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Spectroscopic study of the Herbig Be star HD 100546
We present new results of a spectroscopic investigation performed forthe ~10 Myr old Herbig Be star HD 100546. The data were collected duringthe period from 1992 to 1995 and consist of 80 high resolution spectrafor H? , H? , He I 5876 Angstroms, and Na I D lines. The lineprofiles show rather significant variability on time scales from lessthan a day to months. The analysis of these data gave arguments infavour of a circumstellar disk in an active mass exchange with HD100546. In addition, the data also show that accretion and stellar windmay be two independent sources of activities on HD 100546, and thecoexistence of them can result in the formation of an additionalenvelope at the sides of the equatorial disk. Two episodes of fastdiscrete accretion were noted during the observed period. In the firstone, a red-shifted absorption was developed for the Balmer lines duringtwo nights in 1992 June. A detailed analysis of this event allowed us topropose a geometrical model for the circumstellar disk responsible forthe observed phenomenon. The second event was observed when the objectwas in state of photometric minimum in 1994 March. During this season, anumber of variable features positionally moving toward higher velocitiescould be identified on the H? profiles. A study of the kinematicalcharacteristics of this moving features leads to the conclusion that astar-grazing comet-like body may be the source of this fast discreteaccretion. In addition, an analysis of the distribution of theinterstellar medium toward the region of the sky containing HD 100546gives strong evidence for the physical association between this star andthe dark cloud DC296.2-7.9. Based on observations collected at theAstrophysical National Laboratory (LNA - Brazil) and the EuropeanSouthern Observatory (ESO)
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