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Masers and Galactic structure: Micro-arcsecond astrometry with the VLBA

Published online by Cambridge University Press:  01 March 2007

M. J. Reid ,
A. Brunthaler ,
K. M. Menten ,
Xu Ye ,
Zheng Xing-Wu  and
L. Moscadelli
M. J. Reid
Affiliation:
Harvard-Smithsonian CfA, Cambridge, MA, USA email: reid@cfa.harvard.edu
A. Brunthaler
Affiliation:
MPIfR, Bonn, Germany
K. M. Menten
Affiliation:
MPIfR, Bonn, Germany
Xu Ye
Affiliation:
MPIfR, Bonn, Germany
Zheng Xing-Wu
Affiliation:
Nanjing University, Nanjing, China
L. Moscadelli
Affiliation:
Arcetri Observatory, Firenze, Italy
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Abstract

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Astrometric observations with the VLBA with accuracies approaching ~ 10 μas are being conducted in order to better understand the Galaxy. The location of Sgr A* on infrared images can be determined with an accuracy of a few mas, using stars with SiO maser emission as a calibration grid for infrared images. The apparent proper motion of Sgr A*, which is dominated by the effects of the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0R0 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. When combined with infrared results, this provides overwhelming evidence that Sgr A* is a supermassive black hole. Finally, we are engaged in a large project to map the spiral structure and kinematics of the Galaxy. Preliminary trigonometric parallaxes, obtained with the VLBA, to eight massive star forming regions are presented.

Keywords

Galactic structuresupermassive black holesSiO masersmethanol masersastrometryVLBAparallaxesproper motions
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S242: Astrophysical Masers and their Environments , March 2007 , pp. 348 - 355
Copyright
Copyright © International Astronomical Union 2008

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