IDENTIFICATION OF IONIZING SOURCES AND YOUNG STELLAR OBJECTS IN M17

We have obtained high-quality 2 mu m (K-band) spectra of 25 stars in t he direction of the heavily extincted, Galactic star-forming region M1 7. Interloping cool field giants are a potential source of confusion, but K-band spectra combined with normal JHK colors can identify and di stinguish these stars via their strong CO absorption features at lambd a greater than or equal to 2.29 mu m. Among the other sources, we have identified five stars as O type from their spectral lines of H I, He I, He II, and N III by using a K-band classification system that we ha ve developed. These provide the number of Lyman-continuum photons requ ired by radio continuum observations. The remaining stellar objects, a ll but one with strong near-infrared (NIR) excesses, show completely d ifferent spectral characteristics from known main-sequence stars. Thre e are completely featureless throughout the K band, four (possibly fiv e) show CO bands in emission, and two (candidate FU Orionis-like objec ts) have CO bands in absorption combined with extreme NIR excesses. We suggest that these stellar objects are relatively massive young stell ar objects, still shrouded by circumstellar material.