Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21332502r&link_type=abstract
American Astronomical Society, AAS Meeting #213, #325.02; Bulletin of the American Astronomical Society, Vol. 41, p.381
Astronomy and Astrophysics
Astronomy
Scientific paper
We are conducting a large program with the NRAO Very Long Baseline Array (VLBA) to measure trigonometric parallaxes and proper motions of high-mass star-forming regions across the Milky Way. Early results from about a dozen sources locate several spiral arms and start to yield direct measurement of arm pitch angles. We find that kinematic distances are generally too large, sometimes by factors greater than two. Kinematic distances could be brought into better agreement with the trigonometric parallaxes by reducing the distance to the Galactic center and/or increasing the rotation speed at the Sun, relative to the IAU recommended values. However, a more significant problem with kinematic distances is that star forming regions have large departures from circular orbits in the Galaxy. We measure that star forming regions typically orbit slower than circular rotation, and some also have larger peculiar motions toward the Galactic Center.
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