Distance and Proper Motion Measurement of the Red Supergiant, S Persei, with VLBI H2O Maser Astrometry (original) (raw)
ADS
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Abstract
We have conducted Very Long Baseline Array phase-referencing monitoring of H2O masers around the red supergiant, S Persei, for six years. We have fitted maser motions to a simple expanding-shell model with a common annual parallax and stellar proper motion, and obtained the annual parallax as 0.413 ± 0.017 mas and the stellar proper motion as (-0.49 ± 0.23 mas yr-1, -1.19 ± 0.20 mas yr-1) in right ascension and declination, respectively. The obtained annual parallax corresponds to the trigonometric distance of 2.42+0.11 -0.09 kpc. Assuming a Galactocentric distance of the Sun of 8.5 kpc, the circular rotational velocity of the local standard of rest at a distance of the Sun of 220 km s-1, and a flat Galactic rotation curve, S Persei is suggested to have a non-circular motion deviating from the Galactic circular rotation for 15 km s-1, which is mainly dominated by the anti-rotation direction component of 12.9 ± 2.9 km s-1. This red supergiant is thought to belong to the OB association, Per OB1, so that this non-circular motion is representative of a motion of the OB association in the Milky Way. This non-circular motion is somewhat larger than that explained by the standard density-wave theory for a spiral galaxy and is attributed to either a cluster shuffling of the OB association, or to non-linear interactions between non-stationary spiral arms and multi-phase interstellar media. The latter comes from a new view of a spiral arm formation in the Milky Way suggested by recent large N-body/smoothed particle hydrodynamics numerical simulations.
Publication:
The Astrophysical Journal
Pub Date:
September 2010
DOI:
arXiv:
Bibcode:
Keywords:
- Galaxy: structure;
- masers;
- supergiants;
- Astrophysics - Astrophysics of Galaxies
E-Print:
28 pages, 11 figures, 5 tables, ApJ (accepted)