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J.L. Hora, G.G. Fazio (CfA), L.K. Deutsch (BU/IAR), E.F. Ladd (Bucknell), W.F. Hoffmann, A. Dayal (UA), J. Deane, D.B. Sanders (IfA)
W3 is a well-studied star formation complex that contains objects such as HII regions, embedded IR sources (including the extremely luminous cluster of sources W3 IRS5), and OH and water masers. One unresolved problem in understanding HII regions/molecular cloud complexes is determining the relative importance of the various luminosity components. The main difficulty is the lack of high spatial resolution data in the spectral region where most of the power is emitted. The first observations which detected the bright IR emission regions used relatively large beam sizes which do not allow for identification of the emission sources in the clouds which are separated on the scale of arcseconds. More recently, submillimeter maps of the W3 region (Ladd et al., 1993, ApJ, 419, 186) showed many emission peaks that do not correspond well to the positions of the HII regions in radio images of the field.
We report here the results of mid-infrared imaging of the W3 cloud. A region approximately 3 x 2 arcmin centered on W3 IRS5 was mapped using MIRAC at the NASA IRTF on Mauna Kea. With a pixel size of 0.3 arcsec, nearly diffraction-limited images were obtained at 11.7, 13.2, and 20.6 \micron, which probe the PAH line and continuum emission. Color temperature images and optical depth maps derived from these data will be presented, and a comparison of the distribution of the mid-IR emission to the 2.2 \micron, radio and sub-mm images of the region will be shown.