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

  • M. J. Reid (a1), A. Brunthaler (a2), K. M. Menten (a2), Xu Ye (a2), Zheng Xing-Wu (a3) and L. Moscadelli (a4)...

Abstract

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.

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References

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Keywords

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

  • M. J. Reid (a1), A. Brunthaler (a2), K. M. Menten (a2), Xu Ye (a2), Zheng Xing-Wu (a3) and L. Moscadelli (a4)...

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