Author name code: testa ADS astronomy entries on 2022-09-14 author:"Testa, Paola" ------------------------------------------------------------------------ Title: NExtUP: The Normal-incidence Extreme Ultraviolet Photometer Authors: Garraffo, Cecilia; Jeremy, Drake; Testa, Paola; Gladstone, Randy; Cheimets, . Peter; Koskinen, Tommi; Wolk, Scott; Barstow, Martin; Glocer, Alex; France, Kevin; Mason, James; Siegmund, Oswald; Alvarado Gómez, Julián David; Cohen, Ofer; Kashyap, Vinay; Fleming, Brian; Wargelin, Bradford; Gronoff, Guillaume; Cadwell, David; Monsch, Kristina; Youngblood, Allison; Norton, Timothy; Lopez-Morales, Mercedes; Soufli, Regina Bibcode: 2022cosp...44.1995G Altcode: The evolution and loss of exoplanetary atmospheres depend critically on the host stars' extreme ultraviolet (EUV) spectra and fluxes. EUV radiation is absorbed at high altitude, in the exosphere and upper thermosphere, where the gas can be readily heated to high temperatures conducive to escape. EUV heating is thought to be a dominant atmospheric loss mechanism during most of a planet's life. There are only a handful of accurately measured EUV stellar fluxes, all dating from Extreme Ultraviolet Explorer (EUVE) observations in the '90s. These observations were mostly single snapshots of what are highly variable and often flaring sources. Consequently, current models of stellar EUV emission are uncertain by more than an order of magnitude and are the largest uncertainty in planetary atmospheric loss models. The Normal-incidence Extreme Ultraviolet Photometer (NExtUP) is a smallsat mission concept designed to measure the EUV radiation conditions of exoplanet host stars, and F-M type stars in general. NExtUP will use periodic and aperiodic multilayers on off-axis parabolic mirrors and a prime focus microchannel plate detector to image stars in 5 bandpasses between 150 and 900 A, down to flux limits two orders of magnitude lower than reached by EUVE. NExtUP may also accomplish a compelling array of secondary science goals, including using line-of-sight absorption measurements to understand the structure of the local interstellar medium, and imaging EUV emission from energetic processes on solar system objects at unprecedented spatial resolution. NExtUP is well within smallsat weight limits, requires no special orbital conditions, and would be flown on a spacecraft supplied by MOOG Industries. It draws on decades of mission heritage expertise at SAO and LASP, including similar instruments successfully launched and operated to observe the Sun. Title: Diagnostics of non-Maxwellian electron distributions in solar active regions from Fe XII lines observed by Hinode/EIS and IRIS Authors: Del Zanna, G.; Polito, V.; Dudík, J.; Testa, P.; Mason, H. E.; Dzifčáková, E. Bibcode: 2022arXiv220707026D Altcode: We present joint Hinode/EIS and IRIS observations of Fe XII lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 A / 1349 A observed ratio is consistent with the values predicted by CHIANTI and the coronal approximation in quiescent areas, but not in all active region observations, where the ratio is often lower than expected by up to a factor of about two. We investigate a number of physical mechanisms that could affect this ratio, such as opacity and absorption from cooler material. We find significant opacity in the EIS Fe XII 193 and 195 A lines, but not in the 192.4 A line, in agreement with previous findings. As we cannot rule out possible EUV absorption by H, He and He II in the on-disk observations, we focus on an off-limb observation where such absorption is minimal. After considering these, as well as possible non-equilibrium effects, we suggest that the most likely explanation for the observed low Fe XII 192.4 A / 1349 A ratio is the presence of non-Maxwellian electron distributions in the active regions. This is in agreement with previous findings based on EIS and IRIS observations independently. Title: Parallel Plasma Loops and the Energization of the Solar Corona Authors: Peter, Hardi; Chitta, Lakshmi Pradeep; Chen, Feng; Pontin, David I.; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.; Testa, Paola; Tiwari, Sanjiv K.; Walsh, Robert W.; Warren, Harry P. Bibcode: 2022ApJ...933..153P Altcode: 2022arXiv220515919P The outer atmosphere of the Sun is composed of plasma heated to temperatures well in excess of the visible surface. We investigate short cool and warm (<1 MK) loops seen in the core of an active region to address the role of field-line braiding in energizing these structures. We report observations from the High-resolution Coronal imager (Hi-C) that have been acquired in a coordinated campaign with the Interface Region Imaging Spectrograph (IRIS). In the core of the active region, the 172 Å band of Hi-C and the 1400 Å channel of IRIS show plasma loops at different temperatures that run in parallel. There is a small but detectable spatial offset of less than 1″ between the loops seen in the two bands. Most importantly, we do not see observational signatures that these loops might be twisted around each other. Considering the scenario of magnetic braiding, our observations of parallel loops imply that the stresses put into the magnetic field have to relax while the braiding is applied: the magnetic field never reaches a highly braided state on these length scales comparable to the separation of the loops. This supports recent numerical 3D models of loop braiding in which the effective dissipation is sufficiently large that it keeps the magnetic field from getting highly twisted within a loop. Title: The Solar X-ray Corona Authors: Testa, Paola; Reale, Fabio Bibcode: 2022arXiv220603530T Altcode: The X-ray emission from the Sun reveals a very dynamic hot atmosphere, the corona, which is characterized by a complex morphology and broad range of timescales of variability and spatial structuring. The solar magnetic fields play a fundamental role in the heating and structuring of the solar corona. Increasingly higher quality X-ray solar observations with high spatial (down to subarcsec) and temporal resolution provide fundamental information to refine our understanding of the solar magnetic activity and of the underlying physical processes leading to the heating of the solar outer atmosphere. Here we provide a brief historical overview of X-ray solar observations and we summarize recent progress in our understanding of the solar corona as made possible by state-of-the-art current X-ray observations. Title: Diagnostics of Non-Maxwellian Electron Distributions in Solar Active Regions from Fe XII Lines Observed by the Hinode Extreme Ultraviolet Imaging Spectrometer and Interface Region Imaging Spectrograph Authors: Del Zanna, G.; Polito, V.; Dudík, J.; Testa, P.; Mason, H. E.; Dzifčáková, E. Bibcode: 2022ApJ...930...61D Altcode: We present joint Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) and Interface Region Imaging Spectrograph (IRIS) observations of Fe XII lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 Å/1349 Å observed ratio is consistent with the values predicted by CHIANTI and the coronal approximation in quiescent areas, but not in all active-region observations, where the ratio is often lower than expected by up to a factor of about two. We investigate a number of physical mechanisms that could affect this ratio, such as opacity and absorption from cooler material. We find significant opacity in the EIS Fe XII 193 and 195 Å lines, but not in the 192.4 Å line, in agreement with previous findings. As we cannot rule out possible EUV absorption by H, He, and He II in the on-disk observations, we focus on an off-limb observation where such absorption is minimal. After considering these, as well as possible nonequilibrium effects, we suggest that the most likely explanation for the observed low Fe XII 192.4 Å/1349 Å ratio is the presence of non-Maxwellian electron distributions in the active regions. This is in agreement with previous findings based on EIS and IRIS observations independently. Title: Chromospheric emission from nanoflare heating in RADYN simulations Authors: Bakke, H.; Carlsson, M.; Rouppe van der Voort, L.; Gudiksen, B. V.; Polito, V.; Testa, P.; De Pontieu, B. Bibcode: 2022A&A...659A.186B Altcode: 2022arXiv220111961B Context. Heating signatures from small-scale magnetic reconnection events in the solar atmosphere have proven to be difficult to detect through observations. Numerical models that reproduce flaring conditions are essential in understanding how nanoflares may act as a heating mechanism of the corona.
Aims: We study the effects of non-thermal electrons in synthetic spectra from 1D hydrodynamic RADYN simulations of nanoflare heated loops to investigate the diagnostic potential of chromospheric emission from small-scale events.
Methods: The Mg II h and k, Ca II H and K, Ca II 854.2 nm, and Hα and Hβ chromospheric lines were synthesised from various RADYN models of coronal loops subject to electron beams of nanoflare energies. The contribution function to the line intensity was computed to better understand how the atmospheric response to the non-thermal electrons affects the formation of spectral lines and the detailed shape of their spectral profiles.
Results: The spectral line signatures arising from the electron beams highly depend on the density of the loop and the lower cutoff energy of the electrons. Low-energy (5 keV) electrons deposit their energy in the corona and transition region, producing strong plasma flows that cause both redshifts and blueshifts of the chromospheric spectra. Higher-energy (10 and 15 keV) electrons deposit their energy in the lower transition region and chromosphere, resulting in increased emission from local heating. Our results indicate that effects from small-scale events can be observed with ground-based telescopes, expanding the list of possible diagnostics for the presence and properties of nanoflares. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE). II. Flares and Eruptions Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola; De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito, Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin, Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul; Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub, Leon; The Bibcode: 2022ApJ...926...53C Altcode: 2021arXiv210615591C Current state-of-the-art spectrographs cannot resolve the fundamental spatial (subarcseconds) and temporal (less than a few tens of seconds) scales of the coronal dynamics of solar flares and eruptive phenomena. The highest-resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by the Interface Region Imaging Spectrograph for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), subarcsecond-resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al., which focuses on investigating coronal heating with MUSE. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE). I. Coronal Heating Authors: De Pontieu, Bart; Testa, Paola; Martínez-Sykora, Juan; Antolin, Patrick; Karampelas, Konstantinos; Hansteen, Viggo; Rempel, Matthias; Cheung, Mark C. M.; Reale, Fabio; Danilovic, Sanja; Pagano, Paolo; Polito, Vanessa; De Moortel, Ineke; Nóbrega-Siverio, Daniel; Van Doorsselaere, Tom; Petralia, Antonino; Asgari-Targhi, Mahboubeh; Boerner, Paul; Carlsson, Mats; Chintzoglou, Georgios; Daw, Adrian; DeLuca, Edward; Golub, Leon; Matsumoto, Takuma; Ugarte-Urra, Ignacio; McIntosh, Scott W.; the MUSE Team Bibcode: 2022ApJ...926...52D Altcode: 2021arXiv210615584D The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of a multislit extreme ultraviolet (EUV) spectrograph (in three spectral bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in two passbands around 195 Å and 304 Å). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (≤0.″5) and temporal resolution (down to ~0.5 s for sit-and-stare observations), thanks to its innovative multislit design. By obtaining spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX-Fe XXI 108 Å) covering a wide range of transition regions and coronal temperatures along 37 slits simultaneously, MUSE will, for the first time, "freeze" (at a cadence as short as 10 s) with a spectroscopic raster the evolution of the dynamic coronal plasma over a wide range of scales: from the spatial scales on which energy is released (≤0.″5) to the large-scale (~170″ × 170″) atmospheric response. We use numerical modeling to showcase how MUSE will constrain the properties of the solar atmosphere on spatiotemporal scales (≤0.″5, ≤20 s) and the large field of view on which state-of-the-art models of the physical processes that drive coronal heating, flares, and coronal mass ejections (CMEs) make distinguishing and testable predictions. We describe the synergy between MUSE, the single-slit, high-resolution Solar-C EUVST spectrograph, and ground-based observatories (DKIST and others), and the critical role MUSE plays because of the multiscale nature of the physical processes involved. In this first paper, we focus on coronal heating mechanisms. An accompanying paper focuses on flares and CMEs. Title: Observations of the solar atmosphere - constraints on models, and understanding of the underlying physical processes Authors: Testa, Paola Bibcode: 2021AGUFMSH42B..01T Altcode: I will discuss how high resolution current (and future) oberservations of the solar atmosphere (e.g., with SDO, Hinode, SST, IRIS, PSP), help us advance our understanding of the complex physical processing underlying the observed phenomena. In particular I will discuss the crucial role of the synergy between observations and state-of-the-art models. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE): II. Flares and Eruptions Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola; De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito, Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin, Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah; Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon Bibcode: 2021AGUFMSH51A..08C Altcode: Current state-of-the-art spectrographs cannot resolve the fundamental spatial (sub-arcseconds) and temporal scales (less than a few tens of seconds) of the coronal dynamics of solar flares and eruptive phenomena. The highest resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by IRIS for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), sub-arcsecond resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics, and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al. (2021, also submitted to SH-17), which focuses on investigating coronal heating with MUSE. Title: Preliminary Results from the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) Authors: Winebarger, Amy; Savage, Sabrina; Kobayashi, Ken; Champey, Patrick; Golub, Leon; Walsh, Robert; Athiray, P. S.; Bradshaw, Stephen; Cheimets, Peter; Cirtain, Jonathan; DeLuca, Edward; Del Zanna, Giulio; Mason, Helen; McKenzie, David; Ramsey, Brian; Reeves, Katharine; Testa, Paola; Vigil, Genevieve; Warren, Harry Bibcode: 2021AGUFMSH51A..06W Altcode: Coronal heating mechanisms are notoriously difficult to constrain with current observations. We present new observations from an instrument designed to measure a critical diagnostic of the frequency heating events in active regions. The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket mission that aims to observe the soft x-ray solar spectrum (0.6 2.5 nm) with both spatial and spectral resolution. This wavelength range has several high temperature and abundance diagnostics that can be used to infer the coronal heating frequency. MaGIXS will observe the Sun through a 12 x 33 slot, producing ``overlappograms, where the spatial and spectral information are overlapped and must be unfolded. In this presentation, I will report on the MaGIXS launch and data collection and provide preliminary analysis of MaGIXS observations. Title: Probing the physics of coronal heating with the Multi-slit Solar Explorer (MUSE) Authors: De Pontieu, Bart; Testa, Paola; Martinez-Sykora, Juan; Cheung, Chun Ming Mark Bibcode: 2021AGUFMSH55B1836D Altcode: The Multi-slit Solar Explorer (MUSE) is a proposed NASA MIDEX mission, currently in Phase A, composed of a multi-slit EUV spectrograph (in three narrow spectral bands centered around 171Å, 284Å, and 108Å) and an EUV context imager (in two narrow passbands around 195Å and 304Å). MUSE will provide unprecedented spectral and imaging diagnostics of the solar corona at high spatial (~0.5 arcseconds), and temporal resolution (down to ~0.5 seconds) thanks to its innovative multi-slit design. By obtaining spectra in 4 bright EUV lines (Fe IX 171Å, Fe XV 284Å, Fe XIX-XXI 108Å) covering a wide range of transition region and coronal temperatures along 37 slits simultaneously, MUSE will for the first time be able to ``freeze" (at a cadence as short as 10 seconds) with a spectroscopic raster the evolution of the dynamic coronal plasma over a wide range of scales: from the spatial scales on which energy is released (<0.5 arcsec) to the large-scale often active-region size (~ 170 arcsec x 170 arcsec) atmospheric response. We use advanced numerical modeling to showcase how MUSE will constrain the properties of the solar atmosphere on the spatio-temporal scales (<0.5 arcsec, <20 seconds) and large field-of-view on which various state-of-the-art models of the physical processes that drive coronal heating, solar flares and coronal mass ejections (CMEs) make distinguishing and testable predictions. We describe how the synergy between MUSE, the single-slit, high-resolution Solar-C EUVST spectrograph, and ground-based observatories (DKIST and others) can address how the solar atmosphere is energized, and the critical role MUSE plays because of the multi-scale nature of the physical processes involved. We focus on how comparisons between MUSE observations and theoretical models will significantly further our understanding of coronal heating mechanisms. This is a companion paper to Cheung et al. (2021), also submitted to SH-17. Title: NExtUP: the Normal-incidence Extreme Ultraviolet Photometer Authors: Drake, Jeremy J.; Cheimets, Peter; Garraffo, Cecilia; Wargelin, Bradford; Youngblood, Allison; Kashyap, Vinay L.; Testa, Paola; Caldwell, David; Mason, James; Fleming, Brian; France, Kevin; Wolk, Scott; Siegmund, Oswald; Koskinen, Tommi; Alvarado-Gomez, Julian; Lopez-Morales, Maria Mercedes; Gronoff, Guillaume; Bookbinder, Jay; Barstow, Martin; Windt, David; Gladstone, Randy; Loghry, Christopher; Yarbrough, Rix Bibcode: 2021SPIE11821E..08D Altcode: The Normal-incidence Extreme Ultraviolet Photometer (NExtUP) is a smallsat mission concept designed to measure the EUV radiation conditions of exoplanet host stars, and F-M type stars in general. EUV radiation is absorbed at high altitude in a planetary atmosphere, in the exosphere and upper thermosphere, where the gas can be readily heated to escape temperatures. EUV heating and ionization are the dominant atmospheric loss drivers during most of a planet's life. There are only a handful of accurately measured EUV stellar fluxes, all dating from Extreme Ultraviolet Explorer (EUVE) observations in the `90s. Consequently, current models of stellar EUV emission are uncertain by more than an order of magnitude and dominate uncertainties in planetary atmospheric loss models. NExtUP will use periodic and aperiodic multilayers on off-axis parabolic mirrors and a prime focus microchannel plate detector to image stars in 5 bandpasses between 150 and 900°A down to flux limits two orders of magnitude lower than reached by EUVE. NExtUP may also accomplish a compelling array of secondary science goals, including using line-of-sight absorption measurements to understand the structure of the local interstellar medium, and imaging EUV emission from energetic processes on solar system objects at unprecedented spatial resolution. NExtUP is well within smallsat weight limits, requires no special orbital conditions, and would be flown on a spacecraft supplied by MOOG Industries. It draws on decades of mission heritage expertise at SAO and LASP, including similar instruments successfully launched and operated to observe the Sun. Title: In the Trenches of the Solar-stellar Connection. IV. Solar Full-disk Scans of C II, Si IV, and Mg II by the Interface Region Imaging Spectrograph Authors: Ayres, Thomas; De Pontieu, Bart; Testa, Paola Bibcode: 2021ApJ...916...36A Altcode: About once a month, the Interface Region Imaging Spectrograph conducts day-long raster scans of the full Sun in three ultraviolet spectral channels. These full-disk mosaics are valuable in the solar context, but provide a unique connection to the distant, unresolved stars. Here, 10 deep-exposure scans (4-8 s per slit step), collected during the peak and decline of sunspot Cycle 24, were analyzed. Spatial spectra (2″ pixels) of resonance lines of C II (T ~ 104 K), Si IV (8 × 104 K), and Mg II (8 × 103 K) were fitted with a pseudo-Gaussian model to track the emission strengths, widths, and shifts in the various surface features that comprise the quiet Sun and active regions. The full-disk mosaic spectra compare well to tracings of solar-twin α Centauri A (HD 128620; G2 V). The contrast between disk-average spectra from cycles MIN and MAX is relatively modest (~50% in Si IV), but, remarkably, the brightest solar pixels in active regions, at 2″ resolution, exceed the global-average intensities of the most active Sun-like stars, suggesting a deeper solar-stellar connection. Si IV shows a conspicuous bright ring at the limb, whereas optically thicker C II and Mg II are suppressed (more so for the latter). The Si IV emission favors the bright knots of the large-scale supergranulation network, while the cooler Mg II emission is more ubiquitous and C II intermediate. The non-Gaussian profile of full-disk C IV, similar in formation temperature to Si IV, was previously interpreted as a combination of narrow and broad dynamical components, but the prevalence of the characteristic line shape in the finest resolution spatial pixels of Si IV here provides support for alternative formation scenarios, for example, invoking κ-distributions. Title: A New View of the Solar Interface Region from the Interface Region Imaging Spectrograph (IRIS) Authors: De Pontieu, Bart; Polito, Vanessa; Hansteen, Viggo; Testa, Paola; Reeves, Katharine K.; Antolin, Patrick; Nóbrega-Siverio, Daniel Elias; Kowalski, Adam F.; Martinez-Sykora, Juan; Carlsson, Mats; McIntosh, Scott W.; Liu, Wei; Daw, Adrian; Kankelborg, Charles C. Bibcode: 2021SoPh..296...84D Altcode: 2021arXiv210316109D The Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. IRIS is the highest resolution observatory to provide seamless coverage of spectra and images from the photosphere into the low corona. The unique combination of near- and far-ultraviolet spectra and images at sub-arcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion-neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of waves, the acceleration of non-thermal particles, and various small-scale instabilities. IRIS has provided insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nano-flares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvénic waves, energy release and jet-like dynamics associated with braiding of magnetic-field lines, the role of turbulence and the tearing-mode instability in reconnection, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and various other mechanisms in triggering and driving CMEs. IRIS observations have also been used to elucidate the physical mechanisms driving the solar irradiance that impacts Earth's upper atmosphere, and the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine-learning techniques have played a key role. With the advent of exciting new instrumentation both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST) and the Atacama Large Millimeter/submillimeter Array (ALMA), and space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges. Title: Reconnection nanojets in the solar corona Authors: Antolin, Patrick; Pagano, Paolo; Testa, Paola; Petralia, Antonino; Reale, Fabio Bibcode: 2021NatAs...5...54A Altcode: 2020NatAs.tmp..201A; 2020NatAs.tmp..186A The solar corona is shaped and mysteriously heated to millions of degrees by the Sun's magnetic field. It has long been hypothesized that the heating results from a myriad of tiny magnetic energy outbursts called nanoflares, driven by the fundamental process of magnetic reconnection. Misaligned magnetic field lines can break and reconnect, producing nanoflares in avalanche-like processes. However, no direct and unique observations of such nanoflares exist to date, and the lack of a smoking gun has cast doubt on the possibility of solving the coronal heating problem. From coordinated multi-band high-resolution observations, we report on the discovery of very fast and bursty nanojets, the telltale signature of reconnection-based nanoflares resulting in coronal heating. Using state-of-the-art numerical simulations, we demonstrate that the nanojet is a consequence of the slingshot effect from the magnetically tensed, curved magnetic field lines reconnecting at small angles. Nanojets are therefore the key signature of reconnection-based coronal heating in action. Title: Reconnection Nanojets in the Solar Corona Authors: Antolin, Patrick; Reale, Fabio; Testa, Paola; Pagano, Paolo; Petralia, Antonino Bibcode: 2021cosp...43E1798A Altcode: The solar corona is shaped and mysteriously heated to millions of degrees by the Sun's magnetic field. It has long been hypothesised that the heating results from a myriad of tiny magnetic energy outbursts called nanoflares driven by the fundamental process of magnetic reconnection. Misaligned magnetic field lines can break and reconnect, producing nanoflares in avalanche-like processes. However, no direct and unique observations of such nanoflares exist to date, and the lack of a smoking gun has cast doubt on the possibility of solving the coronal heating problem. From coordinated multi-band high-resolution observations here we report on the discovery of very fast and bursty nanojets, the telltale signature of reconnection-based nanoflares resulting in coronal heating. Isolated and clustered nanojets are detected, and a myriad are observed in an avalanche-like progression, leading to the formation of a coronal loop. Using state-of-the-art numerical simulations we demonstrate that the nanojet is a consequence of the slingshot effect from the magnetically tensed, curved magnetic field lines reconnecting at small angles. Nanojets are therefore the key signature to look for reconnection-based coronal heating in action. Title: Publisher Correction: Reconnection nanojets in the solar corona Authors: Antolin, Patrick; Pagano, Paolo; Testa, Paola; Petralia, Antonino; Reale, Fabio Bibcode: 2021NatAs...5..103A Altcode: 2020NatAs.tmp..204A An amendment to this paper has been published and can be accessed via a link at the top of the paper. Title: High Resolution Observations of the Low Atmospheric Response to Small Heating Events in Active Regions Authors: Testa, P.; Rouppe van der Voort, L.; De Pontieu, B.; Bakke, H. Bibcode: 2020AGUFMSH004..03T Altcode: We investigate the low atmospheric response to small heating events (nano/micro-flares) by analyzing coordinated active region observations with IRIS and SST, and also using the simultaneous SDO/AIA observations to study the coronal emission. The events we observe as intense brightenings in the chromosphere and transition region are clearly associated with heating of the overlying loops to high temperatures (5-10MK), as is clear from the strong Fe XVIII emission observed in the 94A SDO/AIA passband. Some of the chromospheric brightenings have been observed with the SST with the CRISP instrument in Ca II 8542 and H-alpha, as well as with the new CHROMIS instrument in Ca II K, which provides unprecedented resolution. We will present the rich spectral diagnostics offered by IRIS and SST for these events, including insights we obtained by applying a k-means clustering analysis to the SST and IRIS spectra during the heating events. Our observations will help provide more stringent constraints on the properties of non-thermal particles in nanoflares and microflares. Title: Chromospheric and TR diagnostics in a large scale numerical simulation of flux emergence: Synthetic vs Real observables Authors: Hansteen, V. H.; De Pontieu, B.; Testa, P.; Gosic, M.; Martinez-Sykora, J. Bibcode: 2020AGUFMSH0010021H Altcode: Field stored just below or rising to the photosphere will break through the surface and enter the upper atmosphere once the gradient of the subphotospheric field strength becomes sufficiently large. Opposite polarity flux bundles will reconnect in the photosphere and above, to form steadily longer loops that expand into the outer solar atmosphere, forming the corona. Some of the emerging flux is likely due to a local dynamo, but also the direct emergence of large scale magnetic structures from below is important, even in the quiet Sun. A significant proportion of this field likely reaches the chromosphere and may leave imprint on chromospheric dynamics and energetics. Using large scale numerical models (72x72x60) Mm and the high resolution spectra and slit jaw images from IRIS, as well as photospheric data from Hinode/SOT, and SDO/HMI we study the interactions between the magnetic flux caught in the granular flow field and the chromosphere and chromospheric field above. We will compare synthetic observables of the photospheric Fe I 617.3 nm line, the chromospheric Mg II h&k lines, and the transition region Si IV lines, with their observational counterparts. We will also generate synthetic ALMA band 3 images. The comparison of synthetic observational data will let us draw conclusions as to the validity of the numerical modeling and the importance of flux emergence for the dynamics and energetics of the outer solar atmosphere. Title: IRIS Observations of the Low-atmosphere Counterparts of Active Region Outflows Authors: Polito, Vanessa; De Pontieu, Bart; Testa, Paola; Brooks, David H.; Hansteen, Viggo Bibcode: 2020ApJ...903...68P Altcode: 2020arXiv201015945P Active region (AR) outflows have been studied in detail since the launch of Hinode/EIS and are believed to provide a possible source of mass and energy to the slow solar wind. In this work, we investigate the lower atmospheric counterpart of AR outflows using observations from the Interface Region Imaging Spectrograph (IRIS). We find that the IRIS Si IV, C II> and Mg II transition region (TR) and chromospheric lines exhibit different spectral features in the outflows as compared to neighboring regions at the footpoints ("moss") of hot AR loops. The average redshift of Si IV in the outflow region (≍5.5 km s-1) is smaller than typical moss (≍12-13 km s-1) and quiet Sun (≍7.5 km s-1) values, while the C II line is blueshifted (≍-1.1-1.5 km s-1), in contrast to the moss where it is observed to be redshifted by about ≍2.5 km s-1. Further, we observe that the low atmosphere underneath the coronal outflows is highly structured, with the presence of blueshifts in Si IV and positive Mg II k2 asymmetries (which can be interpreted as signatures of chromospheric upflows) which are mostly not observed in the moss. These observations show a clear correlation between the coronal outflows and the chromosphere and TR underneath, which has not been shown before. Our work strongly suggests that these regions are not separate environments and should be treated together, and that current leading theories of AR outflows, such as the interchange reconnection model, need to take into account the dynamics of the low atmosphere. Title: On the Coronal Temperature in Solar Microflares Authors: Testa, Paola; Reale, Fabio Bibcode: 2020ApJ...902...31T Altcode: We present a study of solar imaging and spectral observations of a microflare, focusing on the temperature diagnostics provided by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, and the Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. Our data analysis, in particular from the emission in the 131 and 94 Å channels, indicates that the heated plasma reaches temperatures of ≳10 MK, at odds with a previous analysis of the same event, and we discuss the reason for the discrepancy. A particularly interesting aspect is the likely presence of the Fe XXIII 263.76 Å line, though weak, in EIS spectra in the early phases of the event, supporting the presence of high temperature plasma. Hydrodynamic 1D modeling of a single loop heated with a 3 minute pulse to 12-15 MK reproduces well most observed features along one of the brightening loops, including intensities in the AIA hot channels and their temporal variability, as well as the intensity, Doppler shift, and line width of the EIS Fe XXIII line, and its timing relative to the AIA emission. Overall, we obtain a coherent scenario of a typical microflaring loop system and provide constraints on the intensity of the energy release as well as its spatial and temporal distribution, both along and across the loop. Title: Observation and Modeling of High-temperature Solar Active Region Emission during the High-resolution Coronal Imager Flight of 2018 May 29 Authors: Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.; Ugarte-Urra, Ignacio; Brooks, David H.; Winebarger, Amy R.; Savage, Sabrina; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub, Leon; Kobayashi, Ken; McKenzie, David; Morton, Richard; Rachmeler, Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert Bibcode: 2020ApJ...896...51W Altcode: Excellent coordinated observations of NOAA active region 12712 were obtained during the flight of the High-resolution Coronal Imager (Hi-C) sounding rocket on 2018 May 29. This region displayed a typical active region core structure with relatively short, high-temperature loops crossing the polarity inversion line and bright "moss" located at the footpoints of these loops. The differential emission measure (DEM) in the active region core is very sharply peaked at about 4 MK. Further, there is little evidence for impulsive heating events in the moss, even at the high spatial resolution and cadence of Hi-C. This suggests that active region core heating is occurring at a high frequency and keeping the loops close to equilibrium. To create a time-dependent simulation of the active region core, we combine nonlinear force-free extrapolations of the measured magnetic field with a heating rate that is dependent on the field strength and loop length and has a Poisson waiting time distribution. We use the approximate solutions to the hydrodynamic loop equations to simulate the full ensemble of active region core loops for a range of heating parameters. In all cases, we find that high-frequency heating provides the best match to the observed DEM. For selected field lines, we solve the full hydrodynamic loop equations, including radiative transfer in the chromosphere, to simulate transition region and chromospheric emission. We find that for heating scenarios consistent with the DEM, classical signatures of energy release, such as transition region brightenings and chromospheric evaporation, are weak, suggesting that they would be difficult to detect. Title: The Drivers of Active Region Outflows into the Slow Solar Wind Authors: Brooks, David H.; Winebarger, Amy R.; Savage, Sabrina; Warren, Harry P.; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub, Leon; Kobayashi, Ken; McIntosh, Scott W.; McKenzie, David; Morton, Richard; Rachmeler, Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert Bibcode: 2020ApJ...894..144B Altcode: 2020arXiv200407461B Plasma outflows from the edges of active regions have been suggested as a possible source of the slow solar wind. Spectroscopic measurements show that these outflows have an enhanced elemental composition, which is a distinct signature of the slow wind. Current spectroscopic observations, however, do not have sufficient spatial resolution to distinguish what structures are being measured or determine the driver of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a sounding rocket in 2018 May and observed areas of active region outflow at the highest spatial resolution ever achieved (250 km). Here we use the Hi-C data to disentangle the outflow composition signatures observed with the Hinode satellite during the flight. We show that there are two components to the outflow emission: a substantial contribution from expanded plasma that appears to have been expelled from closed loops in the active region core and a second contribution from dynamic activity in active region plage, with a composition signature that reflects solar photospheric abundances. The two competing drivers of the outflows may explain the variable composition of the slow solar wind. Title: Is the High-Resolution Coronal Imager Resolving Coronal Strands? Results from AR 12712 Authors: Williams, Thomas; Walsh, Robert W.; Winebarger, Amy R.; Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; Golub, Leon; Kobayashi, Ken; McKenzie, David E.; Morton, Richard J.; Peter, Hardi; Rachmeler, Laurel A.; Savage, Sabrina L.; Testa, Paola; Tiwari, Sanjiv K.; Warren, Harry P.; Watkinson, Benjamin J. Bibcode: 2020ApJ...892..134W Altcode: 2020arXiv200111254W Following the success of the first mission, the High-Resolution Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1) on 2018 May 29 from the White Sands Missile Range, NM, USA. On this occasion, 329 s of 17.2 nm data of target active region AR 12712 were captured with a cadence of ≈4 s, and a plate scale of 0.129 arcsec pixel-1. Using data captured by Hi-C 2.1 and co-aligned observations from SDO/AIA 17.1 nm, we investigate the widths of 49 coronal strands. We search for evidence of substructure within the strands that is not detected by AIA, and further consider whether these strands are fully resolved by Hi-C 2.1. With the aid of multi-scale Gaussian normalization, strands from a region of low emission that can only be visualized against the contrast of the darker, underlying moss are studied. A comparison is made between these low-emission strands and those from regions of higher emission within the target active region. It is found that Hi-C 2.1 can resolve individual strands as small as ≈202 km, though the more typical strand widths seen are ≈513 km. For coronal strands within the region of low emission, the most likely width is significantly narrower than the high-emission strands at ≈388 km. This places the low-emission coronal strands beneath the resolving capabilities of SDO/AIA, highlighting the need for a permanent solar observatory with the resolving power of Hi-C. Title: IRIS Observations of Short-term Variability in Moss Associated with Transient Hot Coronal Loops Authors: Testa, Paola; Polito, Vanessa; De Pontieu, Bart Bibcode: 2020ApJ...889..124T Altcode: 2019arXiv191008201T We observed rapid variability (≲60 s) at the footpoints of transient, hot (∼8-10 MK) coronal loops in active region cores, with the Interface Region Imaging Spectrograph (IRIS). The high spatial (∼0"33) and temporal (≲5-10 s) resolution of IRIS is often crucial for the detection of this variability. We show how, in combination with 1D RADYN loop modeling, these IRIS spectral observations of the transition region (TR) and chromosphere provide powerful diagnostics of the properties of coronal heating and energy transport (thermal conduction or nonthermal electrons, NTEs). Our simulations of nanoflare-heated loops indicate that emission in the Mg II triplet can be used as a sensitive diagnostic for nonthermal particles. In our events, we observe a large variety of IRIS spectral properties (intensity, Doppler shifts, broadening, chromospheric/TR line ratios, Mg II triplet emission) even for different footpoints of the same coronal events. In several events, we find spectroscopic evidence for NTEs (e.g., TR blueshifts and Mg II triplet emission), suggesting that particle acceleration can occur even for very small magnetic reconnection events, which are generally below the detection threshold of hard X-ray instruments that provide direct detection of emission of nonthermal particles. Title: The Multi-slit Approach to Coronal Spectroscopy with the Multi-slit Solar Explorer (MUSE) Authors: De Pontieu, Bart; Martínez-Sykora, Juan; Testa, Paola; Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo; Cheung, Mark C. M.; Antolin, Patrick Bibcode: 2020ApJ...888....3D Altcode: 2019arXiv190908818D The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed at understanding the physical mechanisms driving the heating of the solar corona and the eruptions that are at the foundation of space weather. MUSE contains two instruments, a multi-slit extreme ultraviolet (EUV) spectrograph and a context imager. It will simultaneously obtain EUV spectra (along 37 slits) and context images with the highest resolution in space (0.″33-0.″4) and time (1-4 s) ever achieved for the transition region (TR) and corona. The MUSE science investigation will exploit major advances in numerical modeling, and observe at the spatial and temporal scales on which competing models make testable and distinguishable predictions, thereby leading to a breakthrough in our understanding of coronal heating and the drivers of space weather. By obtaining spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX 108Å, Fe XXI 108 Å) covering a wide range of TR and coronal temperatures along 37 slits simultaneously, MUSE will be able to “freeze” the evolution of the dynamic coronal plasma. We describe MUSE’s multi-slit approach and show that the optimization of the design minimizes the impact of spectral lines from neighboring slits, generally allowing line parameters to be accurately determined. We also describe a Spectral Disambiguation Code to resolve multi-slit ambiguity in locations where secondary lines are bright. We use simulations of the corona and eruptions to perform validation tests and show that the multi-slit disambiguation approach allows accurate determination of MUSE observables in locations where significant multi-slit contamination occurs. Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar Magnetic Network Lanes Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.; Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.; Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P. Bibcode: 2019ApJ...887L...8P Altcode: 2019arXiv191102331P We present high-resolution, high-cadence observations of six, fine-scale, on-disk jet-like events observed by the High-resolution Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We combine the Hi-C 2.1 images with images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS), and investigate each event’s magnetic setting with co-aligned line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six events are jetlet-like (having apparent properties of jetlets), (ii) all six are rooted at edges of magnetic network lanes, (iii) four of the jetlet-like events stem from sites of flux cancelation between majority-polarity network flux and merging minority-polarity flux, and (iv) four of the jetlet-like events show brightenings at their bases reminiscent of the base brightenings in coronal jets. The average spire length of the six jetlet-like events (9000 ± 3000 km) is three times shorter than that for IRIS jetlets (27,000 ± 8000 km). While not ruling out other generation mechanisms, the observations suggest that at least four of these events may be miniature versions of both larger-scale coronal jets that are driven by minifilament eruptions and still-larger-scale solar eruptions that are driven by filament eruptions. Therefore, we propose that our Hi-C events are driven by the eruption of a tiny sheared-field flux rope, and that the flux rope field is built and triggered to erupt by flux cancelation. Title: Diagnostics of nanoflare heating in active region core loops from chromospheric and transition region observations and modeling Authors: Testa, P.; Polito, V.; De Pontieu, B.; Reale, F.; Graham, D. Bibcode: 2019AGUFMSH13B..07T Altcode: Rapid variability at the footpoints of active region coronal loops has been observed (Testa et al. 2013, 2014), and provides powerful diagnostics of the properties of coronal heating and energy transport (e.g., Testa et al. 2014, Polito et al. 2018, Reale et al. 2019, Testa et al. 2019).

