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 \sim 50 pc , represents the nearest known region of recent star formation .
Analysis of ASCA and ROSAT spectra indicates characteristic temperatures of \sim 1.7 MK and \sim 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 \sim 1 keV .
The X-ray data show variations in X-ray flux on \stackrel { < } { \sim } 1 hr timescales as well as indications of changes in 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 .
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 .