143 with XRT Authors: Testa, Paola; Saar, Steven Bibcode: 2010cosp...38.2910T Altcode: 2010cosp.meet.2910T Despite decades of X-ray observations of both solar and stellar coronae with various instruments, placing solar X-ray emission levels in a broader astrophysical context is on surprisingly shaky ground. This is largely due to cross-calibration problems and the difficulty of observing the same targets with both solar and stellar instruments. Here we report on a new attempt at direct cross-calibration between solar and stellar missions: observations by the Hinode X-ray Telescope (XRT) of a young X-ray active F star, HD199143. This star has been previously studied by ROSAT and Chandra, and is eclipsed by the Sun every January. We observed the star for a total of 12.6 hours on ingress and egress, and tentatively detect the source at an emission level broadly consistent with expectations based on the most up-to-date calibrations of Hinode, Chandra, and ROSAT count rates for this star. We discuss further observational and analysis plans. Title: Using Solar Regions as Seen by Hinode XRT to Model the Coronae of Inactive Stars and Magnetic Minima Authors: Saar, S.; Testa, P.; Weber, M.; Marsh, J. Bibcode: 2009ASPC..416..543S Altcode: We use carefully calibrated, multi-filter X-ray data from Hinode XRT to compute differential emission measures (DEM) for spatially averaged, less active solar features (coronal holes, quiet Sun, X-ray bright points). We use linear combinations of these regions to construct model quiet coronae for comparison with inactive stars, specifically, stars which may be in Maunder-like magnetic minima. In this way, test how well a mix of existing solar features can be used to model conditions in magnetic minima. Title: Examining the Effect of Local Magnetic Field on Coronal Bright Point Heating and Evolution Authors: Farid, S.; Saar, S.; Govindan, R.; Deluca, E. Bibcode: 2009ASPC..415...15F Altcode: 2010arXiv1001.3241F We investigate the effect of the local magnetic field on the evolution and heating of coronal bright points (BPs) by examining a BP in a coronal hole and a BP in the nearby quiet sun. We attempt to discriminate the heating source of BPs by correlating fluctuations in emission in TRACE 171 Å images, to changes in the unsigned magnetic flux of the associated bipolar region using GONG magnetograms, and potential field extrapolations. We confirm that changes in emission of the larger, quiet-sun bright point can be correlated to fluctuations in the total unsigned magnetic flux as predicted by previous studies. The quiet sun BP also appears to have a potential magnetic configuration over the observation period. However changes in emission in the smaller, coronal hole bright point appears to be less correlated to changes in the bipolar region. We also could not reproduce a potential-like extrapolation at any time during the observation period, possibly indicating the CH bright point may be non-potential. Title: The Activity Cycles and Surface Differential Rotation of Single Dwarfs Authors: Saar, S. H. Bibcode: 2009ASPC..416..375S Altcode: I present an updated overview of activity cycles in cool stars. Long-term study of magnetic proxies such as Ca II HK emission and photometry are the primary tools for investigating stellar activity cycles. I focus on cycle data from these sources, specifically for single dwarf stars. These restrictions reduce two areas of uncertainty: structural changes due to evolution and the effects of binarity. I explore the relationships between cycle period, cycle amplitude and various stellar properties, including rotation and surface differential rotation (SDR). Cycle period relationships are somewhat ambiguous; similar restrictions on the data set for SDR, however, reveal interesting trends. Speculations on what the results might imply for the dynamo are wildly tossed about. Title: Coronal Loop Temperatures Obtained with Hinode XRT: A Toothpaste-Tube Analogy Authors: Schmelz, J. T.; Saar, S. H.; Weber, M. A.; Deluca, E. E.; Golub, L. Bibcode: 2009ASPC..415..299S Altcode: Multi-filter data observed by the Hinode X-Ray Telescope on 10 and 2007 July 13 were used to investigate the thermal properties of coronal loops. At several positions along the loops, differential emission measure analysis revealed a strong peak at log T = 6.1 (which would predict the presence of a TRACE loop) and a much weaker hot component (which we speculated might be a nanoflare signature). TRACE observations, however, did not reveal the predicted loop, so we were forced to re-examine our assumptions. Good differential emission measure results require high- and low-temperature constraints, but our data sets did not contain images from the thinnest and thickest filters, which would be most likely to provide these constraints. Since differential emission measure programs aim to match observed intensities and get low values of χ2, they may place emission measure in high- and low-temperature bins where it does not belong. We draw an analogy to squeezing the toothpaste tube in the middle. Our analysis was repeated for a loop observed on 2007 May 13 when the instrument acquired data in 11 filters and filter combinations, including both the thinnest and thickest filters. These results show that the loop is multi-thermal, with significant emission measure in the range 6.0 < log T < 6.5. Title: Some Like It Hot: Coronal Heating Observations from Hinode X-ray Telescope and RHESSI Authors: Schmelz, J. T.; Kashyap, V. L.; Saar, S. H.; Dennis, B. R.; Grigis, P. C.; Lin, L.; De Luca, E. E.; Holman, G. D.; Golub, L.; Weber, M. A. Bibcode: 2009ApJ...704..863S Altcode: We have used Hinode X-Ray Telescope observations and RHESSI upper limits together to characterize the differential emission measure (DEM) from a quiescent active region. We find a relatively smooth DEM curve with the expected active region peak at log T = 6.4. We also find a high-temperature component with significant emission measure at log T gsim 7. This curve is consistent with previous observations of quiescent active regions in that it does not produce observable Fe XIX lines. It is different from that generated with X-Ray Telescope (XRT) data alone—RHESSI rules out the possibility of a separate high-temperature component with a peak of approximately log T = 7.4. The strength and position of the high-temperature peak in this XRT-only analysis was, however, poorly determined; adding RHESSI flux upper limits in the 4-13 keV energy range provide a strong high-temperature constraint which greatly improves the multi-thermal findings. The results of the present work as well as those from a growing number of papers on this subject imply that our previous understanding of the temperature distribution in active regions has been limited. Hot plasma (log T ≈ 7) appears to be prevalent, although in relatively small quantities as predicted by nanoflare models. Other models may need to be adjusted or updated to account for these new results. Title: Interactions of the Magnetospheres of Stars and Close-In Giant Planets Authors: Cohen, O.; Drake, J. J.; Kashyap, V. L.; Saar, S. H.; Sokolov, I. V.; Manchester, W. B.; Hansen, K. C.; Gombosi, T. I. Bibcode: 2009ApJ...704L..85C Altcode: 2009arXiv0909.3093C Since the first discovery of an extrasolar planetary system more than a decade ago, hundreds more have been discovered. Surprisingly, many of these systems harbor Jupiter-class gas giants located close to the central star, at distances of 0.1 AU or less. Observations of chromospheric "hot spots" that rotate in phase with the planetary orbit, and elevated stellar X-ray luminosities, suggest that these close-in planets significantly affect the structure of the outer atmosphere of the star through interactions between the stellar magnetic field and the planetary magnetosphere. Here, we carry out the first detailed three-dimensional magnetohydrodynamics simulation containing the two magnetic bodies and explore the consequences of such interactions on the steady-state coronal structure. The simulations reproduce the observable features of (1) increase in the total X-ray luminosity, (2) appearance of coronal hot spots, and (3) phase shift of these spots with respect to the direction of the planet. The proximate cause of these is an increase in the density of coronal plasma in the direction of the planet, which prevents the corona from expanding and leaking away this plasma via a stellar wind. The simulations produce significant low temperature heating. By including dynamical effects, such as the planetary orbital motion, the simulation should better reproduce the observed coronal heating. Title: The Activity and Variability of the Sun and Sun-Like Stars. II. Contemporaneous Photometry and Spectroscopy of Bright Solar Analogs Authors: Hall, Jeffrey C.; Henry, Gregory W.; Lockwood, G. Wesley; Skiff, Brian A.; Saar, Steven H. Bibcode: 2009AJ....138..312H Altcode: We present 14 years of contemporaneous photometric and spectroscopic observations of 28 solar analog stars, taken with the Tennessee State University Automatic Photometric Telescopes at Fairborn Observatory and the Solar-Stellar Spectrograph at Lowell Observatory. These are the best observed and most nearly Sun-like of the targets in our magnitude-limited (V <= 7.5) sample. The correlations between luminosity and activity reveal the expected inverse activity-brightness correlations for active stars. Strong direct correlations between activity and brightness are not prevalent for the less active solar age stars, but are precision limited. The Sun does not appear to have unusually low photometric variability when compared with the most Sun-like inactive solar analogs. We present evidence that the activity index R'HK is not a good discriminant of Maunder Minimum candidate stars. On the basis of a star that appears to have transitioned from a low-variability state to a cycling state, we investigate the regime in which stars might switch from faculae-dominated to spot-dominated variations. Title: Computer Vision for The Solar Dynamics Observatory Authors: Martens, Petrus C.; Angryk, R. A.; Bernasconi, P. N.; Cirtain, J. W.; Davey, A. R.; DeForest, C. E.; Delouille, V. A.; De Moortel, I.; Georgoulis, M. K.; Grigis, P. C.; Hochedez, J. E.; Kasper, J.; Korreck, K. E.; Reeves, K. K.; Saar, S. H.; Savcheva, A.; Su, Y.; Testa, P.; Wiegelmann, T.; Wills-Davey, M. Bibcode: 2009SPD....40.1711M Altcode: NASA funded a large international consortium last year to produce a comprehensive system for automated feature recognition in SDO images. The data we consider are all AIA and EVE data plus surface magnetic field images from HMI. Helioseismology is addressed by another group.

We will produce robust and very efficient software modules that can keep up with the relentless SDO data stream and detect, trace, and analyze a large number of phenomena, including: flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, CME's, coronal oscillations, and jets. In addition we will track the emergence and evolution of magnetic elements down to the smallest features that are detectable, and we will also provide at least four full disk nonlinear force-free magnetic field extrapolations per day.

A completely new software element that rounds out this suite is a trainable feature detection module, which employs a generalized image classification algorithm to produce the texture features of the images analyzed. A user can introduce a number of examples of the phenomenon looked and the software will return images with similar features. We have tested a proto-type on TRACE data, and were able to "train" the algorithm to detect sunspots, active regions, and loops. Such a module can be used to find features that have not even been discovered yet, as, for example, sigmoids were in the pre-Yohkoh era.

Our codes will produce entries in the Helio Events Knowledge base, and that will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. Title: Hinode X-Ray Telescope Detection of Hot Emission from Quiescent Active Regions: A Nanoflare Signature? Authors: Schmelz, J. T.; Saar, S. H.; DeLuca, E. E.; Golub, L.; Kashyap, V. L.; Weber, M. A.; Klimchuk, J. A. Bibcode: 2009ApJ...693L.131S Altcode: 2009arXiv0901.3122S The X-Ray Telescope (XRT) on the Japanese/USA/UK Hinode (Solar-B) spacecraft has detected emission from a quiescent active region core that is consistent with nanoflare heating. The fluxes from 10 broadband X-ray filters and filter combinations were used to construct differential emission measure (DEM) curves. In addition to the expected active region peak at log T = 6.3-6.5, we find a high-temperature component with significant emission measure at log T > 7.0. This emission measure is weak compared to the main peak—the DEM is down by almost three orders of magnitude—which accounts of the fact that it has not been observed with earlier instruments. It is also consistent with spectra of quiescent active regions: no Fe XIX lines are observed in a CHIANTI synthetic spectrum generated using the XRT DEM distribution. The DEM result is successfully reproduced with a simple two-component nanoflare model. Title: The Radial Velocity Effects of Stellar Surface Phenomena Authors: Saar, Steven H. Bibcode: 2009AIPC.1094..152S Altcode: 2009csss...15..152S Radial velocity (RV) studies have been a very successful tool for finding and characterizing extrasolar planets. As RV precision increases, and planet searches press to younger, hotter, and evolved stars, however, this method will more and more bump against limitations set by the host stars themselves. Cool stellar surfaces present a range of troublesome phenomena such as spots, plage, and convective cells, which can confuse RV measurements. I review how these phenomena affect precision RV, scaling laws and timescales which characterize their properties, and some methods to mitigate, circumvent, or correct for their effects. Title: Thermal And Statistical Properties of X-ray Bright Points Authors: Saar, S.; Farid, S.; Deluca, E. Bibcode: 2009AIPC.1094..756S Altcode: 2009csss...15..756S HINODE's X-ray Telescope (XRT) offers a unique combination of high spatial (~2'') and thermal resolution, full-Sun observations of the solar corona over a wide range of temperatures (5.8~<log T~<7.6). We use multi-filter Hinode/XRT data to explore the thermal, statistical and spatial properties of X-ray bright points (XBPs). We have developed an automated XBP finder to study BPs over two periods during November 2007 and May 2008. We detect somewhat fewer XBPs than SOHO EIT in 195 Å but find comparable values to the 284 Å band. This is likely due in some part to the somewhat stricter requirements on XBP shape and enhancement above local background that we have adopted. We find that most XBPs appear to be relatively cool on average (log T~6.1), only slightly hotter than the average quiet Sun. There is a trend for larger XBPs to be hotter, with a sub-class of XBPs which are hotter still at all sizes. We further investigate the spatial distribution of XBPs, in particular exploring whether the ``overhot'' XBPs have any tendency to appear in or near coronal holes. We find that there appears to be a notable trend of overhot bright points within the two data sets and a tendency of those to lie within 40'' of coronal holes. Title: The Stars as a Sun: Secular Variations of Cycling and Non-Cycling Stars Authors: Hall, Jeffrey C.; Giampapa, Mark S.; Henry, Gregory W.; Lean, Judith L.; Saar, Steven H.; Soderblom, David R. Bibcode: 2009astro2010S.111H Altcode: No abstract at ADS Title: Mass Transport Processes and their Roles in the Formation, Structure, and Evolution of Stars and Stellar Systems Authors: Carpenter, Kenneth G.; Karvovska, Margarita; Schrijver, Carolus J.; Grady, Carol A.; Allen, Ronald J.; Brown, Alexander; Cranmer, Steven R.; Dupree, Andrea K.; Evans, Nancy R.; Guinan, Edward F.; Harper, Graham; Labeyrie, Antoine; Linsky, Jeffrey; Peters, Geraldine J.; Roberge, Aki; Saar, Steven H.; Sonneborn, George; Walter, Frederick M. Bibcode: 2009astro2010S..40C Altcode: 2009arXiv0903.2433C We summarize some of the compelling new scientific opportunities for understanding stars and stellar systems that can be enabled by sub-mas angular resolution, UV/Optical spectral imaging observations, which can reveal the details of the many dynamic processes (e.g., variable magnetic fields, accretion, convection, shocks, pulsations, winds, and jets) that affect their formation, structure, and evolution. These observations can only be provided by long-baseline interferometers or sparse aperture telescopes in space, since the aperture diameters required are in excess of 500 m - a regime in which monolithic or segmented designs are not and will not be feasible - and since they require observations at wavelengths (UV) not accessible from the ground. Two mission concepts which could provide these invaluable observations are NASA's Stellar Imager (SI; http://hires.gsfc.nasa.gov/si/) interferometer and ESA's Luciola sparse aperture hypertelescope, which each could resolve hundreds of stars and stellar systems. These observatories will also open an immense new discovery space for astrophysical research in general and, in particular, for Active Galactic Nuclei (Kraemer et al. Decadal Survey Science Whitepaper). The technology developments needed for these missions are challenging, but eminently feasible (Carpenter et al. Decadal Survey Technology Whitepaper) with a reasonable investment over the next decade to enable flight in the 2025+ timeframe. That investment would enable tremendous gains in our understanding of the individual stars and stellar systems that are the building blocks of our Universe and which serve as the hosts for life throughout the Cosmos. Title: Extrasolar Giant Planets and X-Ray Activity Authors: Kashyap, Vinay L.; Drake, Jeremy J.; Saar, Steven H. Bibcode: 2008ApJ...687.1339K Altcode: 2008arXiv0807.1308K We have carried out a survey of X-ray emission from stars with giant planets, combining both archival and targeted surveys. Over 230 stars have been currently identified as possessing planets, and roughly one-third of these have been detected in X-rays. We carry out detailed statistical analysis on a volume-limited sample of main-sequence star systems with detected planets, comparing subsamples of stars that have close-in planets with stars that have more distant planets. This analysis reveals strong evidence that stars with close-in giant planets are on average more X-ray active by a factor of ≈4 than those with planets that are more distant. This result persists for various sample selections. We find that even after accounting for observational sample bias, a significant residual difference still remains. This observational result is consistent with the hypothesis that giant planets in close proximity to the primary stars influence the stellar magnetic activity. Title: What can we hope to know about the symmetry properties of stellar magnetic fields? Authors: Moss, David; Saar, Steven H.; Sokoloff, Dmitry Bibcode: 2008MNRAS.388..416M Altcode: We summarize evidence that neither dynamo theory nor the observational data give strong support to the idea that stellar magnetic fields must have dipolar rather than quadrupolar symmetry with respect to the stellar equator. We demonstrate that even the most basic model for magnetic stellar activity, i.e. the Parker migratory dynamo, provides many possibilities for the excitation of large-scale stellar magnetic fields of non-dipolar symmetry. We demonstrate the spontaneous transition of the dynamo-excited magnetic field from one symmetry type to another. We explore observational tests to distinguish between the two types of magnetic field symmetry, and thus detect the presence of quadrupolar magnetic symmetry in stars. Complete absence of quadrupolar symmetry would present a distinct challenge for contemporary stellar dynamo theory. We revisit some observations which, depending on further clarification, may already be revealing some properties of the quadrupolar component of the magnetic fields generated by stellar dynamos. Title: First observation of planet-induced X-ray emission: The system HD 179949 Authors: Saar, S. H.; Cuntz, M.; Kashyap, V. L.; Hall, J. C. Bibcode: 2008IAUS..249...79S Altcode: 2007IAUS..249...79S; 2007arXiv0712.3270S We present the first observation of planet-induced stellar X-ray activity, identified for the HD 179949 system, using Chandra / ACIS-S. The HD 179949 system consists of a close-in giant planet orbiting an F9 V star. Previous ground-based observations already showed enhancements in Ca II K in phase with the planetary orbit. We find an 30% increase in the X-ray flux over quiescent levels coincident with the phase of the Ca II enhancements. There is also a trend for the emission to be hotter at increased fluxes, confirmed by modeling, showing the enhancement at 1 keV compared to 0.4 keV for the background star. Title: The Analysis of Hinode/XRT Observations Authors: Deluca, E. E.; Weber, M.; Savcheva, A.; Saar, S.; Testa, P.; Cirtain, J. W.; Sakao, T.; Noriyuki, N.; Kano, R.; Shimizu, T. Bibcode: 2008AGUSMSP51B..02D Altcode: This poster will present the current state of Hinode/XRT analysis software. We will give an overview of the XRT Analysis Guide. We will include a detailed discussion of the following topics:

Co-alignment with SOT and EIS Spot removal for dynamics studies Filter calibration for thermal studies Dark calibrations

Sample data sets will be discussed and links to the data products will be provided. 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: X-ray Activity and Close-in Giant Planets Authors: Kashyap, Vinay; Drake, J.; Saar, S. Bibcode: 2008HEAD...10.1704K Altcode: We have carried out a survey of X-ray emission from stars with close-in giant planets. Of the greater than 150 stars that have been identified as possessing planets, a third have been detected in observations carried out with ROSAT and XMM. We carry out detailed statistical analyses, comparing subsamples of stars that have close-in planets with stars that have more distant planets. We establish that X-ray activity is higher for stars with close-in giant planets. This result is highly robust and persists for various sample subsets. We attempt to explain this difference as possibly due to sample biases and find that a significant residual difference still remains. We interpret this observational result as being due to the effect of the physical presence of giant planets in close proximity to the stars. Whether this is a causal effect or an accidental correlation cannot be decided with the data at hand. We posit that the interactions between the planetary and stellar magnetospheres could be the physical cause of the enhancement.