We will present results of our detailed analysis of a dozen of IRIS/AIA observations of footpoints brightenings associated with coronal heating, and will present the distribution of the observed properties (e.g., duration of brightenings, intensity ratios, Doppler shifts, non-thermal broadening,..). We will discuss the properties of coronal heating as inferred from the coupling of these high spatial, spectral, and temporal resolution chromospheric/transition region/coronal observations, with modeling.

We will also present results of a new algorithm we have developed for an automatic detection of these footpoint brightenings in AIA observations (Graham et al. 2019), which will allow us, in our next step, to significantly expand the number of events detected, and build more robust statistics of the properties of nanoflares in active region loops. Title: Fine-scale Explosive Energy Release at Sites of Prospective Magnetic Flux Cancellation in the Core of the Solar Active Region Observed by Hi-C 2.1, IRIS, and SDO Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.; De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.; Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.; Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton, Richard J.; Peter, Hardi; Walsh, Robert W. Bibcode: 2019ApJ...887...56T Altcode: 2019arXiv191101424T The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56 UT. Three morphologically different types (I: dot-like; II: loop-like; III: surge/jet-like) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter and shorter in span (70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare’s polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA, and IRIS peak nearly simultaneously for many of these events, and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition region origin. Title: Can superposition of evaporative flows explain broad IRIS Fe XXI line profiles during flares? Authors: Polito, V.; Testa, P.; De Pontieu, B. Bibcode: 2019AGUFMSH44A..07P Altcode: The observation of the high-temperature (>10MK) IRIS Fe XXI 1354A line with the Interface Region Imaging Spectrograph (IRIS) has provided significant insights into the chromospheric evaporation process in flares. In particular, the line is often observed to be completely blueshifted, in contrast to previous observations at lower spatial and spectral resolution, and in agreement with predictions from theoretical models. Interestingly, the line is also observed to be mostly symmetric and significantly broader than expected from thermal motions (assuming the peak formation temperature of the ion is in equilibrium). One popular interpretation for the non-thermal broadening is the superposition of flows from different loop strands. In this work, we test this scenario by forward-modelling the Fe XXI line profile assuming different possible observational scenarios using hydrodynamic simulations of multi-thread flare loops with the 1D RADYN code. Our results indicate that the superposition of flows alone cannot easily reproduce both the symmetry and the significant broadening of the line and that some other physical process, such as turbulence, or a much larger ion temperature than previously expected, likely needs to be invoked in order to explain the observed profiles. Title: The High-Resolution Coronal Imager, Flight 2.1 Authors: Rachmeler, Laurel A.; Winebarger, Amy R.; Savage, Sabrina L.; Golub, Leon; Kobayashi, Ken; Vigil, Genevieve D.; Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.; Peter, Hardi; Testa, Paola; Tiwari, Sanjiv K.; Walsh, Robert W.; Warren, Harry P.; Alexander, Caroline; Ansell, Darren; Beabout, Brent L.; Beabout, Dyana L.; Bethge, Christian W.; Champey, Patrick R.; Cheimets, Peter N.; Cooper, Mark A.; Creel, Helen K.; Gates, Richard; Gomez, Carlos; Guillory, Anthony; Haight, Harlan; Hogue, William D.; Holloway, Todd; Hyde, David W.; Kenyon, Richard; Marshall, Joseph N.; McCracken, Jeff E.; McCracken, Kenneth; Mitchell, Karen O.; Ordway, Mark; Owen, Tim; Ranganathan, Jagan; Robertson, Bryan A.; Payne, M. Janie; Podgorski, William; Pryor, Jonathan; Samra, Jenna; Sloan, Mark D.; Soohoo, Howard A.; Steele, D. Brandon; Thompson, Furman V.; Thornton, Gary S.; Watkinson, Benjamin; Windt, David Bibcode: 2019SoPh..294..174R Altcode: 2019arXiv190905942R The third flight of the High-Resolution Coronal Imager (Hi-C 2.1) occurred on May 29, 2018; the Sounding Rocket was launched from White Sands Missile Range in New Mexico. The instrument has been modified from its original configuration (Hi-C 1) to observe the solar corona in a passband that peaks near 172 Å, and uses a new, custom-built low-noise camera. The instrument targeted Active Region 12712, and captured 78 images at a cadence of 4.4 s (18:56:22 - 19:01:57 UT; 5 min and 35 s observing time). The image spatial resolution varies due to quasi-periodic motion blur from the rocket; sharp images contain resolved features of at least 0.47 arcsec. There are coordinated observations from multiple ground- and space-based telescopes providing an unprecedented opportunity to observe the mass and energy coupling between the chromosphere and the corona. Details of the instrument and the data set are presented in this paper. Title: Unfolding Overlappogram Data: Preparing for the COOL-AID instrument on Hi-C FLARE Authors: Winebarger, A. R.; De Pontieu, B.; Cheung, C. M. M.; Martinez-Sykora, J.; Hansteen, V. H.; Testa, P.; Golub, L.; Savage, S. L.; Samra, J.; Reeves, K. Bibcode: 2019AGUFMSH33A..06W Altcode: During a solar flare, energy released in the corona streams to the solar chromosphere, where plasma is heated and then evaporated upward. The magnitude of these velocities and their evolution as a function of time can provide quantitative information on the magnitude of energy released and the method by which it is transported in a solar flare. Measuring these velocities, however, is quite challenging. Typically, they are measured with single slit spectrometers, where light passing through a long but narrow slit is dispersed and emission lines formed across a range of temperatures are observed. The main issue with using single slit spectrometers to make this measurement is that they are rarely pointed at the right place at the right time. Additionally, their fields of view are limited by narrow slit widths, and although rastering can effectively expand the field of view, it does so at the cost of time. This combination means that single slit spectrometers cannot adequately capture the evolution of the flare velocities. On the contrary, slitless spectrometers can make "overlappograms'', which provide both imaging and spectral information over a large field of view. However, spatial information from different spectral lines can overlap in the dispersion direction, making the data difficult to interpret. Furthermore, the spectral resolution of slitless spectrometers are limited and typically worse than single-slit spectrometers, since no line fitting (and hence sub-pixel sampling) is possible.

