Name/Affiliation: Alexander Brown (CASA, University of Colorado)
X-ray Emission from Young Stars in the TW Hya Association
The 9 Myr old TW Hya Association (TWA) is the nearest group (typical distances of ~50 pc) of pre-main-sequence (PMS) stars with ages less than 10 Myr and contains stars with both actively accreting disks and debris disks. We have studied the coronal X-ray emission from a group of low mass TWA common-proper-motion binaries using the Chandra and Swift satellites. Our aim is to understand better how high energy photons affect the conditions around young stars and their role at early stages in photo-exciting atoms, molecules and dust grains in both the circumstellar disk and lower density circumstellar gas, and later, once planet formation is underway, by influencing protoplanetary evolution and the atmospheric conditions of the newly formed planets. The X-ray properties for 7 individual stars (TWA 13A, TWA 13B, TWA 9A, TWA 9B, TWA 8A, TWA 8B, and TWA 7) and 2 combined binary systems (TWA 3AB and TWA 2AB) have been measured. All the stars with sufficient signal require two-component fits to their CCD-resolution X-ray spectra, typically with a dominant hot (~2 kev (25 MK)) component and a cooler component at ~0.4 keV (4 MK). The brighter sources all show significant X-ray variability (at a level of 50-100% of quiescence) over the course of 5-15 kilosecond observations. We present the detailed X-ray properties for each of the stars and examine how the coronal emission correlates with stellar rotational properties and how it is affecting their circumstellar environment. This work was supported by Chandra grant GO1-12031X and NASA Swift grants NNX09AL59G and NNX10AK88G to the University of Colorado.