Comparison with model calculations suggests that TW Hya produces sufficient hard X-ray flux to produce significant ionization of molecular gas within its circumstellar disk such X-ray ionization may regulate both protoplanetary accretion and protoplanetary chemistry. The X-ray data show variations in X-ray flux on timescales of 1 hr as well as indications of changes in the X-ray absorbing column on timescales of several years, suggesting that flares and variable obscuration are responsible for the large-amplitude optical variability of TW Hya on short and long timescales, respectively. Analysis of ASCA and ROSAT spectra indicates characteristic temperatures of 1.7 and 9.7 MK for the X-ray emitting region(s) of TW Hya, with emission lines of highly ionized Fe dominating the spectrum at energies of 1 keV. We present ASCA and ROSAT X-ray observations of the classical T Tauri star TW Hya, the namesake of a small association that, at a distance of 50 pc, represents the nearest known region of recent star formation. Received 1999 April 26 accepted 1999 June 25 Joel H. Kastner, 1 David P. Huenemoerder, and Norbert S. SchulzĬenter for Space Research, Massachusetts Institute of Technology, NE80-6007, Cambridge, MA 02139ĭepartment of Physics and Astronomy, Vanderbilt University, P.O. X-Ray Spectroscopy of the Nearby, Classical T Tauri Star TW Hydrae Kastner et al., X-Ray Spectroscopy of TWHya
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