For the next generation of the High-resolution Coronal Imager (Hi-C) Rocket Experiment, which we are proposing to launch during a solar flare, we are including the COronal OverLapagram - Ancillary Imaging Diagnostics (COOL-AID) instrument. COOL-AID is a slitless spectrometer based on the COronal Spectrographic Imager in the EUV (COSIE) design, but with a narrow passband coating around 12.9 nm (the same passband as the primary Hi-C telescope), a spatial resolution of ~1"x2", and a velocity resolution of ~5 km/s. The goal of the COOL-AID instrument is to determine the velocity associated with the Fe XXI 12.9 nm spectral line during a solar flare. In this talk, we will demonstrate the unfolding method developed by Cheung et al (2019) to determine the velocity information from a simulated COOL-AID data set. Title: A comprehensive three-dimensional radiative magnetohydrodynamic simulation of a solar flare Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.; Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.; Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen, B.; McIntosh, S. W. Bibcode: 2019NatAs...3..160C Altcode: 2018NatAs...3..160C Solar and stellar flares are the most intense emitters of X-rays and extreme ultraviolet radiation in planetary systems1,2. On the Sun, strong flares are usually found in newly emerging sunspot regions3. The emergence of these magnetic sunspot groups leads to the accumulation of magnetic energy in the corona. When the magnetic field undergoes abrupt relaxation, the energy released powers coronal mass ejections as well as heating plasma to temperatures beyond tens of millions of kelvins. While recent work has shed light on how magnetic energy and twist accumulate in the corona4 and on how three-dimensional magnetic reconnection allows for rapid energy release5,6, a self-consistent model capturing how such magnetic changes translate into observable diagnostics has remained elusive. Here, we present a comprehensive radiative magnetohydrodynamics simulation of a solar flare capturing the process from emergence to eruption. The simulation has sufficient realism for the synthesis of remote sensing measurements to compare with observations at visible, ultraviolet and X-ray wavelengths. This unifying model allows us to explain a number of well-known features of solar flares7, including the time profile of the X-ray flux during flares, origin and temporal evolution of chromospheric evaporation and condensation, and sweeping of flare ribbons in the lower atmosphere. Furthermore, the model reproduces the apparent non-thermal shape of coronal X-ray spectra, which is the result of the superposition of multi-component super-hot plasmas8 up to and beyond 100 million K. Title: Large-amplitude Quasiperiodic Pulsations as Evidence of Impulsive Heating in Hot Transient Loop Systems Detected in the EUV with SDO/AIA Authors: Reale, Fabio; Testa, Paola; Petralia, Antonino; Kolotkov, Dmitrii Y. Bibcode: 2019ApJ...884..131R Altcode: 2019arXiv190902847R Short heat pulses can trigger plasma pressure fronts inside closed magnetic tubes in the corona. The alternation of condensations and rarefactions from the pressure modes drive large-amplitude pulsations in the plasma emission. Here we show the detection of such pulsations along magnetic tubes that brighten transiently in the hot 94 Å EUV channel of the Solar Dynamics Observatory/AIA. The pulsations are consistent with those predicted by hydrodynamic loop modeling, and confirm pulsed heating in the loop system. The comparison of observations and model provides constraints on the heat deposition: a good agreement requires loop twisting and pulses deposited close to the footpoints with a duration of 0.5 minutes in one loop, and deposited in the corona with a duration of 2.5 minutes in another loop of the same loop system. Title: Impulsive Coronal Heating from Large-scale Magnetic Rearrangements: From IRIS to SDO/AIA Authors: Reale, Fabio; Testa, Paola; Petralia, Antonino; Graham, David R. Bibcode: 2019ApJ...882....7R Altcode: 2019arXiv190702291R The Interface Region Imaging Spectrograph (IRIS) has observed bright spots at the transition region footpoints associated with heating in the overlying loops, as observed by coronal imagers. Some of these brightenings show significant blueshifts in the Si IV line at 1402.77 Å ({log}T[{{K}}]≈ 4.9). Such blueshifts cannot be reproduced by coronal loop models assuming heating by thermal conduction only, but are consistent with electron beam heating, highlighting for the first time the possible importance of nonthermal electrons in the heating of nonflaring active regions. Here we report on the coronal counterparts of these brightenings observed in the hot channels of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We show that the IRIS bright spots are the footpoints of very hot and transient coronal loops that clearly experience strong magnetic interactions and rearrangements, thus confirming the impulsive nature of the heating and providing important constraints for their physical interpretation. Title: Multi-component Decomposition of Astronomical Spectra by Compressed Sensing Authors: Cheung, Mark C. M.; De Pontieu, Bart; Martínez-Sykora, Juan; Testa, Paola; Winebarger, Amy R.; Daw, Adrian; Hansteen, Viggo; Antolin, Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young, Peter; MUSE Team Bibcode: 2019ApJ...882...13C Altcode: 2019arXiv190203890C The signal measured by an astronomical spectrometer may be due to radiation from a multi-component mixture of plasmas with a range of physical properties (e.g., temperature, Doppler velocity). Confusion between multiple components may be exacerbated if the spectrometer sensor is illuminated by overlapping spectra dispersed from different slits, with each slit being exposed to radiation from a different portion of an extended astrophysical object. We use a compressed sensing method to robustly retrieve the different components. This method can be adopted for a variety of spectrometer configurations, including single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer mission), and slot spectrometers (which produce overlappograms). Title: Automated Detection of Rapid Variability of Moss Using SDO/AIA and Its Connection to the Solar Corona Authors: Graham, David R.; De Pontieu, Bart; Testa, Paola Bibcode: 2019ApJ...880L..12G Altcode: Active region moss—the upper transition region of hot loops—was observed exhibiting rapid intensity variability on timescales of order 15 s by Testa et al. in a short time series (∼150 s) data set from Hi-C (High-resolution Coronal Imager). The intensity fluctuations in the subarcsecond 193A images (∼1.5 MK plasma) were uncharacteristic of steadily heated moss and were considered an indication of heating events connected to the corona. Intriguingly, these brightenings displayed a connection to the ends of transient hot loops seen in the corona. Following the same active region, AR11520, for 6 days, we demonstrate an algorithm designed to detect the same temporal variability in lower resolution Atmospheric Imaging Assembly (AIA) data, significantly expanding the number of events detected. Multiple analogous regions to the Hi-C data are successfully detected, showing moss that appears to “sparkle” prior to clear brightening of connected high-temperature loops; this is confirmed by the hot AIA channels and the isolated Fe XVIII emission. The result is illuminating, as the same behavior has recently been shown by Polito et al. while simulating nanoflares with a beam of electrons depositing their energy in the lower atmosphere. Furthermore, the variability is localized mostly to the hot core of the region, hence we reinforce the diagnostic potential of moss variability as the driver of energy release in the corona. The ubiquitous nature of this phenomenon, and the ability to detect it in data with extended time series, and large fields of view, opens a new window into investigating the coronal heating mechanism. Title: Can the Superposition of Evaporative Flows Explain Broad Fe XXI Profiles during Solar Flares? Authors: Polito, Vanessa; Testa, Paola; De Pontieu, Bart Bibcode: 2019ApJ...879L..17P Altcode: The observation of the high-temperature (≳10 MK) Fe XXI 1354.1 Å line with the Interface Region Imaging Spectrograph has provided significant insights into the chromospheric evaporation process in flares. In particular, the line is often observed to be completely blueshifted, in contrast to previous observations at lower spatial and spectral resolution, and in agreement with predictions from theoretical models. Interestingly, the line is also observed to be mostly symmetric and significantly broader than expected from thermal motions (assuming the peak formation temperature of the ion is in equilibrium). One popular interpretation for the nonthermal broadening is the superposition of flows from different loop strands. In this work, we test this scenario by forward-modeling the Fe XXI line profile assuming different possible observational scenarios using hydrodynamic simulations of multi-thread flare loops with the 1D RADYN code. Our results indicate that the superposition of flows alone cannot easily reproduce both the symmetry and the significant broadening of the line and that some other physical process, such as turbulence, or a much larger ion temperature than previously expected, likely needs to be invoked in order to explain the observed profiles. Title: Fine-scale explosive energy release at sites of magnetic flux cancellation in the core of the solar active region observed by HiC2.1, IRIS and SDO Authors: Tiwari, Sanjiv K.; Panesar, Navdeep; Moore, Ronald L.; De Pontieu, Bart; Testa, Paola; Winebarger, Amy R. Bibcode: 2019AAS...23411702T Altcode: The second sounding-rocket flight of the High-Resolution Coronal Imager (HiC2.1) provided unprecedentedly-high spatial and temporal resolution (150 km, 4.5 s) coronal EUV images of Fe IX/X emission at 172 Å, of a solar active region (AR NOAA 12712) near solar disk center. Three morphologically-different types (I: dot-like, II: loop-like, & III: surge/jet-like) of fine-scale sudden brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. We complement the 5-minute-duration HiC2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying flux cancellation at the polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. These outflows from both ends of the arch filament system are seen as bi-directional flows in the arch filament system, suggesting that the well-known counter-streaming flows in large classical filaments could be driven in the same way as in this arch filament system: by fine-scale jet-like explosions from fine-scale sites of mixed-polarity field in the feet of the sheared field that threads the filament. Plausibly, the flux cancellation at these sites prepares and triggers a fine scale core-magnetic-field structure (a small sheared/twisted core field or flux rope along and above the cancellation line) to explode. In types I & II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow in the manner of larger jets in coronal holes, quiet regions, and active regions. Title: Radiative MHD Simulation of a Solar Flare Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios; Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto; DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats; De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W. Bibcode: 2019AAS...23431005C Altcode: We present a radiative MHD simulation of a solar flare. The computational domain captures the near-surface layers of the convection zone and overlying atmosphere. Inspired by the observed evolution of NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed to emerge in the vicinity of a pre-existing sunspot. The emergence of twisted magnetic flux generates shear flows that create a pre-existing flux rope underneath the canopy field of the sunspot. Following erosion of the overlying bootstrapping field, the flux rope erupts. Rapid release of magnetic energy results in multi-wavelength synthetic observables (including X-ray spectra, narrowband EUV images, Doppler shifts of EUV lines) that are consistent with flare observations. This works suggests the super-position of multi-thermal, superhot (up to 100 MK) plasma may be partially responsible for the apparent non-thermal shape of coronal X-ray sources in flares. Implications for remote sensing observations of other astrophysical objects is also discussed. This work is an important stepping stone toward high-fidelity data-driven MHD models. Title: Multi-component Decomposition of Astronomical Spectra by Compressed Sensing Authors: Cheung, Mark; De Pontieu, Bart; Martinez-Sykora, Juan; Testa, Paola; Winebarger, Amy R.; Daw, Adrian N.; Hansteen, Viggo; Antolin, Patrick; Tarbell, Theodore D.; Wuelser, Jean-Pierre; Young, Peter R. Bibcode: 2019AAS...23411603C Altcode: The signal measured by an astronomical spectrometer may be due to radiation from a multi-component mixture of plasmas with a range of physical properties (e.g. temperature, Doppler velocity). Confusion between multiple components may be exacerbated if the spectrometer sensor is illuminated by overlapping spectra dispersed from different slits, with each slit being exposed to radiation from a different portion of an extended astrophysical object. We use a compressed sensing method to robustly retrieve the different components. This method can be adopted for a variety of spectrometer configurations, including single-slit, multi-slit (e.g., the proposed MUlti-slit Solar Explorer mission; MUSE) and slot spectrometers (which produce overlappograms). Title: A stellar flare-coronal mass ejection event revealed by X-ray plasma motions Authors: Argiroffi, C.; Reale, F.; Drake, J. J.; Ciaravella, A.; Testa, P.; Bonito, R.; Miceli, M.; Orlando, S.; Peres, G. Bibcode: 2019NatAs...3..742A Altcode: 2019NatAs.tmp..328A; 2019arXiv190511325A Coronal mass ejections (CMEs), often associated with flares1-3, are the most powerful magnetic phenomena occurring on the Sun. Stars show magnetic activity levels up to ten thousand times higher4, and CME effects on stellar physics and circumstellar environments are predicted to be substantial5-9. However, stellar CMEs remain observationally unexplored. Using time-resolved high-resolution X-ray spectroscopy of a stellar flare on the active star HR 9024 observed with the High Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory space telescope, we distinctly detected Doppler shifts in S xvi, Si xiv and Mg xii lines that indicate upward and downward motions of hot plasmas (around 10-25 MK) within the flaring loop, with velocities of 100-400 km s-1, in agreement with a model of a flaring magnetic tube. Most notably, we also detected a later blueshift in the O viii line that reveals an upward motion, with velocity 90 ± 30 km s-1, of cool plasma (about 4 MK), that we ascribe to a CME coupled to the flare. From this evidence we were able to derive a CME mass of 1 .2-0.8+2.6×1 021 g and a CME kinetic energy of 5 .2-3.6+27.7×1 034 erg. These values provide clues in the extrapolation of the solar case to higher activity levels in other stars, suggesting that CMEs could indeed be a major cause of mass and angular momentum loss. Title: Quantifying the Influence of Key Physical Processes on the Formation of Emission Lines Observed by IRIS. I. Non-equilibrium Ionization and Density-dependent Rates Authors: Bradshaw, Stephen J.; Testa, Paola Bibcode: 2019ApJ...872..123B Altcode: 2019arXiv190103935B In the work described here, we investigate atomic processes leading to the formation of emission lines within the Interface Region Imaging Spectrograph wavelength range at temperatures near 105 K. We focus on (1) non-equilibrium and (2) density-dependent effects influencing the formation and radiative properties of S IV and O IV. These two effects have significant impacts on spectroscopic diagnostic measurements of quantities associated with the plasma that emission lines from S IV and O IV provide. We demonstrate this by examining nanoflare-based coronal heating to determine what the detectable signatures are in transition region emission. A detailed comparison between predictions from numerical experiments and several sets of observational data is presented to show how one can ascertain when non-equilibrium ionization and/or density-dependent atomic processes are important for diagnosing nanoflare properties, the magnitude of their contribution, and what information can be reliably extracted from the spectral data. Our key findings are the following. (1) The S/O intensity ratio is a powerful diagnostic of non-equilibrium ionization. (2) Non-equilibrium ionization has a strong effect on the observed line intensities even in the case of relatively weak nanoflare heating. (3) The density dependence of atomic rate coefficients is only important when the ion population is out of equilibrium. (4) In the sample of active regions we examined, weak nanoflares coupled with non-equilibrium ionization and density-dependent atomic rates were required to explain the observed properties (e.g., the S/O intensity ratios). (5) Enhanced S/O intensity ratios cannot be due solely to the heating strength and must depend on other processes (e.g., heating frequency, non-Maxwellian distributions). 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: Broad Non-Gaussian Fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-class Flare Observed by Hinode/EIS Authors: Polito, Vanessa; Dudík, Jaroslav; Kašparová, Jana; Dzifčáková, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin Bibcode: 2018ApJ...864...63P Altcode: 2018arXiv180709361P We analyze the spectra of high-temperature Fe XXIV lines observed by the Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) during the impulsive phase of the X8.3-class flare on 2017 September 10. The line profiles are broad, show pronounced wings, and clearly depart from a single-Gaussian shape. The lines can be well fitted with κ distributions, with values of κ varying between ≈1.7 and 3. The regions where we observe the non-Gaussian profiles coincide with the location of high-energy (≈100-300 keV) hard X-ray (HXR) sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of nonthermal microwave sources with the Expanded Owens Valley Solar Array at and above the HXR loop-top source. We also investigate the effect of taking into account κ distributions in the temperature diagnostics based on the ratio of the Fe XXIII λ263.76 and Fe XXIV λ255.1 EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log(T[K]) ≈ 7.8) if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply nonthermal broadening in excess of 200 km s-1. The nonthermal broadening related to HXR emission is better interpreted by turbulence than by chromospheric evaporation. Title: Broad Non-Gaussian fe XXIV Line Profiles in the Impulsive Phase of the 2017 September 10 X8.3-CLASS Flare Observed by Hinode/eis Authors: Polito, Vanessa; Dudik, Jaroslav; Kasparova, Jana; Dzifcakova, Elena; Reeves, Katharine K.; Testa, Paola; Chen, Bin Bibcode: 2018shin.confE.212P Altcode: We analyze the spectra of high temperature Fe XXIV lines observed by Hinode/EIS during the impulsive phase the X8.3-class flare on September 10, 2017. The line profiles are broad, show pronounced wings, and clearly depart from a single Gaussian shape. The lines can be well fitted with the ? distributions, with values of ? varying between ?1.7 to 3. The region where we observe the non-Gaussian profiles coincides with the location of high-energy (?100-300 keV) HXR sources observed by RHESSI, suggesting the presence of particle acceleration or turbulence, also confirmed by the observations of a non-thermal microwave sources with EOVSA at and above the HXR looptop source. We also investigate the effect of taking into account ? distributions in the temperature diagnostics based on the ratio of the Fe XXIII 263.76 ?A and Fe XXIV 255.1 ?A EIS lines. We found that these lines can be formed at much higher temperatures than expected (up to log(T [K]) ? 7.8), if departures from Maxwellian distributions are taken into account. Although larger line widths are expected because of these higher formation temperatures, the observed line widths still imply non-thermal broadening in excess of 200kms?1. Title: Investigating the Response of Loop Plasma to Nanoflare Heating Using RADYN Simulations Authors: Polito, V.; Testa, P.; Allred, J.; De Pontieu, B.; Carlsson, M.; Pereira, T. M. D.; Gošić, Milan; Reale, Fabio Bibcode: 2018ApJ...856..178P Altcode: 2018arXiv180405970P We present the results of 1D hydrodynamic simulations of coronal loops that are subject to nanoflares, caused by either in situ thermal heating or nonthermal electron (NTE) beams. The synthesized intensity and Doppler shifts can be directly compared with Interface Region Imaging Spectrograph (IRIS) and Atmospheric Imaging Assembly (AIA) observations of rapid variability in the transition region (TR) of coronal loops, associated with transient coronal heating. We find that NTEs with high enough low-energy cutoff ({E}{{C}}) deposit energy in the lower TR and chromosphere, causing blueshifts (up to ∼20 km s-1) in the IRIS Si IV lines, which thermal conduction cannot reproduce. The {E}{{C}} threshold value for the blueshifts depends on the total energy of the events (≈5 keV for 1024 erg, up to 15 keV for 1025 erg). The observed footpoint emission intensity and flows, combined with the simulations, can provide constraints on both the energy of the heating event and {E}{{C}}. The response of the loop plasma to nanoflares depends crucially on the electron density: significant Si IV intensity enhancements and flows are observed only for initially low-density loops (<109 cm-3). This provides a possible explanation of the relative scarcity of observations of significant moss variability. While the TR response to single heating episodes can be clearly observed, the predicted coronal emission (AIA 94 Å) for single strands is below current detectability and can only be observed when several strands are heated closely in time. Finally, we show that the analysis of the IRIS Mg II chromospheric lines can help further constrain the properties of the heating mechanisms. Title: Guided flows in coronal magnetic flux tubes Authors: Petralia, A.; Reale, F.; Testa, P. Bibcode: 2018A&A...609A..18P Altcode: 2017arXiv171104641P; 2017A&A...609A..18P Context. There is evidence that coronal plasma flows break down into fragments and become laminar.
Aims: We investigate this effect by modelling flows confined along magnetic channels.
Methods: We consider a full magnetohydrodynamic (MHD) model of a solar atmosphere box with a dipole magnetic field. We compare the propagation of a cylindrical flow perfectly aligned with the field to that of another flow with a slight misalignment. We assume a flow speed of 200 km s-1 and an ambient magnetic field of 30 G.
Results: We find that although the aligned flow maintains its cylindrical symmetry while it travels along the magnetic tube, the misaligned one is rapidly squashed on one side, becoming laminar and eventually fragmented because of the interaction and back-reaction of the magnetic field. This model could explain an observation made by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory of erupted fragments that fall back onto the solar surface as thin and elongated strands and end up in a hedge-like configuration.
Conclusions: The initial alignment of plasma flow plays an important role in determining the possible laminar structure and fragmentation of flows while they travel along magnetic channels.

