1. The distance to a star forming region in the Outer arm of the Galaxy
- Author
-
Hachisuka, K., Brunthaler, A., Menten, K. M., Reid, M. J., Hagiwara, Y., and Mochizuki, N.
- Subjects
Astrophysics - Galaxy Astrophysics - Abstract
We performed astrometric observations with the VLBA of WB89-437, an H2O maser source in the Outer spiral arm of the Galaxy. We measure an annual parallax of 0.167 +/- 0.006 mas, corresponding to a heliocentric distance of 6.0 +/- 0.2 kpc or a Galactocentric distance of 13.4 +/- 0.2 kpc. This value for the heliocentric distance is considerably smaller than the kinematic distance of 8.6 kpc. This confirms the presence of a faint Outer arm toward l = 135 degrees. We also measured the full space motion of the object and find a large peculiar motion of ~20 km/s toward the Galactic center. This peculiar motion explains the large error in the kinematic distance estimate. We also find that WB89-437 has the same rotation speed as the LSR, providing more evidence for a flat rotation curve and thus the presence of dark matter in the outer Galaxy., Comment: The Astrophysical Journal, accepted, 16 pages, 4 Figures
- Published
- 2009
- Full Text
- View/download PDF