This research was supported by NASA contract NAS8-39073 (CXC), and NASA grants NNG05GJ63G (XMM/GO) and NAG-10360 (Origins). Title: IC 10 X-1 and NGC 300 X-1 - our nearest ULX Authors: Prestwich, A. H.; Carpano, S.; Kilgard, R. E.; Saar, S. H.; Crowther, P. A.; Pollock, A. M. T.; Zezas, A.; Roberts, T. P.; Ward, M. J. Bibcode: 2008xng..conf...54P Altcode: No abstract at ADS Title: A 21st century view of stellar rotation Authors: Barnes, Sydney A.; Meibom, Soeren; Saar, Steven Bibcode: 2008noao.prop..476B Altcode: Cool stars spin down over time. This spindown is simultaneously impressively regular, surprisingly complex, scientifically intriguing, and its study even useful to other branches of astronomy. Some of this beautiful complexity is encapsulated in a new theory of stellar rotation, called `CgI.' We propose here to explore, develop, and test this theory using rotation period data in two carefully chosen Southern open clusters. The proposed data will constitute the definitive rotational study of the selected clusters for some time to come, because of the period- and amplitude sensitivity, the large number of periods, and the multiplexing effects of associated data. Furthermore, the data have a usefulness that transcends any theory. They will allow the empirical determination of the (apparently universal) mass dependence of stellar rotation, several timescales important to rotational spindown, the full interpretation of extant and allocated X-ray spectroscopy of the proposed cluster stars, a deep BVI Color-Magnitude Diagram of the proposed clusters, a make-or-break test of the CgI scenario, and the exploration of connections with multiplicity (in concert with separately proposed observations). 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: The Differential Emission Measure and Analysis of X-Ray Bright Points using Hinode's X-Ray Telescope (XRT) Authors: Farid, S. I.; Saar, S.; Deluca, E.; Golub, L.; Weber, M. Bibcode: 2007AGUFMSH22A0841F Altcode: The X-Ray telescope aboard Hinode utilizes up to thirteen filter combinations with one arc second resolution to provide unprecedented temperature coverage. In this study, we have used eleven X-Ray filters to examine the statistical properties of X-ray bright points including temperature, emission, and size distributions. We have analyzed what appears to be a population of XRBs that are hotter than the main group in order to identify any distinguishing properties.We discuss the results of our analysis and their implications on XBP classification. Title: Response of the Solar Atmosphere to Magnetic Flux Emergence from Hinode Observations Authors: Li, Hui; Sakurai, Takashi; Ichimito, Kiyoshi; Suematsu, Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimizu, Toshifumi; Shine, Richard A.; Tarbell, Theodore D.; Title, Alan M.; Lites, Bruce; Kubo, Masahito; Nagata, Shin'ichi; Kotoku, Jun; Shibasaki, Kiyoto; Saar, Steven H.; Bobra, Monica Bibcode: 2007PASJ...59S.643L Altcode: No abstract at ADS Title: The Orbital Period of the Wolf-Rayet Binary IC 10 X-1: Dynamic Evidence that the Compact Object Is a Black Hole Authors: Prestwich, A. H.; Kilgard, R.; Crowther, P. A.; Carpano, S.; Pollock, A. M. T.; Zezas, A.; Saar, S. H.; Roberts, T. P.; Ward, M. J. Bibcode: 2007ApJ...669L..21P Altcode: 2007arXiv0709.2892P IC 10 X-1 is a bright (LX = 1038 ergs s-1) variable X-ray source in the Local Group starburst galaxy IC 10. The most plausible optical counterpart is a luminous Wolf-Rayet star, making IC 10 X-1 a rare example of a Wolf-Rayet X-ray binary. In this Letter, we report on the detection of an X-ray orbital period for IC 10 X-1 of 34.4 hr. This result, combined with a reexamination of optical spectra, allows us to determine a mass function for the system of f(M)=7.8 Msolar and a probable mass for the compact object of 24-33 Msolar. If this analysis is correct, the compact object is the most massive stellar-mass black hole known. We further show that the observed period is inconsistent with Roche lobe overflow, suggesting that the binary is detached and that the black hole is accreting the wind of the Wolf-Rayet star. The observed mass-loss rate of [MAC92] 17A is sufficient to power the X-ray luminosity of IC 10 X-1. Title: A detailed investigation of coronal/magnetic and rotational changes in cool stars using NGC 3532 Authors: Saar, Steven Bibcode: 2007cxo..prop.2350S Altcode: 2007cxo..prop.2306S We propose to use Chandra ACIS-I to study the one-to-one correspondence recently proposed between coronal/dynamo and rotational changes in cool stars. The goal is insight into the physical basis underlying the 3-part X-ray classification of cool stars (saturated, super-saturated, and normal rotation-activity), crucial to fully interpreting the rotational/magnetic/activity evolution of cool stars. We already have copious optical data on our rich target open cluster NGC 3532, including 83 rotation periods for the cluster members, making it uniquely useful for rotation-activity studies. Furthermore, its age, 300Myr, nicely bridges a gap in the age sequence of the best studied clusters between 100Myr (Pleiades) and 600Myr (Hyades), permitting detailed study of evolution between these epochs. Title: Exploring the Early FUV History of Cool Stars: Transition Regions at 30 Myr Authors: Saar, Steven Bibcode: 2007hst..prop11116S Altcode: Stellar magnetic activity derives from the so-called "dynamo," a hydromagnetic interplay between overturning plasma motions and differential rotation in stars cool enough to support significant surface convection zones. The magnetic fields resulting from dynamo action are in turn are responsible for a wide range of high-energy emissions, including the spectacular outbursts called flares. Dynamo powered magnetic activity is not confined solely to stars, but also must occur, for example, in accretion disks of all descriptions, and in some planets. A great deal is known about magnetic activity in middle-aged G dwarfs like our Sun, thanks to its proximity. Less is known, however, about the much younger stars, newly emerged from the T-Tauri stage. Yet, it is during this phase that they reach the peak of their magnetic activity, and subsidiary influences, such as the impact of ionizing radiation and strong coronal winds on developing solar systems, also are maximum. One of the key missing ingredients in our current understanding are measurements of FUV emissions of such stars, to complement the extensive collections of coronal {1-10 MK} X-ray measurements, particularly from recent ROSAT, Chandra and XMM-Newton surveys. We propose to conduct sensitive ACS/SBC prism ultraviolet spectroscopy of selected fields in two young {30 Myr} Galactic clusters-IC 2391 and IC 2602-to inventory the key C IV emission index { 0.1 MK} over a much larger and more diverse sample of coeval objects than has been possible hitherto. A key question is whether the FUV emissions also suffer the "saturation" and "super-saturation" at short rotation periods seen in coronal X-rays, or whether they continue to rise in the fastest rotating stars. The saturation behavior of the different temperature regimes holds important clues to the organization of the surface active regions on these very young stars, and should allow us to distinguish among several competing models. Title: A Flare-induced mass transfer/accretion event in AM Her? Authors: Saar, Steven H.; Kashyap, Vinay L.; Ringwald, F. A. Bibcode: 2007uasb.conf..249S Altcode: We report on HST observations of a mass transfer/accretion event in AM Her which appears to have been induced by a strong flare on the secondary. UV spectroscopic observations of the magnetic CV, AM Her, were made with STIS towards the end of a deep photometric minimum in late 2003. Our goal was to search for evidence of magnetic activity on the secondary (as seen in the Dopplershifted hot emission lines of C IV and Si IV), one of the fastest rotating cool stars ever studied in the UV. There was evidence for quiescent C IV emission at the velocity of the M star secondary, placing useful limits on its steady transition region emission. One strong flare was seen in C IV (and near flare peak, in Si IV and He II as well), with a velocity consistent with the M dwarf. This was accompanied by a near-simultaneous increase in continuum emission from the white dwarf; the excess had a temperature of about 100,000 K. We suggest that this strong flare may have caused an accretion event on the white dwarf, either by ejecting mass in the form of a CME, or disrupting a large prominence system. Title: The Outer Solar Atmosphere during the Maunder Minimum: A Stellar Perspective Authors: Judge, Philip G.; Saar, Steven H. Bibcode: 2007ApJ...663..643J Altcode: By comparing solar data with data of ``flat activity'' stars at UV and soft X-ray wavelengths, we estimate solar chromospheric, transition region, and coronal emission as it might have existed during the Maunder minimum (1645-1715), the most recent of several episodes of persistently weak sunspot activity. Several flat activity stars from the Mount Wilson S-index survey have been observed with the Hubble Space Telescope and ROSAT. Drawing on published data, we reassess the criteria by which a star may be considered as a Maunder minimum candidate. Of our targets, HD 10700 and HD 143761 are the most likely such candidates. Solar UV spectra from the SOHO and UARS spacecraft, and soft X-ray data from the SNOE spacecraft are compared with the stellar UV and X-ray data. The comparison suggests that the radiative output of the Maunder minimum chromosphere, transition region, and corona were similar to (or at least not much less than) those observed under conditions close to current solar minima. In turn, this suggests that the emitting structures (which on the Sun at sunspot minimum are small scale, <<Rsolar), including the magnetic network, were also similar. These results have implications for the nature of the surface magnetic fields and irradiance during the Maunder and other magnetic minima, and for the solar dynamo. Title: The Sun-as-a-star As Seen By Hinode XRT Authors: Saar, Steven H.; DeLuca, E. E. Bibcode: 2007AAS...210.9424S Altcode: 2007BAAS...39R.221S We study full disk images of the Sun taken in multiple filters with the Hinode XRT during the current low state of the solar cycle (late 2006). Taking advantage of the wide temperature sensitivity of the XRT, we construct spatially averaged emission measure (EM) curves for each of several solar region types, including coronal holes, quiet Sun, bright points, and active regions of various description.

These are used to determine the relative contribution of the various features to the total solar EM, as a starting point for a program to investigate their time variation. We also explore use of the average EM curves for understanding spatially unresolved stellar spectra and their correlation with underlying magnetic fields.

The US XRT team is supported by a contract from NASA to SAO. Hinode is an international project supported by JAXA, NASA, PPARC and ESA.

We are grateful to the Hinode team for all their efforts in the design, development and operation of the mission. Title: Exoplanet-Induced Chromospheric Activity: Realistic Light Curves from Solar-type Magnetic Fields Authors: Cranmer, Steven R.; Saar, Steven H. Bibcode: 2007astro.ph..2530C Altcode: There is growing observational evidence for some kind of interaction between stars and close-in extrasolar giant planets. Shkolnik et al. reported variability in the chromospheric Ca H and K lines of HD 179949 and upsilon And that seemed to be phased with the planet's orbital period, instead of the stellar rotational period. However, the observations also indicate that the chromospheric light curves do not repeat exactly, which may be expected for a planet plowing through a variable stellar magnetic field. Using the complex solar magnetic field (modeled with the Potential Field Source Surface technique) as a guide, we simulate the shapes of light curves that would arise from planet-star interactions that are channeled along magnetic field lines. We also study the orbit-to-orbit variability of these light curves and how they vary from solar minimum (i.e., a more or less axisymmetric stretched dipole) to solar maximum (a superposition of many higher multipole moments) fields. Considering more complex magnetic fields introduces new difficulties in the interpretation of observations, but it may also lead to valuable new diagnostics of exoplanet magnetospheres. Title: Detection of Orbital Period in the Wolf-Rayet X-ray Binary IC 10 X-1 Authors: Prestwich, A. H.; Kilgard, R. E.; Carpano, S.; Saar, S.; Page, K.; Pollock, Andy; Roberts, T.; Ward, M.; Zezas, A. Bibcode: 2006ATel..955....1P Altcode: We detect periodic flux modulations in the Wolf-Rayet X-ray binary IC 10 X-1 using the SWIFT X-ray Telescope and the Chandra X-ray Observatory, with period of 34.82h ± 0.94h. Title: Confirmation of the planet hypothesis for the long-period radial velocity variations of β Geminorum Authors: Hatzes, A. P.; Cochran, W. D.; Endl, M.; Guenther, E. W.; Saar, S. H.; Walker, G. A. H.; Yang, S.; Hartmann, M.; Esposito, M.; Paulson, D. B.; Döllinger, M. P. Bibcode: 2006A&A...457..335H Altcode: 2006astro.ph..6517H Aims.Our aim is to confirm the nature of the long period radial velocity measurements for β Gem first found by Hatzes & Cochran (1993).
Methods: .We present precise stellar radial velocity measurements for the K giant star β Gem spanning over 25 years. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210 000), and Hipparcos photometry was also made to discern the true nature of the long period radial velocity variations.
Results: . The radial velocity data show that the long period, low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. Furthermore, the Ca II K emission, spectral line bisectors, and Hipparcos photometry show no significant variations of these quantities with the radial velocity period. An orbital solution assuming a stellar mass of 1.7 M_⊙ yields a period, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and a semi-major axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02).
Conclusions: .The data presented here confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). β Gem is one of six intermediate mass stars known to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common. Title: A Flare-induced Mass Transfer/Accretion Event in AM Her? Authors: Saar, S. H.; Kashyap, V. L.; Ringwald, F. A. Bibcode: 2006IAUJD...4E..30S Altcode: We report observations of a mass transfer/accretion event in AM Her which appears to have been induced by a strong flare on the secondary. UV observations of the magnetic CV, AM Her, were made with STIS on HST towards the end of a deep photometric minimum in late 2003. Our goal was to search for evidence of magnetic activity on the secondary (as seen in the Doppler-shifted hot emission lines of C IV and Si IV), one of the fastest rotating cool stars ever studied in the UV. There was little evidence for quiescent C IV emission at the velocity of the M star secondary, placing useful limits on its steady transition region emission. One strong flare was seen in C IV (and initially, in Si IV and He II as well), with a velocity consistent with the M dwarf. This was accompanied by a near-simultaneous increase in continuum emission from the white dwarf; the excess had a temperature of about 100,000 K. We argue that this strong flare may have ejected mass in the form of CME, or disturbed a large prominence system, exciting an accretion event on the white dwarf. We discuss implications of the results for low-state CV activity, mass transfer, and cool star activity at extreme rotation rates. Title: The Many Cycles of Cool Stars Authors: Saar, S. H. Bibcode: 2006IAUJD...8E..66S Altcode: Magnetic activity exhibits a rich range time behaviour in cool stars, from cyclic, to multi-cyclic, anharmonically variable, various combinations of these, and finally to the virtually non-variable. I assemble data on cycle periods, amplitudes, and anharmonic degrees, and compare these various key stellar properties, such as rotation, differential rotation, binarity, mass, and convective timescales, in a search for correlations to guide and compare with dynamo theory. The data come from a broad range of observational sources from the typical (Ca II HK emission, photometry) to more the exotic (orbital period variations). The nature of the variation can sometime depend on the diagnostic used. The trends seen (and sometimes lack thereof) pose important tests of dynamo models. I also explore stars with very low activity variability. These seem to be composed of (at least) two kinds: a group of stars which may be unable to cycle, and a group whose dynamos may be temporarily quiescent. Both offer further important clues for how dynamos operate, and the properties which govern them. Title: Maunder Minimum Dwarfs: Defined Out Of Existence? Authors: Saar, Steven H. Bibcode: 2006SPD....37.1201S Altcode: 2006BAAS...38..240S It has recently been suggested that there are very few dwarf stars in the equivalent of a solar Maunder-like magnetic minimum (MM), implying that the Sun is an unusual star for having such states. I investigate this issue by comparing Ca II HK fluxes and stellar properties(Teff, gravity, metallicity M/H) from two large analyses of exoplanet search spectra. The joint sample includes 731 stars, of which 570 are dwarfs (as defined by gravity).The apparent lack of MM dwarfs arises from two problems: the definition of what properties an MM star should have, and issues in the calibration of Ca II HK fluxes. There are indeed very few dwarf stars with normalized Ca II HK fluxes log R'HK < -5.1, the traditional MM level. However, this level was defined using a stellar sample which included subgiants. The new data show that the minimum R'HK in subgiants almost always less than that in dwarfs for all Teff and M/H. Thus, in a sense, MM dwarfs have been defined out of existence by requiring an R'HK level more appropriate for evolved stars. Furthermore, the minimum R'HK observed in dwarfs is a decreasing function of M/H, so that metal-poor minimum activity dwarfs have unusually high R'HK values (e.g., log R'HK -4.85 at log M/H -1.0, compared with log R'HK -4.95 at solar minimum). If MM dwarfs can be metal poor, these stars may also be candidates. The true scarcity of MM dwarfs, and by extension, the uniqueness of the solar case, therefore remains an open question.This work is supported by NASA Origins grant NNG04GL54G. Title: Spot patterns and differential rotation in the eclipsing pre-cataclysmic variable binary, V471 Tau Authors: Hussain, G. A. J.; Allende Prieto, C.; Saar, S. H.; Still, M. Bibcode: 2006MNRAS.367.1699H Altcode: 2006astro.ph..2562H; 2006MNRAS.tmp..295H We present surface spot maps of the K2V primary star in the pre-cataclysmic variable binary system, V471 Tau. The spot maps show the presence of large high-latitude spots located at the sub-white dwarf longitude region. By tracking the relative movement of spot groups over the course of four nights (eight rotation cycles), we measure the surface differential rotation rate of the system. Our results reveal that the star is rotating rigidly with a surface shear rate, dΩ= 1.6 +/- 6mradd-1. The single active star AB Dor has a similar spectral type, rotation period and activity level as the K star in V471 Tau, but displays much stronger surface shear (46 < dΩ < 58mradd-1). Our results suggest that tidal locking may inhibit differential rotation; this reduced shear, however, does not affect the overall magnetic activity levels in active K dwarfs. Title: The Amplitude of Stellar X-ray Cycles Authors: Martens, P. C. H.; Chattterjee, P.; Saar, S. H.; Acton, L. W. A. Bibcode: 2005AAS...20710405M Altcode: 2005BAAS...37R1334M A decade worth of data from the Soft X-ray Telescope onboard the Japan/US/UK mission Yohkoh shows that the Sun has a variation of non-flaring disk-integrated soft X-ray emission (0.4 - 2.4 keV) of about a factor 30 over its sunspot cycle. To date no cyclic variation of that magnitude has been observed in other late-type stars.

We show that this negative result is partly explained by the inclusion of EUV emission in stellar observations done with ROSAT: we calculated what the solar signal would be if observed in the ROSAT passband and found a cycle amplitude of a factor two to three. That leaves open the question of the cycle amplitude in soft X-rays for solar-type stars.

To adress this we analysed ROSAT data for the energy band above the C-K edge, but found no sufficiently frequent observations of individual stars. The next best approach is to compare the measured soft X-ray flux for singly observed stars with the average flux predicted from the star's Rossby number: if cycles with amplitudes as large as that of the Sun exist, the residual fluxes should be statistically significant. From a sample of about 15 single and cyclic late-type stars (as evidenced from Ca-K data) we find that with 99.6% certainty the residual fluxes are due to X-ray cycles that are similar to or greater than that of the Sun. Title: Exploring the use of VO to diagnose spot properties on M dwarfs Authors: O'Neal, D.; Saar, S. H.; Neff, J. E.; Cuntz, M. Bibcode: 2005ESASP.560..853O Altcode: 2005csss...13..853O No abstract at ADS Title: Testing the Reality of Strong Magnetic Fields on T Tauri Stars: The Naked T Tauri Star Hubble 4 Authors: Johns-Krull, Christopher M.; Valenti, Jeff A.; Saar, Steven H. Bibcode: 2004ApJ...617.1204J Altcode: 2004astro.ph..9268J High-resolution optical and infrared (IR) echelle spectra of the naked (diskless) T Tauri star Hubble 4 are presented. The K-band IR spectra include four Zeeman-sensitive Ti I lines along with several magnetically insensitive CO lines. Detailed spectrum synthesis combined with modern atmospheric models is used to fit the optical spectra of Hubble 4 in order to determine its key stellar parameters: Teff=4158+/-56 K; logg=3.61+/-0.50 [M/H]=-0.08+/-0.05 vsini=14.6+/-1.7 km s-1. These stellar parameters are used to synthesize K-band spectra to compare with the observations. The magnetically sensitive Ti I lines are all significantly broadened relative to the lines produced in the nonmagnetic model, while the magnetically insensitive CO lines are well matched by the basic nonmagnetic model. Models with magnetic fields are synthesized and fitted to the Ti I lines. The best-fit models indicate a distribution of magnetic field strengths on the stellar surface characterized by a mean magnetic field strength of 2.51+/-0.18 kG. The mean field is a factor of 2.0 greater than the maximum field strength predicted by pressure equipartition arguments. To confirm the reality of such strong fields, we attempt to refit the observed profiles using a two-component magnetic model in which the field strength is confined to the equipartition value representing plagelike regions in one component and the field is allowed to vary in a cooler component representing spots. It is shown that such a model is inconsistent with the optical spectrum of the TiO bandhead at 7055 Å. Title: Further Results of TiO-Band Observations of Starspots Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.; Cuntz, Manfred Bibcode: 2004AJ....128.1802O Altcode: We present measurements of starspot parameters (temperature and filling factor) on five highly active stars, using absorption bands of TiO, from observations made between 1998 March and 2001 December. We determined starspot parameters by fitting TiO bands using spectra of inactive G and K stars as proxies for the unspotted photospheres of the active stars and spectra of M stars as proxies for the spots. For three evolved RS CVn systems, we find spot filling factors between 0.28 and 0.42 for DM UMa, 0.22 and 0.40 for IN Vir, and 0.31 and 0.35 for XX Tri; these values are similar to those found by other investigators using photometry and Doppler imaging. Among active dwarfs, we measured a lower spot temperature (3350 K) for EQ Vir than found in a previous study of TiO bands, and for EK Dra a lower spot temperature (~3800 K) than found through photometry. For all active stars but XX Tri, we achieved good phase coverage through a stellar rotational period. We also present our final, extensive grid of spot and nonspot proxy stars.

This paper includes data taken at McDonald Observatory of the University of Texas at Austin. Title: Planet-Induced Activity Enhancements in the HD 179949 System Authors: Saar, Steven Bibcode: 2004cxo..prop.1653S Altcode: Many exoplanets are gas giants extremely close (<0.1 AU) to their parent stars, suggesting the possibility of exotic interactions. Recently, weakly enhanced Ca II HK emission was found in the HD 179949 system, phased to the orbital (~3 d) and not to the stellar rotation period (~8 d). Theory suggests this enhancement is due to a magnetic interaction (MI) between the star and planet. Since the resulting heating should be largest in X-rays, we propose to study the system with Chandra to further characterize the MI. We will use HST to study the MI effect on the planet's ablating atmosphere by observing Doppler shifted H~I around quadrature. These datasets will enable us to test interaction theories, and estimate exoplanetary magnetic fields, mass loss and stellar wind properties. 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: Applying Zeeman Doppler imaging to solar spectra Authors: Hussain, G. A. J.; Saar, S. H.; Collier Cameron, A. Bibcode: 2004AN....325..245H Altcode: A new generation of spectro-polarimeters with high throughput (e.g. CFHT/ESPADONS and LBT/PEPSI) is becoming available. This opportunity can be exploited using Zeeman Doppler imaging (ZDI), a technique that inverts time-series of Stokes V spectra to map stellar surface magnetic fields (Semel 1989). ZDI is assisted by ``Least squares deconvolution'' (LSD), which sums up the signal from 1000's of photospheric lines to produce a mean deconvolved profile with higher S:N (Donati & Collier Cameron 1997). Title: Searching for Planets in the Hyades. III. The Quest for Short-Period Planets Authors: Paulson, Diane B.; Saar, Steven H.; Cochran, William D.; Henry, Gregory W. Bibcode: 2004AJ....127.1644P Altcode: 2003astro.ph.12122P We have been using the Keck I High Resolution Spectrograph to search for planetary companions in the Hyades cluster. We selected four stars from this sample that showed significant radial velocity variability on short timescales to search for short-period planetary companions. The radial velocities of these four stars were monitored regularly with the Hobby-Eberly Telescope for approximately 2 months, while sparse data were also taken over ~4 months: we also obtained near-simultaneous photometric observations with one of the automatic photoelectric telescopes at Fairborn Observatory. For three of the stars, we detect photometric variability with the same period present in the radial velocity (vr) measurements, compatible with the expected rotation rates for Hyades members. The fourth star continues to show vr variations and minimal photometric variability but with no significant periodicity. This study shows that for the three stars with periodic behavior, a significant portion of the vr fluctuations are likely due primarily to magnetic activity modulated by stellar rotation rather than planetary companions. Using simple models for the vr perturbations arising from spot and plage, we demonstrate that both are likely to contribute to the observed vr variations. Thus, simultaneous monitoring of photometric (photospheric) and spectroscopic (chromospheric) variations is essential for identifying the cause of Doppler-shifted absorption lines in more active stars.