Movies are available in electronic form at http://www.aanda.org Title: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) Authors: Winebarger, A. R.; Savage, S. L.; Kobayashi, K.; Champey, P. R.; McKenzie, D. E.; Golub, L.; Testa, P.; Reeves, K.; Cheimets, P.; Cirtain, J. W.; Walsh, R. W.; Bradshaw, S. J.; Warren, H.; Mason, H. E.; Del Zanna, G. Bibcode: 2017AGUFMSH44A..06W Altcode: For over four decades, X-ray, EUV, and UV spectral observations have been used to measure physical properties of the solar atmosphere. At wavelengths below 10 nm, however, observations of the solar corona with simultaneous spatial and spectral resolution are limited, and not since the late 1970's have spatially resolved solar X-ray spectra been measured. Because the soft X-ray regime is dominated by emission lines formed at high temperatures, X-ray spectroscopic techniques yield insights to fundamental physical processes that are not accessible by any other means. Using a novel implementation of corrective optics, the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) will measure, for the first time, the solar spectrum from 0.6- 2.4 nm with a 6 arcsec resolution over an 8 arcmin slit. The MaGIXS mission will address on of the fundamental problems of coronal physics: the nature of coronal heating. There are several observables in the MaGIXS wavelength range that will constrain the heating frequency and hence discriminate between competing coronal heating theories. In this presentation, we will present the MaGIXS scientific motivation and provide an update on instrument development. MaGIXS will be launched from White Sands Missile Range in the summer of 2019. Title: Observation and modelling of the Fe XXI line profile observed by IRIS during the impulsive phase of flares Authors: Polito, V.; Testa, P.; De Pontieu, B.; Allred, J. C. Bibcode: 2017AGUFMSH41A2741P Altcode: The observation of the high temperature (above 10 MK) Fe XXI 1354.1 A line with the Interface Region Imaging Spectrograph (IRIS) has provided significant insights into the chromospheric evaporation process in flares. In particular, the line is often observed to be completely blueshifted, in contrast to previous observations at lower spatial and spectral resolution, and in agreement with predictions from theoretical models. Interestingly, the line is also observed to be mostly symmetric and with a large excess above the thermal width. One popular interpretation for the excess broadening is given by assuming a superposition of flows from different loop strands. In this work, we perform a statistical analysis of Fe XXI line profiles observed by IRIS during the impulsive phase of flares and compare our results with hydrodynamic simulations of multi-thread flare loops performed with the 1D RADYN code. Our results indicate that the multi-thread models cannot easily reproduce the symmetry of the line and that some other physical process might need to be invoked in order to explain the observed profiles. Title: Constraints on active region coronal heating properties from observations and modeling of chromospheric, transition region, and coronal emission Authors: Testa, P.; Polito, V.; De Pontieu, B.; Carlsson, M.; Reale, F.; Allred, J. C.; Hansteen, V. H. Bibcode: 2017AGUFMSH43A2804T Altcode: We investigate coronal heating properties in active region cores in non-flaring conditions, using high spatial, spectral, and temporal resolution chromospheric/transition region/coronal observations coupled with detailed modeling. We will focus, in particular, on observations with the Interface Region Imaging Spectrograph (IRIS), joint with observations with Hinode (XRT and EIS) and SDO/AIA. We will discuss how these observations and models (1D HD and 3D MHD, with the RADYN and Bifrost codes) provide useful diagnostics of the coronal heating processes and mechanisms of energy transport. Title: Spectroscopy of Very Hot Plasma in Non-flaring Parts of a Solar Limb Active Region: Spatial and Temporal Properties Authors: Parenti, Susanna; del Zanna, Giulio; Petralia, Antonino; Reale, Fabio; Teriaca, Luca; Testa, Paola; Mason, Helen E. Bibcode: 2017ApJ...846...25P Altcode: 2017arXiv170708445P In this work we investigate the thermal structure of an off-limb active region (AR) in various non-flaring areas, as it provides key information on the way these structures are heated. In particular, we concentrate on the very hot component (> 3 {MK}) as it is a crucial element to distinguish between different heating mechanisms. We present an analysis using Fe and Ca emission lines from both the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) on board the Solar and Heliospheric Observatory (SOHO) and the EUV Imaging Spectrometer (EIS) on board Hinode. A data set covering all ionization stages from Fe x to Fe xix has been used for the thermal analysis (both differential emission measure and emission measure, EM). Ca xiv is used for the SUMER-EIS radiometric cross calibration. We show that the very hot plasma is present and persistent almost everywhere in the core of the limb AR. The off-limb AR is clearly structured in Fe xviii. Almost everywhere, the EM analysis reveals plasma at 10 MK (visible in Fe xix emission), which is down to 0.1% of EM of the main 3 {MK} plasma. We estimate the power-law index of the hot tail of the EM to be between -8.5 and -4.4. However, the question about the possible existence of a small minor peak at around 10 {MK} remains open. The absence in some part of the AR of the Fe xix and Fe xxiii lines (which fall into our spectral range) enables us to determine an upper limit on the EM at these temperatures. Our results include a new Ca xiv 943.59 Å atomic model. Title: Realistic radiative MHD simulation of a solar flare Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios; Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto; DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.; De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W. Bibcode: 2017SPD....4840001R Altcode: We present a recently developed version of the MURaM radiative MHD code that includes coronal physics in terms of optically thin radiative loss and field aligned heat conduction. The code employs the "Boris correction" (semi-relativistic MHD with a reduced speed of light) and a hyperbolic treatment of heat conduction, which allow for efficient simulations of the photosphere/corona system by avoiding the severe time-step constraints arising from Alfven wave propagation and heat conduction. We demonstrate that this approach can be used even in dynamic phases such as a flare. We consider a setup in which a flare is triggered by flux emergence into a pre-existing bipolar active region. After the coronal energy release, efficient transport of energy along field lines leads to the formation of flare ribbons within seconds. In the flare ribbons we find downflows for temperatures lower than ~5 MK and upflows at higher temperatures. The resulting soft X-ray emission shows a fast rise and slow decay, reaching a peak corresponding to a mid C-class flare. The post reconnection energy release in the corona leads to average particle energies reaching 50 keV (500 MK under the assumption of a thermal plasma). We show that hard X-ray emission from the corona computed under the assumption of thermal bremsstrahlung can produce a power-law spectrum due to the multi-thermal nature of the plasma. The electron energy flux into the flare ribbons (classic heat conduction with free streaming limit) is highly inhomogeneous and reaches peak values of about 3x1011 erg/cm2/s in a small fraction of the ribbons, indicating regions that could potentially produce hard X-ray footpoint sources. We demonstrate that these findings are robust by comparing simulations computed with different values of the saturation heat flux as well as the "reduced speed of light". Title: Non-Maxwellian Analysis of the Transition-region Line Profiles Observed by the Interface Region Imaging Spectrograph Authors: Dudík, Jaroslav; Polito, Vanessa; Dzifčáková, Elena; Del Zanna, Giulio; Testa, Paola Bibcode: 2017ApJ...842...19D Altcode: 2017arXiv170502104D We investigate the nature of the spectral line profiles for transition-region (TR) ions observed with the Interface Region Imaging Spectrograph (IRIS). In this context, we analyzed an active-region observation performed by IRIS in its 1400 Å spectral window. The TR lines are found to exhibit significant wings in their spectral profiles, which can be well fitted with a non-Maxwellian κ distribution. The fit with a κ distribution can perform better than a double-Gaussian fit, especially for the strongest line, Si IV 1402.8 Å. Typical values of κ found are about 2, occurring in a majority of spatial pixels where the TR lines are symmetric, I.e., the fit can be performed. Furthermore, all five spectral lines studied (from Si IV, O IV, and S IV) appear to have the same full-width at half-maximum irrespective of whether the line is an allowed or an intercombination transition. A similar value of κ is obtained for the electron distribution by the fitting of the line intensities relative to Si IV 1402.8 Å, if photospheric abundances are assumed. The κ distributions, however, do not remove the presence of non-thermal broadening. Instead, they actually increase the non-thermal width. This is because, for κ distributions, TR ions are formed at lower temperatures. The large observed non-thermal width lowers the opacity of the Si IV line sufficiently enough for this line to become optically thin. Title: Coronal Heating Properties in the Core of Solar Active Regions Authors: Testa, P.; Reale, F.; De Pontieu, B. Bibcode: 2016AGUFMSH33A..02T Altcode: The Interface Region Imaging Spectrograph (IRIS) provides unprecedented high spatial, temporal and spectral resolution observations of the chromosphere and transition region. Joint with coronal observations with Hinode (XRT and EIS), and SDO/AIA, these data cover from the upper photosphere to the corona. I will discuss how IRIS observations of footpoints of hot active region loops in non-flaring conditions, coupled with detailed HD and MHD modeling including chromosphere, transition region and corona, provide tight constraints on the coronal heating mechanisms in the core of active regions. Title: The importance of high-resolution observations of the solar corona Authors: Winebarger, A. R.; Cirtain, J. W.; Golub, L.; Walsh, R. W.; De Pontieu, B.; Savage, S. L.; Rachmeler, L.; Kobayashi, K.; Testa, P.; Brooks, D.; Warren, H.; Mcintosh, S. W.; Peter, H.; Morton, R. J.; Alexander, C. E.; Tiwari, S. K. Bibcode: 2016AGUFMSH31B2577W Altcode: The spatial and temporal resolutions of the available coronal observatories are inadequate to resolve the signatures of coronal heating. High-resolution and high-cadence observations available with the Interface Region Imaging Spectrograph (IRIS) and the High-resolution Coronal Imager (Hi-C) instrument hint that 0.3 arcsec resolution images and < 10 s cadence provide the necessary resolution to detect heating events. Hi-C was launched from White Sands Missile Range on July 11, 2012 (before the launch with IRIS) and obtained images of a solar active region in the 19.3 nm passband. In this presentation, I will discuss the potential of combining a flight in Hi-C with a 17.1 nm passband, in conjunction with IRIS. This combination will provide, for the first time, a definitive method of tracing the energy flow between the chromosphere and corona and vice versa. Title: Bright Hot Impacts by Erupted Fragments Falling Back on the Sun: Magnetic Channelling Authors: Petralia, A.; Reale, F.; Orlando, S.; Testa, P. Bibcode: 2016ApJ...832....2P Altcode: 2016arXiv160904634P Dense plasma fragments were observed to fall back on the solar surface by the Solar Dynamics Observatory after an eruption on 2011 June 7, producing strong extreme-ultraviolet brightenings. Previous studies investigated impacts in regions of weak magnetic field. Here we model the ∼ 300 km s-1 impact of fragments channelled by the magnetic field close to active regions. In the observations, the magnetic channel brightens before the fragment impact. We use a 3D-MHD model of spherical blobs downfalling in a magnetized atmosphere. The blob parameters are constrained from the observation. We run numerical simulations with different ambient densitie and magnetic field intensities. We compare the model emission in the 171 Å channel of the Atmospheric Imaging Assembly with the observed one. We find that a model of downfall channelled in an ∼1 MK coronal loop confined by a magnetic field of ∼10-20 G, best explains qualitatively and quantitatively the observed evolution. The blobs are highly deformed and further fragmented when the ram pressure becomes comparable to the local magnetic pressure, and they are deviated to be channelled by the field because of the differential stress applied by the perturbed magnetic field. Ahead of them, in the relatively dense coronal medium, shock fronts propagate, heat, and brighten the channel between the cold falling plasma and the solar surface. This study shows a new mechanism that brightens downflows channelled by the magnetic field, such as in accreting young stars, and also works as a probe of the ambient atmosphere, providing information about the local plasma density and magnetic field. Title: High Spatial Resolution Fe XII Observations of Solar Active Regions Authors: Testa, Paola; De Pontieu, Bart; Hansteen, Viggo Bibcode: 2016ApJ...827...99T Altcode: 2016arXiv160604603T We use UV spectral observations of active regions with the Interface Region Imaging Spectrograph (IRIS) to investigate the properties of the coronal Fe xii 1349.4 Å emission at unprecedented high spatial resolution (∼0.33″). We find that by using appropriate observational strategies (I.e., long exposures, lossless compression), Fe xii emission can be studied with IRIS at high spatial and spectral resolution, at least for high-density plasma (e.g., post-flare loops and active region moss). We find that upper transition region (TR; moss) Fe xii emission shows very small average Doppler redshifts ({v}{{D}} ∼ 3 km s-1) as well as modest non-thermal velocities (with an average of ∼24 km s-1 and the peak of the distribution at ∼15 km s-1). The observed distribution of Doppler shifts appears to be compatible with advanced three-dimensional radiative MHD simulations in which impulsive heating is concentrated at the TR footpoints of a hot corona. While the non-thermal broadening of Fe xii 1349.4 Å peaks at similar values as lower resolution simultaneous Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) measurements of Fe xii 195 Å, IRIS observations show a previously undetected tail of increased non-thermal broadening that might be suggestive of the presence of subarcsecond heating events. We find that IRIS and EIS non-thermal line broadening measurements are affected by instrumental effects that can only be removed through careful analysis. Our results also reveal an unexplained discrepancy between observed 195.1/1349.4 Å Fe xii intensity ratios and those predicted by the CHIANTI atomic database. Title: Physics & Diagnostics of the Drivers of Solar Eruptions Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan; Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna; Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson, Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris Bibcode: 2016SPD....47.0607C Altcode: We provide an update on our NASA Heliophysics Grand Challenges Research (HGCR) project on the ‘Physics & Diagnostics of the Drivers of Solar Eruptions’. This presentation will focus on results from a data-inspired, 3D radiative MHD model of a solar flare. The model flare results from the interaction of newly emerging flux with a pre-existing active region. Synthetic observables from the model reproduce observational features compatible with actual flares. These include signatures of coronal magnetic reconnection, chromospheric evaporation, EUV flare arcades, sweeping motion of flare ribbons and sunquakes. 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: EUV Flickering of Solar Coronal Loops: A New Diagnostic of Coronal Heating Authors: Tajfirouze, E.; Reale, F.; Peres, G.; Testa, P. Bibcode: 2016ApJ...817L..11T Altcode: 2016arXiv160103935T A previous work of ours found the best agreement between EUV light curves observed in an active region core (with evidence of super-hot plasma) and those predicted from a model with a random combination of many pulse-heated strands with a power-law energy distribution. We extend that work by including spatially resolved strand modeling and by studying the evolution of emission along the loops in the EUV 94 Å and 335 Å channels of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. Using the best parameters of the previous work as the input of the present one, we find that the amplitude of the random fluctuations driven by the random heat pulses increases from the bottom to the top of the loop in the 94 Å channel and from the top to the bottom in the 335 Å channel. This prediction is confirmed by the observation of a set of aligned neighboring pixels along a bright arc of an active region core. Maps of pixel fluctuations may therefore provide easy diagnostics of nanoflaring regions. Title: Time-resolved Emission from Bright Hot Pixels of an Active Region Observed in the EUV Band with SDO/AIA and Multi-stranded Loop Modeling Authors: Tajfirouze, E.; Reale, F.; Petralia, A.; Testa, P. Bibcode: 2016ApJ...816...12T Altcode: 2015arXiv151007524T Evidence of small amounts of very hot plasma has been found in active regions and might be an indication of impulsive heating released at spatial scales smaller than the cross-section of a single loop. We investigate the heating and substructure of coronal loops in the core of one such active region by analyzing the light curves in the smallest resolution elements of solar observations in two EUV channels (94 and 335 Å) from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We model the evolution of a bundle of strands heated by a storm of nanoflares by means of a hydrodynamic 0D loop model (EBTEL). The light curves obtained from a random combination of those of single strands are compared to the observed light curves either in a single pixel or in a row of pixels, simultaneously in the two channels, and using two independent methods: an artificial intelligent system (Probabilistic Neural Network) and a simple cross-correlation technique. We explore the space of the parameters to constrain the distribution of the heat pulses, their duration, their spatial size, and, as a feedback on the data, their signatures on the light curves. From both methods the best agreement is obtained for a relatively large population of events (1000) with a short duration (less than 1 minute) and a relatively shallow distribution (power law with index 1.5) in a limited energy range (1.5 decades). The feedback on the data indicates that bumps in the light curves, especially in the 94 Å channel, are signatures of a heating excess that occurred a few minutes before. Title: Properties of moss emission from joint FeXII IRIS and Hinode observations of active region plasma Authors: Testa, P.; De Pontieu, B.; Hansteen, V. H. Bibcode: 2015AGUFMSH31D..06T Altcode: IRIS provides unprecedented high resolution observations of the solar chromosphere and transition region. Joint with Hinode XRT and EIS, and SDO/AIA, these observations cover from the upper photosphere to the corona and provide tight constraints on the mechanisms of energy transport and heating of the plasma to coronal temperatures. We present new IRIS and Hinode coronal studies of the corona in non-flaring conditions, and compare the spectral line properties of FeXII emission observed with EIS and IRIS in active region moss. We will discuss the implications for the heating of hot coronal loops in the core of active regions. Title: X-Ray Properties of Low-mass Pre-main Sequence Stars in the Orion Trapezium Cluster Authors: Schulz, Norbert S.; Huenemoerder, David P.; Günther, Moritz; Testa, Paola; Canizares, Claude R. Bibcode: 2015ApJ...810...55S Altcode: 2015arXiv150304366S The Chandra HETG Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster that provides high-resolution X-ray spectra of very young stars over a wide mass range (0.7-2.3 {M}⊙ ). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts that are well-characterized at optical and infrared wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction, indicating that the sources are located on the near side of the cluster with respect to the observer as well as that these stars are embedded in more dusty environments. Stellar X-ray luminosities are well above 1031 erg s-1, in some cases exceeding 1032 erg s-1 for a substantial amount of time. The stars during these observations show no flares but are persistently bright. The spectra can be well fit with two temperature plasma components of 10 MK and 40 MK, of which the latter dominates the flux by a ratio 6:1 on average. The total emission measures range between 3-8 × 1054 cm-3 and are comparable to active coronal sources. The fits to the Ne ix He-Like K-shell lines indicate forbidden to inter-combination line ratios consistent with the low-density limit. Observed abundances compare well with active coronal sources underlying the coronal nature of these sources. The surface flux in this sample of 0.6-2.3 {M}⊙ classical T Tauri stars shows that coronal activity increases significantly between ages 0.1 and 10 Myr. The results demonstrate the power of X-ray line diagnostics to study coronal properties of T Tauri stars in young stellar clusters. Title: Thermal Diagnostics with the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions Authors: Cheung, Mark C. M.; Boerner, P.; Schrijver, C. J.; Testa, P.; Chen, F.; Peter, H.; Malanushenko, A. Bibcode: 2015ApJ...807..143C Altcode: 2015arXiv150403258C We present a new method for performing differential emission measure (DEM) inversions on narrow-band EUV images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. The method yields positive definite DEM solutions by solving a linear program. This method has been validated against a diverse set of thermal models of varying complexity and realism. These include (1) idealized Gaussian DEM distributions, (2) 3D models of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a nonlinear force-free field, and (3) thermodynamic models from a fully compressible, 3D MHD simulation of active region (AR) corona formation following magnetic flux emergence. We then present results from the application of the method to AIA observations of Active Region 11158, comparing the region's thermal structure on two successive solar rotations. Additionally, we show how the DEM inversion method can be adapted to simultaneously invert AIA and Hinode X-ray Telescope data, and how supplementing AIA data with the latter improves the inversion result. The speed of the method allows for routine production of DEM maps, thus facilitating science studies that require tracking of the thermal structure of the solar corona in time and space. Title: Pinning Down Coronal Heating Properties in the Presence of Non-Equilibrium Ionization Authors: Bradshaw, Stephen; Testa, Paola Bibcode: 2015TESS....120405B Altcode: We examine the effects that non-equilibrium ionization can have on the evolution of light curves emitted by transition region and coronal ions during impulsive heating, and how this can lead to the plasma and heating properties being misdiagnosed. Furthermore, through detailed numerical and forward modeling we demonstrate how the effects of non-equilibrium ionization can be mitigated and accounted for so that robust diagnostics can be developed. 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: 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: Neon and Oxygen Abundances and Abundance Ratio in the Solar Corona Authors: Landi, E.; Testa, P. Bibcode: 2015ApJ...800..110L Altcode: In this work we determine the Ne/O abundance ratio from Solar and Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) off-disk observations of quiescent streamers over the 1996-2008 period. We find that the Ne/O ratio is approximately constant over solar cycle 23 from 1996 to 2005, at a value of 0.099 ± 0.017 this value is lower than the transition region determinations from the quiet Sun used to infer the neon photospheric abundance from the oxygen photospheric abundance. Also, the Ne/O ratio we determined from SUMER is in excellent agreement with in situ determinations from ACE/SWICS. In 2005-2008, the Ne/O abundance ratio increased with time and reached 0.25 ± 0.05, following the same trend found in the slowest wind analyzed by ACE/SWICS. Further, we measure the absolute abundance in the corona for both oxygen and neon from the data set of 1996 November 22, obtaining A o = 8.99 ± 0.04 and A Ne = 7.92 ± 0.03, and we find that both elements are affected by the first ionization potential (FIP) effect, with oxygen being enhanced by a factor of 1.4-2.1 over its photospheric abundance, and neon being changed by a factor of 0.75-1.20. We conclude that the Ne/O ratio is not constant in the solar atmosphere, both in time and at different heights, and that it cannot be reliably used to infer the neon abundance in the photosphere. Also, we argue that the FIP effect was less effective during the minimum of solar cycle 24, and that the Ne/O = 0.25 ± 0.05 value measured at that time is closer to the true photospheric value, leading to a neon photospheric abundance larger than assumed by ≈40%. We discuss the implications of these results for the solar abundance problem, for the FIP effect, and for the identification of the source regions of the solar wind. Title: Upgrading the Solar-Stellar Connection: News about activity in Cool Stars Authors: Gunther, H. M.; Poppenhaeger, K.; Testa, P.; Borgniet, S.; Brun, A. S.; Cegla, H. M.; Garraffo, C.; Kowalski, A.; Shapiro, A.; Shkolnik, E.; Spada, F.; Vidotto, A. A. Bibcode: 2015csss...18...25G Altcode: 2014arXiv1408.3068G In this splinter session, ten speakers presented results on solar and stellar activity and how the two fields are connected. This was followed by a lively discussion and supplemented by short, one-minute highlight talks. The talks presented new theoretical and observational results on mass accretion on the Sun, the activity rate of flare stars, the evolution of the stellar magnetic field on time scales of a single cycle and over the lifetime of a star, and two different approaches to model the radial-velocity jitter in cool stars that is due to the granulation on the surface. Talks and discussion showed how much the interpretation of stellar activity data relies on the sun and how the large number of objects available in stellar studies can extend the parameter range of activity models. Title: IRIS diagnostics of non-thermal particles in coronal loops heated by nanoflares Authors: Testa, P.; De Pontieu, B.; Allred, J. C.; Carlsson, M.; Reale, F.; Daw, A. N. Bibcode: 2014AGUFMSH53D..08T Altcode: The variability of emission of the "moss", i.e., the upper transition region (TR) layer of high pressure loops in active regions, provides stringent constraints on the characteristics of heating events. We will discuss the new coronal heating diagnostics provided by the Interface Region Imaging Spectrograph (IRIS) together with SDO/AIA. IRIS provides imaging and spectral observations of the solar chromosphere and transition region, at high spatial (0.166 arcsec/pix) and temporal (down to ~1s) resolution at FUV and NUV wavelengths. We discuss how simultaneous IRIS and AIA observations, together with loop modeling (with the RADYN code) including chromosphere, transition region and corona, allow us to study impulsive heating events (nanoflares) and the energy transport mechanism between the corona and the lower atmospheric layers (thermal conduction vs. beams of non-thermal particles). We will show how the modeling of rapid moss brightenings provides diagnostics for the presence and properties of non-thermal particles in nanoflares, which are below the detectability threshold of hard X-ray observations. Title: Bright Hot Impacts by Erupted Fragments Falling Back on the Sun: UV Redshifts in Stellar Accretion Authors: Reale, F.; Orlando, S.; Testa, P.; Landi, E.; Schrijver, C. J. Bibcode: 2014ApJ...797L...5R Altcode: 2014arXiv1410.7193R A solar eruption after a flare on 2011 June 7 produced EUV-bright impacts of fallbacks far from the eruption site, observed with the Solar Dynamics Observatory. These impacts can be taken as a template for the impact of stellar accretion flows. Broad redshifted UV lines have been commonly observed in young accreting stars. Here we study the emission from the impacts in the Atmospheric Imaging Assembly's UV channels and compare the inferred velocity distribution to stellar observations. We model the impacts with two-dimensional hydrodynamic simulations. We find that the localized UV 1600 Å emission and its timing with respect to the EUV emission can be explained by the impact of a cloud of fragments. The first impacts produce strong initial upflows. The following fragments are hit and shocked by these upflows. The UV emission comes mostly from the shocked front shell of the fragments while they are still falling, and is therefore redshifted when observed from above. The EUV emission instead continues from the hot surface layer that is fed by the impacts. Fragmented accretion can therefore explain broad redshifted UV lines (e.g., C IV 1550 Å) to speeds around 400 km s-1 observed in accreting young stellar objects. 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: Observations of Subarcsecond Bright Dots in the Transition Region above Sunspots with the Interface Region Imaging Spectrograph Authors: Tian, H.; Kleint, L.; Peter, H.; Weber, M.; Testa, P.; DeLuca, E.; Golub, L.; Schanche, N. Bibcode: 2014ApJ...790L..29T Altcode: 2014arXiv1407.1060T Observations with the Interface Region Imaging Spectrograph (IRIS) have revealed numerous sub-arcsecond bright dots in the transition region above sunspots. These bright dots are seen in the 1400 Å and 1330 Å slit-jaw images. They are clearly present in all sunspots we investigated, mostly in the penumbrae, but also occasionally in some umbrae and light bridges. The bright dots in the penumbrae typically appear slightly elongated, with the two dimensions being 300-600 km and 250-450 km, respectively. The long sides of these dots are often nearly parallel to the bright filamentary structures in the penumbrae but sometimes clearly deviate from the radial direction. Their lifetimes are mostly less than one minute, although some dots last for a few minutes or even longer. Their intensities are often a few times stronger than the intensities of the surrounding environment in the slit-jaw images. About half of the bright dots show apparent movement with speeds of ~10-40 km s-1 in the radial direction. Spectra of a few bright dots were obtained and the Si IV 1402.77 Å line profiles in these dots are significantly broadened. The line intensity can be enhanced by one to two orders of magnitude. Some relatively bright and long-lasting dots are also observed in several passbands of the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, and they appear to be located at the bases of loop-like structures. Many of these bright dots are likely associated with small-scale energy release events at the transition region footpoints of magnetic loops. 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: Accretion impacts studied on the Sun Authors: Reale, F.; Orlando, S.; Testa, P.; Peres, G.; Landi, E.; Schrijver, C. Bibcode: 2014xru..confE.169R Altcode: Accretion in star-forming regions is a hot topic. The Sun has recently offered an interesting opportunity to study accretion impacts observed in great detail at high energies (Reale et al. 2013, Science, 341, 6143, 251). After the eruption of a dense filament triggered by an energetic flare on June 7, 2011 part of the ejected material falls back onto the solar surface. The impact of the downfalling plasma is similar to that of accretion flows on young stellar objects, and was imaged in the EUV by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). Hydrodynamic simulations confirm that the high energy emission is produced by the impact of high-density plasma at the highest free-fall speeds and show the importance of the absorption in reducing the X-ray emission and of fragmentation in explaining the line broadenings. Impacts such as these present a laboratory for stellar astronomers to study the impact of dense (accreting) circumstellar material in unique detail. 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: Diagnostics of coronal heating and mechanisms of energy transport from IRIS and AIA observations of active region moss Authors: Testa, Paola; De Pontieu, Bart; Allred, Joel C.; Carlsson, Mats; Reale, Fabio; Daw, Adrian N.; Hansteen, Viggo Bibcode: 2014AAS...22431305T Altcode: The variability of emission of the "moss", i.e., the upper transition region (TR) layer of high pressure loops in active regions provides stringent constraints on the characteristics of heating events. The Interface Region Imaging Spectrograph (IRIS), launched in June 2013, provides imaging and spectral observations at high spatial (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV and NUV wavelengths, and together with the high spatial and temporal resolution observations of SDO/AIA, can provide important insights into the coronal heating mechanisms. We present here an analysis of the temporal variability properties of moss regions at the footpoints of hot active region core loops undergoing heating, as observed by IRIS and AIA, covering emission from the corona to the transition region and the chromosphere. We model the observations using dynamic loop models (the Palermo-Harvard code, and RADYN, which also includes the effects of non-thermal particles) and discuss the implications on energy transport mechanisms (thermal conduction vs beams of non-thermal particles). Title: Photometric and Thermal Cross-calibration of Solar EUV Instruments Authors: Boerner, P. F.; Testa, P.; Warren, H.; Weber, M. A.; Schrijver, C. J. Bibcode: 2014SoPh..289.2377B Altcode: 2013arXiv1307.8045B We present an assessment of the accuracy of the calibration measurements and atomic physics models that go into calculating the SDO/AIA response as a function of wavelength and temperature. The wavelength response is tested by convolving SDO/EVE and Hinode/EIS spectral data with the AIA effective area functions and by comparing the predictions with AIA observations. For most channels, the AIA intensities summed over the disk agree with the corresponding measurements derived from the current version (V2) of the EVE data to within the estimated 25 % calibration error. This agreement indicates that the AIA effective areas are generally stable in time. The AIA 304 Å channel, however, does show degradation by a factor of almost 3 from May 2010 through September 2011, when the throughput apparently reached a minimum. We also found some inconsistencies in the 335 Å passband, possibly due to higher-order contamination of the EVE data. The intensities in the AIA 193 Å channel agree to within the uncertainties with the corresponding measurements from EIS full CCD observations. Analysis of high-resolution X-ray spectra of the solar-like corona of Procyon and of EVE spectra allowed us to investigate the accuracy and completeness of the CHIANTI database in the AIA shorter wavelength passbands. We found that in the 94 Å channel, the spectral model significantly underestimates the plasma emission owing to a multitude of missing lines. We derived an empirical correction for the AIA temperature responses by performing differential emission measure (DEM) inversion on a broad set of EVE spectra and adjusting the AIA response functions so that the count rates predicted by the full-disk DEMs match the observations. Title: Thermal Diagnostics with SDO/AIA: A new method and application to Eruptive Active Regions Authors: Cheung, Mark; Boerner, Paul; Testa, Paola Bibcode: 2014AAS...22432322C Altcode: We present a new method for the retrieval of the emission measure (EM) distribution of coronal plasma using SDO/AIA EUV images. Unlike some existing EM inversion algorithms, this inversion scheme does not make assumptions about the functional form (e.g. Gaussian, power law etc.) of the solution. The method returns positive definite solutions and runs at a speed ~O(10^4) pixels per second in a Solarsoft implementation. We apply the method to a selection of eruptive active regions (ARs) to study the thermal evolution of AR loops. In terms of both morphology and temporal evolution, synthetic Hinode/XRT images calculated from EM solutions retrieved using only AIA data show good agreement with actual XRT images. Title: The Temperature of Quiescent Streamers during Solar Cycles 23 and 24 Authors: Landi, E.; Testa, P. Bibcode: 2014ApJ...787...33L Altcode: Recent in-situ determinations of the temporal evolution of the charge state distribution in the fast and slow solar wind have shown a general decrease in the degree of ionization of all the elements in the solar wind along solar cycles 23 and 24. Such a decrease has been interpreted as a cooling of the solar corona which occurred during the decline and minimum phase of solar cycle 23 from 2000 to 2010. In the present work, we investigate whether spectroscopic determinations of the temperature of the quiescent streamers show signatures of coronal plasma cooling during cycles 23 and 24. We measure the coronal electron density and thermal structure at the base of 60 quiescent streamers observed from 1996 to 2013 by SOHO/SUMER and Hinode/EIS and find that both quantities do now show any significant dependence on the solar cycle. We argue that if the slow solar wind is accelerated from the solar photosphere or chromosphere, the measured decrease in the in-situ wind charge state distribution might be due to an increased efficiency in the wind acceleration mechanism at low altitudes. If the slow wind originates from the corona, a combination of density and wind acceleration changes may be responsible for the in-situ results. 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: Thermal structure of a hot non-flaring corona from Hinode/EIS Authors: Petralia, A.; Reale, F.; Testa, P.; Del Zanna, G. Bibcode: 2014A&A...564A...3P Altcode: 2014arXiv1402.6554P
Aims: In previous studies, a very hot plasma component has been diagnosed in solar active regions through the images in three different narrow-band channels of Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). This diagnostic from extreme ultraviolet (EUV) imaging data has also been supported by the matching morphology of emission in the hot Ca XVII line, as observed with Extreme-Ultraviolet Imaging Spectrometer (EIS) on board Hinode. This evidence is debated because of the unknown distribution of the emission measure along the line of sight. Here we investigate in detail the thermal distribution of one such region using EUV spectroscopic data.
Methods: In an active region observed with SDO/AIA, Hinode/EIS, and X-ray telescope (XRT), we select a sub-region with a very hot plasma component and another cooler sub-region for comparison. The average spectrum is extracted for both, and 14 intense lines are selected for analysis that probe the 5.5 < log T < 7 temperature range uniformly. From these lines, the emission measure distributions are reconstructed with the Markov-chain Monte Carlo method. Results are cross-checked in comparison with the two sub-regions, with a different inversion method, with the morphology of the images, and with the addition of fluxes measured with narrow, and broadband imagers.
Results: We find that, whereas the cool region has a flat and featureless distribution that drops at temperature log T ≥ 6.3, the distribution of the hot region shows a well-defined peak at log T = 6.6 and gradually decreasing trends on both sides, thus supporting the very hot nature of the hot component diagnosed with imagers. The other cross-checks are consistent with this result.
