Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003dda....34.0306k&link_type=abstract
American Astronomical Society, DDA meeting #34, #03.06; Bulletin of the American Astronomical Society, Vol. 35, p.1036
Astronomy and Astrophysics
Astronomy
Scientific paper
Using parallaxes and proper motions of a kinematically and spatially unbiased sample of old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon (2000), we have re-estimated the surface density of the Galactic disk in the solar neighborhood within +/- 0.4 kpc of the Sun. We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample, (14.4 +/- 1.5 km/sec), and combine these to derive the surface density of gravitating matter in the Galactic disk, obtaining a value of 44 +/- 9 Msun / pc2 within +/- 400 pc. Furthermore, we find that this gravitating matter is concentrated within a layer of about +/- 200 pc.
The derived values of surface density and concentration of gravitating matter indicate the presence of a thin, dark-matter component to the Galaxy. In the mid-plane of the disk, the volume density of this flattened component is a substantial fraction of the volume density of the observed matter.
This work was supported in part by grant No. AST 0098548 from the National Science Foundation.
Borkova T. V.
Dinescu Dana I.
Girard Terrence M.
Korchagin Vladimir I.
van Altena William F.
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