Some data were obtained with the Hobby-Eberly Telescope (HET). The HET is operated by McDonald Observatory on behalf of The University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

Additional data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA). The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Title: Molecular Band Proxies, Model Atmospheres, and Line Depth Ratios: Comparing Three Methods of Measuring Starspot Parameters on Highly Active Stars Authors: O'Neal, D.; Saar, S.; Aufdenberg, J.; Neff, J. E. Bibcode: 2004IAUS..219..957O Altcode: 2003IAUS..219E.135O In recent years various techniques have been developed to measure the temperatures and areas of dark cool starspots on magnetically active stars. We present comparisons among results obtained by applying three such techniques to the same data sets. The three methods are (1) fitting TiO-band spectra using spectra of proxy stars (2) fitting TiO-band spectra using model atmospheres and (3) fitting spectral line depth ratios. We investigate differences among results obtained by using each of these methods to compute starspot parameters of several active spotted stars. Title: Coronal X-Ray Spectroscopy of Solar Analogs Authors: Telleschi, A.; Güdel, M.; Arzner, K.; Briggs, K.; Audard, M.; Ness, J. -U.; Mewe, R.; Raassen, A. J.; Skinner, S. L.; Cuntz, M.; Saar, S. Bibcode: 2004IAUS..219..930T Altcode: 2003IAUS..219E.203T We present an X-ray study of a series of solar-mass main-sequence stars with different ages based on data from XMM-Newton and Chandra. This investigation aims at a closer understanding of the physical mechanisms of heating and mass transport in magnetically active stars. All targets are proxies of the Sun that essentially differ only in their rotation periods and hence in the efficiency of the magnetic dynamo. We present a spectral analysis that constrains the average elemental composition and the thermal structure of the coronae at different stages of their evolution. Further we use the He-like line triplets to derive characteristic coronal densities and investigate the time variability in the X-ray light curves. We discuss implications for models related to heating physics and coronal structure. Title: Stellar Activity Enhancement by Planets: Theory and Observations Authors: Saar, S. H.; Cuntz, M.; Shkolnik, E. Bibcode: 2004IAUS..219..355S Altcode: 2003IAUS..219E.119S Many of the newly discovered exoplanets are apparently gas giants in close proximity to their parent stars. They therefore raise tides on their host stars and (if similar to Jupiter) will likely have substantial magnetospheres which can interact with stellar fields. Both tidal and magnetospheric interactions can enhance stellar activity levels. An initial search for such planet-induced activity using the Ca II IR triplet found no signal but recently a more sensitive study using the Ca II H and K lines has uncovered evidence for planet-enhanced emission on HD 179949 and hints of it in other systems. The phase dependence of the enhanced emission for HD 179949 suggests a magnetospheric interaction. We discuss a simple model for this interaction the implications of this possible detection for diagnosing exoplanetary magnetospheres and future observations. Title: STIS Far UV Studies of Spatial and Temporal Activity Variations in YY Gem Authors: Saar, S. H.; Bookbinder, J. A. Bibcode: 2003csss...12.1020S Altcode: We analyze STIS data of the eclipsing dM0e+dM0e system YY Gem, finding a spatially variable quiescent level, frequent and sometimes periodic flaring, and evidence for a spatially extended transition region. Title: Terrestrial planets around M dwarfs via precise radial velocities. VLT+UVES observations of Barnard's star = GJ 699 Authors: Kürster, Martin; Endl, Michael; Rouesnel, Frederic; Els, Sebastian; Kaufer, Andreas; Brillant, Stephane; Hatzes, Artie P.; Saar, Steven H.; Cochran, William D. Bibcode: 2003ESASP.539..485K Altcode: 2003toed.conf..485K We report on results from a program carried out at the VLT+UVES in search for terrestrial planets around M dwarf stars with precise radial velocities (RVs). Because of the small mass of M dwarfs planets with a few Earth masses and orbital periods of a few days to weeks can cause RV signals that are detectable with the currently achieved precision of RV surveys of a few m s-1. As an example we present our results for Barnard's star (M = 0.16 Msolar) where we detect the RV secular acceleration as well as variability related to stellar activity. We determine upper limits to the projected mass m sin i of hypothetical planetary companions finding that we can exclude planets with m sin i > 7.5 MEarth in circular orbits throughout the habitable zone of the star, i.e. at separations of 0.034 - 0.082 AU. Over the total range of separations accessible to our data set, i.e. 0.017 - 0.98 AU we exclude planets m sin i > 0.12 MJupiter. The lowest upper limit is found at an orbital period of 2.5 d (separation 0.020 AU) with m sin i = 2.9 MEarth. We also find an anti-correlation of the RV data with an index that measure the filling-in by emission of the core of the Hα line in the sense that the measured RVs become bluer when the Hα emission component becomes stronger. Title: Stellar Intrinsic Radial Velocity Noise: Causes and Possible Cures Authors: Saar, S. H.; Hatzes, A.; Cochran, W.; Paulson, D. Bibcode: 2003csss...12..694S Altcode: We explore the causes and test some possible cures for stellar intrinsic radial velocity noise caused by magnetic activity. Title: Whirling Dervish Dynamos: Magnetic Activity in CV Secondaries Authors: Saar, Steven Bibcode: 2003hst..prop.9852S Altcode: The mass-losing secondary stars of cataclysmic variables {CVs} are the most rapidly rotating cool dwarfs observable. Other rapid rotators show a maximal, "saturated" level of magnetic activity {e.g., X-ray emission}, but there are hints from contact binaries and young clusters that activity may be suppressed at the highest rotation rates. CV secondaries are thus important probes of magnetic dynamos at rotational extremes. Implications for CV evolution {e.g., the ``period gap", accretion variability} may also be profound. Unfortunately, study of CV secondaries is hampered by pesky accretion-related phenomena and reflection effects. As a result, little systematic work has been done. To explore activity in these stars, we therefore propose to study far-UV spectra of AM Her-type systems {which have no accretion disks} in deep photometric minima in which accretion is shut off. Magnetic-related emission from the secondary will be separated {in velocity} from residual accretion emission by observations near quadratures. Lower chromospheric irradiation due to the white dwarf primary will be removed by modeling, yielding the true level of magnetic activity on the secondary. We will compare the results to other dMe stars and draw implications for magnetic dynamos and activity at rotational extremes, and for CV evolution and behavior. Title: The low-level radial velocity variability in Barnard's star (= GJ 699). Secular acceleration, indications for convective redshift, and planet mass limits Authors: Kürster, M.; Endl, M.; Rouesnel, F.; Els, S.; Kaufer, A.; Brillant, S.; Hatzes, A. P.; Saar, S. H.; Cochran, W. D. Bibcode: 2003A&A...403.1077K Altcode: 2003astro.ph..3528K We report results from 2 1/2 yr of high precision radial velocity (RV) monitoring of Barnard's star. The high RV measurement precision of the VLT-UT2+UVES of 2.65 m s-1 made the following findings possible. (1) The first detection of the change in the RV of a star caused by its space motion (RV secular acceleration). (2) An anti-correlation of the measured RV with the strength of the filling-in of the H_alpha line by emission. (3) Very stringent mass upper limits to planetary companions. Using only data from the first 2 years, we obtain a best-fit value for the RV secular acceleration of 5.15+/- 0.89 m s-1 yr-1. This agrees within 0.95sigma with the predicted value of 4.50 m s-1 yr-1 based on the Hipparcos proper motion and parallax combined with the known absolute radial velocity of the star. When the RV data of the last half-year are added the best-fit slope is strongly reduced to 2.97+/- 0.51 m s-1 yr-1 (3.0sigma away from the predicted value), clearly suggesting the presence of additional RV variability in the star. Part of it can be attributed to stellar activity as we demonstrate by correlating the residual RVs with an index that describes the filling-in of the H_alpha line by emission. A correlation coefficient of -0.50 indicates that the appearance of active regions causes a blueshift of photospheric absorption lines. Assuming that active regions basically inhibit convection we discuss the possibility that the fundamental (inactive) convection pattern in this M4V star produces a convective redshift which would indicate that the majority of the absorption lines relevant for our RV measurements is formed in a region of convective overshoot. This interpretation could possibly extend a trend indicated in the behaviour of earlier spectral types that exhibit convective blueshift, but with decreasing line asymmetries and blueshifts as one goes from G to K dwarfs. Based on this assumption, we estimate that the variation of the visible plage coverage is about 20%. We also determine upper limits to the projected mass msin i and to the true mass m of hypothetical planetary companions in circular orbits. For the separation range 0.017-0.98 AU we exclude any planet with msin i> 0.12 MJupiter and m> 0.86 MJupiter. Throughout the habitable zone around Barnard's star, i.e. 0.034-0.082 AU, we exclude planets with msin i> 7.5 MEarth and m> 3.1 MNeptune.

Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO programmes 65.L-0428, 66.C-0446, 267.C-5700, 68.C-0415, and 69.C-0722). Title: V471 Tau: mapping magnetic activity in a pre-CV binary system. Authors: Hussain, G. A. J.; Allende Prieto, C.; Saar, S. H.; Collier Cameron, A.; Still, M. D. Bibcode: 2003AAS...202.0804H Altcode: 2003BAAS...35..708H; 2003AAS...202..804H The technique of Doppler imaging enables us to map starspots at the surfaces of rapidly rotating cool stars. Starspots are probes of magnetic activity, thus the locations of these spots also indicate where the strongest magnetic fields tend to emerge. We present surface spot maps of the K2V component of V471 Tau from 2001-2002. Our spot maps can be used (a) to show that magnetic activity is confined to high latitude regions in the K2V component, (b) to measure surface differential rotation of this component and (c) to evaluate spot lifetimes in rapid rotators. We conclude that the K2V component of V471 Tau shows a similar equator-pole lap-time as the Sun and that its surface spots last on the order of months. Title: XMM-Newton Proposal 02057202 Authors: Saar, Steven Bibcode: 2003xmm..prop..299S Altcode: We propose to study the weak coronae of "flat activity" stars - objects with very low, nearly constant chromospheric emission. There is evidence that in many cases, these coronae are powered by magnetic fields from the residual turbulent dynamo left while the star's cyclic dynamo is in a temporary Maunder-like magnetic minimum. These stars permit us to 1) study the weakest and likely least complex coronae, 2) investigate the coronal product of a turbulent dynamo in a solar mass star, and 3) explore (by proxy) the properties of the solar corona in a Maunder-like minimum. Title: Applying Zeeman Doppler Imaging to Solar Spectra Authors: Hussain, Gaitee A.; Saar, Steven H.; Collier Cameron, Andrew Bibcode: 2003IAUJD...9E..26H Altcode: Advances in instrumentation have led to the development of a new generation of spectro-polarimeters that have a high throughput (e.g. CFHT/ESPADONS). These spectro-polarimeters will enable us to analyse magnetic field configurations on a wide variety of stellar systems. The technique of Zeeman Doppler imaging is an invaluable tool which inverts a time-series of circularly polarized spectra to map surface magnetic fields on rapidly rotating stars. Zeeman Doppler imaging is greatly assisted by least squares deconvolution a technique that ""sums up"" the signal from thousands of lines in order to boost the S:N in a mean deconvolved profile. We test these techniques by applying them to circularly polarized spectra of magnetic features on the solar surface. The assumptions inherent in standard Zeeman Doppler imaging: the weak field regime classical Zeeman splitting and that line profiles are additive are addressed here. Title: Uses of Linear Polarization as a Probe of Extrasolar Planet Atmospheres Authors: Saar, S. H.; Seager, S. Bibcode: 2003ASPC..294..529S Altcode: 2003astro.ph..5436S We point out some advantages of making observations of extrasolar planets in linearly polarized (LP) light. Older cool stars have quite low levels (∼ 10-4 to 10-5) of fractional LP, while extrasolar planets can have relatively high fractional LP (∼ 0.1). Observations in LP light can therefore significantly enhance contrast between the planet and its parent star. Data on LP as a function of planetary orbital phase can be used to diagnose the properties (e.g., composition, size, and shape) of the scatterers in the planetary atmosphere. We discuss the feasibility of LP observations of extrasolar planets. Title: The Effects of Plage on Precision Radial Velocities Authors: Saar, S. H. Bibcode: 2003ASPC..294...65S Altcode: I present the first results of semi-empirical modeling of the effects of magnetic plage on measured radial velocities in G stars. I use solar line bisectors observed in quiet and active regions at a range of disk positions as proxies for stellar bisectors. These are then used to "warp" model line profiles and construct model stars with various V sin i and plage areas. The models predict the sun should show a maximum of 10 m/sec short-term RV fluctuations atop approx. 3 m/sec long-term (cyclic) modulation, while a Hyades age G dwarf with V sin i = 6 km/sec exhibits approx. 90 m/sec (short-term) atop approx. 14 m/sec (long-term). Title: Stellar Dynamos: Scaling Laws and Coronal Connections Authors: Saar, S. Bibcode: 2002ASPC..277..311S Altcode: 2002sccx.conf..311S No abstract at ADS Title: A Lot of Observations of the Coronae of AR Lac Authors: Pease, D.; Drake, J. J.; Kashyap, V.; Ratzlaff, P. W.; Saar, S.; Haisch, B.; Dobrzycki, A.; Adams, N. R.; Wolk, S. J. Bibcode: 2002ASPC..277..551P Altcode: 2002sccx.conf..551P No abstract at ADS Title: Exploring the Role of Acoustic Heating in Cool Dwarfs and Subgiants Authors: Saar, Steven Bibcode: 2002hst..prop.9464S Altcode: 2002hst..prop.5811S Recent observations cast doubt on the importance of acoustic waves for chromospheric heating in stars. These include low upper limits to their contribution to upper layers of the solar chromosphere, and evidence for significant magnetic heating contribution even in ``basal" activity stars. These findings contradict the widely accepted picture that acoustic heating accounts for a significant fraction, the ``basal component'', of chromospheric heating in inactive stars. To help resolve this issue, we propose to observe two very inactive stars with significantly different properties to search for specific signatures of upward propagating acoustic waves: blue-shifts and enhanced blue wings in chromospheric lines. Solar data show that the degree of blue-shift can be used to estimate the acoustic contribution to chromospheric heating. We will compare the data to HST spectra of similar stars, and solar spectra from the SUMER instrument on SOHO. Lack of a significant acoustic signature in our targets would indicate that magnetic heating generated by a local {turbulent, non-cycling} dynamo is responsible for the basal component of chromospheric heating in inactive stars. Our targets may be in a phase analogous to the solar Maunder minimum, and the HST spectra might serve as a proxy for the solar spectrum in this state. The spectra will also be used for emission measure analysis differentially between the Sun and solar-like stars. Title: A new look at dynamo cycle amplitudes Authors: Saar, S. H.; Brandenburg, A. Bibcode: 2002AN....323..357S Altcode: 2002astro.ph..7392S We explore the dependence of the amplitude of stellar dynamo cycle variability (as seen in the Mount Wilson Ca II HK timeseries data) on other stellar parameters. We find that the fractional cycle amplitude A_cyc (i.e. the ratio of the peak-to-peak variation to the average) decreases somewhat with mean activity, increases with decreasing effective temperature, but is not correlated with inverse Rossby number Ro-1. We find that A_cyc increases with the ratio of cycle and rotational frequencies omega_cyc /Omega along two, nearly parallel branches. Title: Searching for Planets in the Hyades. II. Some Implications of Stellar Magnetic Activity Authors: Paulson, Diane B.; Saar, Steven H.; Cochran, William D.; Hatzes, Artie P. Bibcode: 2002AJ....124..572P Altcode: 2002astro.ph..4216P The Hyades constitute a homogeneous sample of stars ideal for investigating the dependence of planet formation on the mass of the central star. Because of their youth, Hyades members are much more chromospherically active than stars traditionally surveyed for planets using high-precision radial velocity techniques. Therefore, we have conducted a detailed investigation of whether magnetic activity of our Hyades target stars will interfere with our ability to make precise radial velocity (vrad) searches for substellar companions. We measure chromospheric activity (which we take as a proxy for magnetic activity) by computing the equivalent of the R'HK activity index (which is corrected for photospheric contributions) from the Ca II K line. The value of <R'HK> is not constant in the Hyades: we confirm that it decreases with increasing temperature in the F stars and also find it decreases for stars cooler than mid K. We examine correlations between simultaneously measured R'HK and radial velocities using both a classical statistical test and a Bayesian odds ratio test. We find that there is a significant correlation between R'HK and the radial velocity in only five of the 82 stars in this sample. Thus, simple R'HK-vrad correlations will generally not be effective in correcting the measured vrad values for the effects of magnetic activity in the Hyades. We argue that this implies long-timescale activity variations (of order a few years; i.e., magnetic cycles or growth and decay of plage regions) will not significantly hinder our search for planets in the Hyades if the stars are closely monitored for chromospheric activity. The trends in the radial velocity scatter (σ'v) with <R'HK>, vsini, and Prot for our stars is generally consistent with those found in field stars in the Lick planet search data, with the notable exception of a shallower dependence of σ'v on <R'HK> for F stars. Data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Title: Origins of Solar Systems: Removing Activity-Related Radial Velocity Noise To Improve Extrasolar Planet Searches Authors: Saar, Steven Bibcode: 2002STIN...0244043S Altcode: We have continued the super high resolution (R is approximately 200,000), high S/N ((greater than) 300) echelle study of joint line bisector and radial velocity variations using the McDonald 2-D (two dimensional) coude. Observing runs in October 2000 and March 2001 were plagued by poor weather, but runs in June and October 2001 were good. We have made a preliminary analysis of the limited data in hand, and find some tantalizing evidence for correlations between median line bisector displacement and radial velocity v r. The correlation appears to be specific to the particular star being considered, probably since it is a function of both spectral type and rotation rate. Title: Hydroxyl 1.563 Micron Absorption from Starspots on Active Stars Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H.; Mines, Jonathan K. Bibcode: 2001AJ....122.1954O Altcode: We present results from a study of starspots on active stars using a pair of vibrational-rotational absorption lines of the OH molecule near 1.563 μm. We detect excess OH absorption due to dark, cool starspots on several active stars of the RS CVn and BY Dra classes. Our results for the single-lined spectroscopic binaries II Pegasi, V1762 Cygni, and λ Andromedae augment those from a previous study that used a less sensitive detector. In this study, we were able for the first time to use molecular absorption features to measure starspot properties on double-lined spectroscopic binaries. Measuring the equivalent widths of these OH lines in inactive giant and dwarf stars of spectral types G, K, and M, we find that the total equivalent width of the line pair increases approximately linearly as effective temperature decreases from 5000 to 3000 K. We measure starspot filling factors by fitting the spectra of active stars with linear combinations of comparison star spectra representing the spot and nonspot regions of the star. Title: A search for Ca II emission enhancement in stars resulting from nearby giant planets Authors: Saar, S. H.; Cuntz, M. Bibcode: 2001MNRAS.325...55S Altcode: We present a search for periodicities (Pchr) in the chromospheric Caii infrared triplet emission of several stars (τ Boo, 51 Peg, υ And, ρ1 Cnc, ρ CrB, 70 Vir and GL 876) which may be directly attributable to interaction with close-in giant planets. Activity enhancements could arise from increased non-radiative heating and dynamo action in planet-induced tidal bulges (with Pchr~Porb/2), or from interactions between the stellar and planetary magnetic fields (with Pchr~Porb). We compare both Pchr and the phase dependence of the activity with the planetary orbital period Porb, the orbital phase, and models. No significant Pchr or phase dependence attributable to planets can be clearly identified. We place approximate upper limits on the amplitude of any planet-induced activity. We identify a possible stellar rotation period for GL 876, and support previous period determinations for four other stars. We discuss the results and possible directions of future research. Title: Extensive serendipitous X-ray coverage of a flare star with ROSAT Authors: Silverman, J. D.; Eriksen, K. A.; Green, P. J.; Saar, S. H. Bibcode: 2001MNRAS.323..577S Altcode: 2000astro.ph.11027S We report the serendipitous discovery of a flare star observed with the ROSAT X-ray observatory. From optical spectra, which show strong and variable emission lines of the hydrogen Balmer series and neutral helium, we classify this object as a M3.0Ve star, and estimate a distance of 52pc from published photometry. Owing to the close proximity of the star (13.6arcmin) to the calibration source and RS CVn binary AR Lacertae, long-term X-ray coverage is available in the ROSAT archive (~50h spanning 6.5yr). Two large flare events occurred early in the mission (1990 June-July), and the end of a third flare was detected in 1996 June. One flare, observed with the Position Sensitive Proportional Counter (PSPC), had a peak luminosity LX=1.1×1030ergs-1, an e-folding rise time of 2.2h and a decay time of 7h. This decay time is one of the longest detected on a dMe star, providing evidence for the possibility of additional heating during the decay phase. A large High Resolution Imager (HRI) flare (peak LX=2.9×1030ergs-1) is also studied. The `background' X-ray emission is also variable - evidence for low-level flaring or microflaring. We find that >=59 per cent of the HRI counts and >=68 per cent of the PSPC counts are caused by flares. At least 41 per cent of the HRI exposure time and 47 per cent of the PSPC are affected by detectable flare enhancement. Title: Further Analysis of Stellar Magnetic Cycle Periods Authors: Saar, S.; Brandenburg, A. Bibcode: 2001ASPC..248..231S Altcode: 2001astro.ph..5070S; 2001mfah.conf..231S We further investigate relationships between activity cycle periods in cool stars and rotation to include new cycle data, and explore different parameterizations of the problem. We find that relations between cycle and rotational frequencies (omega_cyc vs. Omega) and between their ratio and the inverse Rossby number (omega_cyc/Omega vs. Ro^{-1}) show many similarities, including three branches and similar rms scatter. We briefly discuss some implications for dynamo models. Title: Magnetic Fields in Cool Stars (CD-ROM Directory: contribs/moreno) Authors: Moreno Insertis, F.; Saar, S. H.; Solanki, S. K. Bibcode: 2001ASPC..223..435M Altcode: 2001csss...11..435M No abstract at ADS Title: Stellar Dynamos: A Modeling Perspective Authors: Charbonneau, P.; Saar, S. H. Bibcode: 2001ASPC..248..189C Altcode: 2001mfah.conf..189C No abstract at ADS Title: Recent Measurements of (and Inferences About) Magnetic Fields on K and M Stars (CD-ROM Directory: contribs/saar1) Authors: Saar, S. H. Bibcode: 2001ASPC..223..292S Altcode: 2001csss...11..292S No abstract at ADS Title: Correcting High Precision Radial Velocities for the Effects of Stellar Magnetic Activity (CD-ROM Directory: contribs/saar2) Authors: Saar, S. H.; Fischer, D.; Snyder, N.; Smolec, R. Bibcode: 2001ASPC..223.1051S Altcode: 2001csss...11.1051S No abstract at ADS Title: New Measurements of Magnetic Fields on T Tauri Stars (CD-ROM Directory: contribs/krull) Authors: Johns-Krull, C. M.; Valenti, J. A.; Saar, S. H.; Hatzes, A. P. Bibcode: 2001ASPC..223..521J Altcode: 2001csss...11..521J No abstract at ADS Title: Self-Consistent Magnetic/Acoustic Chromosphere Models of Late-Type Stars (CD-ROM Directory: contribs/cuntz1) Authors: Cuntz, M.; Ulmschneider, P.; Rammacher, W.; Musielak, Z. E.; Saar, S. H. Bibcode: 2001ASPC..223..913C Altcode: 2001csss...11..913C No abstract at ADS Title: New Measurements of T Tauri Magnetic Fields: Testing Magnetospheric Accretion Authors: Johns-Krull, C. M.; Valenti, J. A.; Piskunov, N. E.; Saar, S. H.; Hatzes, A. P. Bibcode: 2001ASPC..248..527J Altcode: 2001mfah.conf..527J No abstract at ADS Title: Starspot Temperature and Filling Factor Measurements for Active Dwarfs (CD-ROM Directory: contribs/saar3) Authors: Saar, S. H.; Peterchev, A.; O'Neal, D.; Neff, J. E. Bibcode: 2001ASPC..223.1057S Altcode: 2001csss...11.1057S No abstract at ADS Title: Analyzing the Effects of Planets and Brown Dwarfs on Stellar Chromospheric and Coronal Activity (CD-ROM Directory: contribs/cuntz2) Authors: Cuntz, M.; Musielak, Z. E.; Saar, S. H. Bibcode: 2001ASPC..223.1528C Altcode: 2001csss...11.1528C No abstract at ADS Title: Magnetic Cycles and Activity in FGK Stars in the Framework of Babcock-Leighton Dynamos Authors: Dikpati, M.; Saar, S. H.; Brummell, N.; Charbonneau, P. Bibcode: 2001ASPC..248..235D Altcode: 2001mfah.conf..235D No abstract at ADS Title: Effects of Stellar Magnetic Activity on High Resolution Line Profiles and Radial Velocity Measurements. Authors: Pearson, N. S.; Saar, S. H.; Hatzes, A. P.; Paulsen, D. Bibcode: 2000AAS...197.1107P Altcode: 2000BAAS...32.1417P We study very high resolution (λ /Δ λ ≈ 200,000), high S/N (350 - 550) echelle spectra of five G to early K type stars (β Com, ɛ Eri, 61 UMa, 59 Vir, and ξ Boo A) and construct bisectors for ~30 unblended Fe I absorption lines in each. We collate the bisectors into subgroups based upon absorption line depth and excitation potential, calculate many statistical measures of the bisector position and shape, and average these measurements over the subgroups. We then search for relationships between the averaged bisector properties and various stellar properties, such as temperature, activity and v\ sin\ i; several significant trends are found. We investigate how the bisectors change over time with relation to stellar properties in an effort to find trends between the bisector properties, stellar magnetic surface features, and apparent radial velocity (vr). Such correlations would allow for the correction of some of the scatter in measurements of the vr, permitting easier detection of sub-jovian exoplanets. We find changes in certain bisector measures to be well correlated with vr changes. This work was supported by National Science Foundation grant AST-9731652. Title: When the Dynamo SPUTTERS:THE Corona of a AN Extremely Inactive (maunder MINIMUM?) Star Authors: Saar, Steven Bibcode: 2000cxo..prop..558S Altcode: 2000cxo..prop..427S; 2000chan.prop..427S The Wilson survey identified a group of stars with very low level, near-constant Ca II emission. Weak UV and Xray emission in a few of these stars implies that magnetic heating from a residual (probably turbulent) dynamo still operates. Many of these stars are likely in the stellar analog of the Maunder minimum - a period when the normal cyclic dynamo of the sun was in quiescence. We propose to study the brightest of these stars with Chandra. The stars present a unique opportunity to 1) study the properties of the weakest dwarf star coronae, 2) to investigate the coronal product of a predominantly turbulent dynamo in a high mass star, exploring its dependence on rotation and mass, and 3) to potentially study (indirectly) the properties of the solar corona during magnetic minima. Title: Correcting Radial Velocities for Long-Term Magnetic Activity Variations Authors: Saar, Steven H.; Fischer, Debra Bibcode: 2000ApJ...534L.105S Altcode: We study stars in the Lick planetary survey for correlations between simultaneous measurements of high-precision radial velocities vr and magnetic activity (as measured in an SIR emission index from Ca II λ8662). We find significant correlations in ~30% of the stars. After removing linear trends between SIR and vr, we find that the dispersion in vr in these stars is decreased by an average of 17%, or ~45% of the dispersion above the measurement noise. F stars and less active stars with variable Ca II H and K lines are the most successfully corrected. The magnitude of the slope of the SIR versus vr relations increases proportional to vsini and (excepting M dwarfs) tends to decrease with decreasing Teff. We argue that the main cause of these effects is modification of the mean line bisector shape brought on by long-term, magnetic activity-induced changes in the surface brightness and convective patterns. The correlations can be used to partially correct vr data for the effects of long-term activity variations, potentially permitting study of planets around some (higher mass) younger stars and planets producing smaller stellar reflex velocities. Title: Making Sense of Stellar Activity Cycle Periods Authors: Saar, S. H. Bibcode: 2000SPD....31.1001S Altcode: 2000BAAS...32Q.842S I explore relationships between the magnetic activity cycle frequency ωcyc, the rotational frequency Ω , and other stellar properties in a large sample of dwarfs, evolved stars, active binaries, and the secondaries of CV systems. The cycles are derived from various sources, including periodicities in Ca ii, photometry, and orbital period changes. Dimensional (ωcyc vs. Ω ) and non-dimensional (ωcyc/Ω vs. Ro-1; where Ro is the Rossby number) parameterizations give similar results. Stars are concentrated on three main ``branches" with different relationships between ωcyc and Ω ; the branches may converge at very short Ω . The oldest, lowest activity stars tend to occupy the branch with the highest ωcyc. Some stars have additional secondary ωcyc (perhaps analogous to the Sun's ``Gleissberg" cycle) lying on other branches; the preferred branch of the primary ωcyc may be mass and Ω dependent. The density of stars along each branch also depends on Ω and hence age, indicating ωcyc evolves in time, but in a complex, sometimes multi-valued fashion. I discuss some possible implications for dynamo theory and evolution. This work is supported by NSF grant AST-9528563. Title: Observations of Magnetically Active Binary Stars using Phoenix Authors: O'Neal, D.; Mines, J. K.; Neff, J. E.; Saar, S. H. Bibcode: 2000AAS...196.0514O Altcode: 2000BAAS...32..683O We present observations of several magnetically-active, post-main sequence binary systems (all of the RS CVn class) obtained with the NOAO Phoenix Infrared Spectrograph. Our high-resolution spectra are centered on the 6397cm-1 (1.563μ m) lines of OH. These lines are temperature-sensitive and thus are a good diagnostic of the area coverage of dark, cool starspots on the stars (O'Neal and Neff 1997). Our new observations, using Phoenix, are of higher resolution and greater signal-to-noise than those we presented previously. By modeling the active stars as the sum of an inactive comparison star (to represent the active star's photosphere)and an M star (to represent the spots), we measure starspot filling factors on II Peg, V1762 Cyg, σ Gem, and λ And. We find filling factors similar to those we previously measured for the same stars using TiO bands. We also (for the first time) fit the spectra of double-lined binary stars with this technique, enabling us to determine the level of starspot coverage on the active components. Our spectra also contain the highly Zeeman-sensitive (g=3) Fe I 6388cm-1 line; analysis of this feature enables us to measure the mean field strength and area filling factor of the magnetic regions of the active stars. In the future we will apply Doppler imaging techniques, adapted to our H-band spectra, to our observations in order to derive images of the starspot distributions. The authors were guest observers at Kitt Peak National Observatory, National Optical Astronomy Observatories. Title: On Stellar Activity Enhancement Due to Interactions with Extrasolar Giant Planets Authors: Cuntz, Manfred; Saar, Steven H.; Musielak, Zdzislaw E. Bibcode: 2000ApJ...533L.151C Altcode: We present a first attempt to identify and quantify possible interactions between recently discovered extrasolar giant planets (and brown dwarfs) and their host stars, resulting in activity enhancement in the stellar outer atmospheres. Many extrasolar planets have masses comparable to or larger than Jupiter and are within a distance of 0.5 AU, suggesting the possibility of their significant influence on stellar winds, coronae, and even chromospheres. Beyond the well-known rotational synchronization, the interactions include tidal effects (in which enhanced flows and turbulence in the tidal bulge lead to increased magnetoacoustic heating and dynamo action) and direct magnetic interaction between the stellar and planetary magnetic fields. We discuss relevant parameters for selected systems and give preliminary estimates of the relative interaction strengths. Title: Dynamo mechanisms Authors: Brandenburg, A.; Saar, S. H. Bibcode: 2000ASPC..198..381B Altcode: 2000scac.conf..381B No abstract at ADS Title: Time Evolution of the Magnetic Activity Cycle Period. II. Results for an Expanded Stellar Sample Authors: Saar, Steven H.; Brandenburg, Axel Bibcode: 1999ApJ...524..295S Altcode: We further explore nondimensional relationships between the magnetic dynamo cycle period Pcyc, the rotational period Prot, the activity level (as observed in Ca II HK), and other stellar properties by expanding the stellar sample studied in the first paper in this series. We do this by adding photometric and other cycles seen in active stars and the secondaries of CV systems and by selectively adding less certain cycles from the Mount Wilson HK survey; evolved stars, long-term HK trends and secondary Pcyc are also considered. We confirm that most stars with age t>~0.1 Gyr occupy two roughly parallel branches, separated by a factor of ~6 in Pcyc, with the ratio of cycle and rotational frequencies ωcyc/Ω~Ro-0.5, where Ro is the Rossby number. Using the model of the first paper in this series, this result implies that the α effect increases with mean magnetic field (contrary to the traditional α-quenching concept) and that α and ωcyc decrease with t. Stars are not strictly segregated onto one or the other branch by activity level, though the high-ωcyc/Ω branch is primarily composed of inactive stars. The expanded data set suggests that for t>~1 Gyr, stars can have cycles on one or both branches, though among older stars, those with higher (lower) mass tend to have their primary Pcyc on the lower (upper) ωcyc/Ω branch. The Sun's ~80 yr Gleissberg cycle agrees with this scenario, suggesting that long-term activity ``trends'' in many stars may be segments of long (Pcyc~50-100 yr) cycles not yet resolved by the data. Most very active stars (Prot<3 days) appear to occupy a new, third branch with ωcyc/Ω~Ro0.4. Many RS CVn variables lie in a transition region between the two most active branches. We compare our results with various models, discuss their implications for dynamo theory and evolution, and use them to predict Pcyc for three groups: stars with long-term HK trends, stars in young open clusters, and stars that may be in Maunder-like magnetic minima. Title: Line Bisector Variability in Active Dwarfs and its Relationship to Radial Velocity Variations Authors: Saar, S. H.; Snyder, N. Bibcode: 1999AAS...19410502S Altcode: We study absorption line bisectors as diagnostics of the non-uniform spatial and temporal properties of active, cool dwarf stars. We analyze high resolution (lambda /Delta lambda ~ 125,000), high signal-to-noise (200 <= S/N <= 500) line profiles observed with the stellar echelle spectrograph of the McMath-Pierce Solar telescope. We find that various measures of the bisector shape can vary on timescales of days, implying significant spatial non-uniformity of the surface convective and brightness (starspot) patterns. Observations at fixed rotational phase show the bisectors can evolve on timescales of a few rotations, suggesting rapid rearrangement of the stellar surface structures. We also detect some evidence for correlations between changes in bisector parameters and changes in high precision radial velocities. The results are discussed in the context of stellar surfaces and their effect on radial velocity searches for extrasolar planets. Title: Two-Component Theoretical Chromosphere Models for K Dwarfs of Different Magnetic Activity: Exploring the Ca II Emission-Stellar Rotation Relationship Authors: Cuntz, M.; Rammacher, W.; Ulmschneider, P.; Musielak, Z. E.; Saar, S. H. Bibcode: 1999ApJ...522.1053C Altcode: We compute two-component theoretical chromosphere models for K2 V stars with different levels of magnetic activity. The two components are a nonmagnetic component heated by acoustic waves and a magnetic component heated by longitudinal tube waves. The filling factor for the magnetic component is determined from an observational relationship between the measured magnetic area coverage and the stellar rotation period. We consider stellar rotation periods between 10 and 40 days. We investigate two different geometrical distributions of magnetic flux tubes: uniformly distributed tubes, and tubes arranged as a chromospheric network embedded in the nonmagnetic region. The chromosphere models are constructed by performing state-of-the-art calculations for the generation of acoustic and magnetic energy in stellar convection zones, the propagation and dissipation of this energy at the different atmospheric heights, and the formation of specific chromospheric emission lines that are then compared to the observational data. In all these steps, the two-component structure of stellar photospheres and chromospheres is fully taken into account. We find that heating and chromospheric emission is significantly increased in the magnetic component and is strongest in flux tubes that spread the least with height, expected to occur on rapidly rotating stars with high magnetic filling factors. For stars with very slow rotation, we are able to reproduce the basal flux limit of chromospheric emission previously identified with nonmagnetic regions. Most importantly, however, we find that the relationship between the Ca II H+K emission and the stellar rotation rate deduced from our models is consistent with the relationship given by observations. Title: A Search for Acoustic Heating in the Chromospheres of Low Activity Dwarfs Authors: Saar, Steven Bibcode: 1999hst..prop.8143S Altcode: 1999hst..prop.4477S Recent observations cast doubt on the importance of acoustic waves for chromospheric heating, at least in inactive giant stars, and have set small upper limits to their contribution to upper layers of the Solar chromosphere. These findings contradict the widely accepted picture that acoustic heating accounts for a significant fraction, the ``basal component'', of chromospheric heating in inactive stars across the HR diagram. To help resolve this issue, we propose to observe an extremely inactive {basal} dwarf star {Tau Ceti} to search for specific signatures of upward propagating acoustic waves: blue-shifts and enhanced blue wings in chromospheric lines. Solar data show that the strength of blue-shift can be used to estimate the acoustic contribution to chromospheric heating. We will also analyze archival HST data of an active dwarf of the same spectral type, and solar spectra from the SUMER instrument on SOHO, for comparison with the new data. Lack of a significant acoustic signature in Tau Ceti would indicate that magnetic heating generated by a local {turbulent, non- cycling} dynamo is responsible for the basal component of chromospheric heating in main sequence stars. Tau Cet may be in a phase analogous to the solar Maunder minimum, and HST spectra might serve as a proxy for the solar spectrum in this state. The spectra will also be used for emission measure analysis differentially between the Sun and solar-like stars. Title: Optical and ultraviolet observations of a strong flare in the young, single K2 dwarf LQ Hya Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C. Bibcode: 1999MNRAS.305...45M Altcode: 1998astro.ph.11452M We present high-resolution optical echelle spectra and IUE observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive phase of the flare, which started sometime between 2:42 ut and 4:07 ut, was characterized by strong optical continuum enhancement and blueshifted emission lines with broad wings. The optical chromospheric lines reached their maximum intensity at ~ 5:31 ut, by which time the blueshift vanished and the optical continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased and the lines redshift in a gradual phase that lasted at least two more hours. The Mg II lines behaved similarly. Quiescent C IV flux levels were not recovered until 21 h later, though a data gap and a possible second flare make the interpretation uncertain. In addition to the typically flare-enhanced emission lines (e.g., H alpha and H beta), we observe He I D_3 going into emission, plus excess emission (after subtraction of the quiescent spectrum) in other He I and several strong neutral metal lines (e.g., Mg I b). Flare enhancement of the far-ultraviolet continuum generally agrees with an Si I recombination model. We estimate the total flare energy, and discuss the broad components, asymmetries and Doppler shifts seen in some of the emission lines. Title: Parent Stars of Extrasolar Planets. IV. 14 Herculis, HD 187123, and HD 210277 Authors: Gonzalez, Guillermo; Wallerstein, George; Saar, Steven H. Bibcode: 1999ApJ...511L.111G Altcode: Spectroscopic analyses of 14 Her, HD 187123, and HD 210277, recently reported to harbor planets, reveal that these stars are metal rich. We find [Fe/H]=0.50+/-0.05, 0.16+/-0.05, and 0.24+/-0.05 for 14 Her, HD 187123, and HD 210277, respectively. This is the first spectroscopic analysis of HD 187123; our results for 14 Her and HD 210277 are in agreement with published studies. It is shown that 14 Her and ρ1 Cnc are nearly identical in their bulk physical characteristics. This result, combined with their extreme metallicities, suggests that their physical parameters have been affected by the process that formed their planets. These two stars join a group of about half a dozen stars in the solar neighborhood with [Fe/H]>=0.4. It is also shown that 51 Peg and HD 187123, which have companions with similar orbital periods and masses, are nearly identical. We find vsini~2.0 km s-1 for HD 210277 from a high-resolution spectrum.

Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology, and the National Solar Observatory, Tucson, AZ, administered by AURA, Inc., for the NSF. Title: Time Evolution of the Magnetic Activity Cycle Period: Results for an Expanded Stellar Sample Authors: Saar, S. H.; Brandenburg, A. Bibcode: 1998AAS...193.4404S Altcode: 1998BAAS...30S1315S We explore non-dimensional relationships between the magnetic dynamo cycle period P_cyc, the rotational period P_rot, the activity level (as observed in Ca ii HK), and other stellar properties using a large stellar sample including Ca ii, photometric and other cycles in dwarfs, evolved stars, active binaries, and the secondaries of CV systems. We confirm that most stars with age t ga 0.3 Gyr occupy two roughly parallel branches, separated by a factor of ~ 6 in P_cyc, with P_rot/P_cyc ~ Ro(-0.5) , where Ro is the Rossby number. Using the simple model of Brandenburg, Saar, & Turpin (1998 ApJ 498, L51), this result implies that the alpha effect increases with mean magnetic field B, and that alpha and omega_cyc decrease with age along these branches. Stars are not strictly segregated onto one or the other branch by activity level, though the high P_rot/P_cyc branch is primarily composed of inactive stars. The expanded dataset suggests that for t ga 1 Gyr, stars can have P_cyc on one or both branches (double P_cyc stars), though among older stars, those with higher mass (F) tend to have their primary P_cyc on the low P_rot/P_cyc branch, while lower mass (K) stars occupy the high P_rot/P_cyc branch. The sun's ~ 80 year Gleissberg cycle agrees with this scenario, suggesting that long-term ``trends" in many stars may be segments of long (P_cyc ~ 50-100 yr) cycles not yet resolved by the data. Most extremely active stars (P_rot < 3 days) appear to occupy a third branch with P_rot/P_cyc ~ Ro(0.4) , where some kind of alpha -quenching may be operating. Many RS CVn variables lie in a transition region between the two most active branches. We discuss implications for dynamo theory and evolution, and compare our results with various other models. The results are also used to predict P_cyc for stars with long-term HK trends, a sample of young open cluster members, and a group which may be in the stellar analog of the Maunder minimum. Title: Properties of Flares and Microflares in the RS CVn Variable II Peg Authors: Herczeg, G. J.; Saar, S. H.; Daw, A. Bibcode: 1998AAS...193.9901H Altcode: 1998BAAS...30.1395H We have analyzed two orbits of HST GHRS rapid-readout data of the active RS CVn subgiant II Peg. About 30 min of data were taken at medium resolution centered at C IV apparently during the late decay of a flare. These show strong symmetric C IV lines composed of a narrow (50 km/s FWHM) and a broad (150 km/s FWHM) component. About 45 min of data taken at low resolution show both quiescent emission and a flare. In the quiescent state we detect a wide range of lines including O V (1371 Angstroms) and (possibly) Fe XXI (1354 Angstroms); analysis of density sensitive lines (O IV) imply an electron density of n_e ~ 10(12) cm(-3) in the transition region (TR) at T~10(5) K. Analysis of the time-arrival distribution of photons in the quiescent data suggests an excess at high counts over that expected by Poisson statistics; thus the data can be modeled by a steady-state quiescent (Poisson) process, plus a stochastic process probably due to weak flares and microflares. By fitting the maximum possible Poisson component, we estimate that in the ``quiescent'' state, at least 11% of the flux in TR lines and at least 5% in the chromospheric lines comes from microflare heating. Analysis of the main flare shows it is dominated by continuum emission, which reaches a blackbody temperature of 22,000 K some 2.5 min into the flare. The continuum emission does not appear to be consistent with Si I recombination suggested previously; rather, we suggest reprocessed X-rays are a more likely source. The flare generated red-shifted line emission which rapidly reached +120 km/s and remained constant thereafter. Higher T lines (C IV and Si IV) were more enhanced and changed more rapidly than chromospheric lines (C II). There is some evidence for compression followed by explosive evaporation in the TR during the initial phases of the flare, but the density diagnostics give conflicting results. Title: Two-Component Chromosphere Models for K Dwarf Stars: The Chromospheric Emission --- Stellar Rotation Relationship Authors: Cuntz, M.; Musielak, Z. E.; Ulmschneider, P.; Rammacher, W.; Saar, S. H. Bibcode: 1998AAS...193.4402C Altcode: 1998BAAS...30.1315C We present two-component theoretical chromosphere models for K dwarf stars with different levels of magnetic activity. The two components are: a nonmagnetic component heated by acoustic waves, and a magnetic component heated by longitudinal tube waves. The filling factor for the magnetic component is determined from an observational relationship between the stellar rotation rate and the measured coverage of stellar surface by magnetic fields. The chromosphere models are constructed by performing state-of-the-art calculations of the generation of acoustic and magnetic energy in stellar convection zones, the propagation and dissipation of this energy at the different atmospheric heights, and the formation of specific chromospheric emission lines, which are then compared to the observational data. In all these steps, the two-component structure of stellar photospheres and chromospheres is fully taken into account. We find that due to the presence of magnetic flux tubes, the heating and chromospheric emission is significantly increased in the magnetic component. The heating and chromospheric emission is found to be the strongest in flux tubes with small spreading factors which are expected to be present in fast rotating stars. For stars with very slow rotation we are able to reproduce the basal flux limit of chromospheric emission previously identified as due to pure acoustic heating. Most importantly, however, we find that the relationship between the Ca II H+K emission and the stellar rotation rate deduced from our models is consistent with the empirical relationship given by observations. Title: Measurements of Starspot Parameters on Active Stars using Molecular Bands in Echelle Spectra Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H. Bibcode: 1998ApJ...507..919O Altcode: We present results from a study of starspot areas (fS) and temperatures (TS), primarily on active, single-lined spectroscopic binaries, determined using molecular absorption bands. Expanding upon our previous studies, we have analyzed multiorder echelle spectra of eight systems to simultaneously measure several different molecular bands and chromospheric emission lines. We determined starspot parameters by fitting the molecular bands of interest, using spectra of inactive G and K stars as proxies for the nonspotted photosphere of the active stars, and using spectra of M stars as proxies for the spots. At least two bands with different Teff sensitivities are required. We found that fitting bands other than the TiO 7055 and 8860 Å features does not greatly extend the temperature range or sensitivity of our technique. The 8860 Å band is particularly important because of its sharply different temperature sensitivity. We did not find any substantial departures from fS or TS that we have measured previously based on single-order spectra. We refined our derived spot parameters using contemporaneous photometry where available. We found that using M giants as spot proxies for subgiant active stars often underestimates fS needed to fit the photometry; this is presumably due to the increase in strength of the TiO bands with decreasing gravity. We also investigated correlations between fS and chromospheric emission, and we developed a simple method to measure nonspot temperature (TQ) solely from our echelle spectra. Title: Spectroscopic Evidence for Nonuniform Starspot Properties on II Pegasi Authors: O'Neal, Douglas; Saar, Steven H.; Neff, James E. Bibcode: 1998ApJ...501L..73O Altcode: We present spectroscopic evidence for multiple spot temperatures on the RS CVn star II Pegasi (HD 224085). We model the strengths of the 7055 and 8860 Å TiO absorption bands in the spectrum of II Peg using weighted sums of inactive comparison spectra: a K star to represent the nonspotted photosphere and an M star to represent the spots. The best fit yields independent measurements of the starspot filling factor (fS) and mean spot temperature (<TS>) averaged over the visible hemisphere of the star. During three-fourths of a rotation of II Peg in late 1996, we measure a constant fS~55%+/-5%. However, <TS> varies from 3350+/-60 to 3550+/-70 K. We compute <TS> for two simple models: (1) a star with two distinct spot temperatures, and (2) a star with different umbral/penumbral area ratios. The changing <TS> correlates with emission strengths of Hα and the Ca II infrared triplet in the sense that cooler <TS> accompanies weaker emission. We explore possible implications of these results for the physical properties of the spots on II Peg and for stellar surface structure in general. Title: Time Evolution of the Magnetic Activity Cycle Period Authors: Brandenburg, Axel; Saar, Steven H.; Turpin, Christen R. Bibcode: 1998ApJ...498L..51B Altcode: We propose a new interpretation of the relationships between the dynamo cycle period (Pcyc) as observed in Ca II H and K, the rotational period (Prot), the activity level, and other stellar properties. Viewed within this framework, the data suggest that the dynamo α-parameter increases with magnetic field strength, contrary to the conventional idea of α-quenching. The data also suggest a possibly discontinuous dependence of the ratio of cycle to rotation frequency, ωcyc/Ω, as a function of Rossby number, Ro (or equivalently, activity or age). Stars evolve with ωcyc/Ω~t-0.35 (or Ro-0.7), until age t~2-3 Gyr (roughly at the Vaughan-Preston gap), where a sharp transition occurs, in which ωcyc/Ω increases by a factor of ~6. Thereafter, evolution with ωcyc/Ω~t-0.35 continues. The age at which transition occurs may be mass dependent, with K stars making the transition first. Title: Magnetic Activity-related Radial Velocity Variations in Cool Stars: First Results from the Lick Extrasolar Planet Survey Authors: Saar, Steven H.; Butler, R. Paul; Marcy, Geoffrey W. Bibcode: 1998ApJ...498L.153S Altcode: The discovery of the radial velocity (vr) signatures of planets around several solar-like stars highlights the importance of exploring the sources of vr variations intrinsic to the stars themselves. We study the stars in the Lick planetary survey for vr variations related to stellar activity: the rotation of starspots and convective inhomogeneities and their temporal evolution. We study the relationships between the weighted vr dispersion, σ'v (which has first been corrected for the orbital contribution from known planets and the mean internal error), and spectral type, rotation, and activity (as measured by Ca II H and K). We find that the largest σ'v values occur among both the coolest (dMe) and the warmest (active F) stars. Values of σ'v increase with H and K emission and scale proportional to vsini in G and K stars and proportional to (vsini)1.3 in F stars. For a G star with vsini ~ 8-10 km s-1 (age ~0.3 Gyr), for example, 20 m s-1<~σ'v<~45 m s-1, roughly consistent with the predicted σ'v levels due to magnetic activity (Saar & Donahue). All the stars with proposed planetary companions show σ'v values typical for their spectral type, activity, and/or rotation. However, before the planetary vr perturbations are removed, these stars show significantly enhanced σ'v values. We develop a simple model that can predict the σ'v expected for a given star (within ~40%) as a function of vsini, spectral type, photometric variability, and macroturbulent velocity. The implications for extrasolar planet searches are discussed. Title: Physical properties of active stars and stellar systems Authors: Osten, R. A.; Saar, S. H. Bibcode: 1998MNRAS.295..257O Altcode: We study spectra of 18 active stars and stellar systems, drawn from lists of known active binaries or newly discovered extreme-ultraviolet and soft X-ray sources. Using spectral synthesis and template modelling, we measure (often for the first time) a variety of physical properties of the stars, including spectral types, luminosities and vsini values. We report direct observation of previously undetected secondary components in three systems, and refine the orbital elements for two of these (HR 7275 and HD 217344). Title: PZ Mon - An Active Evolved Star Authors: Saar, Steven H. Bibcode: 1998IBVS.4580....1S Altcode: An Hipparcos parallax and new high-resolution spectra show that PZ Mon, long considered a spotted UV Ceti flare star, is actually a distant active giant (K1III+?), probably an RS CVn, with km s Title: Non-Radiative Heating in ``Flat Activity'' Stars Authors: Saar, S. H. Bibcode: 1998ASPC..154..211S Altcode: 1998csss...10..211S The Mount Wilson Ca ii program has identified a group of stars with very low level, non-variable chromospheric emission over the ~25 year survey. Many of these stars are very likely in the stellar analog of the solar Maunder minimum --- a period when the normal cyclic (alpha Omega) dynamo was in temporary quiescence. I study UV and X-ray emission for a sample of these ``flat activity'' stars. While their chromospheric Ca ii and C ii emission is consistent with ``basal'' (possibly acoustic) flux levels, and increase with T_eff, their transition region (TR) and coronal fluxes 1) are lower than in normal cyclic stars, 2) increase towards cooler T_eff, and 3) are independent of rotation. The TR and coronal fluxes thus appear to be formed by a largely non-acoustic process which is weak, non-variable, and depends on mass (convection zone depth) rather than rotation. These properties are consistent with magnetic heating due to a turbulent, distributed, convection zone dynamo. Turbulent dynamos thus likely operate at some level in all cool stars. I discuss implications of these results for dynamos and magnetic activity in late-type stars. Title: The Contribution of Flares to Transition Region Heating in Active G and K Dwarfs Authors: Saar, S. H.; Bookbinder, J. A. Bibcode: 1998ASPC..154.1560S Altcode: 1998csss...10.1560S We present the preliminary results of an analysis of HST GHRS rapid readout spectra covering the region 1380 AA - 1670 AA for two active dwarfs of approximately Pleiades age: HD 129333 (G0V, P_rot ~2.8 days) and LQ Hya (K2V, P_rot ~1.6 days). Both were observed for >= 4 orbits at 1 second time resolution (total exposure time > 13,000 s each). The time series of the transition region (TR) fluxes (the sum of C iv + Si iv) shows many low-level flares in both stars, making the quiescent level somewhat difficult to identify. We assume that TR heating in the stars is a combination of a steady background (due to e.g., MHD wave heating) plus superimposed flares. The distribution of TR photons per unit time, N(n_TR), should thus have a component at the low counts which can be fit by a Poisson function. The best-fit Poisson to the low count end of N(n_T) then defines the the average background TR heating rate (from the Poisson mean), and an upper limit to the total steady heating unaffected by flares (from the Poisson amplitude). Our analysis suggests that at least 8% of TR flux of HD 129333 and 11% of TR flux of LQ Hya arose from flares during our observations. We also discuss the flare rates as a function of energy. This represents the first detailed information on flare heating rates for active G and K dwarfs. Title: II Peg: Spectroscopic Evidence for Multiple Starspot Temperatures Authors: O'Neal, Douglas; Saar, Steven H.; Neff, James E. Neff Bibcode: 1998ASPC..154.1439O Altcode: 1998csss...10.1439O We present spectroscopic evidence for multiple spot temperatures on the RS CVn star II Pegasi (HD 224085). We fit the strengths of the 7055 AAg and 8860 AAg TiO absorption bands in the spectrum of an active star using weighted sums of comparison spectra: the spectrum of an inactive K star to represent the non-spotted photosphere and the spectrum of an M star to represent the spots. We can thus independently measure starspot filling factor (fspot) and temperature (tspot). During 3/4 of a rotation of II Peg in Sept.-Oct. 1996, we measure fspot approximately constant at 55+/-5%. However, tspot varies from 3350 K to 3500 K. Since our method yields one derived tspot integrated over the visible hemisphere of the star, we present the results of simple models of a star with two distinct spot temperatures and compute the tspot we would derive in those cases. The changing tspot correlates with emission strengths of Hα and the Ca 2 infrared triplet, in the sense that cooler \tspot accompanies weaker emission. We explore the consequences of these results for the physical properties of the spots on II Peg and for stellar surface structure in general. Title: A Strong Flare on the K Dwarf LQ Hya Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C. Bibcode: 1998ASPC..154.1508M Altcode: 1998csss...10.1508M We present high resolution optical echelle spectra and IUE SWP observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The temporal evolution of the flare consists of an initial impulsive phase, characterized by strong continuum enhancement, which started between 02:42 UT (quiescent spectrum) and 04:36 UT (first spectrum with a strong increase in the chromospheric lines). The chromospheric lines reached their maximum intensity ~55 min later, by which time the continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased in a gradual phase that lasted at least until the end of the observation (07:29 UT). IUE data indicate that quiescent C iv flux levels were not recovered after ~4 UT on the following day. We describe the variation of the continuum enhancement, the optical and the UV lines during the flare. In addition to the emission lines that show strong flare enhancement (e.g., Hα and Hβ), we observe He i D3 going into emission. After subtraction of the quiescent spectrum, we also observe excess emission in He i lines at 4921.9, 5015.7, and 6678.1AA, and in other metal lines such as the Na i D1 and D2, the Mg i b triplet and several Fe i and Fe ii lines. We estimate the energy release during the flare, and analyze the broad components and asymmetries seen in some of the emission lines. Title: Eclipse Mapping the Chromosphere of the M4 Ve Binary CM Dra: First Results Authors: Saar, S. H.; Bookbinder, J. A. Bibcode: 1998ASPC..154.2042S Altcode: 1998csss...10.2042S We present a preliminary analysis of HST FOS rapid readout spectra (1 s resolution) of Mg ii during two secondary eclipses in the dM4e binary CM Dra. Several flares were observed in both the Mg ii line and in the nearby continuum, which we use to estimate the contribution of flares to atmospheric heating. After removing the flares, we study the shape of the eclipse in Mg ii. The Mg ii lightcurve during the first eclipse shows subtle differences between ingress and egress, implying a non-uniform chromosphere. Larger differences between eclipses suggest that short-term evolution may be significant. We discuss the prospects for inverting the lightcurve to produce maps of Mg ii variations across the stellar surface. Analysis of a FUV spectrum of CM Dra reveals C ii, Si iv and C iv emission for the first time. Title: Further Evidence for Activity-Related Radial Velocity Variations in Cool Stars Authors: Saar, S. H.; Butler, R. P.; Marcy, G. W. Bibcode: 1998ASPC..154.1895S Altcode: 1998csss...10.1895S The discovery of planets around several solar-like stars by means of high precision radial velocity (vr) measurements makes it important to explore sources of vr variations intrinsic to the stars themselves. Such studies guard against false planet detections, and can guide planet searches towards stars with low vr ``noise" levels. We explore vr variations related to stellar activity - the rotation and temporal evolution of starspots and convective inhomogeneities - by studying the weighted RMS of vr variations (= sigma_v) for stars in the Lick planetary survey. After removing vr effects of known planets and binaries, and correcting sigma_v for the mean internal error (thus removing measurement RMS to first order), we study relationships between sigma_v and spectral type, rotation, and activity. Excluding binaries and evolved stars in the sample, we find sigma_v decreases with decreasing Teff, increases with activity level, and scales propto v sin i. For a G star with v sin i ~8-10 km s^{-1} (age ~0.3 Gyr), for example, sigma_v ~20-45 m s^{-1}, roughly consistent with the predictions of Saar & Donahue (1997). Implications for planet searches are discussed. Title: High-resolution Infrared Spectroscopy of Starspots on RS CVn Stars Authors: O'Neal, D.; Neff, J. E.; Saar, S. H. Bibcode: 1997AAS...191.4515O Altcode: 1997BAAS...29.1283O We present results from a study of magnetically active stars using the PHOENIX infrared spectrograph at KPNO. We constrain starspot coverages on RS CVn stars using high-resolution observations of two temperature-sensitive OH lines near 1.563mu m (6397 cm(-1) ). The use of these features holds two advantages over the TiO bands that we have used previously: the OH lines are visible in spots up to ~ 4500 K; and spots are much brighter, relative to the unspotted photosphere, in the infrared than in the visible. These properties also make these OH lines excellent candidates for the first Doppler imaging study to use high-resolution observations of infrared spectral features. Using the OH lines, we also search for previously unknown secondary stars in ``single-lined'' RS CVn binary systems, including II Pegasi (HD 224085). Title: HeI D3 absorption and its relation to rotation and activity in G and K dwarfs. Authors: Saar, S. H.; Huovelin, J.; Osten, R. A.; Shcherbakov, A. G. Bibcode: 1997A&A...326..741S Altcode: We have obtained high resolution, high S/N spectra of the He I D3 line (5876 Å) for 53 stars. Combining these data with previous measurements, we investigate correlations between the flux absorbed by D3, F_D3_, rotation and other stellar activity indicators for a set of 76 G and K dwarfs. We find that F_D3_{prop.to}P_rot_^-1.2^ for P_rot_>=4days. For P_rot_<4days, F_D3_ behaviour depends on spectral type, either remaining roughly constant (G stars), decreasing (K stars), or even going into emission (a few late K stars). We study correlations between D3 and chromospheric (Ca II HK), transition region (C IV 1550Å) and coronal emission, and find, for P_rot_>4days, F_D3_{prop.to}{DELTA}F_HK_^1.5^, F_D3_{prop.to}F_CIV_^0.7^, and F_D3_{prop.to}F_X_^0.6^, respectively. Thus, D3 has a response intermediate between Ca II HK and C IV in low to moderate activity stars, consistent with its formation in the upper chromosphere. Our data suggest that the maximum flux absorbed by D3 is F_D3_{prop.to}T_eff_^9.3^=~2x10^5^erg/cm^2^/s in G stars (equivalent widths Wlambda_<=80mÅ), and about 40% of that value (or Wlambda_<=50mÅ) in K stars, less than predicted by current theoretical models. We discuss the implications of our results for stellar activity and He I line formation, and suggest future avenues of study. Title: Activity-Related Radial Velocity Variation in Cool Stars Authors: Saar, Steven H.; Donahue, Robert A. Bibcode: 1997ApJ...485..319S Altcode: Planets have been detected orbiting several solar-type stars with the use of high-precision radial velocity (vr) measurements. While changes in vr can be measured with an accuracy of a few meters per second, there has been relatively little study of how other astrophysical processes, such as magnetic activity, may affect the observed velocities. In this paper, we use published data and simple models to explore the contributions to vr from two activity-related sources, starspots and convective inhomogeneities, as these features rotate across the disk and evolve in time.

Radial velocity perturbations due to both of these sources increase with rotation and the level of surface activity. Our models indicate that for solar-age G stars, the amplitude of perturbations due to spots is AS <~ 5 m s-1, increasing to AS ~ 30-50 m s-1 for Hyades-age G stars. If fS is the starspot area coverage, we find that AS~f0.9Sv sin i. The effects of convective inhomogeneities (as observed in line bisector variations) appear to depend on both rotation and spectral type. Young (active) F and G dwarfs can have convective vr perturbations with amplitudes AC <~ 50 m s-1, while vr amplitudes are reduced for stars with lower v sin i and cooler Teff. We show that vr data from the literature display similar trends with v sin i and Teff. AS and AC will be strongest at or near timescales related to magnetic activity variations: rotation, active region growth and decay, and activity cycles. Thus, knowledge of these timescales and typical AS and AC values are important in searching for extrasolar planets, especially those around younger, more active stars or those with small vr reflex amplitudes (i.e., <~20 m s-1). We discuss implications of our results for current planet detections and planet search strategies. Title: The Emergence of Magnetic Flux Loops in Sunlike Stars Authors: DeLuca, Edward E.; Fan, Yuhong; Saar, Steven H. Bibcode: 1997ApJ...481..369D Altcode: We explore the latitude of emergence of flux tubes at the surface of G stars as a function of the rotation rate, magnetic flux, and injection latitude at the bottom of the convective zone. Our analysis is based on a thin flux tube evolution code that has been developed to study the emergence of magnetic flux in the Sun and is well calibrated by detailed comparisons with solar observations. We study solar models with rotation rates between 1/3 and 10 times solar, injection latitudes φI between 1° and 40°, and tubes with a range of field strengths, B0, and fluxes. For our range of input parameters, we find that the mean latitude of emergence, <φE>, increases and its range decreases with higher rotation rates, that φE <= 45° for stars with rotational periods >=27 days, that φE increases with B0 in rapid rotators, while the reverse is true for slow rotators, that the dependence of φE on B0 decreases with increasing φI, that tubes with higher flux emerge at larger φE, and that the footpoint separation depends linearly on B0. We compare our results to other calculations and with observations of magnetic features on stars and suggest future observations and extensions of this research. Our results suggest that for near-polar starspots to occur, either active stars must have a larger range of φI than inferred for the Sun, or differential rotation and meridional flows are more important for magnetic flux redistribution in these stars. Our models also imply that flux appearing near the equator of active stars may be generated by a distributed, rather than a boundary layer, dynamo. Title: Rotation, turbulence and evidence for magnetic fields in southern dwarfs Authors: Saar, S. H.; Osten, R. A. Bibcode: 1997MNRAS.284..803S Altcode: We model high-resolution spectra using a simple radiative transfer analysis to derive projected rotational velocities (v sin i) and macroturbulent velocity dispersions (v_mac) for 49 southern dwarf stars (including many first-ever measurements). We compare our results with previous values, and estimate rotation periods (P_rot) and sin i values where possible. We confirm that v_mac generally decreases with decreasing temperature for T_eff >= 5000 K. Magnetically active stars tend to show enhanced values of v_mac. This may be due to a difference in the mean stellar convective properties, a change in the mean stellar temperature structure, or a combination of both. We identify a group of stars that exhibit correlations between the derived velocities and line Lande g_eff values, implying the presence of significant surface magnetic flux. Title: Magnetic field measurements on moderately active cool dwarfs. Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H. Bibcode: 1997A&A...318..429R Altcode: We present a careful analysis of 13 high-quality optical spectra of low to moderately active late-type dwarfs (G1-K5) aimed at determining their magnetic parameters. Among our sample only one star, ɛ Eri (spatially averaged field strength=~165+/-30G), exhibits the unambiguous signature of a magnetic field, a few are candidates and the remaining show no sign of a magnetic field in the observed spectra. Our analysis is based on an inversion of the spectra using detailed numerical solutions of the Unno-Rachkovsky equations, for multiple spectral lines at different positions on the stellar disk, and including magneto-optical effects. It gives results for ɛ Eri which are in good agreement with the detailed analysis of infrared spectra by Valenti et al. (1995ApJ...439..939V). However, the low value of the spatially averaged field strength of these recent analyses imply that most values of the magnetic flux determined previously for moderately active stars are probably too large, often by considerable amounts. We find that the magnetic flux can be reliably determined if considerable care is taken in the analysis, but the magnetic field strength and filling factor cannot be determined separately for moderately active stars with optical spectra of spectral resolution <=10^5^ and S/N<=250. In the case of ɛ Eri we are able to constrain the temperature of the detected magnetic features, which we find to be similar to or hotter than the non-magnetic surroundings, providing the first direct evidence that the detected field is in the form of plages. We also find that if an inversion approach is used, which determines various line broadening parameters simultaneously in a self-consistent manner, the presence of a magnetic field is not as obvious as some previous analyses have suggested. In addition, we determine fundamental parameters of the stellar sample. Title: Properties of Sun-like Stars with Planets: 51 Pegasi, 47 Ursae Majoris, 70 Virginis, and HD 114762 Authors: Henry, Gregory W.; Baliunas, Sallie L.; Donahue, Robert A.; Soon, Willie H.; Saar, Steven H. Bibcode: 1997ApJ...474..503H Altcode: Radial velocity variations have revealed planets orbiting 51 Peg, 47 UMa, and 70 Vir, and a low-mass companion orbiting HD 114762. We analyze parallel records of photometric measurements in Strömgren b and y and Johnson V, R, and I passbands and Ca II H and K fluxes in those stars. In the case of 51 Peg, the high precision of the differential photometric measurements made by the 0.75 m Automatic Photoelectric Telescope and the nonvariability of the star would allow the detection of a transit of a planet as small as Earth (corresponding to an amplitude of 0.0001 mag) if its orbit were nearly coplanar with our line of sight. No transits were observed.

For 51 Peg and 70 Vir, the upper limit of nondetection of photometric variability at their companion's orbital periods is Δ(b + y)/2 < 0.0002 +/- 0.0002 mag. For HD 114762, it is ΔV < 0.0007 +/- 0.0004 mag. Such small amplitudes of photometric variability seem to eliminate periodic velocity variations expected from p-mode oscillations.

All four stars are magnetically quiet; that is, they lack the typical Ca II and photometric variability due to rotation and activity cycles expected from surface magnetic activity in solar-type stars. Such quiescence produces an interesting observational bias that favors the detection of planets from low-amplitude radial velocity or photometric variations by minimizing the contribution from intrinsic stellar variability. We discuss the circumstances for which the probability of planet detections is improved by the reduced level of variability from surface magnetic activity in G and K stars. Stars with low variability in surface activity should be the best candidates for planet searches using radial velocity and photometric techniques. Searches for planets around younger, more active stars will be impeded by variations in velocity or brightness caused by time-varying surface features.

The Ca II H and K fluxes indicate that all four stars are older than 5 Gyr. Ages were estimated from the average levels of Ca II H and K fluxes and an existing relationship of the decrease of Ca II fluxes with age on the lower main sequence and were drawn from previous results based on theoretical isochrone fitting. Values of the projected rotational velocity, v sin i, are determined for 70 Vir and 47 UMa from high-resolution spectra.