Conclusions: This study provides a completion of the analysis of active region components, and the resulting scenario supports the presence of a minor very hot plasma component in the core, with temperatures log T > 6.6. Title: Diagnostics of coronal heating and mechanisms of energy transport from IRIS and AIA observations of active region moss Authors: Testa, Paola; Reale, Fabio; De Pontieu, Bart; Hansteen, Viggo; Carlsson, Mats; Allred, Joel; Daw, Adrian Bibcode: 2014cosp...40E3323T Altcode: The variability of emission of the "moss", i.e., the upper transition region (TR) layer of high pressure loops in active regions provides stringent constraints on the characteristics of heating events. The Interface Region Imaging Spectrograph (IRIS), launched in June 2013, provides imaging and spectral observations at high spatial (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV and NUV wavelengths, and together with the high spatial and temporal resolution observations of SDO/AIA, can provide important insights into the coronal heating mechanisms. We present here an analysis of the temporal variability properties of moss regions at the footpoints of hot active region core loops undergoing heating, as observed by IRIS and AIA, covering emission from the corona to the transition region and the chromosphere. We model the observations using dynamic loop models (the Palermo-Harvard code, and RADYN, which also includes the effects of non-thermal particles) and discuss the implications on energy transport mechanisms (thermal conduction vs beams of non-thermal particles). Title: Thermal Diagnostics with SDO/AIA: A new method and application to Eruptive Active Regions Authors: Cheung, Mark; Testa, Paola; Boerner, Paul Bibcode: 2014cosp...40E.535C Altcode: We present a new method for the retrieval of the emission measure (EM) distribution of coronal plasma using SDO/AIA EUV images. Unlike some existing EM inversion algorithms, this inversion scheme does not make assumptions about the functional form (e.g. Gaussian, power law etc.) of the solution. The method returns positive definite solutions and runs at a speed ~O(10^4) pixels per second in a Solarsoft implementation. We apply the method to a selection of eruptive active regions (ARs) to study the thermal evolution of AR loops. In terms of both morphology and temporal evolution, synthetic Hinode/XRT images calculated from EM solutions retrieved using only AIA data show good agreement with actual XRT images. Title: The HETG Orion Legacy Project: X-Ray Properties of Trapezium Stars Authors: Schulz, Norbert S.; Huenemoerder, David P.; Testa, Paola; Canizares, Claude R. Bibcode: 2013prpl.conf1K095S Altcode: The ONC is an ideal astrophysical laboratory to study very young stars. The HETG Orion Legacy Project is designed to obtain a large number of high-resolution X-ray spectra of very young late type pre-main sequence stars, and several young massive and intermediate mass stars. Its extreme proximity and youth makes the core of the ONC a Chandra legacy project involving the only high resolution spectroscopic study of young embedded cluster stars for decades to come. For several PMS stars we derive abundance fractions from temperature-insensitive line ratios using an approximation with respect to the non-detection of the O~VII line in most cases. From these fraction we consrtuct a single abundance distribution involving O, Mg, Ne, Si, S, Ar, and Fe to fit all X-ray spectra simultaneously. We compare this common abundance distribution to abundances determined recently in more massive Orion Trapezium stars and results from several other abundance studies of Orion stars and clusters. Title: Bright Hot Impacts by Erupted Fragments Falling Back on the Sun: A Template for Stellar Accretion Authors: Reale, Fabio; Orlando, Salvatore; Testa, Paola; Peres, Giovanni; Landi, Enrico; Schrijver, Carolus J. Bibcode: 2013Sci...341..251R Altcode: Impacts of falling fragments observed after the eruption of a filament in a solar flare on 7 June 2011 are similar to those inferred for accretion flows on young stellar objects. As imaged in the ultraviolet (UV)-extreme UV range by the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, many impacts of dark, dense matter display uncommonly intense, compact brightenings. High-resolution hydrodynamic simulations show that such bright spots, with plasma temperatures increasing from ~104 to ~106 kelvin, occur when high-density plasma (>>1010 particles per cubic centimeter) hits the solar surface at several hundred kilometers per second, producing high-energy emission as in stellar accretion. The high-energy emission comes from the original fragment material and is heavily absorbed by optically thick plasma, possibly explaining the lower mass accretion rates inferred from x-rays relative to UV-optical-near infrared observations of young stars. Title: Observing Coronal Nanoflares in Active Region Moss Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan; DeLuca, Ed; Hansteen, Viggo; Cirtain, Jonathan; Winebarger, Amy; Golub, Leon; Kobayashi, Ken; Korreck, Kelly; Kuzin, Sergey; Walsh, Robert; DeForest, Craig; Title, Alan; Weber, Mark Bibcode: 2013ApJ...770L...1T Altcode: 2013arXiv1305.1687T The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193Å images of the upper transition region moss at an unprecedented spatial (~0.''3-0.''4) and temporal (5.5 s) resolution. The Hi-C observations show in some moss regions variability on timescales down to ~15 s, significantly shorter than the minute-scale variability typically found in previous observations of moss, therefore challenging the conclusion of moss being heated in a mostly steady manner. These rapid variability moss regions are located at the footpoints of bright hot coronal loops observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly in the 94 Å channel, and by the Hinode/X-Ray Telescope. The configuration of these loops is highly dynamic, and suggestive of slipping reconnection. We interpret these events as signatures of heating events associated with reconnection occurring in the overlying hot coronal loops, i.e., coronal nanoflares. We estimate the order of magnitude of the energy in these events to be of at least a few 1023 erg, also supporting the nanoflare scenario. These Hi-C observations suggest that future observations at comparable high spatial and temporal resolution, with more extensive temperature coverage, are required to determine the exact characteristics of the heating mechanism(s). Title: Multi-wavelength Observations of Solar Flares with a Constrained Peak X-Ray Flux Authors: Bowen, Trevor A.; Testa, Paola; Reeves, Katharine K. Bibcode: 2013ApJ...770..126B Altcode: We present an analysis of soft X-ray (SXR) and extreme-ultraviolet (EUV) observations of solar flares with an approximate C8 Geostationary Operational Environmental Satellite (GOES) class. Our constraint on peak GOES SXR flux allows for the investigation of correlations between various flare parameters. We show that the duration of the decay phase of a flare is proportional to the duration of its rise phase. Additionally, we show significant correlations between the radiation emitted in the flare rise and decay phases. These results suggest that the total radiated energy of a given flare is proportional to the energy radiated during the rise phase alone. This partitioning of radiated energy between the rise and decay phases is observed in both SXR and EUV wavelengths. Though observations from the EUV Variability Experiment show significant variation in the behavior of individual EUV spectral lines during different C8 events, this work suggests that broadband EUV emission is well constrained. Furthermore, GOES and Atmospheric Imaging Assembly data allow us to determine several thermal parameters (e.g., temperature, volume, density, and emission measure) for the flares within our sample. Analysis of these parameters demonstrate that, within this constrained GOES class, the longer duration solar flares are cooler events with larger volumes capable of emitting vast amounts of radiation. The shortest C8 flares are typically the hottest events, smaller in physical size, and have lower associated total energies. These relationships are directly comparable with several scaling laws and flare loop models. Title: X-ray and EUV Observations of GOES C8 Solar Flare Events Authors: Bowen, Trevor A.; Testa, Paola; Reeves, Katharine K. Bibcode: 2013enss.confE..39B Altcode: 2013arXiv1305.1680B We present an analysis of soft X-rays (SXR) and extreme-ultraviolet (EUV) imaging and spectral observations of solar flares with an approximate C8 GOES class. Our constraint on peak GOES SXR flux allows for the investigation of correlations between various flare parameters. We show that the the duration of the decay phase is proportional to the duration of its rise phase. Additionally, we show significant correlations between the radiation emitted in the rise and decay phases of a flare: the total radiated energy of a given flare is proportional to the energy radiated during the rise phase alone. This partitioning of radiated energy between the rise and decay phases is observed in both soft X-ray (SXR) extreme ultraviolet (EUV) wavelengths. Though observations from the EUV Variability Experiment (EVE) show significant variation in the behavior of individual EUV spectral lines during different C8 events, we show that the broadband EUV emission is well constrained. Furthermore, using GOES and AIA data, we determine several thermal parameters of these events: temperature, volume, density, and emission measure. Analysis of these parameters demonstrate that the longer duration solar flares are cooler events with larger volumes capable of emitting vast amounts of radiation. The shortest C8 flares are typically the hottest events, smaller in physical size, and have lower associated total energies. These relationships are directly comparable with several sample scaling laws and flare loop models. Title: Hot Thermal X-Ray Emission from the Be Star HD 119682 Authors: Torrejón, J. M.; Schulz, N. S.; Nowak, M. A.; Testa, P.; Rodes, J. J. Bibcode: 2013ApJ...765...13T Altcode: 2013arXiv1301.2913T We present an analysis of a series of four consecutive Chandra high-resolution transmission gratings observations, amounting to a total of 150 ks, of the Be X-ray source HD 119682 (=1WGA J1346.5-6255), a member of the new class of γ Cas analogs. The Chandra light curve shows significant brightness variations on timescales of hours. However, the spectral distribution appears rather stable within each observation and during the whole campaign. A detailed analysis is not able to detect any coherent pulsation up to a frequency of 0.05 Hz. The Chandra High Energy Transmission Gratings spectrum seems to be devoid of any strong emission line, including Fe Kα fluorescence. The continuum is well described with the addition of two collisionally ionized plasmas of temperatures kT ≈ 15 keV and 0.2 keV, respectively, by the apec model. Models using photoionized plasma components (mekal) or non-thermal components (powerlaw) give poorer fits, providing support for the pure thermal scenario. These two components are absorbed by a single column with N H = (0.20+0.15 -0.03) × 1022 cm-2 compatible with the interstellar value. We conclude that HD 119682 can be regarded as a pole-on γ Cas analog. 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: The Thermal Structure of the Corona as observed with SDO/AIA, With and Without Image Deconvolution Authors: Boerner, P.; Cheung, C.; Schrijver, C.; Testa, P.; Weber, M. Bibcode: 2012AGUFMSH33B2240B Altcode: We describe a fast, robust method for deriving a differential emission measure function DEM(T) that matches the observations in the six coronal channels of SDO/AIA pixel-by-pixel over the full image, and present some of the results obtained by applying this technique to AIA movies of a variety of phenomena including "AIA waves," post-flare loops, and coronal holes. In addition, we discuss the effect of deconvolving the AIA point-spread function from the images on the inferred temperature structures.; Title: Investigating the Reliability of Coronal Emission Measure Distribution Diagnostics using Three-dimensional Radiative Magnetohydrodynamic Simulations Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan; Hansteen, Viggo; Carlsson, Mats Bibcode: 2012ApJ...758...54T Altcode: 2012arXiv1208.4286T Determining the temperature distribution of coronal plasmas can provide stringent constraints on coronal heating. Current observations with the Extreme ultraviolet Imaging Spectrograph (EIS) on board Hinode and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory provide diagnostics of the emission measure distribution (EMD) of the coronal plasma. Here we test the reliability of temperature diagnostics using three-dimensional radiative MHD simulations. We produce synthetic observables from the models and apply the Monte Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with the "true" distributions from the model, we assess the limitations of the diagnostics as a function of the plasma parameters and the signal-to-noise ratio of the data. We find that EMDs derived from EIS synthetic data reproduce some general characteristics of the true distributions, but usually show differences from the true EMDs that are much larger than the estimated uncertainties suggest, especially when structures with significantly different density overlap along the line of sight. When using AIA synthetic data the derived EMDs reproduce the true EMDs much less accurately, especially for broad EMDs. The differences between the two instruments are due to the: (1) smaller number of constraints provided by AIA data and (2) broad temperature response function of the AIA channels which provide looser constraints to the temperature distribution. Our results suggest that EMDs derived from current observatories may often show significant discrepancies from the true EMDs, rendering their interpretation fraught with uncertainty. These inherent limitations to the method should be carefully considered when using these distributions to constrain coronal heating. 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: Temperature Diagnostics of a Solar Active Region Using a Single-Filter Observation of Hinode/XRT Authors: Terzo, S.; Testa, P.; Reale, F. Bibcode: 2012ASPC..456..141T Altcode: Broad-band X-ray observations can provide limited temperature diagnostics through filter ratios. A high cadence observation of an active region made with a single Hinode/XRT filter allows us to use an alternative approach in which we measure the time fluctuations of the pixel count rate and use the variance as temperature proxy. We show the results and discuss limitations of method. Title: The HETG Orion Legacy Project: Abundances in Trapezium Stars Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Shen, N.; Testa, P.; Nichols, J.; Canizares, C. R. Bibcode: 2012AAS...22052306S Altcode: The ONC is an ideal astrophysical laboratory to study very young stars. The HETG Orion Legacy Project is designed to obtain a large number of high-resolution X-ray spectra of very young late type pre-main sequence stars, and several young massive and intermediate mass stars. Its extreme proximity and youth makes the core of the ONC a Chandra legacy project involving the only high resolution spectroscopic study of young embedded cluster stars for decades to come. For several PMS stars we derive abundance fractions from temperature-insensitive line ratios. From these fractions we construct a single abundance distribution involving O, Mg, Ne, Si, S, Ar, and Fe to fit all X-ray spectra simultaneously. We compare this common abundance distribution to abundances determined recently in more massive Orion Trapezium stars and to results from several other abundance studies of Orion stars and clusters. Title: Statistical Analysis of Eruptive Events Reported by the Flare Detective Module Authors: Winter, Henry D., III; Testa, P. Bibcode: 2012AAS...22020108W Altcode: As part of the Feature Finding Team (FFT) software suite the Flare Detective Module automatically detects and characterizes solar flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). Basic quantities such as time intervals, positions, and peak fluxes have been calculated and provided to the Heliophysics Event Knowledgebase (HEK) to allow the module to keep up with the extremely large size of the incoming data stream and provide near real-time information for space weather monitoring. Physically important parameters such as temperatures and emission measures, projected areas, light-curves, etc., are calculated in a second, post-processing step. While flares have been traditionally studied in isolation, the wealth of information provided by the Flare Detective Module allows for the study of the distribution flare properties across a large number of events. In this work we will investigate the correlation between the clustering of eruptive events with flare parameters such as peak temperature, duration, and projected extent of flares, as well as present other examples of statistical analyses that are possible with the Flare Detective Module. Title: Hinode/EIS Spectroscopic Validation of Very Hot Plasma Imaged with the Solar Dynamics Observatory in Non-flaring Active Region Cores Authors: Testa, Paola; Reale, Fabio Bibcode: 2012ApJ...750L..10T Altcode: 2012arXiv1204.0041T We use coronal imaging observations with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), and Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) spectral data to explore the potential of narrowband EUV imaging data for diagnosing the presence of hot (T >~ 5 MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging and EIS spectral data, including the Ca XVII line (at 192.8 Å), which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful co-alignment of the imaging and spectral data, we compare the morphology in a three-color image combining the 171, 335, and 94 Å AIA spectral bands, with the image obtained for Ca XVII emission from the analysis of EIS spectra. We find that in the selected active regions the Ca XVII emission is strong only in very limited areas, showing striking similarities with the features bright in the 94 Å (and 335 Å) AIA channels and weak in the 171 Å band. We conclude that AIA imaging observations of the solar corona can be used to track hot plasma (6-8 MK), and so to study its spatial variability and temporal evolution at high spatial and temporal resolution. Title: Hot Plasma Detected in Active Regions by HINODE/XRT and SDO/AIA Authors: Reale, F.; Testa, P.; Guarrasi, M.; DeLuca, E.; Peres, G.; Golub, L. Bibcode: 2012ASPC..456..129R Altcode: Multiple ratios of Hinode/XRT filters showed evidence of a minor very hot emission measure component in active regions. Recently also SDO/AIA detected hot plasma in the core of an active region. Here we provide estimates showing that the amount of emission measure of the hot component detected with SDO is consistent with that detected with Hinode/XRT. Title: Using 3D MHD realistic simulations of the solar corona to test plasma diagnostics Authors: Testa, P.; De Pontieu, B.; Martinez-Sykora, J.; Hansteen, V.; Carlsson, M. Bibcode: 2012decs.confE..27T Altcode: We synthesize coronal images and spectra from advanced 3D MHD simulations obtained from the state-of-the art Bifrost code, and explore how well they reproduce coronal observations with SDO/AIA and Hinode/EIS. We apply standard diagnostic techniques (e.g., density, and temperature diagnostics) to the synthetic observations and investigate how accurately the derived physical information matches the plasma parameters of the model. We discuss the limitations of the diagnostics and their implications. Title: Monte Carlo Markov chain DEM reconstruction of isothermal plasmas Authors: Landi, E.; Reale, F.; Testa, P. Bibcode: 2012A&A...538A.111L Altcode: 2011arXiv1112.2857L Context. Recent studies carried out with SOHO and Hinode high-resolution spectrometers have shown that the plasma in the off-disk solar corona is close to isothermal. If confirmed, these findings may have significant consequences for theoretical models of coronal heating. However, these studies have been carried out with diagnostic techniques whose ability to reconstruct the plasma distribution with temperature has not been thoroughly tested.
Aims: In this paper, we carry out tests on the Monte Carlo Markov chain (MCMC) technique with the aim of determining: 1) its ability to retrieve isothermal plasmas from a set of spectral line intensities, with and without random noise; 2) to what extent can it discriminate between an isothermal solution and a narrow multithermal distribution; and 3) how well it can detect multiple isothermal components along the line of sight. We also test the effects of 4) atomic data uncertainties on the results, and 5) the number of ions whose lines are available for the DEM reconstruction.
Methods: We first use the CHIANTI database to calculate synthetic spectra from different thermal distributions: single isothermal plasmas, multithermal plasmas made of multiple isothermal components, and multithermal plasmas with a Gaussian DEM distribution with variable width. We then apply the MCMC technique on each of these synthetic spectra, so that the ability of the MCMC technique at reconstructing the original thermal distribution can be evaluated. Next, we add a random noise to the synthetic spectra, and repeat the exercise, in order to determine the effects of random errors on the results. We also we repeat the exercise using a different set of atomic data from those used to calculate synthetic line intensities, to understand the robustness of the results against atomic physics uncertainties. The size of the temperature bin of the MCMC reconstruction is varied in all cases, in order to determine the optimal width.
Results: We find that the MCMC technique is unable to retrieve isothermal plasmas to better than Δlog T ≃ 0.05. Also, the DEM curves obtained using lines calculated with an isothermal plasma and with a Gaussian distribution with FWHM of log T ≃ 0.05 are very similar. Two near-isothermal components can be resolved if their temperature separation is Δlog T = 0.2 or larger. Thus, DEM diagnostics has an intrinsic resolving power of log T = 0.05. Atomic data uncertainties may significantly affect both temperature and peak DEM values, but do not alter our conclusions. The availability of small sets of lines also does not worsen the performance of the MCMC technique, provided these lines are formed in a wide temperature range.
Conclusions: Our analysis shows the present limitations in our ability to identify the presence of strictly isothermal plasmas in stellar and solar coronal spectra. Title: Testing EUV/X-Ray Atomic Data for the Solar Dynamics Observatory Authors: Testa, Paola; Drake, Jeremy J.; Landi, Enrico Bibcode: 2012ApJ...745..111T Altcode: 2011arXiv1110.4611T The Atmospheric Imaging Assembly (AIA) and the Extreme-ultraviolet Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) include spectral windows in the X-ray/EUV band. Accuracy and completeness of the atomic data in this wavelength range is essential for interpretation of the spectrum and irradiance of the solar corona, and of SDO observations made with the AIA and EVE instruments. Here, we test the X-ray/EUV data in the CHIANTI database to assess their completeness and accuracy in the SDO bands, with particular focus on the 94 Å and 131 Å AIA passbands. Given the paucity of solar observations adequate for this purpose, we use high-resolution X-ray spectra of the low-activity solar-like corona of Procyon obtained with the Chandra Low Energy Transmission Grating Spectrometer (LETGS). We find that while spectral models overall can reproduce quite well the observed spectra in the soft X-ray range λ <~ 50 Å, and at the EUV wavelengths λ >~ 130 Å, they significantly underestimate the observed flux in the 50-130 Å wavelength range. The model underestimates the observed flux by a variable factor ranging from ≈1.5, at short wavelengths below ~50 Å, up to ≈5-7 in the ~70-125 Å range. In the AIA bands covered by LETGS, i.e., 94 Å and 131 Å, we find that the observed flux can be underestimated by large factors (~3 and ~1.9, respectively, for the case of Procyon presented here). We discuss the consequences for analysis of AIA data and possible empirical corrections to the AIA responses to model more realistically the coronal emission in these passbands. 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: Initial Calibration of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) Authors: Boerner, Paul; Edwards, Christopher; Lemen, James; Rausch, Adam; Schrijver, Carolus; Shine, Richard; Shing, Lawrence; Stern, Robert; Tarbell, Theodore; Title, Alan; Wolfson, C. Jacob; Soufli, Regina; Spiller, Eberhard; Gullikson, Eric; McKenzie, David; Windt, David; Golub, Leon; Podgorski, William; Testa, Paola; Weber, Mark Bibcode: 2012SoPh..275...41B Altcode: The Atmospheric Imaging Assembly (AIA) instrument onboard the Solar Dynamics Observatory (SDO) is an array of four normal-incidence reflecting telescopes that image the Sun in ten EUV and UV wavelength channels. We present the initial photometric calibration of AIA, based on preflight measurements of the response of the telescope components. The estimated accuracy is of order 25%, which is consistent with the results of comparisons with full-disk irradiance measurements and spectral models. We also describe the characterization of the instrument performance, including image resolution, alignment, camera-system gain, flat-fielding, and data compression. Title: Models and Comparisons of Long Duration and Impulsive Solar Flare Events from SDO Authors: Bowen, Trevor; Testa, P.; Reeves, K. Bibcode: 2012AAS...21914407B Altcode: We compare observational signatures of two GOES C8-class solar flares through instrumentation on Solar Dynamics Observatory (SDO). Data from the Atmospheric Imaging Assembly (AIA) and the Extreme Ultraviolet Variability Experiment (EVE) provide a unique look at the sun through global scale, fast cadence, high-resolution photometric and spectral measurements; this data is ideal for analyzing the temporal evolution of flare properties. The two flares studied differ in both time scale and morphology, one may be classified as a long duration event (LDE), while the other is highly impulsive. Differences are noted in behavior in the AIA EUV bands as well as several spectral lines. Furthermore, we apply both zero and one dimensional multi-threaded hydrodynamic loop models to synthesize light curves and spectra for each flare. Funding provided by NSF REU solar physics program at CfA, grant number ATM-0851866 and Marlboro College. Title: Forward Modeling of Emission in Solar Dynamics Observatory/Atmospheric Imaging Assembly Passbands from Dynamic Three-dimensional Simulations Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Testa, Paola; Hansteen, Viggo Bibcode: 2011ApJ...743...23M Altcode: 2011arXiv1109.0704M It is typically assumed that emission in the passbands of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) is dominated by single or several strong lines from ions that under equilibrium conditions are formed in a narrow range of temperatures. However, most SDO/AIA channels also contain contributions from lines of ions that have formation temperatures that are significantly different from the "dominant" ion(s). We investigate the importance of these lines by forward modeling the emission in the SDO/AIA channels with three-dimensional radiative MHD simulations of a model that spans the upper layer of the convection zone to the low corona. The model is highly dynamic. In addition, we pump a steadily increasing magnetic flux into the corona, in order to increase the coronal temperature through the dissipation of magnetic stresses. As a consequence, the model covers different ranges of coronal temperatures as time progresses. The model covers coronal temperatures that are representative of plasma conditions in coronal holes and quiet Sun. The 131, 171, and 304 Å AIA passbands are found to be the least influenced by the so-called non-dominant ions, and the emission observed in these channels comes mostly from plasma at temperatures near the formation temperature of the dominant ion(s). On the other hand, the other channels are strongly influenced by the non-dominant ions, and therefore significant emission in these channels comes from plasma at temperatures that are different from the "canonical" values. We have also studied the influence of non-dominant ions on the AIA passbands when different element abundances are assumed (photospheric and coronal), and when the effects of the electron density on the contribution function are taken into account. Title: Testing coronal plasma diagnostics using 3D MHD models of the solar atmosphere Authors: Testa, P.; Martinez-Sykora, J.; Hansteen, V. H.; De Pontieu, B.; Carlsson, M. Bibcode: 2011AGUFMSH53C..06T Altcode: We synthesize coronal images and spectra from advanced 3D radiative MHD simulations obtained from the state-of-the-art Bifrost code, and explore how well they reproduce coronal observations with SDO/AIA and Hinode/EIS and XRT. We apply standard diagnostic techniques (e.g., density, temperature, abundance diagnostics) to the synthetic observations and investigate how accurately the derived physical information matches the plasma parameters of the model. We discuss the limitations of the diagnostics and their implications. Title: Comparing Long Duration and Impulsive Solar Flares Using SDO Data Authors: Bowen, T.; Testa, P.; Reeves, K. K. Bibcode: 2011AGUFMSH13B1943B Altcode: We present observations of two solar flares as recorded by instruments on the Solar Dynamics Observatory (SDO). Combining observations from the Atmospheric Imaging Assembly (AIA) and the Extreme Ultraviolet Variability Experiment (EVE) Spectrometer provide a robust set of data for solar flare analysis. The two instruments together provide a unique look at the sun through global scale, fast cadence, high resolution images and spectral measurements. Our study compares two solar flares--occurring on 05/29/2011 and 06/21/2011--of similar GOES X-ray flux classification, but which differ in both time scale and morphology. We note striking differences between the two flares; particularly in the behavior of the 131Å, 304Å, and 335Å wavebands. The results of this study have implications for numeric simulations of flaring loops, and may help constrain certain free parameters in modeling flare dynamics. We show that for the long duration flare, both EVE lightcurves and the peak flare spectrum are successfully simulated by multi-threaded loop models. Furthermore, we show that these same models accurately reproduce the lightcurves of hotter AIA channels for both flare types. Title: Cross-Calibration and Thermal Analysis with SDO/AIA Authors: Boerner, P.; Warren, H. P.; Testa, P.; Weber, M.; Schrijver, C. J. Bibcode: 2011AGUFMSH13B1955B Altcode: The measured intensity in each pixel of the images from SDO/AIA and similar narrowband EUV imagers can be used to perform quantitative analysis of the temperature and density of the plasma along the line of sight. This type of analysis depends very sensitively on the accuracy of the instrument calibration and the atomic physics models used to estimate the plasma emissivity. Unfortunately, it is difficult to assess the accuracy of these parameters, other than by verifying the consistency of datasets from different instruments and analysis techniques. Here we use differential emission measure models of the plasma temperature structure constrained by spectroscopic observations from SDO/EVE and Hinode/EIS to assess the AIA temperature response functions. The response functions generated using the CHIANTI database underestimate the emission from the non-flaring corona in the 94 and 131 Å channels. We find empirical corrections to the temperature response functions for these channels that are internally consistent and provide good agreement with DEMs obtained from other instruments. We present an assessment of the reliability of thermal analysis using AIA data based on the current state of the instrument calibration and spectral models. Title: Fe IX Calculations for the Solar Dynamics Observatory Authors: Foster, Adam R.; Testa, Paola Bibcode: 2011ApJ...740L..52F Altcode: 2011arXiv1107.0470F New calculations of the energy levels, radiative transition rates, and collisional excitation rates of Fe IX have been carried out using the Flexible Atomic Code, paying close attention to experimentally identified levels and extending existing calculations to higher energy levels. For lower levels, R-matrix collisional excitation rates from earlier work have been used. Significant emission is predicted by these calculations in the 5f-3d transitions, which will impact analysis of Solar Dynamics Observatory Atmospheric Imaging Assembly observations using the 94 Å filter. Title: Observations and Interpretation of a Low Coronal Shock Wave Observed in the EUV by the SDO/AIA Authors: Ma, Suli; Raymond, John C.; Golub, Leon; Lin, Jun; Chen, Huadong; Grigis, Paolo; Testa, Paola; Long, David Bibcode: 2011ApJ...738..160M Altcode: 2011arXiv1106.6056M Taking advantage of both the high temporal and spatial resolutions of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we studied a limb coronal shock wave and its associated extreme ultraviolet (EUV) wave that occurred on 2010 June 13. Our main findings are: (1) the shock wave appeared clearly only in the channels centered at 193 Å and 211 Å as a dome-like enhancement propagating ahead of its associated semi-spherical coronal mass ejection (CME) bubble; (2) the density compression of the shock is 1.56 according to radio data and the temperature of the shock is around 2.8 MK (3) the shock wave first appeared at 05:38 UT, 2 minutes after the associated flare has started and 1 minute after its associated CME bubble appeared; (4) the top of the dome-like shock wave set out from about 1.23 R sun and the thickness of the shocked layer is ~2 × 104 km (5) the speed of the shock wave is consistent with a slight decrease from about 600 km s-1 to 550 km s-1 and (6) the lateral expansion of the shock wave suggests a constant speed around 400 km s-1, which varies at different heights and directions. Our findings support the view that the coronal shock wave is driven by the CME bubble, and the on-limb EUV wave is consistent with a fast wave or at least includes the fast wave component. Title: Solar Dynamics Observatory Discovers Thin High Temperature Strands in Coronal Active Regions Authors: Reale, Fabio; Guarrasi, Massimiliano; Testa, Paola; DeLuca, Edward E.; Peres, Giovanni; Golub, Leon Bibcode: 2011ApJ...736L..16R Altcode: 2011arXiv1106.1591R One scenario proposed to explain the million degree solar corona is a finely stranded corona where each strand is heated by a rapid pulse. However, such fine structure has neither been resolved through direct imaging observations nor conclusively shown through indirect observations of extended superhot plasma. Recently, it has been shown that the observed difference in the appearance of cool and warm coronal loops (~1 MK and ~2-3 MK, respectively)—warm loops appearing "fuzzier" than cool loops—can be explained by models of loops composed of subarcsecond strands, which are impulsively heated up to ~10 MK. That work predicts that images of hot coronal loops (gsim 6 MK) should again show fine structure. Here we show that the predicted effect is indeed widely observed in an active region with the Solar Dynamics Observatory, thus supporting a scenario where impulsive heating of fine loop strands plays an important role in powering the active corona. Title: Detailed X-Ray Line Properties of θ2 Ori A in Quiescence Authors: Mitschang, Arik W.; Schulz, Norbert S.; Huenemoerder, David P.; Nichols, Joy S.; Testa, Paola Bibcode: 2011ApJ...734...14M Altcode: 2010arXiv1009.1896M We investigate X-ray emission properties of the peculiar X-ray source θ2 Ori A in the Orion Trapezium region using more than 500 ks of HETGS spectral data in the quiescent state. The amount of exposure provides tight constraints on several important diagnostics involving O, Ne, Mg, and Si line flux ratios from He-like ion triplets, resonance line ratios of the H- and He-like lines, and line widths. Accounting for the influence of the strong UV radiation field of the O9.5V star, we can now place the He-like line origin well within two stellar radii of the O-star's surface. The lines are resolved with average line widths of 341 ± 38 km s-1. In the framework of standard wind models, this likely implies a rather weak wind with moderate post-shock velocities. The emission measure distribution of the X-ray spectrum, as reported previously, includes very high temperature components which are not easily explained in this framework. The X-ray properties are also not consistent with coronal emissions from an unseen low-mass companion nor with typical signatures from colliding wind interactions. The properties are more consistent with X-ray signatures observed in the massive Trapezium star θ1 Ori C which has recently been successfully modeled with a magnetically confined wind model. Title: The HETG Orion Legacy Project Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Canizares, C. R.; Testa, P.; Nichols, J.; Mitschang, A. Bibcode: 2011AAS...21822832S Altcode: 2011BAAS..43G22832S The ONC is an ideal astrophysical laboratory to study very young stars. The HETG Orion Legacy Project is designed to obtain a large number of high-resolution X-ray spectra of very young late type pre-main sequence stars, and several young massive and intermediate mass stars. Its extreme proximity and youth makes the core of the ONC a Chandra legacy project involving the only high resolution spectroscopic study of young embedded cluster stars for decades to come. We present new results for the second most massive star θ 2 Ori A, the intermdiate mass binary θ 1 Ori E, and six late-type stars including MT Ori and LQ Ori. Title: Magneto-thermal convection in solar prominences Authors: Berger, Thomas; Testa, Paola; Hillier, Andrew; Boerner, Paul; Low, Boon Chye; Shibata, Kazunari; Schrijver, Carolus; Tarbell, Ted; Title, Alan Bibcode: 2011Natur.472..197B Altcode: Coronal cavities are large low-density regions formed by hemispheric-scale magnetic flux ropes suspended in the Sun's outer atmosphere. They evolve over time, eventually erupting as the dark cores of coronal mass ejections. Although coronal mass ejections are common and can significantly affect planetary magnetospheres, the mechanisms by which cavities evolve to an eruptive state remain poorly understood. Recent optical observations of high-latitude `polar crown' prominences within coronal cavities reveal dark, low-density `bubbles' that undergo Rayleigh-Taylor instabilities to form dark plumes rising into overlying coronal cavities. These observations offered a possible mechanism for coronal cavity evolution, although the nature of the bubbles, particularly their buoyancy, was hitherto unclear. Here we report simultaneous optical and extreme-ultraviolet observations of polar crown prominences that show that these bubbles contain plasma at temperatures in the range (2.5-12)×105 kelvin, which is 25-120 times hotter than the overlying prominence. This identifies a source of the buoyancy, and suggests that the coronal cavity-prominence system supports a novel form of magneto-thermal convection in the solar atmosphere, challenging current hydromagnetic concepts of prominences and their relation to coronal cavities. Title: Temperature Distribution of a Non-flaring Active Region from Simultaneous Hinode XRT and EIS Observations Authors: Testa, Paola; Reale, Fabio; Landi, Enrico; DeLuca, Edward E.; Kashyap, Vinay Bibcode: 2011ApJ...728...30T Altcode: 2010arXiv1012.0346T We analyze coordinated Hinode X-ray Telescope (XRT) and Extreme Ultraviolet Imaging Spectrometer (EIS) observations of a non-flaring active region to investigate the thermal properties of coronal plasma taking advantage of the complementary diagnostics provided by the two instruments. In particular, we want to explore the presence of hot plasma in non-flaring regions. Independent temperature analyses from the XRT multi-filter data set, and the EIS spectra, including the instrument entire wavelength range, provide a cross-check of the different temperature diagnostics techniques applicable to broadband and spectral data, respectively, and insights into cross-calibration of the two instruments. The emission measure distributions, (EM(T)), we derive from the two data sets have similar width and peak temperature, but show a systematic shift of the absolute values, the EIS (EM(T)) being smaller than the XRT (EM(T)) by approximately a factor two. We explore possible causes of this discrepancy, and we discuss the influence of the assumptions for the plasma element abundances. Specifically, we find that the disagreement between the results from the two instruments is significantly mitigated by assuming chemical composition closer to the solar photospheric composition rather than the often adopted "coronal" composition. We find that the data do not provide conclusive evidence on the high temperature (log T(K) >~ 6.5) tail of the plasma temperature distribution, however, suggesting its presence to a level in agreement with recent findings for other non-flaring regions. 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: Element Abundances in X-ray Emitting Plasmas in Stars Authors: Testa, Paola Bibcode: 2010SSRv..157...37T Altcode: 2010SSRv..tmp..138T; 2010arXiv1012.0343T Studies of element abundances in stars are of fundamental interest for their impact in a wide astrophysical context, from our understanding of galactic chemistry and its evolution, to their effect on models of stellar interiors, to the influence of the composition of material in young stellar environments on the planet formation process. We review recent results of studies of abundance properties of X-ray emitting plasmas in stars, ranging from the corona of the Sun and other solar-like stars, to pre-main sequence low-mass stars, and to early-type stars. We discuss the status of our understanding of abundance patterns in stellar X-ray plasmas, and recent advances made possible by accurate diagnostics now accessible thanks to the high resolution X-ray spectroscopy with Chandra and XMM-Newton. Title: Thermal study of active region plasma from Hinode and SDO observations Authors: Testa, P. Bibcode: 2010AGUFMSH41E..04T Altcode: We investigate temporal variability and temperature structuring of active region plasma by using Hinode and SDO observations, which provide complementary diagnostics and excellent temporal resolution and temperature coverage. We also discuss some limits of the diagnostics in the light of the estimated completeness and accuracy of the atomic data, in particular in the SDO/AIA passbands. Title: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) Authors: Golub, L.; Cirtain, J. W.; Kobayashi, K.; Winebarger, A. R.; Korreck, K. E.; Testa, P. Bibcode: 2010AGUFMSH11B1631G Altcode: We present a novel design for a stigmatic grazing incidence X-ray spectrograph for flight on a NASA sounding rocket. MaGIXS is comprised of a Wolter I telescope, a slit, a pair of parabolic mirrors, a plano variable line-spaced grating and a CCD detector. This design and layout have been optimized to produce an optical system with peak effective area of 5 mm^2, a wavelength range of 0.6-2.4 nm, spectral resolution of 2.0 pm, and spatial pixels of 2.5 arcsec along a 5 arcminute slit. The resulting instrument will resolve the solar spectrum for features in the solar corona with a two orders of magnitude increase over previous soft x-ray spectrographs in spatial and spectral resolution. Title: X-ray Flares of EV Lac: Statistics, Spectra, and Diagnostics Authors: Huenemoerder, David P.; Schulz, Norbert S.; Testa, Paola; Drake, Jeremy J.; Osten, Rachel A.; Reale, Fabio Bibcode: 2010ApJ...723.1558H Altcode: 2010arXiv1006.2558H We study the spectral and temporal behavior of X-ray flares from the active M dwarf EV Lac in 200 ks of exposure with the Chandra/HETGS. We derive flare parameters by fitting an empirical function which characterizes the amplitude, shape, and scale. The flares range from very short (<1 ks) to long (~104 s) duration events with a range of shapes and amplitudes for all durations. We extract spectra for composite flares to study their mean evolution and to compare flares of different lengths. Evolution of spectral features in the density-temperature plane shows probable sustained heating. The short flares are significantly hotter than the longer flares. We determined an upper limit to the Fe K fluorescent flux, the best-fit value being close to what is expected for compact loops. Title: Testing Atomic Data for the SDO AIA and EVE Missions Authors: Testa, Paola; Landi, E.; Drake, J. Bibcode: 2010AAS...21640203T Altcode: 2010BAAS...41..873T The Solar Dynamic Observatory carries two instruments, AIA and EVE, that include spectral windows in the X-ray/EUV band ( 15-170A). Accuracy in the atomic data in this wavelength range is essential for the interpretation of the solar EUV irradiance data from EVE and of the variability of the high temperature corona. Here we carry out a detailed benchmark of X-ray/EUV data in the CHIANTI 6.0.1 database to assess their completeness and accuracy. Given the paucity of solar observations, we use high-resolution X-ray spectra of the low-activity corona of Procyon obtained with the Low Energy Transmission Grating Spectrometer onboard Chandra. 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: The SDO flare detective Authors: Grigis, Paolo; Davey, A.; Martens, P.; Testa, P.; Timmons, R.; Su, Y.; SDO Feature Finding Team Bibcode: 2010AAS...21640208G Altcode: 2010BAAS...41..874G We present the flare detective, a software module to automatically detect and characterize solar flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The flare detective works in two steps. First, flares are detected in EUV images by analyzing lightcurves in macropixels. At this time, only basic quantities such as time intervals, positions, and peak fluxes will be determined. This will allow the module to keep up with the extremely large size of the incoming data stream and provide near real-time information for space weather monitoring. Second, the flare detective will be run again on the subset of images around the time intervals where a flare has been already detected, where more sophisticated (and slower) processing will be performed to better characterize the flare and provide physically important parameters such as temperatures and emission measures, projected areas and lightcurves in different channels. The events detected will be made available to the Heliophysics Events Knowledgebase (HEK) and also as a flare list in text format accessible on the web. This module is part of a larger effort to detect and track solar features and events that is optimized to run on the very large datasets provided by SDO. Title: X-ray emission processes in stars and their immediate environment Authors: Testa, Paola Bibcode: 2010PNAS..107.7158T Altcode: 2010arXiv1008.4343T A decade of X-ray stellar observations with Chandra and XMM-Newton has led to significant advances in our understanding of the physical processes at work in hot (magnetized) plasmas in stars and their immediate environment, providing new perspectives and challenges, and in turn the need for improved models. The wealth of high-quality stellar spectra has allowed us to investigate, in detail, the characteristics of the X-ray emission across the Hertzsprung-Russell (HR) diagram. Progress has been made in addressing issues ranging from classical stellar activity in stars with solar-like dynamos (such as flares, activity cycles, spatial and thermal structuring of the X-ray emitting plasma, and evolution of X-ray activity with age), to X-ray generating processes (e.g., accretion, jets, magnetically confined winds) that were poorly understood in the preChandra/XMM-Newton era. I will discuss the progress made in the study of high energy stellar physics and its impact in a wider astrophysical context, focusing on the role of spectral diagnostics now accessible. 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: XRT Detection of Hot Plasma in Active Regions and Nanoflare Heating Authors: Reale, F.; Klimchuk, J. A.; Parenti, S.; Testa, P. Bibcode: 2009ASPC..415..256R Altcode: Nanoflares occurring in sub-resolution strands have been long invoked as strong candidates for the heating of active region (AR) coronal loops. However, the frequent occurrence of nanoflares requires the steady presence of flare-hot plasma in the active region, which has been difficult to detect so far. We report on the analysis of multi-filter Hinode/XRT observations of an active region, which may show the widespread presence of 10 MK plasma. 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: The Chandra HETG Orion Legacy Project Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Testa, P.; Canizares, C. R. Bibcode: 2009AAS...21460408S Altcode: The HETG Orion Legacy Project is designed to accumulate a large number of high resolution X-ray spectra from young massive, intermediate mass, and low mass stars. The status as the nearest site of massive star formation and rich low-mass, pre-main sequence stellar population makes the core of the ONC an ideal Chandra Legacy high resolution spectroscopic study of young embedded cluster stars. This Chandra project is a unique enterprise to uncover properties and origins of the X-ray emission in young stellar objects with unprecedented spectral resolution.

