ON THE APPARENT POSITIONS OF T-TAURI STARS IN THE H-R DIAGRAM

We investigate the spread in apparent luminosities of T Tauri stars caused by occultation and emission from protostellar disks. A random distribution of disk inclination angles, coupled with a plausible range of accretion rates, introduces a significant scatter in apparent luminosities for intrinsically identical stars. The observed dispersion of luminosities for K7-M1 Hayashi track stars thought to have disks in Taurus-Auriga is similar to predictions of the simple accretion disk model, which suggests that age determinations for many pre-main-sequence stars are uncertain. Our results also suggest that Stahler's "birthline" for convective track pre-main-sequence stars may be located at slightly lower luminosities than previously thought.