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P. M. Harvey (University of Texas), c2d Team
The Serpens dark cloud is one of five large, nearby star-forming complexes observed in the Spitzer Legacy Program ``Cores to Disks'' (c2d). The observations have been completed and preliminary analysis performed on the mapping done in all four bands of IRAC and three MIPS bands. The total area surveyed is about one square degree and includes the well-studied cluster at 18h 30m +1deg 15' (J2000), as well as a region of known pre-main-sequence emission-line stars to the south, and the Herbig Ae-Be star VV Ser even further to the south. The Serpens cloud has the lowest galactic latitude of all the c2d regions, and thus exhibits the largest amount of background star contamination. Nevertheless, the wide wavelength coverage, excellent angular resolution, and deep sensitivity of Spitzer make it possible to identify easily an embedded young stellar population that is distributed over almost the entire area surveyed. The most significant contaminant, in fact, is background galaxies many of which can have colors similar to young stars at the faint end of our survey limit.
We find a wide range of infrared excesses around objects believed to be young members of the star-forming population in Serpens. These include objects that fit readily into the classification system proposed by Lada, based on the slope of the energy distribution, as well as objects that might more appropriately be described as having an inner-disk-hole. The population of young objects exhibits significant clustering, while still being distributed over essentially the whole surveyed area. The most significant new grouping of young stars is around the location of several known emission-line stars. We find of order a dozen objects, some with very strong mid- and far-infrared excesses, consistent with ``Class I'' characteristics. Diffuse, extended emission is also apparent over much of the region surveyed. The IRAC colors suggest a substantial component of this is produced by small PAH grains. A compact diffuse nebula is seen around VV Ser that can be modelled as a diffuse population of grains illuminated by a central star with a circumstellar disk (Pontoppidan et al., in press).
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.