Getman, Konstantin - X-ray flares, coronae and disks in Orion young stars
Kashyap, Vinay - Detection of Short Timescale Variability in Capella
Shukla, Sonali J. - Characterization of X-ray emission from T Tauri stars
Spitzbart, Brad - An archive of Chandra observations of regions of star formation (ANCHORS)
Townsley, Leisa - Chandra's X-ray View of Massive Star-forming Regions
Tsujimoto, Masahiro - An X-ray Imaging Study of the Stellar Population in RCW49
Westbrook, Owen - X-Atlas: An Online Archive of Chandra's Stellar HETG Observations
Jeremy Drake (SAO) , Barbara Ercolano (SAO), Douglas Swartz (MSFC)
X-ray spectra from stellar coronae are reprocessed by the underlying photosphere through scattering and photoionization events. While reprocessed X-ray spectra reaching a distant observer are at a flux level of only a few percent of that of the corona itself, characteristic lines formed by inner shell photoionization of some abundant elements can be significantly stronger. The emergent photospheric spectra are sensitive to the distance and location of the fluorescing radiation and can provide diagnostics of coronal geometry and abundance. Here we present Monte Carlo simulations of the photospheric K
doublet arising from quasi-neutral Fe irradiated by a coronal X-ray source. Fluorescent line strengths have been computed as a function of the height of the radiation source, the temperature of the ionising X-ray spectrum, and the viewing angle. We also illustrate how the fluorescence efficiencies scale with the photospheric metallicity and the Fe abundance. Based on the results we make three comments: (1) fluorescent Fe lines seen from pre-main sequence stars mostly suggest flared disk geometries and/or super-solar disk Fe abundances; (2) the extreme 
lines.
Jeremy Drake (SAO) , Barbara Ercolano (SAO), Jay Bookbinder (SAO)
The remarkable agreement between the observed solar oscillation spectrum and that predicted by solar models has been thrown into discord in recent years by evidence suggesting the photospheric C, N, O and Ne content has been overestimated by %. Monte Carlo calculations of the Ne K
K. We briefly describe the instrumental characteristics required to observe the lines and how they can be used to determine the photospheric Ne and O content and discriminate between competing solar abundance recommendations.
Konstantin Getman (Penn State University) , E. Feigelson (PSU), P. Broos (PSU), G. Garmire (PSU)
Pre-main sequence (PMS) stars are known to produce powerful X-ray flares which resemble magnetic reconnection solar flares scaled by factors upto 10^4. Several puzzles are present: the stability of implied magnetic loops 10 times the stellar radius; possible magnetic loops extending to the protoplanetary disk; and the origin of slow-rise flares. To investigate these issues in detail, we examine >200 of the brightest flares from >160 COUP stars which constitute the largest known homogeneous dataset of PMS flares ever acquired. We use an innovative method to trace the evolution of the flare plasma from an adaptively smoothed X-ray median energy of flare counts, and standard solar flare models to derive sizes of flaring coronal structures. We classify COUP flares into several morphological groups including "typical" rapid-rise-slow-decay and "slow-rise-and/or-top-flat" (SRTF). Rise and decay times range from hours to >1day, peak luminosities span 10^30.5-10^32.9erg/s range, and peak plasma temperatures - 20->100MK. For 800f the flares, inferred coronal loop sizes span 0.5-6Rstar while the remainder have even larger loops. Two main results are obtained. First, we find evidence that the coronal extent of PMS stars with inner circumstellar disks does not exceed the Keplerian corotation radius. In contrast, 300f stars without inner disks have coronas extending upto two corotation radii. This supports the model of Jardine et al. (2006) for coronal stripping by circumstellar disks. However, there is no relationship found between flare morphology and an inner disk indicative that star-disk field lines produce distinctive flare types. Second, our analyses indicate that the rapidly accreting PMS stars lack long-lasting and morphologically complex flare events such as SRTFs, events which could involve multiple flares from the entire coronal magnetosphere. We speculate that the progression of magnetic reconnection in multipolar magnetospheres ceases when it reaches an accretion hotspot with mass loaded coronal loops.
Konstantin Getman (Penn State University) , E. Feigelson (PSU), W. Lawson (UNSW-ADFA), P. Broos (PSU), G. Garmire (PSU)
The mysterious high galactic latitude cometary globule (CG) CG12 has been observed with the ACIS detector on board the Chandra X-ray Observatory. We detect 128 X-ray sources, of which a half are likely young stars formed within the globule's head. This new population of >=50 T-Tauri stars and one new embedded protostar is far larger than the previously reported few intermediate-mass and two protostellar members of the cloud. Most of the newly discovered stars have masses 0.2-0.7Msun, and 9-15
Vinay Kashyap (SAO/CXC) , Jennifer Posson-Brown (CXC)
Capella is a bright active binary (G1 III/G8 III) whose coronal luminosity has been remarkably steady over many decades of EUV and X-ray observations, and thus has been a frequent target for calibration observations. Numerous studies have attempted to detect intensity variability on it over various timescales, and have found long term variations of . Here, we analyze 205 ks of Capella data obtained for calibration purposes with the HRC-I on Chandra. Capella registers at approx 22 ct/s in this configuration, and due to the high data quality, unambiguously we detect variability on Capella at the 2-7 0.000000e+00vel at timescales of 5-20 ks. This work was supported by NASA Contract NAS8-39073 to the Chandra X-Ray Center.
