The atmospheres of T Tauri stars. I - High-resolution calibrated observations of moderately active stars

Calibrated optical spectra from 3700 to 8700 Å with high resolution and signal-to-noise ratio have been obtained quasi-simultaneously for three pairs of cool low- and intermediate-activity southern T Tauri stars and one G2 T Tauri star with well-defined photospheric spectra. Together with observations of spectral standards, these are used to obtain spectral types, reddening corrections, radial velocities, v sin i, and in combination with near-IR and IRAS data, photospheric and systemic luminosities. From positions in the H-R diagram, the authors determine the mass, radius, and surface gravity for each object. Surface fluxes in the emission lines are discussed. For all targets, ratio or difference plots versus appropriate standards are analyzed and show that important features of T Tauri spectra are clearly chromospheric.