X-ray diagnostics of grain depletion in matter accreting onto T Tauri stars

Details X-ray diagnostics of grain depletion in matter accreting onto T Tauri stars X-ray diagnostics of grain depletion in matter accreting onto T Tauri stars

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005sfet.confe..21t&link_type=abstract

"Star Formation in the Era of Three Great Observatories, meeting abstracts from the conference held July 13-15, 2005 in Cambridg

Physics

Scientific paper

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.

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