1997A&A...326..237Z

We present high resolution Brα and Brγ spectra for 15 near main-sequence O and B stars in a broad range in vsin i 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 vsini<50km/s) 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 β Cephei stars, both of which also show HeI (4.049µm) emission. This indicates a significant increase in the degree of ionization in the outer layers of these B2-3 stars. For the higher vsin i 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., 1995A&A...299..574Z).