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Session 6 - HII Regions & Massive Star Formation.
Display session, Wednesday, January 07
Two key factors combine to affect the infrared spectral energy distribution(SED) of a massive star-forming (H II) region: the stellar population; and the distribution of dust and gas around the luminous stars, particularly the solid angle subtended by molecular material as viewed from the stars. The molecular cloud ``covering fraction'' decreases from 4\pi sr to 2\pi sr to practically zero as the H II region evolves through compact, blister, and extended, low-density phases, respectively.
Using data from the COBE Diffuse Infrared Background Experiment (DIRBE), we have measured the IR SEDs of five isolated massive star-forming regions: S 90, Cep A, S 187, W5 NE, and S 287. In addition to the 1 - 240 \mum DIRBE SEDs, we present J, H and K band photometry derived from recently obtained near-IR images of these regions. With the aid of future 2 \mum spectroscopic observations it will be possible to locate and classify visually obscured O and early-B type stars, providing a direct census of the stellar populations, virtually uncompromised by extinction effects. Information about the distribution of molecular and diffuse interstellar matter around the stars can be derived from multiwavelength survey data. From these independent data sets we will develop a classification scheme for the IR SEDs. Such a scheme might some day be useful in interpretations of galactic spectral energy distributions, which vary in form and often are the only available source of information about galactic star forming activity.
Program listing for Wednesday