Spectroscopy of dwarf O stars in the region 6250 to 7150 Å

We present moderate-resolution spectra of normal dwarf O stars taken over the commonly ignored spectral range from 6250 to 7150 Å. Numerous, strong, telluric absorption features, particularly the prominent O₂ feature beyond 6850 Å, have made the study of stellar photospheres over this spectral region very difficult in the past. In this study, we use a method for removing the atmospheric absorption features during the reduction process. With our cleaned spectra, we have been successful in identifying the He II 6891 Å line in O dwarf stars that has until now been too heavily contaminated by telluric features to be clearly detected.