HAMILTON ECHELLE SPECTRA OF YOUNG STARS .1. OPTICAL VEILING

We present a extensive set of veiling measurements of T Tauri stars covering almost the entire optical spectrum. These are based on Hamilton echelle spectra obtained during 1987-1989. We have studied a full range of T Tauri stars, from "weak" to "continuum" stars. In some cases we have several spectra of a given target in which the veiling has changed, occasionally dramatically. We determined the veilings using two new methods: one which concentrates on the residual intensities of selected spectral lines, and the other which compares the autocorrelation functions for a T Tauri star and a veiled standard. We discuss some of the difficulties associated with veiling determinations, particularly the choice of "appropriate" standards. We tried both field subgiants and Hyades dwarfs as standards; the latter proved preferable. A line-ratio method is employed for spectral type matching. The general shape of the veiling is often as predicted by accretion disk models: almost flat in the red and increasing in the blue. Cooler stars have generally higher veiling, implying that the veiling power is relatively independent of stellar mass. The relation between veiling and the narrow and broad emission lines supports a nonstellar origin for the veiling and broad line components, and a stellar origin for the narrow lines. When the veiling changes, the variations in Hα suggest it is powered by the same source as the veiling continuum when the line is strong. This work leaves us satisfied that the disk accretion model for T Tauri stars is sensible, and that the strong line emission may be formed along with the continuum in the interface between star and accretion disk. The veilings found will serve as important constraints in refining further disk models.