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. 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. 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. 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 (Refer to PDF file for exact formulas).

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Also archived in: arXiv: astro-ph/9905126 v2 25 May 1999 Primary support for this work was provided by NASA ASCA data analysis grant NAG 5-4959 to Massachusetts Institute of Technology. Research by J. H. K., D. P. H., and N. S. S. at Massachusetts Institute of Technology is also supported by the Chandra X-ray Observatory Science Center as part of Smithsonian Astrophysical Observatory contract SVI-61010 under NASA Marshall Space Flight Center. Support for research by D. A. W. and J. H. K. was also provided by NASA Origins of Solar Systems program grant NAG 5-8295 to Vanderbilt University.ISSN:1538-4365 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

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Department, Program, or Center

Chester F. Carlson Center for Imaging Science (COS)


RIT – Main Campus