Abstract:

Despite its importance for understanding the nature of early stellargenerations and for constraining Galactic bulge formation models, atpresent little is known about the metal-poor stellar content of thecentral Milky Way. This is a consequence of the great distances involvedand intervening dust obscuration, which challenge optical studies.However, the Apache Point Observatory Galactic Evolution Experiment(APOGEE), a wide-area, multifiber, high-resolution spectroscopic surveywithin Sloan Digital Sky Survey III (SDSS-III), is exploring thechemistry of all Galactic stellar populations at infrared wavelengths,with particular emphasis on the disk and the bulge. An automatedspectral analysis of data on 2,403 giant stars in twelve fields in thebulge obtained during APOGEE commissioning yielded five stars with lowmetallicity([Fe/H]$\le-1.7$), including two that are very metal-poor[Fe/H]$\sim-2.1$ by bulge standards. Luminosity-based distance estimatesplace the five stars within the outer bulge, where other 1,246 of theanalyzed stars may reside. A manual reanalysis of the spectra verifiesthe low metallicities, and finds these stars to be enhanced in the$\alpha$-elements O, Mg, and Si without significant $\alpha$-patterndifferences with other local halo or metal-weak thick-disk stars ofsimilar metallicity, or even with other more metal-rich bulge stars.While neither the kinematics nor chemistry of these stars can yetdefinitively determine which, if any, are truly bulge members, ratherthan denizens of other populations co-located with the bulge, thenewly-identified stars reveal that the chemistry of metal-poor stars inthe central Galaxy resembles that of metal-weak thick-disk stars atsimilar metallicity.

Notes:

6 pages, 3 figures, 2 tables

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