Date Published:

April 1, 2013

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, is exploring the chemistry of allGalactic stellar populations at infrared wavelengths, with particularemphasis on the disk and the bulge. An automated spectral analysis ofdata on 2403 giant stars in 12 fields in the bulge obtained duringAPOGEE commissioning yielded five stars with low metallicity ([Fe/H]<= -1.7), including two that are very metal-poor [Fe/H] ~-2.1 by bulge standards. Luminosity-based distance estimates placethe 5 stars within the outer bulge, where 1246 of the other analyzedstars may reside. A manual reanalysis of the spectra verifies the lowmetallicities, and finds these stars to be enhanced in theα-elements O, Mg, and Si without significant α-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, the newlyidentified stars reveal that the chemistry of metal-poor stars in thecentral Galaxy resembles that of metal-weak thick-disk stars at similarmetallicity.

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