Based on observations made at Mount Wilson Observatory, operated by the Mount Wilson Institute under an agreement with the Carnegie Institution of Washington, and at the National Solar Observatory, administered by AURA, Inc. for the NSF. Title: PHOENIX (IR) and Optical Observations of Magnetic Fields on M Dwarfs Authors: Valenti, J.; Johns-Krull, C. M.; Saar, S.; Hinkle, K.; Joyce, D. Bibcode: 1996AAS...189.7804V Altcode: 1996BAAS...28.1377V We compare high quality IR and optical spectra of EV Lac (M3.5 Ve) and Gliese 725B (M3.5 V) to obtain new constraints on magnetic regions on EV Lac. While EV Lac is very active (L_X/L_bol = -2.6), Gliese 725B is rather inactive (L_X/L_bol = -5.2). Nonetheless, TiO line strengths are similar in the two stars, making Gliese 725B an excellent inactive reference. Using the Zeeman--broadened Fe{I} 8468.40 Angstroms line and a temperature sequence of inactive standards, Johns--Krull & Valenti (1996) detected 3.8 +/- 0.5 kG magnetic fields covering 50 +/- 13% of EV Lac. Using this same line, we find similar field strengths in several other active M dwarfs. We have also extended the EV Lac analysis to include several other atomic lines. We generate synthetic spectra using the latest Allard & Hauschildt (1996) model atmospheres and extensive atomic and TiO line lists. A generalized Feautrier technique is used to solve the radiative transfer equation for all four Stokes components. By comparing model and observed spectra, we show that current TiO line lists have wavelength errors large enough to hinder detailed analysis. For certain bands, we determined empirical wavelength corrections from our data. Alternatively, dividing the EV Lac spectrum by Gliese 725B empirically removes most TiO features, leaving only the differences in Zeeman sensitive atomic lines. We successfully determine magnetic parameters by fitting these ratio spectra. Unlike M dwarfs, active G and K dwarfs typically have field strengths <= 2 kG covering < 10% of their surface. Detecting these weaker fields in the optical has proven difficult, but they are measurable in the IR because Zeeman splitting grows more quickly than line broadening (Delta lambda (2) vs. Delta lambda ). In preparation for an IR survey of magnetic properties in late-type stars, we obtained 2.2 mu m Phoenix spectra (S/N = 100, R = 60,000) of EV Lac and Gliese 725B, containing several Ti{I} lines that are potentially useful as magnetic diagnostics. Quite surprisingly, we see broad absorption lines in both stars, but lines in Gliese 725B also have a narrow component with no apparent analog in EV Lac. We will discuss various interpretations (both magnetic and nonmagnetic) of these data and assess the use of these lines to measure magnetic fields. Title: Possible Detection of a Residual Non-Cyclic Distributed Dynamo in ``Maunder Minimum'' Stars Authors: Saar, S. H.; Deluca, E. E.; Baliunas, S. L.; Donahue, R. A. Bibcode: 1996AAS...189.8104S Altcode: 1996BAAS...28.1382S We have analyzed HST and IUE ultraviolet spectra of five dwarfs which have extremely low, non-variable levels of Ca II HK emission. These stars appear to be in the stellar analog of the solar ``Maunder minimum'' - a period when the normal cyclic magnetic dynamo went into temporary quiescence. The stars all have very low levels of chromospheric and transition region (TR) emission. The ratio of TR (Si IV and C IV) to chromospheric emission (C II) is smaller than expected from published estimates of the ``basal'' emission, and increases with decreasing T_eff. This is in contrast to the lack of such a trend in dwarfs with variable Ca II HK (``normal'' operating magnetic dynamos) and the reverse of the trend expected if the emission was acoustic in origin. The existence of significant TR emission in ``Maunder minimum'' stars suggests that they are still generating magnetic flux, but it is apparently in some form which enhances chromospheric emission relative to the TR. A possible explanation for the observations is that a residual ``Maunder minimum'' magnetic flux is a generated by a non-cyclic distributed-type dynamo (a less efficient mechanism which operates throughout the convective zone, and thus grows with increased convective zone depth). If this scenario is correct, our data are the first observational evidence of such a dynamo operating in a star which is not fully convective. Title: A Relationship between Mean Rotation Period in Lower Main-Sequence Stars and Its Observed Range Authors: Donahue, Robert A.; Saar, Steven H.; Baliunas, Sallie L. Bibcode: 1996ApJ...466..384D Altcode: Chromospheric Ca II H and K fluxes have been measured in a sample of ~100 stars on or near the main sequence at Mount Wilson Observatory. Observations were made several times a week and span more than ten years. Within an observing season, many stars show periodic variations due to rotation. Thirty-six of the stars have highly-significant periods in at least five seasons. We compute the range in the observed period, Delta P, and suggest that it is a measure of, and a lower limit to, the surface differential rotation (SDR). Several physical and selection effects can affect the measured Delta P value. An analysis of the cumulative variance distribution at various time scales, however, demonstrates that Ca II variations due to active region growth and decay are of longer period and smaller amplitude than those due to rotation. We argue that other effects (e.g., multiple active regions, latitude bands) are either small, or primarily act to reduce the measured Delta P relative to its true value. Including results for the Sun, we find that Delta P depends on the mean seasonal rotation period

, such that Delta P is proportional to

to the power of 1.3 +/- 0.1, independent of mass. We briefly discuss this in the context of dynamo models, and other observations of surface differential rotation and active region structure. Title: Rapid UV Variability: the Contribution of Flare Heating in the Atmospheres of Active, Evolved Stars Authors: Saar, Steven Bibcode: 1996hst..prop.6676S Altcode: 1996hst..prop.3087S The question of the contribution of flares and microflares tothe non-radiatively heated outer atmospheres of late-typestars has been studied with very limited success for over adecade using IUE, a variety of X--ray satellites, and ground-based studies. HST presents the best opportunity to place afirm lower limit on the fraction of the transition region fluxresulting from short timescale events. Our analysis of HSTdata on one M dwarf shows that up to 60% of the transitionregion flux is directly attributable to stellar flares andmicroflares. This leaves little room for the traditional``quiescent" emission. Such a result, if confirmed for otherstars, promises to revitalize the study of their outeratmospheres, with the recognition that they are far moredynamic than static. We now propose to observe two active,evolved stars to probe the importance of flare heating intheir outer atmospheres: the RS CVn binary II Peg, and FKComae, a rapidly rotating single giant (possibly the result ofa coalesced binary). It is important to make theseobservations before STIS, since the even moderate flares onthese stars could saturate the MAMA detectors in strong lines. Title: Measurements of Starspot Area and Temperature on Five Active, Evolved Stars Authors: O'Neal, Douglas; Saar, Steven H.; Neff, James E. Bibcode: 1996ApJ...463..766O Altcode: We resent results from a study of starspot areas and temperatures on active stars using the 7055 and 8860 Å bands of the titanium oxide molecule. Because the two bands have different temperature sensitivities, the ratio of their strengths provides a measure of the spot temperature, while their absolute strengths are a function of total starspot area. We have analyzed the TiO bands of four active, evolved, single-lined spectroscopic binaries (EI Eridani, σ Geminorum, V1762 Cygni, and II Pegasi) and of the FK Comae star V1794 Cygni. Where possible, we compare our results with contemporaneous photometry, which is used to refine our estimate of the nonspotted photospheric temperature. We find that, over multiple epochs of observation, the spot filling factor ranges from below our detection threshold (≍8%) to just under 60%. In some cases, we find that significant starspot coverage was likely present at historical light maxima. Our results suggest a possible correlation between increasing surface gravity and the temperature difference between the spotted and nonspotted photosphere. This might result from smaller starspot magnetic field strengths on active stars of lower gravity and the corresponding decrease in the pressure and temperature contrast between the photosphere and the umbra. Title: Optical and X-Ray Characteristics of Stars Detected in the Einstein Slew Survey Authors: Schachter, Jonathan F.; Remillard, Ron; Saar, Steven H.; Favata, Fabio; Sciortino, Salvatore; Barbera, Marco Bibcode: 1996ApJ...463..747S Altcode: We detect X-rays for the first time from 63 cool (types AM) stars. These stars are part of the 229 total stellar X-ray sources identified to date in the Einstein Slew Survey (hereafter Slew). We also list new X-ray data on one A star that may have a corona, five OB stars, and report discoveries of two new T Tauri stars and two new cataclysmic variables. The stellar content of the Slew high-latitude subset (currently 93% identified for |b_II_| > 20^deg^) is 26%. This agrees well with the Einstein Extended Medium Sensitivity Survey (EMSS) stellar sample, which only considered high latitudes. Because of the large solid angle covered by the Slew, and its shallow limiting flux, the sample will better probe the bright end of the stellar X-ray luminosity function (L_X_ > 10^30^ ergs s^-1^). Presently (based on the 221 Slew stars with known spectral types), the sample is dominated by late-type systems (cooler than F; 68%). These include dMe's, BY Dra, RS CVn, and FK Comae systems. Based on the limiting magnitudes of catalogs searched to date, the Slew is assessed to be complete for spectral types earlier than K. Hence, K and M systems will be prominent in the ~50 as yet unidentified stars. We have embarked on an extensive program to (1) confirm the X-ray identifications with the optical counterparts; (2) search for Ca II H and K and Balmer line emission as activity signatures; and (3) search for supporting evidence of magnetic activity by measuring rotational velocities and relating them to X-ray luminosity level. Of 64 proposed coronal systems observed to date, we have confirmed 44 active stars, while in the remaining 20 we have been unable to find definitive activity. We have confirmed an additional 19 active stars from stellar database searches, and reclassified nine systems as having nonstellar optical counterparts from optical follow-up identification work and extragalactic database searches. We discuss notable new discoveries. From the sample of single active F7-MS Slew stars with measured ν sin i-values, we find a strong (99.9% confidence level) linear correlation of X-ray luminosity with ν sin i and with stellar radius (R). However, L_X_ is uncorrelated with angular rotation speed at the 99% level. For the combined Slew and EMSS single star F7-MS sample, we find the same 99.9% ν sin i-L_X_ and R-L_X_ correlations. The L_X_-ν sin i relation for the combined sample appears to flatten with respect to the quadratic behavior seen for optically selected stellar samples at rotational velocities in excess of ~16 km s^-1^. For the unevolved subset of the Slew single star sample, we also find a correlation between L_X_ and Rossby number (R_0_; more than 99% confidence). A least-squares fit gives L_X_ ~ R_0_^-0.4^, which is similarly flatter than the quadratic dependence seen in optical samples. Using the stellar surface X-ray flux F_X_ versus B - V diagram, we interpret these results as saturation of the stellar surface by active regions at F_X_/F_bol_ ~ 10^-3^. Title: Deep SWP spectra of marginal by DRA stars and UV spectra of the super-cycle star: HD 10780 Authors: Saar, Steven H. Bibcode: 1996sao..reptS....S Altcode: A deep short wavelength prime (SWP) spectrum of the marginal BY Dra star GL 256 shows no obvious C IV or other transition region line emission. This is at odds with other members of the class and raises the question of whether GL 256 is a bonafide member of this group. An analysis of the optical high resolution spectra indicates that the star is somewhat warmer than previously suspected. We suggest that GL 256 is in fact not a marginal BY Dra star. Two sets of International Ultraviolet Explorer (IUE) observations of the star HD 10780 were obtained in September 1992 and January 1993. An analysis of these data indicates that the star appears to have confounded expectations and does not have a simple, quasi-sinusoidal dynamo cycle. Title: The Age-related Properties of the HD 98800 System Authors: Soderblom, David R.; Henry, Todd J.; Shetrone, Matthew D.; Jones, Burton F.; Saar, Steven H. Bibcode: 1996ApJ...460..984S Altcode: We present optical spectroscopy of the field K star system HD 98800, which has been found to have significant infrared emission from circumstellar material. The lithium abundances of the stars in HD 98800 are well above those of Pleiades of similar color, but activity levels and rotation in these stars are at or below Pleiades level. Thus, it is not yet possible to say whether HD 98800 is or is not a pre-mainsequence system, and it is possible that its components are on or near the zero-age main sequence.

