EMISSION FEATURES IN BR-ALPHA AND BR-GAMMA SPECTRA OF NORMAL O-STAR AND B-STAR

We present high resolution Br alpha and Br gamma spectra for 15 near m ain-sequence O and B stars in a broad range in nu sin i and with spect ral type between O9-B2. The HI infrared lines probe the outer regions in the atmosphere and the onset of the stellar wind. The slowly rotati ng stars (with nu sin i < 50 kms(-1)) show weak, single-peaked emissio n features on top of a broad absorption line. The most likely explanat ion is a non-LTE effect in the outer photosphere causing emission at l ine center. The slow rotators include two beta Cephei stars, both of w hich also show HeI (4.049 mu m) emission. This indicates a significant increase in the degree of ionization in the outer layers of these B2- 3 stars. For the higher nu sin i stars we find two cases (out of six) in which weak, double-peaked emission is visible on top of the photosp heric absorption. These two stars probably have low-density discs whic h are apparent only in the infrared HI lines (Zaal et al., 1995).