Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...187.6604h&link_type=abstract
American Astronomical Society, 187th AAS Meeting, #66.04; Bulletin of the American Astronomical Society, Vol. 27, p.1376
Astronomy and Astrophysics
Astronomy
Scientific paper
I have obtained high-quality 2 mu m 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 mu m 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 mu m 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.
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