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Session 66 - Young Clusters, High-Mass YSOs and Their Environment.
Oral session, Tuesday, January 16
Salon del Rey Central, Hilton
I have obtained high-quality 2 \mum spectra of more than 30 stars in the direction of the very young, heavily extinguished Galactic star-forming region M17. I have identified seven stars as O type from their spectral lines of H I, He I, He II, and N III using the 2 \mum spectral classification system that I developed for this purpose. Two of these O stars are behind more than 15 magnitudes of visible extinction and provide unprecedented opportunities for absorption studies of dark interstellar clouds at optical and near-infrared wavelengths. The O stars found are able to provide the number of Lyman continuum photons required to explain radio continuum observations of the region. A set of stellar objects, all but one with strong excess emission in the infrared, show completely different spectral characteristics from known main-sequence stars. Three are completely featureless throughout the 2 \mum window, four (possibly five) show molecular CO in emission and two have CO in absorption combined with extremely large near-infrared excesses. Extrapolating from the number of early-O stars found in the M17 region and assuming a normal stellar mass function, photometric surveys of the field suggest the number of late-O and B stars found is far below the number expected. The peculiar stellar objects I found may be massive, young stellar objects, possibly the ``missing'' late-O and B stars, still shrouded by circumstellar material. Because the early-O stars in the field are already free of their circumstellar material, the most massive stars must have a very short accretion phase. Either the majority of their mass comes from the proto-stellar collapse phase or the current models used for forming intermediate- and low-mass stars cannot be extrapolated to the most massive stars.
This thesis was completed in October, 1995, at the University of Colorado, Boulder under the direction of Peter S.\ Conti.
