Astron. Astrophys. 326, 237-248
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Emission features in Br and Br spectra of normal O and B stars*
P.A. Zaal1, L.B.F.M. Waters1,2, T.R. Geballe3, and J.M. Marlborough4
1Astronomical Institute Anton Pannekoek, University of
Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
Received 6 November 1996 / Accepted 15 April 1997
We present high resolution Br and Br spectra for 15 near main-sequence O and B stars in a broad range in and with spectral type between O9-B2. The HI infrared lines probe the outer regions in the atmosphere and the onset of the stellar wind. The slowly rotating stars (with < 50 kms-1) show weak, single-peaked emission features on top of a broad absorption line. The most likely explanation is a non-LTE effect in the outer photosphere causing emission at line center. The slow rotators include two Cephei stars, both of which also show HeI (4.049 µm) emission. This indicates a significant increase in the degree of ionization in the outer layers of these B2-3 stars. For the higher stars we find two cases (out of six) in which weak, double-peaked emission is visible on top of the photospheric absorption. These two stars probably have low-density discs which are apparent only in the infrared HI lines (Zaal et al., 1995).
Key words: stars: atmospheres - stars: early-type - stars: circumstellar matter - infrared: stars - line: formation
*Data published here were obtained at
Infrared Telescope (UKIRT) which is operated by the Royal Observatory,
Edinburgh on behalf of the Science and Engineering Research Council.
Send offprint requests to: P.A. Zaal
© European Southern Observatory (ESO) 1997
Online publication: September 9, 1997