Infrared Spectroscopy of Compact Galactic Plane Sources

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Session 22 -- Galactic Structure; Galactic Center
Display presentation, Monday, 9, 1995, 9:20am - 6:30pm

[22.04] Infrared Spectroscopy of Compact Galactic Plane Sources

R.A.Hermann (Willamette University), R.W.Canterna (University of Wyoming), J.A.Hackwell (The Aerospace Corporation)

Intermediate resolution of infrared (2.9 - 13.5 $\mu$m) spectra are presented for a random, flux-limited sample of sources in the galactic plane (galactic latitudes less than $2\deg$). The spectra fall into four distinct groups: those with strong [NeII] emission, with weak 10-11 $\mu$m features, with broad long-wavelength emission, and with deep silicate absorption. The IRAS [12]-[25] and [25]-[60] colors of the sources show that objects of each spectral group lie near each other in distinct regios of the color-color plane. A large fraction (40\%) show silicate absorption features which are among the deepest measured. The sample is shown to be made up of HII regions and embedded B stars, and evolved stars with circumstellar shells which range from optically thin to extremely thick. Three new carbon stars are identified, and one star with what appears to be silicate absorption superposed on silicon carbide emission is presented. Distances are calculated for the objects and are found to range from 4.1 to 7.3 kpc, implying a range of infrared luminosities in the sample of from 8000 to 3,000,000 solar luminosities. Simple evolutionary scenarios are presented which are shown to be in general agreement with standard models of late stellar evolution. Several of the objects, however, exhibit higher mass-loss rates and redder colors than those found in the published models.

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