The project so far has acquired about half a dozen HETG spectra of young stars in the ONC with up to 600 ks of exposure since the launch of the Chandra X-ray Observatory. These observations have allowed tremendous advances in our understanding of young stars, the origin of their X-ray emission, and the structure of their winds and coronae. We present most recent results and outline future perspectives. Title: The SDO Flare Detective Authors: Grigis, P. C.; Davey, A. R.; Martens, P. C.; Su, Y.; Testa, P.; Timmons, R. P. Bibcode: 2009AGUFMSH51B1277G Altcode: We present the flare detective, a software module to automatically detect and characterize solar flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The flare detective works in two steps. First, flares will be detected in EUV images by analysing lightcurves in macropixels. At this time, only basic quantities such as time intervals, positions, and peak fluxes will be determined. This will allow the module to keep up with the extremely large size of the incoming data stream and provide near real-time information for space weather monitoring. Second, the flare detective will be run again on the subset of images around the time intervals where a flare has been already detected, where more sophisticated (and slower) processing will be performed to better characterize the flare and provide physically important parameters such as temperatures and emission measures, projected areas and lightcurves in different channels. The events detected will be made available to the Heliophysics Knowledgebase (HEK) and also as a flare list in text format accessible on the web. This module is part of a larger effort to detect and track solar features and events that is optimized to run on very large datasets such as the ones provided by SDO. Title: X-Ray Emission and Corona of the Young Intermediate-Mass Binary θ1 Ori E Authors: Huenemoerder, David P.; Schulz, Norbert S.; Testa, Paola; Kesich, Anthony; Canizares, Claude R. Bibcode: 2009ApJ...707..942H Altcode: 2009arXiv0911.0189H θ1 Ori E is a young, moderate mass binary system, a rarely observed case of spectral-type G-giants of about 3 solar masses, which are still collapsing toward the main sequence, where they presumably become X-ray faint. We have obtained high-resolution X-ray spectra with Chandra and find that the system is very active and similar to coronal sources, having emission typical of magnetically confined plasma. It has a broad temperature distribution with a hot component and significant high energy continuum; narrow emission lines from H- and He-like ions, as well as a range of Fe ions, and relative luminosity, Lx /L bol = 10-3, at the saturation limit. Density, while poorly constrained, is consistent with the low density limits, our upper limits being ne < 1013 cm-3 for Mg XI and ne < 1012 cm-3 for Ne IX. Coronal elemental abundances are sub-solar, with Ne being the highest at about 0.4 times solar. We find a possible trend in Trapezium hot plasmas toward low relative abundances of Fe, O, and Ne, which is hard to explain in terms of the dust depletion scenarios of low-mass young stars. Variability was unusually low during our observations relative to other coronally active stars. Qualitatively, the emission is similar to post-main-sequence G-stars. Coronal structures could be compact or comparable to the dimensions of the stellar radii. From comparison to X-ray emission from similar mass stars at various evolutionary epochs, we conclude that the X-rays in θ1 Ori E are generated by a convective dynamo, present during contraction, but which will vanish during the main-sequence epoch possibly to be resurrected during post-main-sequence evolution. Title: Hinode/XRT and STEREO Observations of a Diffuse Coronal "Wave"-Coronal Mass Ejection-Dimming Event Authors: Attrill, Gemma D. R.; Engell, Alexander J.; Wills-Davey, Meredith J.; Grigis, Paolo; Testa, Paola Bibcode: 2009ApJ...704.1296A Altcode: We report on observations of the first diffuse coronal wave detected by Hinode/XRT. The event occurred near the west solar limb on 2007 May 23, originating from active region (AR) 10956 and was associated with a coronal mass ejection (CME) and coronal dimmings. The bright emission forming the coronal wave expanded predominantly to the east and south of the AR. We use X-Ray Telescope (XRT) and STEREO Behind (B) data combined with a potential magnetic field extrapolation to derive an understanding of the global magnetic field connectivity. We attribute the brightening to the east of the AR to compression and channeling of the plasma along large-scale loops. The brightening to the south of the AR expands across the quiet Sun, making the southern component a likely candidate for identification as a diffuse coronal wave. We analyze the bright front in STEREO/EUVI (B) 171, 195, and 284 Å images, as well as in XRT data, finding the strongest components to be largely cospatial in all bandpasses. We also exploit the near-limb location of this event by combining STEREO/COR1 and Extreme Ultra-Violet Imaging Telescope (EUVI) data. Using all the data, we derive a full picture of the low-coronal development of the eruption. The COR1 data show that the southernmost outer edge of the CME is progressively displaced southward during the expansion. EUVI data below the COR1 occulting disk show that the CME is significantly distorted in the low corona as a result of the associated filament eruption. The core coronal dimmings map to the core of the CME; the secondary coronal dimmings map to the CME cavity; and the diffuse coronal wave maps to the outermost edge of the expanding CME shell. The analysis of this near-limb event has important implications for understanding earlier eruptions originating from the same AR on 2007 May 16, 19, and 20. Title: Comparison of Hinode/XRT and RHESSI Detection of Hot Plasma in the Non-Flaring Solar Corona Authors: Reale, Fabio; McTiernan, James M.; Testa, Paola Bibcode: 2009ApJ...704L..58R Altcode: 2009arXiv0909.2529R We compare observations of the non-flaring solar corona made simultaneously with Hinode/XRT and RHESSI. The analyzed corona is dominated by a single active region on 2006 November 12. The comparison is made on emission measures. We derive emission measure distributions versus temperature of the entire active region from multifilter XRT data. We check the compatibility with the total emission measure values estimated from the flux measured with RHESSI if the emission comes from isothermal plasma. We find that RHESSI and XRT data analyses consistently point to the presence of a minor emission measure component peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI results is within a factor of a few and indicates an acceptable level of cross-consistency. Title: X-ray emission processes in stars and their immediate environment Authors: Testa, Paola Bibcode: 2009cfdd.confE...5T Altcode: A decade of X-ray stellar observations with Chandra and XMM-Newton has led to significant advances in our understanding of the physical processes at work in hot (magnetized) plasmas in stars and their immediate environment, providing new perspectives and challenges, and in turn the need for improved models. The wealth of high-quality stellar spectra has allowed us to investigate, in detail, the characteristics of the X-ray emission across the HR diagram. Progress has been made in addressing issues ranging from classical stellar activity in stars with solar-like dynamos (such as, flares, activity cycles, spatial and thermal structuring of the X-ray emitting plasma, evolution of X-ray activity with age,...), to X-ray generating processes (e.g. accretion, jets, magnetically confined winds,..) that were poorly understood in the pre-Chandra/XMM-Newton era. I will discuss the progress made in the study of high energy stellar physics and its impact in a wider astrophysics context, focusing on the role of spectral diagnostics now accessible. Title: Summing Flares From EV Lac Authors: Huenemoerder, David; Testa, Paola; Schulz, Norbert; Drake, Jeremy; Reale, Fabio; Canizares, Claude; Osten, Rachel Bibcode: 2009cfdd.confE.118H Altcode: We present preliminary results of a study of the spectral and temporal behavior of flares from the active M-dwarf EV Lac. We will apply three powerful techniques: high-resolution spectroscopic diagnostics to infer flaring loop conditions (temperature, density, dynamics); measurement of flare scale heights from Fe K fluorescence; and state-of-the-art hydrodynamic flare models. The high rate of short flares, the X-ray signature of high density, and the evidence for opacity in X-ray resonance lines make EV Lac an ideal target. A deep flare exposure obtained by summing short events will provide some of the best high-resolution time-resolved spectra possible for constraining physical models of M-dwarf coronae and flares with detail which can only be achieved through high resolution X-ray spectroscopy. Title: X-ray emission mechanism in the Be star HD 42054 Authors: Testa, Paola Bibcode: 2009cxo..prop.2782T Altcode: We propose to obtain a HETGS spectrum of the Be star HD 42054 to investigate the X-ray emission mechanisms in this mid B-type emission line star characterized by hot and variable X-ray thermal emission. This study, through detailed line-based diagnostics accessible only with high resolution spectroscopy, will allow us to shed light into the issue of X-ray emission from Be stars. Remarkably, beta Cephei is the only Be star to date for which high-resolution X-ray spectra have been obtained, excluding the very peculiar class of gamma Cas analogs. Title: Evidence of Widespread Hot Plasma in a Nonflaring Coronal Active Region from Hinode/X-Ray Telescope Authors: Reale, Fabio; Testa, Paola; Klimchuk, James A.; Parenti, Susanna Bibcode: 2009ApJ...698..756R Altcode: 2009arXiv0904.0878R Nanoflares, short and intense heat pulses within spatially unresolved magnetic strands, are now considered a leading candidate to solve the coronal heating problem. However, the frequent occurrence of nanoflares requires that flare-hot plasma be present in the corona at all times. Its detection has proved elusive until now, in part because the intensities are predicted to be very faint. Here, we report on the analysis of an active region observed with five filters by Hinode/X-Ray Telescope (XRT) in 2006 November. We have used the filter ratio method to derive maps of temperature and emission measure (EM) both in soft and hard ratios. These maps are approximate in that the plasma is assumed to be isothermal along each line of sight. Nonetheless, the hardest available ratio reveals the clear presence of plasma around 10 MK. To obtain more detailed information about the plasma properties, we have performed Monte Carlo simulations assuming a variety of nonisothermal EM distributions along the lines of sight. We find that the observed filter ratios imply bi-modal distributions consisting of a strong cool (log T ~ 6.3 - 6.5) component and a weaker (few percent) and hotter (6.6 < log T < 7.2) component. The data are consistent with bi-modal distributions along all lines of sight, i.e., throughout the active region. We also find that the isothermal temperature inferred from a filter ratio depends sensitively on the precise temperature of the cool component. A slight shift of this component can cause the hot component to be obscured in a hard ratio measurement. Consequently, temperature maps made in hard and soft ratios tend to be anti-correlated. We conclude that this observation supports the presence of widespread nanoflaring activity in the active region. 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: Observations of Nanoflare Produced Hot ( 10 Mk) Plasma Authors: Klimchuk, James A.; Reale, F.; Testa, P.; Parenti, S. Bibcode: 2009SPD....40.1214K Altcode: Indirect observational evidence suggests that some or most of the corona is heated impulsively on sub-resolution scales by nanoflares. Theoretical studies of possible heating mechanisms also support this picture. However, the most direct evidence of nanoflares---plasma hotter than 5 MK---has been difficult to obtain because the emission is expected to be very faint. The reason is two-fold: first, hot plasma cools very rapidly by thermal conduction; and second, densities are small because chromospheric evaporation has not had time to fill the corona. Recent observations from several instruments have now provided strong evidence of hot plasma. We report here on the detection of 10 MK plasma by the X-Ray Telescope (XRT) on Hinode. We show that the intensity of the emission is consistent with nanoflare models, but is extremely difficult to explain with steady heating. Title: Hinode/XRT and Stereo Observations of the May 2007 Coronal Wave-cme-dimming Events Authors: Attrill, Gemma; Engell, A. J.; Wills-Davey, M. J.; Grigis, P.; Testa, P. Bibcode: 2009SPD....40.2108A Altcode: We report observations of the first diffuse coronal wave detected by Hinode/XRT. The event occurred near the West solar limb on 23 May 2007, originating from active region (AR) 10956. The bright emission expanded both to the East and South of the AR. We combine the XRT results with data from STEREO (B) and a potential magnetic field extrapolation to understand the global magnetic field connectivity. We consider that the brightenings seen to the East and South of the source AR are generated by different physical processes, due to the distinct magnetic environments in these regions. We attribute the brightening to the East of the AR to compression and channelling of the plasma along large-scale loops. The brightening to the South of the AR expands across the quiet Sun, making the southern component a likely candidate for a classical diffuse coronal wave.