However, the two visible objects that make up HD 98800 both have high levels of lithium and activity, strongly suggesting that they are physically related to one another. As shown by Torres and coworkers, having these stars physically tied implies that their relative orbit is highly eccentric and highly inclined to our line of sight, and it also means that we are viewing the HD 98800 system at an unusual time in its orbit. Title: Recent magnetic fields measurements of stellar Authors: Saar, S. H. Bibcode: 1996IAUS..176..237S Altcode: No abstract at ADS Title: Recent Measurements of Stellar Magnetic Fields Authors: Saar, S. H. Bibcode: 1996mpsa.conf..367S Altcode: 1996IAUCo.153..367S No abstract at ADS Title: TiO Band Measurement of Starspot Temperature and Area on Active Stars Authors: O'Neal, D.; Neff, J. E.; Saar, S. H. Bibcode: 1996ASPC..109..621O Altcode: 1996csss....9..621O No abstract at ADS Title: TiO Band Measurement of Starspot Temperature and Area on Active Stars. Authors: O'Neal, D.; Neff, J. E.; Saar, S. H. Bibcode: 1996ASPC..109..261O Altcode: 1996csss....9..261O No abstract at ADS Title: Absolute Measurements of Starspot Area and Temperature: II Pegasi in 1989 October Authors: Neff, James E.; O'Neal, Douglas; Saar, Steven H. Bibcode: 1995ApJ...452..879N Altcode: We are developing an empirical spectrum synthesis technique that yields independent measurements of starspot filling factor, f5, and starspot temperature, TS, by fitting TiO bands of differing temperature sensitivity. The absolute depth of the TiO bands constrains fS, while the ratio of their depths is a function only of TS. One strength of this technique is its ability to determine the spot parameters in traditionally difficult cases: slowly rotating stars, uniformly spotted stars, and stars that always have spots. For this initial study, we have used a simpler procedure of measuring the band depths in the most spotted star in our survey (the single-lined RS CVn binary system II Pegasi) and for a full grid of comparison stars (inactive G, K, and M dwarfs and giants). This yields TS and fS for a given assumed temperature of the nonspotted photosphere, TQ. The latter was further constrained by the use of simultaneous photometry. We have analyzed a series of spectra of II Peg obtained throughout a single 6.7 day rotational cycle in 1989 October. We find that starspots on II Peg are better modeled by comparison spectra of giants than by dwarfs. Combining TiO analysis with contemporaneous photometry, we find that cool starspots (TS ≍ 3500 K) are always visible, with a fractional projected coverage of the visible hemisphere varying from 54% to 64% as the star rotates. The nonspotted photosphere has a temperature TQ ≍ 4800 K. Our results imply that even at the historical light maximum of V = 7.2, at least 34% of II Peg was covered by starspots. Title: Rapid UV Variability: the Contribution of Flare Heating in Active Dwarf Atmospheres Authors: Saar, Steven Bibcode: 1995hst..prop.5871S Altcode: 1995hst..prop.2344S The question of the contribution of flares and microflares to the non-radiatively heated outer atmospheres of late-type stars has been studied with at best very limited success for over a decade using IUE, a variety of X--ray satellites, and ground-based studies. However, HST presents the possibility for being able to place a firm lower limit on the fraction of the transition region flux that is the direct result of short timescale events. Our analysis of HST data on one M dwarf shows that up to 60 percent attributable to stellar flares and microflares. This leaves little room for the traditional ``quiescent" emission. Such a result, if confirmed for other stars, promises to revitalize the study of these atmospheres, with the recognition that the atmospheres are far more dynamic than static. We are now proposing to observe 3 new targets, including a very youthful solar analog and a fully convective star. Title: Dead or Just Sleeping? Status of Magnetic Dynamos in ''maunder Minumum'' Stars Authors: Saar, Steven Bibcode: 1995hst..prop.5870S Altcode: 1995hst..prop.2343S The Maunder minimum (and similar episodes occurring every few centuries) is a poorly understood 75 year period in which the normal solar magnetic dynamo cycle was temporarily interrupted. Its study is important for understanding the generation and evolution of solar/stellar magnetic fields, and for the possible influence of magnetic flux on the Sun's luminosity and hence on earth's climate. We propose to study the Maunder mimimum state by obtaining HRS spectra of a sample of solar-like stars which appear to be in the stellar analog of the Maunder minimum: i.e., stars with weak, nonvariable Ca II emission and long periods of rotation. Using transition region line emission as a proxy for magnetic fields, we will determine the residual magnetic activity levels of Maunder stars, the magnetic contribution to the total energy budget of their outer atmospheres, and explore the relations between Maunder activity levels and stellar mass and rotation. Only HST has the sensitivity to detect or usefully constrain the very weak emission seen in these stars. The results will be used to explore the evolution of dynamos with time, define the dependence of Maunder minimum activity on mass and rotation rate, test non-linear dynamo models, and estimate what solar conditions are like during a Maunder episode. Title: Using TiO Spectroscopy to Further Constrain Doppler Imaging Authors: O'Neal, D.; Neff, J. E.; Saar, S. H. Bibcode: 1995IAUS..176P..32O Altcode: No abstract at ADS Title: A Possible Relationship Between Starspot Temperature Deficit and Surface Gravity Authors: Saar, S. H.; O'Neal, D.; Neff, J. E. Bibcode: 1995IAUS..176P.105S Altcode: No abstract at ADS Title: Starspot Areas and Temperatures on Active Stars from TiO Bands Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H. Bibcode: 1994AAS...185.4507O Altcode: 1994BAAS...26.1380O We present results from a study of starspot areas and temperatures on active stars using the 7055 Angstroms and 8860 Angstroms absorption bands of the titanium oxide (TiO) molecule. These two bands have different temperature sensitivities, so the ratio of their strengths in a spotted star spectrum constrains the spot temperature, while the absolute strengths are a function of total starspot area. This spectroscopic technique complements Doppler Imaging and light-curve modeling studies because it can measure spot distributions on even uniformly-spotted or slowly-rotating stars. We present results for four active giant or subgiant stars: EI Eridani, V1794 Cygni, Sigma Geminorum, and V1762 Cygni. In multiple epochs of observation, the spot coverages we detected on those stars ranged from below our sensitivity level to approximately 35%. Title: New Measurements of Rotational and Turbulent Velocities for Southern Dwarfs Authors: Osten, R. A.; Saar, S. H. Bibcode: 1994AAS...18512503O Altcode: 1995BAAS...27..760O No abstract at ADS Title: Possible detection of a stellar flare-generated particle beam in polarized light Authors: Saar, S. H.; Martens, P. C. H.; Huovelin, J.; Linnaluoto, S. Bibcode: 1994A&A...286..194S Altcode: We present broadband linear polarization measurements of the active dK5e flare star, BD +26 730, which show a rapid change in polarization amplitude and direction over a two hour period. We conclude that impact polarization resulting from flare-generated particle beams is the most likely cause of the polarization variations. If this interpretation is correct, this event represents the most direct evidence to date for flare-generated particle beams in a star other than the Sun. With proton beams as the most probable source, energy fluxes of the order of 10^9-10^ erg/cm2/s are required to power the observed polarization changes. Using the non-flare polarization level (likely produced by stellar magnetic regions) and simple models, we estimate a lower limit of 7% for the inhomogeneous component of the magnetic region area filling factor. We compare our results with solar flares and suggest future observational and theoretical efforts. 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: Simultaneous SPOT and Chromosphere Maps of FK Comae Authors: Piskunov, N. E.; Huenemoerder, D.; Saar, S. H. Bibcode: 1994ASPC...64..658P Altcode: 1994csss....8..658P Maps of the local T_eff and chromospheric intensity (from He I D3) from a surface imaging analysis of 51 echelle spectra of FK Comae show a complex relationship between spots and activity. Title: Are Magnetic Features on epsilon ERI Cold or Hot? Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H. Bibcode: 1994ASPC...64..465R Altcode: 1994csss....8..465R We analyse high-quality spectra of epsilon Eri with the aim of determining its magnetic and thermal parameters. From a careful analysis we conclude that it is not possible to separate the field strength and filling factor of this star based on data obtained in the visible spectral range. The data do suggest, however, that the magnetic field of the star is concentrated in cool, starspot-like structures. Title: How Accurate Are Stellar Magnetic Field Measurements? II. Analysis of Disk-Integrated Flux Tube Models Authors: Saar, S. H.; Buente, M.; Solanki, S. K. Bibcode: 1994ASPC...64..474S Altcode: 1994csss....8..474S We analyze disk-integrated line profiles generated in atmospheres embedded with fluxtubes to test the accuracy of simple radiative transfer (RT) analyses in determining stellar magnetic parameters. Title: Spatial and Temporal Activity Variations on AD Leo Authors: Saar, S. H.; Morgan, M. R.; Bookbinder, J. A.; Neff, J. E.; Walter, F. M.; Valenti, J.; Misch, T.; Bopp, B. W.; Hale, A. Bibcode: 1994ASPC...64..471S Altcode: 1994csss....8..471S Multiwavelength measurements of AD Leo show rotational modulation of magnetic and quiescent C IV fluxes, and UV emission variability on all timescales 1 s < t < 60 s. Si IV flux arises from quiescent:microflare:flare heating in approximately a 35:25:40 ratio. Title: Stellar Dynamo Models: From F to K Authors: Brandenburg, A.; Saar, S. H.; Moss, D.; Tuominen, I. Bibcode: 1994ASPC...64..357B Altcode: 1994csss....8..357B We extend the two-dimensional solar dynamo models to stars of different spectral types. Dynamo action is restricted to the overshoot layer. Title: The Evolution of Stellar Dynamo Variations. Authors: Saar, S. H.; Brandenburg, A.; Donahue, R. A.; Baliunas, S. L. Bibcode: 1994ASPC...64..468S Altcode: 1994csss....8..468S No abstract at ADS Title: Measurements of Starspot Area and Temperature on II Peg Authors: O'Neal, D.; Neff, J. E.; Saar, S. H. Bibcode: 1994ASPC...64..726O Altcode: 1994csss....8..726O We are developing an empirical spectral synthesis technique that will yield independent measurements of starspot area and temperature. We have tested this technique on a series of spectra of the single-lined spectroscopic binary II Pegasi (HD 224085). II Peg is an RS CVn star from which evidence for magnetic activity has been observed in many wavelength bands. Title: The Variability of Magnetic Fields, Related Surface Structures, and Activity Authors: Saar, S. H. Bibcode: 1994svsp.coll..147S Altcode: 1994IAUCo.143P.147S I review information from a variety of sources, including magnetic field measurements, Doppler imaging, and various photometric and spectroscopic survey and monitoring programs for clues concerning the physical properties, spatial structure, variability and evolution of magnetic regions and associated activity on cool stars. Based on these data, I sketch a scenario of what the surfaces of cool stars look like as a function of spectral type and age/rotation/activity level. 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 Time Evolution of Magnetic Flux, Dynamos, and Surface Structures on Cool Stars Authors: Saar, S. H. Bibcode: 1994ASPC...64..319S Altcode: 1994csss....8..319S I briefly summarize recent observations related to the time evolution of magnetic flux, associated surface features (spots and network/plage), and the dynamo mechanism which produces them. Title: Infrared Measurements of Stellar Magnetic Fields Authors: Saar, S. H. Bibcode: 1994IAUS..154..437S Altcode: No abstract at ADS Title: New Infrared Measurements of Magnetic Fields on Cool Stars Authors: Saar, S. H. Bibcode: 1994IAUS..154..493S Altcode: I review the advantages, techniques, and results of measurement of magnetic fields on cool stars in the infrared (IR). These measurements have generated several important results, including: the first data on the magnetic parameters of dMe and RS CVn variables; evidence for field strength confinement by photospheric gas pressure; support for the correlation between magnetic flux and rotation, with possible saturation at high rotation rates; indications of horizontal and/or vertical magnetic field structure; and evidence of spatial variations in B over a stellar surface. I discuss these results in detail, and suggest future directions for IR magnetic field research. Title: Multiepoch Magnetic Surface Images of LQ Hya Authors: Saar, S. H.; Piskunov, N. E.; Tuominen, I. Bibcode: 1994ASPC...64..661S Altcode: 1994csss....8..661S We study several epochs of magnetic surface images of the active single dwarf LQ Hya to explore the surface differential rotation (SDR) rate and the correlation between magnetic flux Phi_B and T_eff. Title: Measurements of Starspot Area and Temperature on II Pegasi Authors: O'Neal, Douglas; Neff, James E.; Saar, Steven H. Bibcode: 1993AAS...183.1505O Altcode: 1993BAAS...25.1313O We are developing an empirical technique that yields independent measurements of starspot area and starspot temperature on active stars. Our technique involves fitting observed spectra near TiO absorption bands with synthetic spectra derived for various combinations of starspot and non-spot temperatures and starspot filling factors. Our comparison grid is generated from observed spectra of inactive G and K stars and of M dwarfs and giants. The absolute depth of the TiO bands in the spectra of active stars is a measure of the starspot filling factor, while the relative strength of different bands constrains the starspot temperature. We have analyzed a series of spectra of the single-lined spectroscopic binary system II Pegasi (HD 224085), K2 IV-V, P=6.7d. We find that cool starspots (Teff ~ 3400K) are always visible, covering from 35% to 50% as the star rotates. However, the absolute and relative depths of TiO bands are not by themselves sufficient to establish the temperature of the non-spot photosphere. When coupled with a temperature difference provided by multi-color photometry, this technique will enable us to uniquely determine temperatures and relative filling factors of both the spot and non-spot components of spotted stars. Title: The interchange instability of stellar magnetic flux tubes Authors: Bunte, M.; Saar, S. H. Bibcode: 1993A&A...271..167B Altcode: We investigate the stability of magnetic flux tubes in the surface layers of late-type stars, concentrating on the interchange (fluting) instability. Flux tubes on low gravity stars (log g ≲ 3.5) are generally unaffected by this instability. On stars with higher surface gravity, tubes are stable if their magnetic flux exceeds 1019 - 1021 Mx (the precise value depending on Teff and log g). Smaller structures on these stars may be stabilized by a sufficient external whirl flow. The magnitude of the required whirl flow shows only weak dependence on Teff but increases sharply with log g. In some stars, the whirl velocities needed for stabilization are larger than extant photo spheric velocities. In these cases, stable tubes are possibly separated into two regimes of permitted fluxes. Consequences for the field structure on the surfaces of late-type stars are discussed. Title: Broad-band Linear Polarization in Cool Stars. II. Amplitude and Wavelength Dependence for Magnetic and Scattering Regions Authors: Saar, Steven H.; Huovelin, Juhani Bibcode: 1993ApJ...404..739S Altcode: We have developed a model to estimate the amplitude and wavelength dependence of broad-band linear polarization (BLP) from magnetic regions on cool stars. The model includes corrections both for line blends and for the partial cancellation of polarization in the vector sum over the stellar disk. Our results agree with recent calculations of BLP in the red, but show larger amplitudes and a different wavelength dependence in the blue. We find that the detailed wavelength dependence of the polarization is complex and varies with effective temperature and gravity due to changes in line blanketing. The BLP amplitudes depend strongly on field strength, blanketing, and magnetic region filling factor and geometry. We make rough estimates of the maximum BLP for stars of various spectral types and demonstrate a method for deriving a lower limit to the filling factor from the maximum observed BLP. This lower limit is related to the fractional area covered by the spatially asymmetric component of magnetic regions. Title: Magnetic Doppler Imaging and UV Emission of an Active K Dwarf Authors: Saar, Steven H. Bibcode: 1993iue..prop.4584S Altcode: Our objective is to determine, for the first time ever, the functional and spatial relationships between magnetic flux, outer atmospheric emission, and temperature inhomogeneities on the surface of an active cool dwarf star. We have developed and successfully tested a new method, magnetic doppler imaging, for mapping the surface temperature and magnetic field distributions on rapid rotators. We will apply this method to the young, rapidly rotating, spotted K2 dwarf, HD 82558, covering the star with a phase resolution of 0.1 over two full rotations. The second rotation is crucial for separating out the effects of flares and/or active region evolution. The UV spectra will be combined with EUVE and ROSAT data to determine the longitudinal extent and the brightness of stellar active regions from the photosphere to the corona. These surface brightness maps will be directly compared with the magnetic flux and temperature maps to study stellar plage/spot properties, and serve as a basis for more realistic two-component models (quiet +plage/spot) for the outer atmospheres of active solar-like dwarfs. Title: Absolute measurements of starspot area and temperature Authors: Neff, J. E.; O'Neal, D.; Saar, S. H. Bibcode: 1993ASPC...40..193N Altcode: 1993ist..proc..193N; 1993IAUCo.137..193N No abstract at ADS Title: Accretion Disk Chromospheres and the Star-Disk Connection Authors: Horne, K.; Saar, S. H.; Marsh, T. R. Bibcode: 1993AnIPS..10..123H Altcode: No abstract at ADS Title: Magnetic Surface Images of the BY DRA Star HD 82558 Authors: Saar, S. H.; Piskunov, N. E.; Tuominen, I. Bibcode: 1992ASPC...26..255S Altcode: 1992csss....7..255S We present preliminary results of a new analysis method applied to spectra of the BY Dra star HD 82558. We invert a time series of unpolarized line profiles with different Lande g_eff values to derive both temperature and magnetic field maps of the star. We find strong fields (B > 2 kG) near cool spots and weaker fields elsewhere, with <B> ~ 1 kG. Title: The Star-Disk Connection Authors: Horne, K.; Saar, S. H.; Marsh, T. R. Bibcode: 1992ASPC...26..273H Altcode: 1992csss....7..273H No abstract at ADS Title: Evidence for a Complex Distribution of Magnetic Field Strengths on the Flare Star AD Leo Authors: Saar, S. H. Bibcode: 1992ASPC...26..252S Altcode: 1992csss....7..252S I present a preliminary analysis of four Ti I lines from a high S/N IR spectrum of the flare star AD Leo. The lines show consistent evidence for a complex magnetic field distribution, and may be fit with either (a) fields arising from a single atmospheric component but having a large vertical gradient, or (b) a two component field with B_1 ~ 2 x B_2. Title: The Magnetic Cycle of Kappa Ceti Authors: Saar, S. H.; Baliunas, S. L. Bibcode: 1992ASPC...27..197S Altcode: 1992socy.work..197S Observations of chromospheric Mg II and Ca II fluxes and photospheric magnetic flux (spanning 10, 22, and 6 years, respectively) of the active G5 dwarf, Kappa Ceti, show long-term variations analogous to the solar cycle. Ca II emission varies with a period of P_cyc = 5.6 yr, and we detect a decrease in magnetic flux (~ fB) during the declining phase of a recent cycle (1984-1988) of the form: Delta F_HK ~ (fB)^{0.4 +/- 0.2}. This is the first direct evidence for a magnetic cycle on a star other than the Sun. Title: Recent Advances in Stellar Cycle Research Authors: Saar, S. H.; Baliunas, S. L. Bibcode: 1992ASPC...27..150S Altcode: 1992socy.work..150S We review recent work on stellar cycles, focusing on a preliminary analysis of the first 25 years of data from the Mount Wilson Ca II program. Cyclic variations are generally solar-like (rapid increase, slow decline), but some stars show multiple cycle periods. About 10-15% of the stars may be in the stellar equivalent of "Maunder minima": epochs when cycles, but not all magnetic activity, temporarily cease. Well-determined cycle periods show no clear dependence on single stellar parameters, but do show correlations with more complex formulations (e.g., alpha-Omega dynamo number) when normalized to the magnetic diffusion timescale. The relation between this normalized cycle frequency (Omega*_cyc) and dynamo number appears to change with activity or age. Cycle amplitudes also correlate with Omega*_cyc, and tend to increase with convection zone depth and P_rot. Giants in young clusters also exhibit many of these phenomena, suggesting similar, dynamo-related origins. Stellar differential rotation can differ markedly from the Sun in both amplitude and form. Photometric variability increases rapidly with increasing Ca II emission, first reversing, and eventually eliminating the correlation between brightness and activity. Dynamos of active stars thus appear to produce a larger spot-to-plage ratio than inactive stars; more high-latitude spots are also seen. Surface convective properties may also change during the cycle. Title: UV Spectra of the "Super-Cycle" Star: HD 10780 Authors: Saar, Steven H. Bibcode: 1992iue..prop.4308S Altcode: HD 10780 is a moderately active K0 dwarf star with the largest known dynamo cycle amplitude (as seen in the Ca II S index) of any known dwarf. Its Ca II cycle amplitude is almost a factor of three higher than the highest seen among normal dwarfs. In 1989, HD 10780 underwent an extraordinary increase in activity, Delta S/S ~ 40%, from its cycle minimum. There are only three previous IUE observations, all LWP, and all of these spectra were taken before the recent "cycle outburst". The stars' activity levels appear to have peaked, and may now be starting a steep decline. We propose an extensive campaign to study the star in detail, combining new IUE SWP and LWP observation, plus optical spectroscopy, magnetic field and ROSAT X-ray measurements to, determine (1) the activity characteristics of this unusual star near its cycle maximum; and (2) any unusual characteristics of the star which may explain its extraordinary behavior. Results will further understanding of stellar activity, dynamos, and intermediate term variability. Title: Deep SWP Spectra of "Marginal" BY Dra Stars Authors: Saar, Steven H. Bibcode: 1992iue..prop.4295S Altcode: Recent optical and UV surveys of M dwarfs have resulted in the discovery of a number of objects with intermediate activity levels (H-alpha in weak emission but strong Ca, II and UV emission). Available data suggest these stars have a level of chromospheric activity (and perhaps an evolutionary status) midway between active BY Dra/dMe stars and quiet dM's. These "marginal" BY Dra (mBY) stars provide us with a class of objects rotating very near a "trigger velocity" (about 5 km s^-1) which appears to divide active BY Dra stars from quiet dM's. Unfortunately, only poor far UV spectra have been obtained to date (<= 5 hours). We propose to take about 20 hour SWP spectra of two mBYs by combining an ESA shift with NASA US1 and US2 (first half). These new spectra will allow us to accurately probe the upper chromospheres and transition regions of these important transitional stars for the first time. Infrared magnetic field measures will be used to explore the connection between fieldstrength/filling-factor and atmospheric heating. Comparison of these data with published information on active dMe and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "high" to "low" activity. Title: How Accurate are Stellar Magnetic Field Measurements? Authors: Saar, S. H.; Solanki, S. K. . Bibcode: 1992ASPC...26..259S Altcode: 1992csss....7..259S We study the accuracy of two magnetic analysis methods by applying them to a large grid of lines computed using detailed 1.5-D radiative transfer (RT) calculations in a variety of stellar atmospheres imbedded with fluxtubes. We find errors of < +/- 20% when using the more realistic analysis method if the fluxtube and external quiet atmospheres are similar; errors can increase substantially if this condition is relaxed. Title: Characteristics of "Marginal" BY DRA Stars Authors: Saar, S. H.; Bopp, B. W. Bibcode: 1992ASPC...26..288S Altcode: 1992csss....7..288S We analyze new UV and optical spectra of "marginal" BY Dra stars, and find support for the idea that they form a class of objects intermediate in activity (and perhaps age) between dM and dMe stars. Title: Unfolding Mysteries of Stellar Cycles Authors: Baliunas, S.; Saar, S. Bibcode: 1992Ast....20...42B Altcode: No abstract at ADS Title: Absolute Starspot Area and Temperature Measurements on Single-Lined RS CVn's Authors: Neff, J. E.; Saar, S. H. Bibcode: 1991BAAS...23.1384N Altcode: No abstract at ADS Title: The Distribution of Magnetic Fields and Related Activity on A'D Leo Authors: Saar, S. H.; Bookbinder, J. A.; Neff, J.; Bromage, G.; Bastian, T. Bibcode: 1991BAAS...23.1383S Altcode: No abstract at ADS Title: Rotation and Emission Lines in Stars and Accretion Disks Authors: Horne, Keith; Saar, Steven H. Bibcode: 1991ApJ...374L..55H Altcode: In the accretion disks of quiescent dwarf novae, Doppler mapping studies reveal that Balmer emission lines increase sharply toward the center of the disk, with surface brightnesses scaling roughly as R exp -3/2 varies as Omega(Kep). Similarly, among chromospherically active stars the H-alpha and Ca II H and K emission cores are stronger in the more rapidly rotating stars, with surface brightnesses scaling again roughly as Omega(rot). Since in both cases the emission lines scale linearly with the rotation frequency, it is proposed that the mechanism powering the emission lines in quiescent accretion disks is the same as that in chromospherically active stars, namely, the emergence of magnetic flux generated by the action of a dynamo, and its interaction with the atmosphere. If this empirical connection between disks and stars is in fact due to magnetic dynamos, the range of rotation rates available for testing dynamo theories expands from a factor of 1000 to 10 to the 7th. Title: Broad-Band Linear Polarization in Cool Stars. I. Models and Spatial Effects for Magnetic and Scattering Regions Authors: Huovelin, Juhani; Saar, Steven H. Bibcode: 1991ApJ...374..319H Altcode: We have developed models of broad-band linear polarization (BLP) arising from magnetic regions on cool stars. The models include an improved treatment of spatial effects in which the BLP is explicitly integrated over the stellar surface. We find that for magnetic region filling factors, f larger than ≍1% of a hemisphere, direct disk-integration yields results which are often significantly different from a simple linear scaling of BLP with region area, especially for regions near the limb. In particular, the amplitude of the BLP reaches a maximum for f ≍ 24%, which is a consequence of cancellation of the polarization signal within the region itself. The line-of-sight angle at which the region exhibits maximum polarization increases with region size.

We study the effects of bipolar pairs of regions, and single regions with small-scale bipolarity. The most important effect of bipolarity is the reduction in the influence of Faraday rotation on the integrated polarization. Spatial effects become more important as the size of the bipolar spot pair is increased.

