Previous | Session 40 | Next | Author Index | Block Schedule
M. J. Reid (Harvard-Smithsonian CfA), Y. Xu (MPIfR), X. W. Zheng (Nanjing University), K. M. Menten (MPIfR)
We have used the VLBA to determine a trigonometric parallax for W3OH, a massive star forming region in the Perseus spiral arm, with an accuracy of 10 micro-arcseconds. W3OH is at a distance of 1.953 ±0.04~kpc. This resolves a long-standing difference between kinematic distances (>4~kpc) and O-star luminosity distances (\approx2.2~kpc) to this region of the Perseus arm. The O-star luminosity distances are correct and this region is strongly kinematically anomalous. We have also measured the proper motion of W3OH, relative to extragalactic sources, and find a peculiar motion of 22~km/s directed inward and counter to Galactic rotation. This is in qualitative agreement with spiral density wave theory, but seems larger than expected for reasonably density enhancements. We are now conducting a large program with the VLBA to determine parallaxes and proper motions to a sample of a dozen massive star forming regions. The goals of this project are to determine the locations of spiral arms of the Galaxy and to test the spiral density wave paradigm.
Previous | Session 40 | Next
Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.