a1 Mizusawa VLBI observatory, NAOJ, Osawa, Mitaka, Tokyo, 181-8588, Japan email: [email protected]
a2 Department of Astronomical Science, School of Physical Sciences, The Graduate University of Advanced Studies (Sokendai), Osawa, Mitaka, Tokyo, 181-8588, Japan
Since 2007 VERA (VLBI Exploration of Radio Astrometry) has been producing astrometric results (distances and/or proper motions) for Galactic maser sources. Nearly 30 parallaxes have been obtained for star-forming regions and late-type stars. By using VERA's astrometric results for star-forming regions, combined with those obtained with VLBA and EVN, fundamental Galactic parameters and Galactic structure may be derived. Our results show that R 0 = 8.4 ± 0.4 kpc and Ω⊙ ≡ Ω0 + V ⊙/R 0=30.7±0.8 km s−1 kpc−1, and also show that the rotation curve of the Galaxy is nearly flat. The determinations of Galactic parameters and structures demonstrate that the maser astrometry can not only contribute significantly to research of individual maser sources, but also to studies of the structure of the Galaxy.