THE ATMOSPHERES OF T-TAURI STARS .2. CHROMOSPHERIC LINE FLUXES AND VEILING

A set of high-resolution calibrated spectra of southern T Tauri Stars (TTS), comprising objects with Halpha equivalent widths ranging from 3 to 40 angstrom are used to derive one-component plane-parallel chromo spheric models. Our motivation is to discover how much emission activi ty can truly be ascribed to stellar activity, using real calibrated st ellar data. We find that simple models can reproduce the Ca II line at 8542 angstrom for most of the stars. The chromospheric enhancements a re comparable to the ones found among active main-sequence stars of si milar spectral type. These models cannot account for the veiling obser ved in TTS. Likewise, realistic TTS chromospheres are unable to create the observed Balmer jumps. The targets have a range of Halpha strengt h that allow us to study possible correlations among narrow symmetric emission lines, and Halpha which probes nonstellar regions. On the bas is of their stellar versus systemic luminosities, Sz 77, Sz 82, and Sz 19 present signatures of disk accretion, in addition to the previousl y reported case of Sz 98. By correlating the fluxes of the Ca II IR li ne, Halpha and the near-infrared excess we conclude that disk accretio n may enhance the luminosity of typical chromospheric emission lines.