AAS 195th Meeting, January 2000
Session 5. Looking Towards The Galactic Center
Display, Wednesday, January 12, 2000, 9:20am-6:30pm, Grand Hall

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[5.02] Is the Galactic Center Source, IRS 21, as Large as It Appears?

A.M. Tanner, A.M. Ghez, M. Morris, E.E. Becklin (UCLA), A. Cotera (NASA/Ames Research Center, SETI), M. Werner (JPL)

Within the galaxy's central cluster there are a number of enigmatic sources (IRS 1, 5, 8, 10, and 21) that have eluded classification since their discovery more than two decades ago. These sources have featureless near-infrared spectra and spectral energy distributions (SEDs) that peak near 10 microns. Also, they are all apparently embedded in or superimposed upon the ``Northern Arm'', an infalling stream of partially ionized gas in Sgr A West. These properties have led to a variety of proposed classifications including high density dust clumps, embedded early-type stars, dusty Wolf Rayet stars, and protostars.

We present diffraction limited near- and mid-infrared images obtained with the W. M. Keck 10-m telescope that spatially resolve the cool Galactic Center source IRS 21. Modeled as a Gaussian, its azimuthally averaged intensity profile have HWHM radius of 720±30 AU at 2.2 microns and comparable sizes at 8.8-25 microns. This size along with its color temperature favor the hypothesis that IRS 21 is self-luminous rather than an externally heated dust clump. Based on the size alone, the remaining possible dust geometries are (1) an intrinsic inflow or outflow or (2) an extrinsic dust distribution, in which case IRS 21 is simply embedded in the Northern Arm. We have modeled the near- and mid-infrared photometry as scattered and thermal emission, respectively. Combined with polarization data from the literature, these results favor the hypothesis that IRS 21 is a luminous star which is fortuitously embedded in the gas and dust of the Northern Arm.

The author(s) of this abstract have provided an email address for comments about the abstract: tanner@astro.ucla.edu

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