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SPECTROSCOPIC STUDY OF THE HERBIG BE STAR HD 100546

We present new results of a spectroscopic investigation performed for the≈10 Myr old Herbig Be star HD 100546. The data were collected during the period from 1992 to 1995 and consist of 80 high resolution spectra for H α, Hβ, Hei 5876Å, and Nai D lines. The line profiles show rather significant variability on time scales from less than a day to months. The analysis of these data gave arguments in favour of a circumstellar disk in an active mass exchange with HD 100546. In addition, the data also show that accretion and stellar wind may be two independent sources of activities on HD 100546, and the coexistence of them can result in the formation of an additional envelope at the sides of the equatorial disk. Two episodes of fast discrete accretion were noted during the observed period. In the first one, a red-shifted absorption was developed for the Balmer lines during two nights in 1992 June. A detailed analysis of this event allowed us to propose a geometrical model for the circumstellar disk responsible for the observed phenomenon. The second event was observed when the object was in state of photometric minimum in 1994 March. During this season, a number of variable features positionally moving toward higher velocities could be identified on the H α profiles. A study of the kinematical characteristics of this moving features leads to the conclusion that a star-grazing comet-like body may be the source of this fast discrete accretion. In addition, an analysis of the distribution of the interstellar medium toward the region of the sky containing HD 100546 gives strong evidence for the physical association between this star and the dark cloud DC296.2 −7.9.