We construct similar models for Rayleigh and Thomson scattering regions in order to compare the signatures of BLP from these sources. Like magnetic BLP, scattering-induced BLP shows a maximum in polarization amplitude (at f ≍ 18%), but the line-of-sight angle of the maximum first decreases (for f ≤ 10%) and then increases with increasing region size. We also present approximate formulas for the scaling of magnetically induced and scattering-induced polarization as a function of f We discuss the importance of the differences found in the rotational phase dependence for discerning the source of the polarization. Use of the phase dependence requires detailed comparisons of polarization observed at several rotational phases, with the success of application depending on the specific geometry of the polarizing regions. The general applicability of the models depends on the accuracy in determining the instrumental and interstellar polarization (in modeling of polarization degree P) and/or the orientation of the stellar rotation axis on the plane of the sky (in modeling of Stokes parameters PQ and PU) Title: Coordinated Observations of AD Leonis Authors: Bookbinder, J.; Saar, S. Bibcode: 1991IAUC.5255....2B Altcode: 1991IAUC.5255....1B J. Bookbinder and S. Saar, Center for Astrophysics, write: "We have organized a major campaign to provide a comprehensive study of the dynamics and energetics of stellar flares by utilizing high- time-resolution spectroscopy and photometry. Observations of AD Leo (R.A. = 10h16m52s.51 +/- 0s.03, Decl. = +20 07'17".2 +/- 0".5, equinox 1950.0, epoch 1991.4) are currently scheduled for May 8 and 9 UT with the Hubble Space Telescope, IUE, ROSAT, GINGA, VLA, and at Arecibo and many other ground-based facilities in the U.S. and Europe. We request additional ground-based spectroscopy and photometry from all interested parties. To standardize comparisons of results from ground-based optical observations, please use the following stars as standards: SAO 81296 = HD 89471 (R.A. = 10h17m09s.6, Decl. = +20 39'21", mv = 8.4), and SAO 81313 = HD 89772 (R.A. = 10h19m11s.5, Decl. = +20 18'23", mv = 8.9). For more details on the planned observing, please contact Bookbinder at telephone 617-495- 7058 (e-mail bookbind@cfa.harvard.edu) or Saar at 617-495-7046 (SPAN e-mail 6702::saar)." Title: Linear Polarization and Magnetic Fields in Cool Stars Authors: Huovelin, J.; Saar, S. H. Bibcode: 1991LNP...380..420H Altcode: 1991IAUCo.130..420H; 1991sacs.coll..420H Observations and theoretical models of broadband linear polarization (BLP) in cool stars are discussed. Two effects, 1) differential saturation in magnetically sensitive absorption lines and, 2) Rayleigh and Thomson scattering are considered as the possible causes of the BLP. Results of theoretical models, and comparisons with observations are summarized. Title: Recent Measurements of Stellar Magnetic Fields (With 3 Figures) Authors: Huovelin, J.; Saar, S. H. Bibcode: 1991mcch.conf..273H Altcode: 1991mcch.conf..273S I review recent measurements of magnetic fields on two interesting cool stars: a nearly pole-on BY Dra variable (BD +26 730) and a (possibly) very young K dwarf (HD 17925). These data are combined with previous measurements to investigate correlations between magnetic, chromospheric and coronal fluxes. Implications for atmospheric heating are briefly discussed. Title: Long-Term Variability of Magnetic Structures on BD +26 730 Authors: Saar, Steven H. Bibcode: 1991iue..prop.4028S Altcode: BD +26 730 , a rapidly rotating, BY Dra variable, is one of the most magnetically active K dwarfs known, and is the most active of the few stars with a known magnetic cycle period. The star is viewed nearly poleon; thus, almost all variability results from the evolution of activity in time, rather than rotational modulation. Direct measurement of the magnetic field strength and area coverage of plages on the star is possible. BD +26*730 thus presents a unique opportunity for observing long-term, purely temporal variability due to a magnetic cycle. IUE observations at two epochs already exist. We propose to continue monitoring the longterm variability of this star, now nearing starspot (and magnetic activity) maximum, with IUE in order to study the time-variability of the chromospheric and transition-region activity on long time-scales. Contemporaneous photometry, optical spectra, linear polarization, and magnetic line broadening measurements will be combined with the IUE data to explore the connections between photospheric magnetic fields, and the structure and energy balance of the hot, upper-atmospheric layers of the star. Comparison of the UV fluxes with earlier epoch IUE spectra, some taken near activity minimum, will allow us to investigate differences in stellar activity over the magnetic cycle of the star, yielding fundamental data on the behavior of stellar dynamos at high activity levels. Our study will be the first investigation of strictly temporal evolution of magnetic fields and related activity over the activity cycle on a star other than the Sun. Title: Recent Advances in the Observation and Analysis of Stellar Magnetic Fields Authors: Saar, Steven Bibcode: 1991LNP...380..389S Altcode: 1991sacs.coll..389S; 1991IAUCo.130..389S There has been considerable progress recently in the study of magnetic fields on late-type stars. Advances in the theory include investigation of systematic effects, new and improved methods of analysis for unpolarized and circularly polarized lines, new models of stellar dynamos and of broadband linear polarization, and the first studies of the thermodynamic nature of stellar magnetic regions and their vertical structure. Observationally, there have been new measurements, particularly of young and active stars (including the first detection of a field on a pre-main sequence object, a new monitoring campaign, the first indications of the relative temperatures in stellar plages, and the first measurements of fields in a single stellar active region. I discuss the results in the framework of stellar activity and surface structure. Title: The Time Evolution of Magnetic Fields on Solar-Like Stars Authors: Saar, Steven H. Bibcode: 1991suti.conf..848S Altcode: Magnetic fields play a crucial role in governing the rotational evolution of solarlike stars. Techniques for measuring stellar magnetic fields are reviewed, and the most recent determinations of magnetic-field strengths and surface-area coverages on cool stars are analyzed for correlations with age. Tentative evidence for a decrease in magnetic flux with age is found, primarily caused by a reduction in the magnetic area filling factor with time. Title: Long-Term Variation of Magnetic and Chromospheric Flux on κ Ceti Authors: Saar, S. H.; Baliunas, S. L. Bibcode: 1990BAAS...22.1200S Altcode: No abstract at ADS Title: Long- and short-timescale variability of magnetic activity on the BY Dra star BD + 26°730 Authors: Saar, S. H.; Golub, L.; Bopp, B.; Herbst, W.; Huovelin, J. Bibcode: 1990ESASP.310..431S Altcode: 1990eaia.conf..431S No abstract at ADS Title: Physical parameters for three chromospherically active binaries. Authors: Saar, S. H.; Nordstrom, B.; Andersen, J. Bibcode: 1990A&A...235..291S Altcode: High-resolution spectroscopy, photoelectric radial-velocity observations, and uvby photometry are reported for three southern late-type binaries. Data obtained at ESO during 1988 and 1989 are combined with previously published results in extensive tables and graphs and analyzed in detail. HD 57853 is found to be at least a triple system with period 122.2 d and components of strongly differing luminosity; the primary component rotates rapidly (v sin i = 22 km/sec) and has an age of about 80 Myr. HD 114630 comprises two components of equal mass (at least 1.07 solar mass) and luminosity, with orbital inclination about 90 deg, period 4.23 d, rotation v sin i = about 17 km/sec, and age about 2 Gyr. HD 119285 has rotational period 12.031 d, with a K2IVe primary rotating at v sin i = 6.5 km/sec and a very low-mass secondary; its X-ray surface flux is estimated as 5.5 x 10 to the 6th erg/sq cm sec. Title: Results of Coordinated Multiwavelength Observations of Solar-Type Stars Authors: Huovelin, J.; Saar, S. H. Bibcode: 1990IAUS..138..443H Altcode: No abstract at ADS Title: Line Asymmetries in G and K Dwarfs - Dependence on Spectral Type and Activity Authors: Saar, Steven H.; Bruning, David H. Bibcode: 1990ASPC....9..168S Altcode: 1990csss....6..168S Observations of photospheric line asymmetries in 12 G and 11 K dwarfs, particularly the Fe I 6151.62 A line, are examined to determine the amplitudes and shapes of the bisectors. Bisector shapes are compared for magnetically inactive and active stars, and correlations between the slope and the stellar angular velocity are investigated. G stars have increasingly negative slopes with larger stellar angular velocity while K-star slopes become more positive, an effect which is shown to be consistent with recent hydrodynamical models. Title: The Wavelength Dependence of Broadband Linear Polarization in Cool Stars Authors: Saar, Steven H.; Huovelin, Juhani Bibcode: 1990ASPC....9...85S Altcode: 1990csss....6...85S A model is developed to investigate the effect of wavelength dependence of magnetically generated broadband linear polarization (BLP) in late-type stars as a function of line blanketing, observation filters, and other variables. Linear polarization is assumed to be a single 'average' line and the line opacity, magnetic area filling factor, and continuum intensity are incorporated to establish an equation for disk-generated BLP. The method is investigated by computing special models for the flare star BY Dra and the sun which are compared to previous calculations. The model is shown to agree with the calculations of BLP, and the magnetic BLP dependent on wavelengths varies significantly from the simple power law dependences on wavelength. The model sets lower limits to the area occupied by magnetic regions, and an upper limit to the expected BLP also results from the formulation. Title: Magnetic Fields on Solar-like Stars: The First Decade Authors: Saar, S. H. Bibcode: 1990IAUS..138..427S Altcode: I review progress made over the last decade in the measurement of magnetic fields on solar-like stars. I describe the evolution of magnetic analysis techniques, summarize our current understanding of stellar magnetic properties, and outline some future research directions. Title: Models of Broadband Linear Polarization in Cool Stars Authors: Huovelin, J.; Saar, S. H. Bibcode: 1990ASPC....9..174H Altcode: 1990csss....6..174H No abstract at ADS Title: Spectroscopic measurements of magnetic fields on solar-like stars : techniques and results. Authors: Saar, Steven H. Bibcode: 1990MmSAI..61..559S Altcode: This paper reviews the basic requirements for, and difficulties in, measuring magnetic fields on cool stars. The main types of the analysis methods are described, including methods that employ Fourier transforms; line profile models; the Mathys and Solanki (1989) method based on the difference between Fm and Fq (where Fm is the profile in nonmagnetic regions and Fq is the profile in magnetic regions); and the Basri and Marcy (1991) method based on the fact that, for optically thick lines, Zeeman splitting will increase a line's equivalent width of the Fq. The assumptions made in each case are examined and the results obtained are summarized. Title: Studies of Intermediate Activity M Dwarfs Authors: Saar, Steven H. Bibcode: 1990iue..prop.3754S Altcode: Recent optical spectroscopic surveys of dwarf M stars have resulted in the discovery of a number of objects with intermediate activity levels (H-alpha in weak emission). Available optical data suggest these stars have a level of chromospheric activity (and perhaps an evolutionary status) midway between active BY Dra stars and quiet dM's. These "marginal" BY Dra stars are single objects whose rotation velocities parallel their chromospheric activity, i.e., higher than those of quiet dM stars but below that of active BY Dra objects. The marginal BY Dra stars provide us with a class of objects rotating very near a "trigger velocity" (believed to be 5 km s^-1) which appears to divide active BY Dra stars from quiet dM's. As only four "marginal" BY Dra stars have been observed in the UV to date, we propose to considerably enlarge the UV database for these objects. UV data on Mg II emission fluxes and strength of transition region features such as C IV will serve to fix activity levels in the marginal objects and determine chromosphere and transition-region heating rates. Simultaneous optical magnetic field measures will be used to explore the connection between field-strength/filling-factor and atmospheric heating. Comparison of these data with published information on active and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "low" to "high" activity. Title: Rotational Enhancement of Line Asymmetries in F9-G2 Dwarfs Authors: Bruning, David H.; Saar, Steven H. Bibcode: 1990ASPC....9..165B Altcode: 1990csss....6..165B Disk integration of solar intensity profiles suggests that rotation enhances intermediate strength line asymmetries up to v sin i of about 6 km/s, after which the slope of the line bisector remains constant. Observed stellar line profiles do not show such a simple relation. Fast rotators exhibit large variations, owing presumably to stellar activity. Caution is advised with respect to the use of slow rotating or inactive star line profiles to determine the broadening of faster rotators. Title: First Evidence for Particle Beams in a Stellar Flare Authors: Saar, S. H.; Martens, P.; Huovelin, J. Bibcode: 1989BAAS...21.1192S Altcode: No abstract at ADS Title: Line Asymmetries in G and K Dwarfs Authors: Bruning, D. H.; Saar, S. H. Bibcode: 1989BAAS...21.1116B Altcode: No abstract at ADS Title: The Active Chromosphere Binary HD 17433 (VY Arietis) Authors: Bopp, Bernard W.; Saar, Steven H.; Ambruster, Carol; Feldman, Paul; Dempsey, Robert; Allen, Morgan; Barden, Samuel C. Bibcode: 1989ApJ...339.1059B Altcode: The sixth-magnitude K star HD 17433 (VY Ari) is shown to be an active-chromosphere binary with an orbital period of 13.198 days. A photometric (rotational) period of 17.4 days is indicated by the existing photometry, implying that HD 17433 is not in synchronous rotation. In the optical, H-alpha is seen in emission, with variable profile and intensity; He I lambda-5876 is present in absorption. IUE observations show chromospheric and transition-region emission lines with surface fluxes up to 200 times greater than those observed in the quiet sun. The luminosity and radius are appropriate for a subgiant, and the kinematics suggest Pleiades group membership. The presence of a lithium absorption feature indicates it may either be a young object, possibly a pre-main sequence star or an evolved spotted RS CVn system. Interpretations from the optical measurement of the magnetic field strength of HD 17433 are given. Title: Relations between the Photospheric Magnetic Field and the Emission from the Outer Atmospheres of Cool Stars. I. The Solar CA II K Line Core Emission Authors: Schrijver, C. J.; Cote, J.; Zwaan, C.; Saar, S. H. Bibcode: 1989ApJ...337..964S Altcode: Observations of a solar active region complex and its surroundings are used to establish a quantitative relation between the Ca II K line core intensity and magnetic flux density. The Ca II K line core intensity is transformed to a Ca II H + K line core flux density to facilitate a comparison of solar and stellar data. A new absolute calibration for the Mount Wilson Ca II H + K fluxes for G-type dwarfs is derived. The minimum Ca II K flux, found in the centers of supergranulation cells in quiet regions on the sun, is identical to the minimum flux that is observed for solar-type stars. An expression is presented for the nonlinear trend between the Ca II H + K line core excess flux density and the absolute value of the magnetic flux density. Models that explain the nonlinearity of the mean trend and the large intrinsic scatter about it are discussed. The solar data define a relation that is similar to the relation between stellar hemisphere-average magnetic flux densities and Ca II H + K excess flux densities. Title: Line Asymmetries in Late-Type Dwarf Photospheres Authors: Bruning, D. H.; Saar, S. H. Bibcode: 1989ASIC..263..145B Altcode: 1989ssg..conf..145B No abstract at ADS Title: IUE Emission Line and Magnetic Field Variability of the Sub Giant K Star HD 17433 Authors: Ambruster, C. W.; Saar, S. Bibcode: 1988BAAS...20..995A Altcode: No abstract at ADS Title: Correlations Between He I D3 and Rotation for G and K Dwarfs Authors: Saar, S. H.; Huovelin, J.; Shcherbakov, A. I.; Gustafsson, B.; Andersen, J. Bibcode: 1988BAAS...20..997S Altcode: No abstract at ADS Title: C IV fluxes from the Sun as a star, and the correlation with magnetic flux Authors: Schrijver, C. J.; Linsky, J. L.; Bennett, J.; Brown, A.; Saar, S. H. Bibcode: 1988jila.reptR....S Altcode: A total of 144 C IV wavelength 1548 Solar Maximum Mission (SMM)-UVSP spectroheliograms of solar plages were analyzed, some of which are series of exposures of the same region on the same day. Also analyzed were the C IV wavelength 1551 rasters of plages and C IV wavelength 1548 rasters of the quiet sun. The sample contained data on 17 different plages, observed on 50 different days. The center-to-limb variations of the active regions show that the optical thickness effects in the C IV wavelength 1548 line can be neglected in the conversion from intensity to flux density. As expected for the nearly optically thin situation, the C IV wavelength 1548 line is twice as bright as the C IV 1551 line. The average C IV wavelength 1548 flux density for a quiet region is 2700 ergs/cm/s and, with surprisingly little scatter, 18,000 erg/cm/s for plages. The intensity histograms of rasters obtained at disk center can be separated into characteristic plage and quiet sun contributions with variable relative filling factors. The relationship between the C IV and magnetic flux densities for spatially resolved data is inferred to be almost the same, with only an additional factor of order unity in the constant of proportionality. Title: C 4 fluxes from the sun as a star and the correlation with magnetic flux Authors: Schrijver, C. J.; Linsky, J. L.; Bennett, J.; Brown, A.; Saar, S. H. Bibcode: 1988jila.reptQ....S Altcode: A total of 144 C 4 wavelength 1548 SMM-UVSP spectroheliograms of solar plages were analyzed, some of which are series of exposures of the same region on the same day. Also analyzed were C 4 wavelength 1551 rasters of plages and C 4 1548 rasters of the quiet sun. The sample contains data on 17 different plages, observed on 50 different days. The center-to-limb variations of the active regions show that the optical thickness effects in the C 4 wavelength 1548 line can be neglected in the conversion from intensity to flux density. As expected for the nearly optically thin situation, the C 4 1548 line is twice as bright as the C 4 wavelength 1551 line. The average C 4 wavelength 1548 flux density for a quiet is 2700 erg/cm/s and, with surprisingly little scatter, 18,000 erg/cm/s for plages. The intensity histograms of rasters obtained at disk centers can be separated into characteristic plage and quiet-sun contributions with variable relative filling factors. The disk-averaged flux density in the C 4 doublet and the disk-averaged magnitude of the magnetic flux density are related. The relationship between the C 4 and magnetic flux densities for spatially resolved data is inferred to be almost the same, with only an additional factor of order unity in the constant of proportionality. Title: Relations between Broad-Band Linear Polarization and CA II H and K Emission in Late-Type Dwarf Stars Authors: Huovelin, Juhani; Saar, Steven H.; Tuominen, Ilkka Bibcode: 1988ApJ...329..882H Altcode: The authors compare broad-band UBV linear polarization observations of a sample of late-type (F5 - K5) dwarfs with contemporaneous measurements of Ca II H and K line core emission. Various parameters representing the degree of polarization are studied in relation to chromospheric activity. A weighted average of the largest values of the polarization degree appears to be the best parameter for activity diagnostics. The authors suggest stellar magnetic fields and the resulting saturation in the Zeeman-sensitive absorption lines to be the most probable source of linear polarization in late-type main-sequence stars, consistent with the weak trend found with Ca II flux and with inverse Rossby number. The analysis of short term variability in nearly simultaneous polarimetric and Ca-emission observations of ξ Boo A and HD 206860 suggests at least three active areas on both stars. Title: Spectral Line Asymmetries in Late-type Dwarf Photospheres Authors: Bruning, D. H.; Saar, S. H. Bibcode: 1988BAAS...20..696B Altcode: No abstract at ADS Title: Measurements of Magnetic Fields on Cool Stars Authors: Saar, S. H. Bibcode: 1988IAUS..132..295S Altcode: The author discusses some of the techniques used (and problems involved) in measuring stellar magnetic fields on cool stars, and details how these measurements are broadening our understanding of stellar magnetic activity. Title: Improved Methods for the Measurement and Analysis of Stellar Magnetic Fields Authors: Saar, Steven H. Bibcode: 1988ApJ...324..441S Altcode: The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent. Title: The Magnetic Fields on Cool Stars and Their Correlation with Chromospheric and Coronal Emission Authors: Saar, S. H. Bibcode: 1988ASIC..249..139S Altcode: 1988htpa.conf..139S No abstract at ADS Title: Multiwavelength observations of magnetic fields and related activity on Xi Bootis A. Authors: Saar, S. H.; Huovelin, J.; Giampapa, M. S.; Linsky, J. L.; Jordan, C. Bibcode: 1988ASSL..143...45S Altcode: 1988acse.conf...45S The authors present preliminary results of coordinated observations of magnetic fields and related activity on the active dwarf, ξ Boo A. Combining the magnetic fluxes with the linear polarization data, a simple map of the stellar active regions has been constructed. Title: Temporal Variability of Magnetic Structures on BD +26 730 Authors: Saar, Steven H. Bibcode: 1988iue..prop.3175S Altcode: BD +26 730 is perhaps the most magnetically active K dwarf known, a rapidly rotating (P = 1.8 day) flare star with enormous chromospheric and transition-region line emission, highly variable X-ray flux, and large starspots with a known 60 year activity cycle period. Since the star is viewed nearly pole-on, almost all variability will be the result of the evolution of activity in time, rather than rotational modulation. Direct measurement of the magnetic field strength and fractional surface coverage of plages on the star is also possible through the careful analysis of magnetic line broadening. We propose to observe the star, now approaching starspot (and magnetic activity) maximum, with the IUE at multiple phases in order to study the time-variability of the chromospheric and transition-region activity. Simultaneous measurements of photometric colors, linear polarization, and magnetic line broadening will be combined with the IUE data to study the growth and decay of active regions, and explore the connections between photospheric magnetic fields, and the structure and energy balance of the hot, upper-atmospheric layers of the star. Comparison of the UV fluxes with earlier epoch IUE spectra taken near activity minimum will allow us to investigate differences in stellar activity at extremes in the magnetic cycle of the star. Our study will be the first investigation of strictly temporal evolution of magnetic fields and related activity on any star other than the Sun. Title: Comparison of Predicted vs. Measured Stellar Magnetic Fields Authors: Quillen, A.; Golub, L.; Harnden, F. R., Jr.; Saar, S. Bibcode: 1987BAAS...19.1027Q Altcode: No abstract at ADS Title: HD 1743 (VY Ari): A Young Chromospherically Active Binary Authors: Bopp, B. W.; Saar, S.; Feldman, P. A.; Dempsey, R.; Allen, M.; Ambruster, C.; Barden, S. P. Bibcode: 1987BAAS...19..709B Altcode: No abstract at ADS Title: The Spatial Distribution of Magnetic Fields on Xi Bootis A Authors: Saar, S. H.; Huovelin, J.; Giampapa, M. S. Bibcode: 1987BAAS...19..703S Altcode: No abstract at ADS Title: 4 meter FTS observations of photospheric magnetic fields on M dwarfs. Authors: Saar, Steven H.; Linsky, Jeffrey L.; Giampapa, Mark S. Bibcode: 1987LIACo..27..103S Altcode: 1987oahp.proc..103S Much of the observed activity on M dwarfs (e.g., spots, flares, chromospheric and coronal emission) has been attributed to the interaction of magnetic fields with the stellar atmosphere. Since data on the magnetic field parameters of M dwarfs can potentially reveal much about the physical mechanisms behind these phenomena and, additionally, about stellar dynamos and the evolution of stellar angular momentum, the authors have begun a program to measure the mean magnetic field strength in stellar active regions, and the surface filling factor of these regions for a sample of M dwarfs. In this paper some preliminary results of this survey are discussed. Title: The Photospheric Magnetic Fields of Cool Stars: Recent Results of Survey and Time-Variability Programs (Invited review) Authors: Saar, Steven H. Bibcode: 1987LNP...291...10S Altcode: 1987csss....5...10S; 1987LNP87.291...10S The past decade has seen considerable advances in our ability to measure magnetic fields on cool stars. New observational and analytical techniques have been employed, producing a considerable body of data on the mean magnetic field strength in stellar active regions (B) and the fraction (filling factor = f) of the stellar surface covered by these fields (f) for G, K, and M dwarfs. I focus on some of the recent results of observational programs aimed at surveying magnetic parameters on a broad range of stars and studying the time-variability of B and f. Title: Empirical Relations Between Magnetic Fluxes and Atmospheric Radiative Losses for Cool Dwarf Stars Authors: Saar, Steven H.; Schrijver, C. J. Bibcode: 1987LNP...291...38S Altcode: 1987csss....5...38S We derive and discuss relations between magnetic, X-ray, and Ca II H+K flux densities for a sample of G, K, and M dwarfs. Title: Observations and Analysis of the Photospheric Magnetic Fields on Dwarf g, K and M Stars. Authors: Saar, Steven Herbert Bibcode: 1987PhDT.........3S Altcode: 1987DiAbI..48.1385S I have developed an improved technique for the analysis of magnetic broadening in stellar absorption line profiles. Unlike previous methods, the new technique is based on a model that includes radiative transfer effects and the full Zeeman patterns. The effects of weak blends on the profiles can be reduced by comparing identical lines in two stars of the same spectral type, one of which is chromospheric inactive. After adjusting for differences in line strength and doppler broadening, the difference profile can be modeled to determine both the fraction of the stellar surface covered by magnetic regions (f) and the mean field strength in these regions (B). Accuracies of about 20% in B and f are possible. I find that previous Zeeman analysis methods systematically overestimate f, especially for cooler stars, due to their neglect of line saturation and blends. I have applied the new technique to two sets of high resolution, low noise spectra. The first set consists of 29 stars, spanning spectral types from GO to M4.5 and a broad range of rotational rates and ages. I have made the first ever detection of photospheric magnetic fields on a BY Draconis variable (EQ Vir) and a dMe flare star (AD Leo). Several major trends are apparent from the results. The stellar magnetic field strength is in pressure equilibrium with the photospheric gas pressure and is thus a function of spectral type. The filling factor, f is a linear function of angular velocity. The total magnetic flux on a star is thus a function of the star's rotation rate, in agreement with simple dynamo theories. A constant B and an f value decreasing with time explains the observed decline in stellar rotational velocities and activity levels with age. There is no correlation between f and B, or between B and rotation. Contrary to some theoretical models, I find dM stars have little magnetic flux. The highest filling factors are found on flare stars. I have also used the new technique to study the spatial and temporal behavior of f and B on the active star Epsilon Eri. Eleven observations were made over two months with contemporaneous measurements of the chromospheric Ca II emission flux. I find no correlation between B and phase or Ca II flux. The filling factor, however, shows a weak phase dependence and is linearly proportional to the Ca II emission, consistent with many interpretations of the solar data. Title: Measurements of Stellar Magnetic Fields: Empirical Constraints on Stellar Dynamo and Rotational Evolution Theories Authors: Linsky, Jeffrey L.; Saar, Steven H. Bibcode: 1987LNP...291...44L Altcode: 1987LNP87.291...44L; 1987csss....5...44L We explore the implications of empirical stellar magnetic parameters for dynamo theories, stellar activity theories, and models of the evolution of stellar angular momentum. Title: Broadband Linear Polarization and Chromospheric Ca II H and K Emission in Late-Type Main Sequence Stars Authors: Huovelin, J.; Saar, Steven H.; Tuominen, I.; Linnaluoto, S.; Virtanen, H. Bibcode: 1987LNP...291...41H Altcode: 1987LNP87.291...41H; 1987csss....5...41H We discuss correlations between broadband linear polarization, intrinsic stellar parameters, and Ca 11 H+K emission in G and K dwarfs. 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: 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: A Detailed Study of Photospheric Magnetic Fields on Late-type Dwarfs Authors: Saar, S. H. Bibcode: 1986BAAS...18R.961S Altcode: No abstract at ADS Title: The Magnetic Field of the BY Draconis Flare Star EQ Virginis Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M. Bibcode: 1986ApJ...302..777S Altcode: High resolution, high S/N-ratio line profiles of the BY Draconis-type flare star EQ Vir obtained with the MMT are presently subjected to a novel Zeeman analysis procedure which includes radiative transfer effects and compensation for blends. A mean field of 2500 + or - 300 G covering 80 + or 15 percent of EQ Vir is determined. This constitutes the first positive detection of a magnetic field in a BY Draconis-type flare star, confirming that magnetic fields are present on these stars. The value of 2500 G obtained for the photospheric field strength is similar to the value derived by assuming equipartition of magnetic and thermal energy densities in the photosphere and scaling from the solar network fields, suggesting that equipartition may determine the mean field strength in the nonspotted portion of the flare star photosphere. Title: The Surface Magnetic Fields of dM and dMe Stars Authors: Saar, S. H.; Linsky, J. L.; Giampapa, M. S. Bibcode: 1986BAAS...18..670S Altcode: No abstract at ADS Title: New measurements of photospheric magnetic fields in late-type stars and emerging trends Authors: Saar, S. H.; Linsky, J. L. Bibcode: 1986AdSpR...6h.235S Altcode: 1986AdSpR...6..235S We report on recent results of our program to measure photospheric magnetic field strengths and filling factors from the analysis of unpolarized high spectral resolution and S/N line profiles. We have analyzed spectra obtained with the KPNO 4-m FTS, the MMT, and the McMath Reticon Spectrograph. With the latter instrument we now have an extensive data set through our synoptic and survey observing programs. Photospheric magnetic field parameters are obtained by comparison of observed and theoretical line profiles using an LTE code that includes line saturation and the full Zeeman pattern. We determine the nonmagnetic line broadening parameters for a star by fitting profiles of low Landé g lines formed under conditions similar to the high g lines which are used to infer magnetic fields. The effects of line blending are cancelled to first order by fitting profiles of the same high g lines in comparison inactive stars of the same spectral type. We have measured field parameters (outside of starspots) in dwarf stars of spectral type GO to dM3.5e (Ad Leo). We find a trend of increasing field strength with later spectral type, consistent with equal gas and magnetic pressure in the photosphere, and a trend of increasing filling factor with activity. Our data are inconsistent with the hypothesis of a constant number of magnetic flux tubes on active stars.

Staff Member, Quantum Physics Division, National Bureau of Standards. Title: The Time Variability of Magnetic Fields on Epsilon Eridani Authors: Saar, Steven H.; Linsky, Jeffrey L.; Duncan, Douglas K. Bibcode: 1986LNP...254..275S Altcode: 1986csss....4..275S No abstract at ADS Title: The Detection of Magnetic Fields on Late Type Stars - Progress Problems and Future Needs Authors: Saar, S. H. Bibcode: 1986tswo.work...44S Altcode: No abstract at ADS Title: Further Observations of Magnetic Fields on Active Dwarf Stars Authors: Saar, Steven H.; Linsky, Jeffrev L. Bibcode: 1986LNP...254..278S Altcode: 1986csss....4..278S No abstract at ADS Title: The photospheric magnetic field of the dM3.5e flare star AD Leonis. Authors: Saar, S. H.; Linsky, J. L. Bibcode: 1985ApJ...299L..47S Altcode: A high-resolution infrared spectrum of the dM3.5e flare star AD Leo, obtained with the Kitt Peak 4 m Fourier Transform Spectrometer, clearly shows the presence of strong magnetic fields. Five absorption lines in the 4400-4600 per cm region have been modeled, and it is inferred that 73 percent + or - 6 percent of the surface of AD Leo is covered by active regions outside of dark spots containing a mean field strength of 3800 + or - 260 G. If these active regions are brighter than the quiet photosphere, the surface filling factor will be somewhat smaller. Since simultaneous H-alpha observations exhibited no evidence of flares, the observations probably represent the quiescent magnetic flux level. The inferred field strength is consistent with equipartition of magnetic and thermal pressures in the photosphere and is similar to values derived using the scaling laws of Golub. The large observed filling factor is consistent with efficient dynamo generation of magnetic flux in this rapidly rotating star. Title: An extensive survey of photospheric magnetic fields in G and K dwarfs. Authors: Saar, S. H.; Linsky, J. L. Bibcode: 1985BAAS...17..879S Altcode: No abstract at ADS Title: An Extensive Survey of Photospheric Magnetic Fields in G and K Dwarfs Authors: Saar, S. H.; Linsky, J. L. Bibcode: 1985BAAS...17..751S Altcode: No abstract at ADS Title: First Measurement of Magnetic Fields on a BY Draconis Flare Star: EQ Virginis Authors: Saar, S. H.; Linsky, J. L.; Beckers, J. M. Bibcode: 1984BAAS...16Q.517S Altcode: 1984BAAS...16..517S No abstract at ADS Title: A search for diffuse band profile variations in the rho OPH cloud. Authors: Snow, T. P.; Timothy, J. G.; Saar, S. Bibcode: 1982ApJ...262..611S Altcode: (Previously announced in STAR as N82-30203) Title: The Profile of the λ4430 Diffuse Interstellar Band, Observed with the MAMA Detector Authors: Snow, T. P.; Timothy, J. G.; Saar, S. Bibcode: 1981BAAS...13..825S Altcode: No abstract at ADS