Xiang-Xiang Xue, Zhibo Ma, Hans-Walter Rix, Heather L. Morrison, Paul Harding, Timothy C. Beers, Inese I. Ivans, Heather R. Jacobson, Jennifer Johnson, Young Sun Lee, Sara Lucatello, Constance M. Rockosi, Jennifer S. Sobeck, Brian Yanny
We present an online catalog of distance determinations for 4781 K giants, most of which are members of the Milky Way's stellar halo. Their spectra from SDSS/SEGUE provide metallicities with accuracies \Delta [Fe/H]\approx\pm0.2 dex and giant-dwarf distinction. The distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g-r)_0 color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to propagate the errors in metallicities, magnitudes, and colors properly into distance uncertainties. We also fold in {\it prior} information about the giant-branch luminosity function and different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays little role in the distance estimates, but that neglecting the luminosity prior would lead to a systematic distance modulus bias of up to 0.2 mag. We find a median distance precision of 12%, with distance estimates most precise for the least metal-poor stars near the tip of the red-giant branch. We use globular and open clusters to verify the precision and accuracy of our distance estimates. The stars in our publicly available catalog are up to 110 kpc distant from the Galactic center, with 270 stars beyond 50 kpc, forming the largest sample of distant tracers in the Galactic halo.
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http://arxiv.org/abs/1211.0549
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