Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.1403o&link_type=abstract
American Astronomical Society, AAS Meeting #211, #14.03; Bulletin of the American Astronomical Society, Vol. 39, p.759
Astronomy and Astrophysics
Astronomy
Scientific paper
Just a few years ago, we had only a "reasonable" idea of the size and mass of the Milky Way (e.g., Olling & Merrifield; 2000, 2001): both the rotation speed (V) of the Milky Way, and the distance to the galactic center [R0] were known to +/- 10% or so. However, these seemingly small uncertainties translate to a factor of two uncertainty in V at 2*R0 due to the nature of the kinematic tracers that are being used to determine the galactic rotation curve (RC) at larger distances (Olling & Merrifield, 1998). This factor of two uncertainty in the galactic RC is about 100 times larger than for external galaxies. Currently, astrometric techniques are successfully used to determine R0 [Eisenhauer etal, 2003], Theta(R0) [Reid & Brunthaler, 2005] and Theta(2R0) [Honma etal 2007]. Here I report on efforts to determine R0 from the distribution of Red-Clump giants (RCGs) from the 2MASS catalog. The RCGs are identified from local color-magnitude diagrams and the extinction-free index QJHK. From the observed color, the known color (extinction) and the known absolute magnitude of the RCGs, I determine the space/surface density of RCGs covering roughly 30% of the Milky Way. Centering of this distribution yields R0. A naive estimate based on just the number of RCGs indicates that R0 might be determined to +/- 0.07%.
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