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   52004
   Recent studies of the classical T Tauri star (TTS) TW Hya and of five
   other nearby "isolated TTS" demonstrate that these 6 stars comprise a
   cloudless TTS association that lies only 30 pc from the Sun. All 6
   systems are bright X-ray sources, with X-ray fluxes that are an order
   of magnitude larger, on average, than the (absorption-corrected) X-ray
   fluxes of T Tauri stars in well-studied dark clouds like Taurus (D=140
   pc). We propose to observe these 6 stars with ASCA, to study high-
   temperature emission and circumstellar absorption in nearby TTS that
   are not obscured by cloud material. These observations will provide a
   new foundation for the intrepretation of X-ray spectra of cloud TTS, as
   well as new constraints on the rates of X-ray ionization and heating of
   circumstellar gas.
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