Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-09-06
Astronomy and Astrophysics
Astrophysics
7 pages and 4 figures, Accepted by PASJ (Vol. 59, No. 5, October 25, 2007 issue)
Scientific paper
We have performed high-precision astrometry of H2O maser sources in Galactic star forming region Sharpless 269 (S269) with VERA. We have successfully detected a trigonometric parallax of 189+/-8 micro-arcsec, corresponding to the source distance of 5.28 +0.24/-0.22 kpc. This is the smallest parallax ever measured, and the first one detected beyond 5 kpc. The source distance as well as proper motions are used to constrain the outer rotation curve of the Galaxy, demonstrating that the difference of rotation velocities at the Sun and at S269 (which is 13.1 kpc away from the Galaxy's center) is less than 3%. This gives the strongest constraint on the flatness of the outer rotation curve and provides a direct confirmation on the existence of large amount of dark matter in the Galaxy's outer disk.
Bushimata Takeshi
Choi Yoon Kyung
Hirota Tomoya
Honma Mareki
Imai Hiroshi
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