SOFIA/FORCAST and Spitzer/IRAC imaging of the ultracompact H II region W3(OH) and associated protostars in W3

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We present infrared observations of the ultracompact H II region W3(OH) made by the FORCAST instrument aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) and by the Spitzer/Infrared Array Camera. We contribute new wavelength data to the spectral energy distribution (SED), which constrains the optical depth, grain size distribution, and temperature gradient of the dusty shell surrounding the H II region. We model the dust component as a spherical shell containing an inner cavity with radius 600 AU, irradiated by a central star of type O9 and temperature 31, 000 K. The total luminosity of this system is 7.1 × 10 L . An observed excess of 2.2-4.5 μm emission in the SED can be explained by our viewing a cavity opening or clumpiness in the shell structure whereby radiation from the warm interior of the shell can escape. We claim to detect the nearby water maser source W3 (H O) at 31.4 and 37.1 μm using beam deconvolution of the FORCAST images. We constrain the flux densities of this object at 19.7-37.1 μm. Additionally, we present in situ observations of four young stellar and protostellar objects in the SOFIA field, presumably associated with the W3 molecular cloud. Results from the model SED fitting tool of Robitaille etal. suggest that two objects (2MASS J02270352+6152357 and 2MASS J02270824+6152281) are intermediate-luminosity (236-432 L ) protostars; one object (2MASS J02270887+6152344) is either a high-mass protostar with luminosity 3 × 10 L or a less massive young star with a substantial circumstellar disk but depleted envelope; and the other (2MASS J02270743+6152281) is an intermediate-luminosity (768 L ) protostar nearing the end of its envelope accretion phase or a young star surrounded by a circumstellar disk with no appreciable circumstellar envelope. © © 2012. The American Astronomical Society. All rights reserved.. 4 3 ⊙ 2 ⊙ ⊙ ⊙

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