We analyse the bright front in STEREO/EUVI 171, 195 and 284 A images, as well as in XRT data, finding it to be largely co-spatial in all bandpasses. The expansion velocity of the diffuse bright front is 250 (± 85) km/s. We also exploit the near-limb properties of this event by combining STEREO/COR1 and EUVI data to derive a full picture of the low-coronal development of the eruption. The COR1 data show that the southern-most outer edge of the CME is progressively displaced southward. The core coronal dimmings map to the bright core of the CME; the secondary coronal dimmings map to the CME cavity; and the diffuse coronal "wave” maps to the outermost edge of the expanding CME shell. The analysis of this near-limb event has implications for understanding earlier eruptions originating from the same AR. In particular, we present a new analysis of the 19 May 2007 event.

NASA grants NNX09AB11G and NNH07AB97C supported this work. Title: Pre-flight Calibration Of The AIA Instrument On SDO Authors: Wolfson, C. Jacob; Boerner, P.; Soufli, R.; Podgorski, W.; Title, A.; Lemen, J.; Rausch, A.; Shing, L.; Stern, R.; McKenzie, D.; Testa, P.; Weber, M. Bibcode: 2009SPD....40.1704W Altcode: The Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) is a set of four reflecting telescopes designed to acquire high-resolution images of the solar atmosphere in a variety of extreme ultraviolet, ultraviolet and visible-light wavelength bands (see Lemen et al.). AIA takes images in ten wavelength channels, whose bandpasses are determined by the collecting area dedicated to each channel and the efficiency of the mirror coatings, filters, and detector. We describe the measurements of each of these components, and present the resulting effective area as functions of wavelength. The measured effective area functions will be cross-calibrated on orbit by comparing full-disk integrated fluxes from each of the AIA channels with the calibrated irradiance measurements from the EUV Variability Experiment (EVE) on SDO. The AIA effective areas are used to calculate temperature response functions and expected count rates in each channel for observations of various solar features. Title: Testing magnetically confined wind shock models for β Cephei using XMM-Newton and Chandra phase-resolved X-ray observations Authors: Favata, F.; Neiner, C.; Testa, P.; Hussain, G.; Sanz-Forcada, J. Bibcode: 2009A&A...495..217F Altcode: 2008arXiv0806.2275F Aims: We have performed a set of high- and low-spectral resolution phase-resolved X-ray observations of the magnetic B star β Cep, for which theoretical models predict the presence of a confined wind emitting X-rays from stationary shocks. Given the peculiar geometry of β Cep, some of the models predict strong rotational modulation of the X-ray emission, while other models predict a much lower amplitude modulation at 90 deg phase shift from the modulation predicted from the first group of models. Our observations were designed to provide a stringent test of such models.
Methods: We obtained four observations spaced in rotational phase with XMM-Newton (using both the EPIC cameras and the RGS spectrograph) and with Chandra (using the LETG spectrograph). A detailed analysis of the data was performed to derive both photometric and spectral parameters from the EPIC data, searching for rotational modulation, and to derive the location of the X-ray plasma from the line ratios in the He-like triplets of N, O, and Ne from the RGS data. The LETG data were used to constrain the presence of bulk motions in the plasma.
Results: The strong rotational modulation predicted by the early, static magnetically-confined wind model for the X-ray emission is not observed in β Cep. The small modulation present goes in the opposite direction, pointing to the absence of any optically thick disk of neutral material, and showing a modulation consistent with the later, dynamic models of magnetically-confined wind models in B stars. The lack of observed bulk motion points to the plasma being confined by a magnetic field, but the low plasma temperature and lack of any flaring show that the plasma is not heated by magnetic reconnection. Therefore, the observations point to X-ray emission from shocks in a magnetically confined wind, with no evidence of an optically thick, dense disk at the magnetic equator. Title: Characterization of X-ray emission from T Tauri Stars Authors: Shukla, Sonali J.; Weintraub, David; Kastner, Joel; Huenemoerder, David; Schulz, Norbert; Testa, Paola Bibcode: 2009AIPC.1094..333S Altcode: 2009csss...15..333S We are analyzing high-resolution Chandra ACIS-S/HETGS long integration spectra for a sample of young stars, including classical, weak-lined, and post-T Tauri stars as well as a young main sequence star. We have identified flaring and quiescent periods, based on overall X-ray luminosity, for several of the stars. We have measured line fluxes in the He-like ions separately in the flaring and quiescent epochs to determine forbidden-to-intercombination line ratios. Results from out analysis of four wTTS and one post-T Tauri star with Chandra/HETGS are included in this presentation. The temperature and density diagnostics for V987 Tau indicate that X-rays are emitted by a cool, high density plasma in the quiescent phase. Title: Neon and Chemical Fractionation Trends in Late-type Stellar Atmospheres Authors: García-Alvarez, David; Drake, Jeremy J.; Testa, Paola Bibcode: 2009AIPC.1094..796G Altcode: 2008arXiv0808.1794G; 2009csss...15..796G A survey of Ne, O and Fe coronal abundances culled from the recent literature for about 60 late-type stars confirms that the Ne/O ratio of stellar outer atmospheres is about two times the value recently recommended by Asplund et al. The mean Ne/O remains flat from the most active stars down to at least intermediate activity levels (-5<LX/Lbol<-2), with some evidence for a decline toward the lowest activity levels sampled. The abundances surveyed are all based on emission measure distribution analyses and the mean Ne/O is about 0.1 dex lower than that found from line ratios in the seminal study of mostly active stars by Drake & Testa (2005), but is within the systematic uncertainties of that study. We also confirm a pattern of strongly decreasing Fe/O with increasing stellar activity. The observed abundance patterns are reminiscent of the recent finding of a dependence of the solar Ne/O and Fe/O ratios on active region plasma temperature and indicate a universal fractionation process is at work. The firm saturation in stellar Ne/O at higher activity levels combined with variability in the solar coronal Ne/O leads us to suggest that Ne is generally depleted in the solar outer atmosphere and photospheric values are reflected in active stellar coronae. The solution to the recent solar model problem would then appear to lie in a combination of the Asplund et al. (2005) O abundance downward revision being too large, and the Ne abundance being underestimated for the Sun by about a factor of 2. Title: Polar Exploration and Coronal Structure in the Active Binary HR 5110 Authors: Huenemoerder, David P.; Osten, Rachel A.; Kesich, Anthony; Testa, Paola; Schulz, Norbert Bibcode: 2009AIPC.1094..656H Altcode: 2009csss...15..656H Overwhelming evidence exists for the importance of polar regions in controlling stellar atmospheric structure and dynamics in active binary systems. Uncertainties about the geometry of coronal emission have made conclusions about coronal structures on such stars ambiguous. We have obtained Chandra, VLA and VLBA observations of the nearly pole-on active binary system HR 5110 in order to investigate coronal structures without such ambiguity. The X-ray spectra will constrain thermal coronal volumes through determinaion of electron densities; radio observations will constrain non-thermal coronal volumes directly, and allow an estimation of the relative importance of thermal and nonthermal plasma in controlling and structuring active stellar coronae. Here we present preliminary results from the Chandra observations. Title: Structure and Evolution of Pre-Main Sequence Stars Authors: Schulz, Norbert S.; Allen, Glenn; Bautz, Mark W.; Canizares, Claude C.; Davis, John; Dewey, Dan; Huenemoerder, David P.; Heilmann, Ralf; Houck, John; Marshall, Herman L.; Nowak, Mike; Schattenburg, Mark; Audard, Marc; Drake, Jeremy; Gagne, Marc; Kastner, Joel; Kallman, Tim; Lautenegger, Maurice; Lee, Julia; Miller, Jon; Montmerle, Thierry; Mukai, Koji; Osten, Rachel; Parerels, Frits; Pollock, Andy; Preibisch, Thomas; Raymond, John; Reale, Fabio; Smith, Randall; Testa, Paola; Weintraub, David Bibcode: 2009astro2010S.263S Altcode: 2009arXiv0904.3385S; 2009astro2010S.263A Low-mass pre-main sequence (PMS) stars are strong and variable X-ray emitters, as has been well established by EINSTEIN and ROSAT observatories. It was originally believed that this emission was of thermal nature and primarily originated from coronal activity (magnetically confined loops, in analogy with Solar activity) on contracting young stars. Broadband spectral analysis showed that the emission was not isothermal and that elemental abundances were non-Solar. The resolving power of the Chandra and XMM X-ray gratings spectrometers have provided the first, tantalizing details concerning the physical conditions such as temperatures, densities, and abundances that characterize the X-ray emitting regions of young star. These existing high resolution spectrometers, however, simply do not have the effective area to measure diagnostic lines for a large number of PMS stars over required to answer global questions such as: how does magnetic activity in PMS stars differ from that of main sequence stars, how do they evolve, what determines the population structure and activity in stellar clusters, and how does the activity influence the evolution of protostellar disks. Highly resolved (R>3000) X-ray spectroscopy at orders of magnitude greater efficiency than currently available will provide major advances in answering these questions. This requires the ability to resolve the key diagnostic emission lines with a precision of better than 100 km/s. Title: Understanding X-ray emission from Young Stars Authors: Shukla, Sonali J.; Weintraub, D.; Huenemoerder, D.; Schulz, N.; Testa, P.; Kastner, J. Bibcode: 2009AAS...21341404S Altcode: 2009BAAS...41..224S High-resolution X-ray observations over long integration times have advanced our understanding of the X-ray emitting plasmas of young stars. We have identified and are analyzing a sample of ten stars from the Chandra archives observed with the High Energy Transmission Grating Spectrometer (HETGS) spanning the various evolutionary phases (classical, weak-lined, post-T Tauri and main sequence) of young stars. We have identified flaring and quiescent periods, based on overall X-ray luminosity, for several of the stars. By measuring the X-ray line fluxes from these stars, we are able to discern temperatures, densities, and abundances that indicate the physical characteristics of the X-ray emitting plasmas. Of the analysis thus far, the temperature and density diagnostics for V987 Tau in quiescence indicate a cool, high density plasma. Title: Fe Kα and Hydrodynamic Loop Model Diagnostics for a Large Flare on II Pegasi Authors: Ercolano, Barbara; Drake, Jeremy J.; Reale, Fabio; Testa, Paola; Miller, Jon M. Bibcode: 2008ApJ...688.1315E Altcode: 2008arXiv0807.2093E The observation by the Swift X-ray Telescope of the Fe Kα1, α2 doublet during a large flare on the RS CVn binary system II Peg represents one of only two firm detections to date of photospheric Fe Kα from a star other than our Sun. We present models of the Fe Kα equivalent widths reported in the literature for the II Peg observations and show that they are most probably due to fluorescence following inner shell photoionization of quasi-neutral Fe by the flare X-rays. Our models constrain the maximum height of flare the to 0.15R* assuming solar abundances for the photospheric material, and 0.1R* and 0.06R* assuming depleted photospheric abundances ([M/H] = -0.2 and -0.4, respectively). Accounting for an extended loop geometry has the effect of increasing the estimated flare heights by a factor of ~3. These predictions are consistent with those derived using results of flaring-loop models, which are also used to estimate the flaring loop properties and energetics. From loop models we estimate a flare loop height of 0.13R*, plasma density of ~4 × 1012 cm-3, and emitting volume of ~6 × 1030 cm3. Our estimates for the flare dimensions and density allow us to estimate the conductive energy losses to Econd <= 2 × 1036 erg, consistent with upper limits previously obtained in the literature. Finally, we estimate the average energy output of this large flare to be ~1033 erg s-1, or 1/10th of the stellar bolometric luminosity. Title: X-Ray Emission from Young Stellar Objects in the epsilon Chamaeleontis Group: The Herbig Ae Star HD 104237 and Associated Low-Mass Stars Authors: Testa, Paola; Huenemoerder, David P.; Schulz, Norbert S.; Ishibashi, Kazunori Bibcode: 2008ApJ...687..579T Altcode: 2008arXiv0807.0059T We present Chandra HETGS observations of the Herbig Ae star HD 104237 and the associated young stars comprising lower mass stars, in the 0.15-1.75 M⊙ mass range, in their pre-main-sequence phase. The brightest X-ray source in the association is the central system harboring the Herbig Ae primary and a K3 companion. Its X-ray variability indicates modulation possibly on timescales of the rotation period of the Herbig Ae star, and this would imply that the primary significantly contributes to the overall emission. The spectrum of the Herbig Ae+K3 system shows a soft component significantly more pronounced than in other K-type young stars. This soft emission is reminiscent of the unusually soft spectra observed for the single Herbig Ae stars HD 163296 and AB Aur, and therefore we tentatively attribute it to the Herbig Ae of the binary system. The HETGS spectrum shows strong emission lines corresponding to a wide range of plasma temperatures. The He-like triplet of Mg XI and Ne IX suggests the presence of plasma at densities of about 1012 cm-3, possibly indicating an accretion-related X-ray production mechanism. The analysis of the zeroth-order spectra of the other sources indicates X-ray emission characteristics typical of pre-main-sequence stars of similar spectral type, with the exception of the T Tauri HD 104237-D, whose extremely soft emission is very similar to the emission of the classical T Tauri star TW Hya and suggests X-ray production by shocked accreting plasma. 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: Diagnostics of the Thermal Structure of Off-Disk Quiet Sun Plasmas Authors: Testa, P.; Landi, E. Bibcode: 2008AGUSMSP51A..02T Altcode: It has been suggested recently that the quiet solar corona, when observed outside the solar disk, is isothermal or near isothermal. If true, this result has profound consequences for any theoretical model trying to explain the thermal structure and the temperature of the quiet solar corona. In this work we study the thermal structure of the solar corona by combining simultaneous, long-exposure SOHO/SUMER and Hinode/EIS observations of the quiet solar corona that include the entire wavelength range of both instruments. We also analyze simultaneous Hinode/XRT observations of the study region. This comprehensive dataset includes lines emitted by many different types of transitions and by a very large number of ions, that enable us to obtain a very accurate determination of the thermal structure of the quiet solar corona. Title: X-Ray Properties of Very Young Massive Stars in the Orion Trapezium Cluster Authors: Schulz, N. S.; Huenemoerder, D. P.; Testa, P.; Canizares, C. R. Bibcode: 2008ASPC..387..355S Altcode: The HETG Orion Legacy Project aims to study plasma properties of a large number of highly resolved X-ray spectra from young stars over a large range of masses and evolutionary stages. The spectra are collected throughout the lifetime of Chandra and thus not only provide highly significant X-ray line strengths for detailed plasma diagnostics but also longterm X-ray monitoring. The heart of the Orion Nebula Cluster (ONC) with a dynamic age of ∼ 3× 10^5 yr is one of the youngest and closest star forming regions to our Sun and contains an ensemble of the youngest massive and intermediate mass stars we know in the Galaxy. Three out of at least four of the most massive ZAMS stars, θ^1 Ori A, C and θ^2 Ori A show coronal properties indicative of magnetic activity that is very likely not due to known or unseen low-mass PMS companions. θ^1 Ori E, now identified as an intermediate mass PMS binary, is the second most luminous X-ray source in the ONC, and shows very high persistent X-ray temperatures and high plasma densities which are quite unusual properties in comparison with the coronal activities observed in low-mass PMS stars in the neighborhood. Title: Geometry Diagnostics of a Stellar Flare from Fluorescent X-Rays Authors: Testa, Paola; Drake, Jeremy J.; Ercolano, Barbara; Reale, Fabio; Huenemoerder, David P.; Affer, Laura; Micela, Giuseppina; Garcia-Alvarez, David Bibcode: 2008ApJ...675L..97T Altcode: 2008arXiv0801.3857T We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum of the single G-type giant HR 9024 during a large flare. In analogy to solar X-ray observations, we interpret the observed Fe Kα line as being produced by illumination of the photosphere by ionizing coronal X-rays, in which case, for a given Fe photospheric abundance, its intensity depends on the height of the X-ray source. The HETGS observations, together with three-dimensional Monte Carlo calculations to model the fluorescence emission, are used to obtain a direct geometric constraint on the scale height of the flaring coronal plasma. We compute the Fe fluorescent emission induced by the emission of a single flaring coronal loop that well reproduces the observed X-ray temporal and spectral properties according to a detailed hydrodynamic modeling. The predicted Fe fluorescent emission is in good agreement with the observed value within observational uncertainties, pointing to a scale height lesssim 0.3R*. Comparison of the HR 9024 flare with that recently observed on II Peg by Swift indicates the latter is consistent with excitation by X-ray photoionization. Title: The HETG Orion Legacy Project Authors: Schulz, Norbert S.; Testa, P.; Huenemoerder, D. P.; Canizares, C. R. Bibcode: 2008HEAD...10.1312S Altcode: The HETG Orion Legacy Project aims to study high energy plasma properties of a large number of highly resolved X-ray spectra from young stars over a large range of masses and evolutionary stages. The spectra are collected throughout the lifetime of Chandra and thus not only provide highly significant X-ray line strengths for detailed plasma diagnostics but also long-term X-ray monitoring.

The heart of the Orion Nebula Cluster with a dynamic age of 300000 yr is one of the youngest and closest star forming regions to our Sun and contains an ensemble of the youngest stars the Galaxy. The survey produces emission measure distributions and allows us to perform

plasma diagnostics using H-, He-, Li-like lines in over a dozen stars. We investigate the hypothesis further that X-ray production in very young massive stars is consistent with the standard model but very weak and low in energy unless there

is enhancement by additional processes. The survey produces HETG spectra for about a dozen of mostly K-type T Tauri stars various quality levels.

By spreading the observing time over many Chandra observation cycles the recording of HETG spectra of a few serendipitous flares is anticipated.

This work was supported by NASA through the Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 for the Chandra

