The Proper Motion of SGR A*

Details The Proper Motion of SGR A* The Proper Motion of SGR A*

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...191.9706r&link_type=abstract

American Astronomical Society, 191st AAS Meeting, #97.06; Bulletin of the American Astronomical Society, Vol. 29, p.1366

Astronomy and Astrophysics

Astronomy

2

Scientific paper

Since 1991, we have conducted observations with the VLBA designed to measure the distance to the Galactic Center via a trigonometric parallax. A time series of measurements of the position of Sgr A* relative to extragalactic sources should show the effects of the annual ~+/-0.12 mas signature of the Earth's orbit around the Sun (trigonometric parallax), the ~6 mas yr(-1) secular motion caused by the Sun's orbit around the Galactic Center, and perhaps the motion of Sgr A* itself. We have demonstrated an accuracy of about 0.1 and 0.4 mas in the East-West and North-South directions, respectively, for the position of Sgr A* relative to background quasars. This has allowed us to measure the angular rotation rate of the Sun around the Galactic Center (Theta_0 /R_0)with an uncertainty of about 8% over a time span of only 1 year. Assuming a flat rotation curve for the Galaxy, this also provides a direct measurement of Oort's constants with a similar uncertainty. Finally, our observations can put stringent limits, or perhaps detect, any peculiar motion of Sgr A* (beyond that expected from our moving vantage point at the Sun). If Sgr A* is a very massive (e.g., >10(6) M_sun) black hole at the dynamical center of the Galaxy, one would expect a peculiar motion of order 1 km s(-1) , owing to gravitational perturbations from close encounters with massive stars in the central star cluster. However, were Sgr A* to be a lower mass system, commensurate with its modest total luminosity, it would be expected to have a much larger peculiar motion.

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