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Session 107 - The Galactic Center & Bulge.
Display session, Saturday, January 10
Exhibit Hall,

[107.02] Observations of High Velocity Proper Motion of Ionized Gas at the Galactic Center

D. A. Roberts (U. Illinois), F. Yusef-Zadeh (Northwestern U.), J. Biretta (STScI)

We present detailed results of a proper motion experiment, which reveal that several small-scale features in the inner 0.2 pc of the Galactic center have high velocities in the plane of the sky (V \approx 1000 km s^-1). These proper motions have been determined by combining continuum observations of the center of the Galaxy, using the image correlation technique of Biretta et al. 1989, ApJ 342, 128. The experiment used VLA A-configuration observations at 2 cm taken in three epochs (1986, 1990, and 1995), as described in a related talk by Yusef-Zadeh et al. There are a few locations where small-scale features show large proper motions, suggesting that they are are on unbound orbits and are unrelated to large-scale motions of gas. One unusual source, called the ``Bullet,'' is a few arcseconds northwest of Sgr A* and has a head-tail morphology. The proper motion velocity derived from the image correlation technique is about 1100 km s^-1. This velocity is large enough that the positions of the peak are displaced by a significant fraction of the synthesized beam on the plane of the sky between the various epochs. The velocity determined from measuring the displacement agrees with that determined by the correlation method. Furthermore, the most recent image (1995) shows the peak to be at the position of the head of the source, with the tail pointing directly toward the head in the earlier observations. Several other sources near Sgr A* show a similar velocity of the order of 1000 km s^-1, one of which (IRS13) is coincident with an cluster observed at infrared wavelengths.

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