1-μm spectroscopy of normal OB stars

We have obtained spectra of 70 normal OB stars in the near-IR I (1-mu m) band. The strongest features are those due to lines of the hydrogen Paschen series and neutral and ionized helium, which are, for the most part, in absorption. The information content in this spectral range is sufficient for only a rough classification of hot stars into 'early O', 'late O' and 'B' types. Curiously, the leading He I triplet line, He I lambda 1.0830 mu m, is usually not detectable, although in a few stars it is in emission; its behaviour generally correlates with the leading helium singlet line, He I lambda 2.058 mu m. These two features appear to be present in emission only in stars with extremes of mass loss or wind extension.