Previous abstract Next abstract
HD 50138 has been proposed as a possible pre-main-sequence star with an accretion disk, i.e., as a Herbig Ae/Be star. It has a large infrared excess, and the C IV resonance lines sometimes show absorption from accreting gas (Grady et al.\ 1994, ASP Conf.\ Ser.\ 62, p.\ 409). In order to test further the hypothesis of an accretion disk, we studied CCD \'echelle spectra obtained from 1993 Nov.\ to 1995 Mar.\ with the 1-m telescope of Ritter Observatory. The spectral resolution of this material is 0.23 \AA\ at $\lambda$5800, and the SNR ranges from about 20 to about 100. The spectral coverage consists of 9 disjoint 70-\AA\ regions in the yellow and red; features of interest in these spectra are H$\alpha$, [O~I] $\lambda$6364 and $\lambda$5577, the Na D lines, He~ I $\lambda$5876, and Si II $\lambda$$\lambda$6347, 6371. The [O I] lines show little or no variability. Transient, blue-shifted absorption features occasionally occur (not simultaneously) in H$\alpha$ and the D lines; similar features were observed by Doazan (1965, Ann.\ d'Ap., 28, 1). H$\alpha$ is a strong, double-peaked emission feature, with the central absorption approximately at rest with respect to the center of mass of the star. The He I and Si II lines have their absorption minima at this same velocity, but they show weak emission on the short-wavelength shoulder and an extended red wing---in short, an inverse P-Cygni profile. The long-wavelength wing is strongly variable, occasionally disappearing completely to leave a symmetrical absorption feature (although the short-wavelength emission persists at these times). These line profile characteristics support the claim that this star is accreting gas, and they are consistent with a disk geometry. \\[\bigskipamount] These observations were carried out as part of a multiwavelength campaign involving several individuals, including C. Grady (CSC), K. Bjorkman (U. Wisc.), and R. Schulte-Ladbeck (U. Pitt.). MB's participation in this research was supported by the REU program of the NSF.
Monday program listing