X-ray Spectroscopy of the Contact Binary VW Cephei

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 d) is a relatively bright, partially eclipsing, and 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 3.0E+10 - 18.0E+10 /cm^3. We conclude that the corona is predominantly on the polar regions of the primary star and compact.Comment: Accepted for publication in the Astropysical Journal, 23 June 2006; 22 pages, 15 figure

Gyrochronology of Wide Binaries in the Kepler K2 Campaign 5 Field

We are determining rotation periods for an ensemble of over 100 wide non-interacting binary stars in the K2 Campaign 5 field that contain two main sequence dwarfs, as well as a smaller sample containing at least one white dwarf component. Observations of such coeval pairs provide the basis for our new investigation of rotation-based age determinations. Such “gyrochronology” ages can achieve a precision that exceeds most other current method of stellar age determination. Here we present a status report on our analysis of the light curves extracted from the K2 Campaign 5 field

Testing the Gyrochronology Paradigm Using Wide Coeval Binary Stars

Gyrochronology—the empirical relation between rotation and age among lower main sequence stars—has the potential to provide useful age estimates in regimes where other techniques break down. However, its usefulness depends on the precision with which stellar rotation periods can be determined. To quantify the uncertainties associated with several period-finding algorithms, our team visually assessed a sample of almost 4000 main sequence binaries observed by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission. Machine learning and deep learning algorithms were then employed to assess the quality of the TESS light curves, using the visually analyzed light curves as a training set. We present a status report and a comparison of various gyrochronology models. Acknowledgments: Support for this project from the NSF AAG grant AST-1910396 and NASA ADAP grant 80NSSC22K0622 to Embry-Riddle Aeronautical University is gratefully acknowledged. Funding for the TESS mission is provided by NASA’s Science Mission directorate

Stellar Coronal Spectroscopy with the Chandra HETGS

Spectroscopy with the Chandra High Energy Transmission Grating Spectrometer provides details on X-ray emission and activity from young and cool stars through resolution of emission lines from a variety of ions. We are beginning to see trends in activity regarding abundances, emission measures, and variability. Here we contrast spectra of TV Crt, a weak-lined T Tauri star, with TW Hya, a Classical T Tauri star. TV Crt has a spectrum more like magnetic activity driven coronae, relative to the TW Hya spectrum, which we have interpreted as due to accretion-produced X-rays. We have also observed the long period system, IM Pegasi to search for rotational modulation, and to compare activity in a long period active binary to shorter period systems and to the pre-main sequence stars. We detected no rotational modulation, but did see long-duration flares.Comment: 5 pages, 2 figures; to be published in IAU Symposium 219: "Stars as Suns: Activity, Evolution, Planets" (Ed. A. Dupree and A. O. Benz