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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.
Program listing for Tuesday