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Micro-arcsecond astrometry with the VLBA

Published online by Cambridge University Press:  01 October 2007

M. J. Reid
M. J. Reid*
Affiliation:
Harvard-Smithsonian CfA, Cambridge, MA, 02138, USA email: reid@cfa.harvard.edu
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Abstract

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The VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

Keywords

Galactic: structurestars: kinematicsblack hole physicsmasersastrometryinstrumentation: interferometersstars: fundamental parameterscosmological parameters
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S248: A Giant Step: from Milli- to Micro-arcsecond Astrometry , October 2007 , pp. 141 - 147
Copyright
Copyright © International Astronomical Union 2008

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