Sonali J. Shukla (Vanderbilt University) , David Weintraub (Vanderbilt University), Joel Kastner (Rochester Institute of Technology), David Huenemoerder (MIT), Norbert Schulz (MIT), Paola Testa (MIT)
Although young stellar objects are known to be luminous and variable X-ray sources, the generation mechanism(s) of their X-rays are still unresolved. We have identified a sample of stars in the Chandra archives for which Chandra ACIS-S/HETGS long integration, high spectral resolution data exists. Our sample consists of both classical, weak-lined, and post-T Tauri stars as well as a young main sequence star. We are analyzing this data in a globally-consistent way to determine physical characteristics of the X-ray emitting plasma including temperature, density, and elemental abundances for each star. In addition, we are looking to confirm the results of recent studies that have shown that T Tauri stars have well-correlated H-alpha equivalent widths and f/i line ratios in He-like ions. Line density diagnostics have also shown that low-densities are associated with cool plasmas indicative of accretion shocks. Combining these diagnostic techniques for the variety of stars in our sample will enable us to identify similarities and differences among those stars that are thought to be actively accreting material from their circumstellar regions and those that have little or no accretion signatures in other wavelength regimes. We report on the first phase of our analysis of this sample of stars.
Brad Spitzbart (SAO)
ANCHORS is an archive of Chandra observations of regions of star formation. It is designed to aid both the X-ray astronomer with a desire to compare X-ray datasets and the star formation astronomer wishing to compare stars across the spectrum. We are completing a Phase 2 repro cessing of all datasets (80+ observations, 50+ distinct fields) to provide improved analysis and greater uniformity. The data consist of X-ray source prop erties including position, net count rates, flux, hardness ratios, lightcurve statistics and plots. Spectra are fit using several models, with final parameters and plots recorded in the archive. Multi-wavelength images and data are cross-linked to other resources such as 2MASS and SIMBAD. We will demonstrate the system, examine scientific pilot studies using the archive, and solicit users' feedback. This project is supported by Chandra archival grant AR5-6002A and NASA contract NAS8-39073.
Paola Testa (MIT Kavli Institute for Astrophysics and Space Research) , Norbert S. Schulz (MIT), David P. Huenemoerder (MIT), Claude R. Canizares (MIT), Joel Kastner (RIT)
The Orion Trapezium Cluster (OTC) at the heart of the Orion Nebula is one of the youngest and closest star forming regions to our Sun. Early Chandra observations resolved a large number of bright X-ray sources in the OTC from very young (
yr) stars of masses ranging from substellar to several tens of solar masses. Over the last eight Chandra observing cycles we scanned the OTC with the HETGS to obtain a homogenuous sample of high resolution X-ray spectra from very young stars which are assumed to be coeval in terms of their star formation history, possess similar chemical composition,and span a large mass range. So far we have accumulated over 85f the anticipated 590 ks of exposure. The set includes good quality spectra of several massive ZAMS stars, and we have identified three processes of X-ray production: standard line driven wind shocks, magnetic confinement of winds, and most recently binary induced magnetic reconnection. The most compelling cases for magnetic activity have been made for 
Ori E) and several PMS stars of K/M spectral type (e.g., MT Ori). The results include X-ray emissivities, temperatures, mission radii, plasma densities as well as short- and longterm variability of these sources. We compare the new results with properties previously found in some of these sources as well as other hot and cool stars.
Leisa Townsley (Penn State University)
Chandra is providing remarkable new views of massive star-forming regions, revealing the effects of massive stars on their surroundings. We will explore the latest data on several such regions, highlighting physical processes that characterize the life of a massive stellar cluster, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. X-ray observations reveal hundreds of pre-main sequence stars accompanying the massive stars that power these great HII region complexes; this X-ray selected sample of young stars can be used to study disk frequency and evolution in the proximity of massive stars. The most massive stars themselves are often anomalously hard X-ray emitters; this may be a new indicator of close binarity. These complexes are sometimes suffused by diffuse X-ray structures, signatures of multi-million-degree plasmas created by fast O-star winds. In older regions we see the X-ray remains of the deaths of massive stars that stayed close to their birthplaces, exploding as cavity supernovae within the superbubbles that these clusters created.
Masahiro Tsujimoto (Pennsylvania State University) , Feigelson, E. D., Townsley, L. K., Broos, P. B., Getman, K. V., Wang, J. Garmire, G. P. (Penn State), Baba, D. (Nagoya), Nagayama, T. (Kyoto), Tamura, M. (NAOJ), Churchwell, E. B. (Wisconsin)
We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW49 and its central OB association Westerlund 2. We obtained a 40 ks X-ray image of a 17'x17' field using the Chandra X-ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric 8'3x8'3 region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer Space Telescope MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically-identified early-type stars in this region. (2) Most (86
Owen Westbrook (MIT) , Nancy Remage Evans, Scott J. Wolk, Vinay L. Kashyap, Joy S. Nichols (SAO), Peter J. Mendygral (University of Minnesota), Jonathan D. Slavin, and Wayne L. Waldron
We have compiled a database of all stellar observations made with Chandra's High Energy Transmission Grating (HETG) to facilitate the rapid comparison, characterization, and analysis of high-resolution stellar X-ray spectra. This database, known as X-Atlas, is accessible through a web interface with extensive searching and interactive plotting capabilities. For each target, X-Atlas also features predictions of the low-resolution ACIS spectra convolved from the HETG data for comparison with stellar sources in archival ACIS images. X-Atlas offers more than 130 observations of over 65 stars and will be updated as additional observations become public. The atlas is currently expanding to non-stellar point sources and eventually will include Low Energy Transmission Grating data as well.