Spatially Resolved Observations of the Galactic Center Source, IRS 21

A. Tanner(1), A. M. Ghez(1), M. Morris(1), E. E. Becklin(1) A. Cotera (2), M. Ressler, M. Werner (3) P. Wizinowich(4)

(1) UCLA Department of Physics and Astronomy, Los Angeles, CA 90095-1562
(2) Steward Observatory, University of Arizona, Tucson, AZ 85721
(3) Jet Propulsion Lab, 169-327, 4800 Oak Grove Drive, Pasadena, CA, 91109
(4) W.M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743

Paper: ApJ, in press

EPrint Server: astro-ph/0204372


We present diffraction-limited 2-25 micron images obtained with the W. M. Keck 10-m telescopes that spatially resolve the cool source, IRS 21, one of a small group of enigmatic objects in the central parsec of our Galaxy that have eluded classification. Modeled as a Gaussian, the azimuthally-averaged intensity profile of IRS 21 has a half-width half-maximum (HWHM) size of 650+/-80 AU at 2.2 micron and an average HWHM size of 1600+/-200 AU at mid-infrared wavelengths. These large apparent sizes imply an extended distribution of dust. The mid-infrared color map indicates that IRS 21 is a self-luminous source rather than an externally heated dust clump as originally suggested. The spectral energy distribution has distinct near- and mid-infrared components. A simple radiative transfer code, which simultaneously fits the near- and mid- infrared photometry and intensity profiles, supports a model in which the near-infrared radiation is scattered and extincted light from an embedded central source, while the mid-infrared emission is from thermally re-radiating silicate dust. We argue that IRS 21 (and by analogy the other luminous sources along the Northern Arm) is a massive star experiencing rapid mass loss and plowing through the Northern Arm, thereby generating a bow shock, which is spatially resolved in our observations.

Preprints available from the authors at , or the raw TeX (no figures) if you click here.

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