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The Mass of the Galaxy from Large Samples of Field Horizontal-Branch Stars in the SDSS Early Data Release

  • Timothy C. Beers (a1), Masashi Chiba (a2), Tsuyoshi Sakamoto (a3), Ron Wilhelm (a4), Carlos Allende Prieto (a5), Jesper Sommer-Larsen (a6), Heidi J. Newberg (a7), Brian Yanny (a8), Brian Marsteller (a1) and Jeffrey R. Pier (a9)...

Abstract

We present a new estimate of the mass of the Milky Way, making use of a large sample of 955 field horizontal-branch (FHB) stars from the Early Data Release of the Sloan Digital Sky Survey. This sample of stars has been classified on the basis of an automated analysis approach, in combination with other methods, in order to obtain estimates of the physical parameters of the stars, i.e., Teff, log g, [Fe/H], and should be relatively free of contamination from halo blue stragglers. the stars all have measured radial velocities and photometric distance estimates, and the sample includes objects as distant as ~ 75 kpc from the Galactic center. Application of a Bayesian likelihood method, for a specific model of the Galaxy, indicates that the total mass of the Galaxy lies in the range 1.5 − 4.0 × 1012 M⊙. Our sample appears to reveal a clear signature of a dual halo population of FHB stars, with the boundary between the inner and outer halo around 20 kpc, and the possibility of rather striking differences in the rotational properties of the Galaxy at low metallicity.

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References

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