Occultation of young stellar objects by circumstellar disks
I. Theoretical expectations and preliminary comparison with observations
Received 3 May 2000 / Accepted 7 September 2000
The hypothesis that partial occultation of young stars by their circumstellar disks is responsible for UX Ori and T Tauri Type III photometric variability is quantitatively studied. We construct accretion disk models in which reprocessing of stellar and accretion luminosity leads to flaring of the disk (assumed to be in vertical hydrostatic equilibrium), and compute the probability to observe the star through the disk atmosphere. The mass accretion rate is found to primarily determine the range of view angles over which the star is fully or partially obscured by the disk. For average disk/star parameters relevant to active T Tauri stars, the probability of observing occultation events is 0.15, while it is typically 0.2 for parameters relevant to UX Ori. A preliminary analysis of available photometric data confirms these estimates and allows us to uncover in some stars cyclic variability on a time-scale of weeks to years that may tentatively be attributed to disk inhomogeneities or warps. These results suggest that direct observational study of the disk structure may be possible for a sizable fraction of young stellar objects.
Key words: accretion, accretion disks stars: formation stars: pre-main sequence stars: variables: general
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000