X-Ray Center and Science Instruments. Title: HETG Observations of Hot Stars: From Predicted to Bizarre Authors: Schulz, Norbert S.; Testa, Paola; Huenemoerder, David P.; Canizares, Claude R. Bibcode: 2008ChNew..15....1S Altcode: No abstract at ADS Title: Evidence for Accretion in the High-Resolution X-Ray Spectrum of the T Tauri Star System Hen 3-600 Authors: Huenemoerder, David P.; Kastner, Joel H.; Testa, Paola; Schulz, Norbert S.; Weintraub, David A. Bibcode: 2007ApJ...671..592H Altcode: 2007arXiv0708.4393H We present high-resolution X-ray spectra of the nearby multiple T Tauri star (TTS) system Hen 3-600, obtained with the High Energy Transmission Grating Spectrograph (HETGS) aboard the Chandra X-Ray Observatory. Both principal binary components of Hen 3-600 (A and B, separation 1.4") were detected in the zeroth-order Chandra HETGS X-ray image. Hen 3-600-A, the component with a large mid-infrared excess, is a factor of ~2-3 fainter in X-rays than Hen 3-600-B, due to a large flare at Hen 3-600-B during our observation. The dispersed X-ray spectra of the two primary components overlap significantly, so spectral analysis was performed primarily on the first-order spectrum of the combined A + B system, with analysis of the individual dispersed spectra limited to regions where the contributions of A and B can be disentangled via cross-dispersion profile fitting. This analysis results in two lines of evidence indicating that the X-ray emission from Hen 3-600 A + B is derived, in part, from accretion processes. (1) The line ratios of He-like O VII in the spectrum of Hen 3-600 A + B indicate that the characteristic density of its X-ray-emitting plasma is significantly larger than those of coronally active main-sequence and pre-main-sequence stars. (2) A significant component of low-temperature (2-3 MK) plasma is present in the Hen 3-600 A + B spectrum; this ``soft excess'' appears somewhat stronger in component A. These results for Hen 3-600 A + B are consistent with, although less pronounced than, results obtained from X-ray grating spectroscopy of more rapidly accreting TTS systems. Indeed, all of the emission signatures of Hen 3-600 A + B that are potential diagnostics of accretion activity-from its high-resolution X-ray spectrum, through its UV excess and Hα emission-line strengths, to its weak near-infrared excess-suggest that its components (and component A in particular) represent a transition phase between rapidly accreting, classical T Tauri stars and nonaccreting, weak-lined T Tauri stars. Title: Magnetic Activity in Orion's Massive Young Stars Authors: Huenemoerder, David; Schulz, N.; Testa, P.; Kastner, J.; Canizares, C. Bibcode: 2007AAS...21114506H Altcode: 2007BAAS...39..998H In the heart if the Orion Nebula Cluster, one of the youngest and nearest star forming regions, is an ensemble of the youngest massive stars we know in the Galaxy. Having a dynamic age of about 300,000 years, it harbors a number of very young and hot ZAMS stars. Recent X-ray studies implied that some of these stars showed coronal type X-ray spectra, but some seemingly not. So far the most compelling cases for magnetic activity in these cases have been made for Theta-1 Ori C and Theta-2 Ori A. As part of our HETG Orion Legacy Project we are in the process of obtaining high quality and highly resolved X-ray spectra from all massive Trapezium stars. We will present spectra and analysis of some of these stars, including line-based spectral

characterization of spectra and dynamics. This work was supported by NASA through the Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 for the Chandra X-Ray Center and Science Instruments. Title: On X-Ray Optical Depth in the Coronae of Active Stars Authors: Testa, Paola; Drake, Jeremy J.; Peres, Giovanni; Huenemoerder, David P. Bibcode: 2007ApJ...665.1349T Altcode: 2007arXiv0706.4080T We have investigated the optical thickness of the coronal plasma through the analysis of high-resolution X-ray spectra of a large sample of active stars observed with the High Energy Transmission Grating Spectrometer on Chandra. In particular, we probed for the presence of significant resonant scattering in the strong Lyman series lines arising from hydrogen-like oxygen and neon ions. The active RS CVn-type binaries II Peg and IM Peg and the single M dwarf EV Lac show significant optical depth. For these active coronae, the Lyα/Lyβ ratios are significantly depleted as compared with theoretical predictions and with the same ratios observed in similar active stars. Interpreting these decrements in terms of resonance scattering of line photons out of the line of sight, we are able to derive an estimate for the typical size of coronal structures, and from these we also derive estimates of coronal filling factors. For all three sources we find that both the photon path length as a fraction of the stellar radius and the implied surface filling factors are very small and amount to a few percent at most. The measured Lyα/Lyβ ratios are in good agreement with APED theoretical predictions, thus indicating negligible optical depth, for the other sources in our sample. We discuss the implications for coronal structuring and heating flux requirements. For the stellar sample as a whole, the data suggest increasing quenching of Lyα relative to Lyβ as a function of both LX/Lbol and the density-sensitive Mg XI forbidden-to-intercombination line ratio, as might generally be expected. Title: Detailed Diagnostics of an X-Ray Flare in the Single Giant HR 9024 Authors: Testa, Paola; Reale, Fabio; Garcia-Alvarez, David; Huenemoerder, David P. Bibcode: 2007ApJ...663.1232T Altcode: 2007astro.ph..3422T We analyze a 96 ks Chandra HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters. A time-dependent one-dimensional hydrodynamic model of a loop with half-length L=5×1011 cm (~R*/2) and cross-sectional radius r=4.3×1010 cm, with a heat pulse of 15 ks and 2×1011 ergs cm-2 s-1 deposited at the loop footpoints, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission. For the first time we can compare predictions from the hydrodynamic model with single spectral features, other than with global spectral properties. We find that the model closely matches the observed line emission, especially for the hot (~108 K) plasma emission of the Fe XXV complex at ~1.85 Å. The model loop has L/R*~1/2 and aspect ratio r/L~0.1, as typically derived for flares observed in active stellar coronae, suggesting that the underlying physics is the same for these very dynamic and extreme phenomena in stellar coronae independently of stellar parameters and evolutionary stage. Title: Magnetic Activity in Orion's Very Young Massive Stars Authors: Schulz, Norbert S.; Huenemoerder, D. P.; Testa, P.; Kastner, J. H.; Canizares, C. R. Bibcode: 2007AAS...210.4007S Altcode: 2007BAAS...39R.154S The heart of the Orion Nebula Cluster contains an ensemble of the youngest massive stars we know in the Galaxy. The Orion Trapezium is Cluster is one of the youngest and closest star forming regions to our Sun. With a dynamic age of about 300000 yr it harbors a number of very young and hot ZAMS stars. Recent X-ray studies implied that some of these stars show coronal type X-ray spectra, but some seemingly not. So far the most compelling cases for magnetic activity have been made for θ 1 Ori C and θ 2 Ori A. As part of our HETG Orion Legacy Project we are in the process of obtaining high quality and highly resolved X-ray spectra from a large number of Trapezium cluster stars. With now 380 ks of

exposure we have high spectral quality for all massive Trapezum stars but θ 1 Ori D, which is surprisingly faint. With few exceptions

the spectra appear of coronal nature. We present results on emissivity, temperatures, emission radius, density as well as longterm variability. We compare the new results with properties previously found specifically for θ 1 Ori C and θ 2 Ori A as well as other hot and cool stars. Title: X-Ray Variability in the Young Massive Triple θ2 Orionis A Authors: Schulz, Norbert S.; Testa, Paola; Huenemoerder, David P.; Ishibashi, Kazunori; Canizares, Claude R. Bibcode: 2006ApJ...653..636S Altcode: 2006astro.ph..8420S Massive stars rarely show intrinsic X-ray variability. One exception is θ2 Ori A, which has shown strong variability over the last 5 years. We observed a large outburst of the X-ray source with the High Energy Transmission Grating Spectrometer on board Chandra and compare the emissivity and line properties in states of low and high flux. The low state indicates temperatures well above 25 MK. In the high state we find high emissivities in the range from 3 to over 100 MK. The outburst event in stellar terms is one of the most powerful ever observed and the most energetic one in the ONC, with a lower total energy limit of 1.5×1037 ergs. The line diagnostics indicate that the line-emitting regions in the low states are as close as within 1-2 stellar radii from the O star's photosphere, whereas the hard states suggest a distance of 3-5 stellar radii. We discuss the results in the context of stellar flares, magnetic confinement, and binary interactions. By matching the dates of all observations with the orbital phases of the spectroscopy binary orbit, we find that outbursts occur very close to the periastron passage of the stars. We argue that the high X-ray states are possibly the result of reconnection events from magnetic interactions of the primary and secondary stars of the spectroscopic binary. Effects from wind collisions seem unlikely for this system. The line properties in the low state seem consistent with some form of magnetic confinement. We also detect Fe fluorescence indicative of the existence of substantial amounts of neutral Fe in the vicinity of the X-ray emission. Title: X-ray Variability in the Young Massive Triple θ2 Ori A Authors: Schulz, Norbert S.; Testa, P.; Huenemoerder, D. P.; Ishibashi, K.; Canizares, C. R. Bibcode: 2006AAS...20913305S Altcode: 2006BAAS...38.1080S Massive stars rarely show intrinsic X-ray variability. The only O-stars credited to be intrinsically variable are theta1 Ori C due to effects from magnetic confinement of its wind, and theta2 Ori A suspected of similar activity. In the latter case early Chandra observations have shown rapid variability on time scales of hours. We determined X-ray fluxes from all observations with Chandra and find that the star shows very strong variability over the last 5 years in addition to short term varibility. There indications that this variability is connnected to the 21 day orbital period of the massive spectrocopic binary causing eruptive outbursts near periastron. A second large outburst of the X-ray source in November 2004 was observed with the high resolution transmission grating spectrometer onboard Chandra and we compare the emissivity and line properties in states of low and high flux. The outburst event in stellar terms is one of the most powerful ever observed and the most energetic one in the ONC with a lower total energy limit of 1.5 ×1037 ergs. Both flux states reveal high X-ray emissivities with temperatures well above 25 MK, during outbursts over 100 MK. The line diagnostics show that under the assumption that the He-like ions are photoexcited the line emitting regions in the low states are very close to the O-star's photosphere, whereas the high states indicate somewhat larger separation. We discuss the results in the context of stellar flares, magnetic reconnection, and binary interactions. We argue that the high X-ray states are possibly the result of reconnection events from magnetic interactions of the primary and secondary star of the spectroscopic binary. Effects from wind collisions seem unlikely for this system. The low state emissivity and R-ratios strengthen the predicament that X-ray emission is enhanced by magnetic confinement of the primary wind. Title: Extraordinarily Hot X-Ray Emission from the O9 Emission-Line Star HD 119682 Authors: Rakowski, Cara E.; Schulz, N. S.; Wolk, S. J.; Testa, Paola Bibcode: 2006ApJ...649L.111R Altcode: 2006astro.ph..8321R We present new optical and X-ray observations to show that the X-ray source 1WGA J1346.5-6255 previously associated with the SNR G309.2-0.6 can be unequivocally identified with the emission-line star HD 119682 located in the foreground open cluster NGC 5281. Images from Chandra in the X-ray band as well as from Magellan in the narrow optical Hα band show a coincidence of the source positions within 0.5". The X-ray source appears extremely hot for an OB star identified as of O9.7e type. XMM-Newton spectra show plasma temperatures of 1 and >8 keV with an X-ray luminosity of (6.2+/-0.1)×1032 ergs s-1. The optical and X-ray properties are very reminiscent of the prototype emission-line star γ Cas. We discuss the ramifications of this similarity with respect to very early type emission-line stars as a new class of hard X-ray sources. Title: X-Ray Spectroscopy of the Contact Binary VW Cephei Authors: Huenemoerder, David P.; Testa, Paola; Buzasi, Derek L. Bibcode: 2006ApJ...650.1119H Altcode: 2006astro.ph..6690H Short-period binaries represent extreme cases in the generation of stellar coronae via a rotational dynamo. Such stars are important for probing the origin and nature of coronae in the regimes of rapid rotation and activity saturation. VW Cep (P=0.28 days) is a relatively bright, partially eclipsing, very active object. Light curves made from Chandra HETGS data show flaring and rotational modulation but no eclipses. Velocity modulation of emission lines indicates that one component dominates the X-ray emission. The emission measure is highly structured, having three peaks. Helium-like triplet lines give electron densities of about (3-18)×1010 cm-3. We conclude that the corona is predominantly on the polar regions of the primary star and is compact. Title: X-ray spectral diagnostics of accretion processes in pre-main sequence stars: TWA14 Authors: Testa, Paola Bibcode: 2006cxo..prop.2107T Altcode: We propose to obtain a 160 ks Chandra LETG+ACIS-S spectrum of TWA14, one of the very few accreting pre-main sequence stars easily accessible to high-resolution spectroscopy, being in the nearby TW Hydrae Association and X-ray bright. This observation will provide unique X-ray diagnostics of accretion and grain depletion of accreting gas, and will determine the role of accretion and star-disk interaction in the high energy emission of classical T Tauri stars. Title: Chandra/HETGS Observation of Young Stellar Objects in the epsilon Chamaeleontis Group: Probing Proto-planetary Disk Systems in the HD 102437 Field Authors: Testa, Paola; Huenemoerder, D. P.; Schulz, N. S.; Ishibashi, K.; Canizares, C. R. Bibcode: 2006HEAD....9.0307T Altcode: 2006BAAS...38..346T We present 150 ks Chandra/HETGS observations of a group of young stars comprising a Herbig Ae star (HD 102437), three T Tauri stars (one classical T Tauri star, and two weak-lined T Tauri stars), and a supposed brown dwarf. The HETG spectrum of the Herbig Ae star shows strong emission lines corresponding to a wide range of plasma temperatures; spectral diagnostics provide clues to the yet unestablished X-ray production mechanisms in young intermediate mass stars. We also present 0th order spectra, obtained for all group members. Title: X-ray Flare on the Single Giant HR9024 Authors: Testa, P. Bibcode: 2006hrxs.confE..39T Altcode: We analyze a Chandra-HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters (thermal distribution, abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with semi-length 1012 cm (~Rstar), and impulsive footpoint heating triggering the flare, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission. Title: Chandra/HETGS Observations of the Capella System: The Primary as a Dominating X-Ray Source Authors: Ishibashi, Kazunori; Dewey, Daniel; Huenemoerder, David P.; Testa, Paola Bibcode: 2006ApJ...644L.117I Altcode: 2006astro.ph..5383I Using the Chandra/High Energy Transmission Grating Spectrometer (HETGS), we have detected the Doppler motion of Capella's X-ray emission lines in the 6-25 Å wave band. The observed motion follows the expected orbital motion of Capella's primary. This finding implies that the primary G8 III star, not the secondary G1 III star in the Hertzsprung gap, has been the dominant source of hot 106.8-107 K plasma at least in the last 6 years. In addition, the results demonstrate the long-term stability of the HETGS, and they demonstrate small uncertainties of 25 and 33 km s-1 in the velocity determination with the High and Medium Energy Gratings (HEG and MEG), respectively. Title: X-ray Flare Modeling in the Single Giant HR 9024 Authors: Testa, P.; Garcia-Alvarez, D.; Reale, F.; Huenemoerder, D. Bibcode: 2006ESASP.604..117T Altcode: 2006xru..conf..117T; 2005astro.ph.12624T We analyze a Chandra-HETGS observation of the single G-type giant HR 9024. The high flux allows us to examine spectral line and continuum diagnostics at high temporal resolution, to derive plasma parameters (thermal distribution, abundances, temperature, ...). A time-dependent 1D hydrodynamic loop model with semi-length 10$^{12}$cm ($\sim R_{\star}$), and impulsive footpoint heating triggering the flare, satisfactorily reproduces the observed evolution of temperature and emission measure, derived from the analysis of the strong continuum emission. The observed characteristics of the flare appear to be common features in very large flares in active stars (also pre-main sequence stars), possibly indicating some fundamental physics for these very dynamic and extreme phenomena in stellar coronae. Title: The `solar model problem' solved by the abundance of neon in nearby stars Authors: Drake, Jeremy J.; Testa, Paola Bibcode: 2005Natur.436..525D Altcode: 2005astro.ph..6182T The interior structure of the Sun can be studied with great accuracy using observations of its oscillations, similar to seismology of the Earth. Precise agreement between helioseismological measurements and predictions of theoretical solar models has been a triumph of modern astrophysics. A recent downward revision by 25-35 per cent of the solar abundances of light elements such as C, N, O and Ne (ref. 2) has, however, broken this accordance: models adopting the new abundances incorrectly predict the depth of the convection zone, the depth profiles of sound speed and density, and the helium abundance. The discrepancies are far beyond the uncertainties in either the data or the model predictions. Here we report neon-to-oxygen ratios measured in a sample of nearby solar-like stars, using their X-ray spectra. The abundance ratios are all very similar and substantially larger than the recently revised solar value. The neon abundance in the Sun is quite poorly determined. If the Ne/O abundance in these stars is adopted for the Sun, the models are brought back into agreement with helioseismology measurements. Title: X-Ray Diagnostics of Grain Depletion in Matter Accreting onto T Tauri Stars Authors: Drake, Jeremy J.; Testa, Paola; Hartmann, Lee Bibcode: 2005ApJ...627L.149D Altcode: 2005astro.ph..6185H Recent analysis of high-resolution Chandra X-ray spectra has shown that the Ne/O abundance ratio is remarkably constant in stellar coronae. Based on this result, we point out the utility of the Ne/O ratio as a discriminant for accretion-related X-rays from T Tauri stars and for probing the measure of grain depletion of the accreting material in the inner disk. We apply the Ne/O diagnostic to the classical T Tauri stars BP Tau and TW Hya-the two stars found to date whose X-ray emission appears to originate, at least in part, from accretion activity. We show that TW Hya appears to be accreting material that is significantly depleted in O relative to Ne. In contrast, BP Tau has an Ne/O abundance ratio consistent with that observed for post-T Tauri stars. We interpret this result in terms of the different ages and evolutionary states of the circumstellar disks of these stars. In the young BP Tau disk (age ~0.6 Myr), dust is still present near the disk corotation radius and can be ionized and accreted, rereleasing elements depleted onto grains. In the more evolved TW Hya disk (age ~10 Myr), evidence points to ongoing coagulation of grains into much larger bodies, and possibly planets, that can resist the drag of inward-migrating gas, and the accreting gas is consequently depleted of grain-forming elements. Title: X-ray diagnostics of grain depletion in matter accreting onto T Tauri stars Authors: Testa, Paola; Drake, Jeremy; Hartmann, Lee Bibcode: 2005sfet.confE..21T Altcode: Recent analysis of high resolution Chandra X-ray spectra has shown that the Ne/O abundance ratio is remarkably constant in stellar coronae. Based on this result, we point out the utility of the Ne/O ratio as a discriminant for accretion-related X-rays from T Tauri stars, and for probing the measure of grain-depletion of the accreting material in the inner disk. We apply the Ne/O diagnostic to the classical T Tauri stars BP Tau and TW Hya---the two stars found to date whose X-ray emission appears to originate, at least in part, from accretion activity. We show that TW Hya appears to be accreting material which is significantly depleted in O relative to Ne. In constrast, BP Tau has an Ne/O abundance ratio consistent with that observed for post-T Tauri stars. We interpret this result in terms of the different ages and evolutionary states of the circumstellar disks of these stars. In the young BP Tau disk (age ∼ 0.6 Myr) dust is still present near the disk corotation radius and can be ionized and accreted, re-releasing elements depleted onto grains. In the more evolved TW Hya disk (age ∼ 10 Myr), evidence points to ongoing coagulation of grains into much larger bodies that can resist the drag of inward-migrating gas, and accreting gas is consequently depleted of grain-forming elements. Title: The structure of coronal plasma in active stellar coronae from density measurements Authors: Testa, P.; Drake, J. J.; Peres, G. Bibcode: 2005ESASP.560..997T Altcode: 2005csss...13..997T No abstract at ADS Title: Emission Measure Distribution in Loops Impulsively Heated at the Footpoints Authors: Testa, Paola; Peres, Giovanni; Reale, Fabio Bibcode: 2005ApJ...622..695T Altcode: 2004astro.ph.12482T This work is prompted by evidence of sharply peaked emission measure distributions in active stars and by the claims of isothermal loops in solar coronal observations, at variance with the predictions of hydrostatic loop models with constant cross section and uniform heating. We address the problem with loops heated at the footpoints. Since steady heating does not allow static loop model solutions, we explore whether pulse-heated loops can exist and appear as steady loops on a time average. We simulate pulse-heated loops, using the Palermo-Harvard 1-D hydrodynamic code, for different initial conditions corresponding to typical coronal temperatures of stars ranging from intermediate to active [T~(3-10)×106 K]. We find long-lived quasi-steady solutions even for heating concentrated at the footpoints over a spatial region of the order of ~1/5 of the loop half-length and broader. These solutions yield an emission measure distribution with a peak at high temperature, and the cool side of the peak is as steep as ~T5, in contrast to the usual ~T3/2 of hydrostatic models with constant cross section and uniform heating. Such peaks are similar to those found in the emission measure distribution of active stars around 107 K. Title: Size of coronal structures in active stellar coronae from the detection of X-ray resonant scattering Authors: Testa, P.; Drake, J. J.; Peres, G.; Deluca, E. E. Bibcode: 2005ESASP.560...43T Altcode: 2005csss...13...43T No abstract at ADS Title: X-Ray Diagnostics of Grain Depletion in Matter Accreting onto T Tauri Stars Authors: Drake, J. J.; Testa, P.; Hartmann, L. Bibcode: 2005prpl.conf.8167D Altcode: 2005LPICo1286.8167D No abstract at ADS Title: The Density of Coronal Plasma in Active Stellar Coronae Authors: Testa, Paola; Drake, Jeremy J.; Peres, Giovanni Bibcode: 2004ApJ...617..508T Altcode: 2004astro.ph..5019T We have analyzed high-resolution X-ray spectra of a sample of 22 active stars observed with the High Energy Transmission Grating Spectrometer on Chandra in order to investigate their coronal plasma density. Densities were investigated using the lines of the He-like ions O VII, Mg XI, and Si XIII. Si XIII lines in all stars of the sample are compatible with the low-density limit (i.e., ne<~1013 cm-3), casting some doubt on results based on lower resolution Extreme Ultraviolet Explorer (EUVE) spectra finding densities ne>1013 cm-3. Mg XI lines betray the presence of high plasma densities up to a few times 1012 cm-3 for most of the sources with higher X-ray luminosity (>~1030 ergs s-1) stars with higher LX and LX/Lbol tend to have higher densities at high temperatures. Ratios of O VII lines yield much lower densities of a few times 1010 cm-3, indicating that the ``hot'' and ``cool'' plasma resides in physically different structures. In the cases of EV Lac, HD 223460, Canopus, μ Vel, TY Pyx, and IM Peg, our results represent the first spectroscopic estimates of coronal density. No trends in density-sensitive line ratios with stellar parameters effective temperature and surface gravity were found, indicating that plasma densities are remarkably similar for stars with pressure scale heights differing by up to 3 orders of magnitude. Our findings imply remarkably compact coronal structures, especially for the hotter (~7 MK) plasma emitting the Mg XI lines characterized by the coronal surface filling factor, fMgXI, ranging from 10-4 to 10-1, while we find fOVII values from a few times 10-3 up to ~1 for the cooler (~2 MK) plasma emitting the O VII lines. We find that fOVII approaches unity at the same stellar surface X-ray flux level as characterizes solar active regions, suggesting that these stars become completely covered by active regions. At the same surface flux level, fMgXI is seen to increase more sharply with increasing surface flux. These results appear to support earlier suggestions that hot 107 K plasma in active coronae arises from flaring activity and that this flaring activity increases markedly once the stellar surface becomes covered with active regions. Comparison of our measured line fluxes with theoretical models suggests that significant residual model inaccuracies might be present and, in particular, that cascade contributions to forbidden and intercombination lines resulting from dielectronic recombination might be to blame. Title: Detection of X-Ray Resonance Scattering in Active Stellar Coronae Authors: Testa, Paola; Drake, Jeremy J.; Peres, Giovanni; DeLuca, Edward E. Bibcode: 2004ApJ...609L..79T Altcode: 2004astro.ph..5520T An analysis of Lyman series lines arising from hydrogen-like oxygen and neon ions in the coronae of the active RS CVn-type binaries II Peg and IM Peg, observed using the Chandra High Resolution Transmission Grating Spectrograph, shows significant decrements in the Lyα/Lyβ ratios as compared with theoretical predictions and with the same ratios observed in similar active binaries. We interpret these decrements in terms of resonance scattering of line photons out of the line of sight; these observations present the first strong evidence of this effect in active stellar coronae. The net line photon loss implies a nonuniform and asymmetric surface distribution of emitting structures on these stars. Escape probability arguments, together with the observed line ratios and estimates of the emitting plasma density, imply typical line-of-sight sizes of the coronal structures that dominate the X-ray emission of 1010 cm at temperatures of 3×106 K and of 108 cm at 107 K. These sizes are an order of magnitude larger than predicted by simple quasi-static coronal loops models but are still very small compared to the several 1011 cm radii of the underlying stars. Title: Hydrodynamic Model of Loops Heated by Microflares at the Footpoints Authors: Testa, P.; Peres, G. Bibcode: 2003SPD....34.1702T Altcode: 2003BAAS...35..837T We simulate loops maintained in coronal conditions by random heat pulses concentrated close to the footpoints, by using the Palermo-Harvard 1-D hydrodynamic code. We have explored the existence of dynamic but quasi-static solutions when the heating is very concentrated at footpoints whereas the heating concentrated at footpoints does not allow static loop models solutions. We studied the characteristics of the solutions (in terms of stability, density and temperature structure, emission measure distribution) as a function of the parameters that define the heating function, for three different loop lengths.

We found stable solutions even for heating concentrated over spatial regions of the order of L/5 and higher values. For these stable solutions, the average temperature profiles as a function of the loop coordinate show a flatter or even inverted profile (for the case with more concentrated heating) with respect to the standard static models; the emission measure distribution as a function of temperature is much steeper (up to ∼ T5) than the usual behavior as T3/2 of the hydrostatic standard models. Title: Temperature and Density Structure of Hot and Cool Loops Derived from the Analysis of TRACE Data Authors: Testa, P.; Peres, G.; Reale, F.; Orlando, S. Bibcode: 2002ApJ...580.1159T Altcode: We study the transversal structure (in particular the filamentation) and the longitudinal plasma stratification in two sets of solar coronal loops observed with TRACE in the 171 and 195 Å passbands. The density stratification and the thermal structuring of the plasma along the fibrils that form the loops are derived using two techniques simultaneously: (1) a filter ratio diagnostic (195/171 Å) and (2) modeling intensity profiles along the fibrils with hydrostatic models; in both techniques we remove the background flux. We find consistent values of temperature and density with both methods in the coronal structures selected. We find evidence of a very warm fibril (T~5×106 K) and of rather cold ones (T~2×105 K). The hot fibril appears to have a thermal structure with a maximum at the apex compatible with temperature and density stratification, dictated by energy balance, typical of a nonisothermal hydrostatic loop. The cold fibrils appear to be isothermal and are probably in dynamical conditions. Title: Temperature and density structure of hot and cool loops derived from the analysis of TRACE data Authors: Testa, P.; Peres, G.; Reale, F.; Orlando, S. Bibcode: 2002ESASP.505..203T Altcode: 2002solm.conf..203T; 2002IAUCo.188..203T We address the plasma structuring both across and along the magnetic field in two sets of solar coronal loops, observed with TRACE in the 171 Å and 195 Å passbands. We derive, after proper background removal, the density stratification and the thermal structure of the plasma in the fibrils forming the loops with two techniques: a) filter ratio diagnostic (195 Å/171 Å) and b) modeling intensity profiles along the fibrils with hydrostatic models. We find evidence of a hot fibril (T ~ 5×106K), with temperature and density stratification well-described with a typical non-isothermal hydrostatic loop model, and evidence of rather cold fibrils (T ~ 2×105K), isothermal and probably in dynamic conditions. Title: Temperature and density structure of hot and cool loops derived from the analysis of TRACE data Authors: Testa, P.; Peres, G.; Reale, F.; Orlando, S. Bibcode: 2001ESASP.493..389T Altcode: 2001sefs.work..389T No abstract at ADS