We present 2 micron spectra of O and early-B main-sequence stars. These stars show absorption features at Br-gamma, 2.113 micron He I, 2.189 micron He II, and emission at 2.116 micorn N III, which vary with spectral subtype in a sufficiently "well behaved" manner that they can be used as a rough classification system for hot stars. We also show spectra of several O8f, late-O, and early-B giant and supergiant stars. Subtype classification of these stars is also possible, but the luminosity criteria are more subtle. We intend to use our K-band classification system to investigate hot stars embedded in shrouded H II regions to study formation processes and early evolution of the most massive stars. K-band spectra of the Galactic center stars are unlike any of our "standard" stars but do appear superficially similar to our spectrum of an Oe star, which has a disklike geometry, although the mechanism for the line formation is probably quite different.
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Hanson et al. (1994) studied this question.