Radio Continuum Structure of IRS 13 and Proper Motions of Compact HII Components at the Galactic Center

Details Radio Continuum Structure of IRS 13 and Proper Motions of Compact HII Components at the Galactic Center Radio Continuum Structure of IRS 13 and Proper Motions of Compact HII Components at the Galactic Center

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...499l.163z&link_type=abstract

Astrophysical Journal Letters v.499, p.L163

Astronomy and Astrophysics

Astronomy

24

Galaxy: Center, Astrometry, Waves, Ism: H Ii Regions, Radio Continuum: Stars

Scientific paper

A compact H II region, IRS 13, is located 3" to the SW of Sgr A*, the compact radio source at the Galactic center. The source is double, IRS 13E and 13W, at 7 and 13 mm as observed with resolutions of 0."06. A rising spectrum with spectral index of alpha =0.9 is observed for IRS 13E probably arising from a high-density, ionized stellar wind. IRS 13W has a flat spectrum; in addition, the radio morphology suggests that the emitting material in IRS 13W has been swept off from the stellar envelope associated with IRS 13E by a strong wind and/or an outflow emanating from the IRS 16 complex and/or Sgr A*. Based on two epoch observations between 1991 and 1996, IRS 13E shows no significant proper motion less than 4 mas yr-1 (3 sigma ), while IRS 13W shows a proper motion mu _α=0.4+/-0.7 , mu _δ=6.2+/-1.1 mas yr-1, with respect to Sgr A*. In addition, proper motions of 57 compact H II components at the Galactic center are determined. The proper motion observations suggest that the minicavity is expanding with a speed of 200 km s-1. The mean transverse velocity of 700 km s-1 is inferred for the IRS 9 complex, which is located at the SW rim of the eastern cavity. Large proper motions (up to 30 mas yr-1, or ~1200 km s-1) are found for a number of H II components associated with filamentary structures, such as the Bullet and the Loop. The large proper motion measured from the compact H II components can be explained by motions of clumpy H II gas accelerated by either strong winds and outflows or explosive events at the Galactic center. Large pattern speeds due to wave motions in the circumnuclear medium at the Galactic center can also be responsible for some components of the observed proper motions.

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