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Session 22 - YSOs' Variability.
Display session, Monday, January 15
North Banquet Hall, Convention Center
HD 163296 is commonly classified as an isolated Herbig Ae star, and therefore it may be a pre-main-sequence star with an accretion disk. Because this star is spectroscopically one of the most strongly variable members of its class and because spectrum variability may provide clues to the dynamics of the disk, we studied 7 CCD échelle spectra obtained from 1994 Jul.\ to 1995 Sep.\ with the 1-m telescope of Ritter Observatory. The spectral resolution of this material is 0.23 Å\ at \lambda5800, and the continuum SNR ranges from about 15 to about 90. The spectral coverage consists of 9 disjoint 70-Å\ regions in the yellow and red; features of interest in these spectra are H\alpha, He I \lambda5876, and Si II \lambda\lambda6347, 6371. The He I line in these spectra is broad, weak, and variable, usually with emission on the blue wide of the absorption. We searched for an extended red wing, which would indicate accreting gas, but, if present, it is weak and obscured by telluric H_2O absorption lines.
Published H\alpha profiles of this star show strong variability with a P Cygni and a double-peaked line shape appearing with about equal frequency. Although our spectra include an example of each of these line shapes, they also include a pure emission morphology with ``bumps'' but no real absorption core. Since this line shape is not only newly observed for this star but also unlike the H\alpha profile of any other Herbig Ae/Be star that we have seen, we conclude that our observation caught the stellar envelope in an unusual state. The variable morphology of H\alpha in this star calls into question the physical significance of dividing the Herbig stars into subgroups according to the line profile of H\alpha (P Cygni or otherwise). [\bigskipamount]
MLB's participation in this research was supported by the NSF.
