Suchergebnisse

We report the first APOGEE metallicities and alpha-element abundances measured for 3600 red giant stars spanning a large radial range of both the Large (LMC) and Small Magellanic Clouds, the largest Milky Way (MW) dwarf galaxies. Our sample is an order of magnitude larger than that of previous studies and extends to much larger radial distances. These are the first results presented that make use of the newly installed southern APOGEE instrument on the du Pont telescope at Las Campanas Observatory. Our unbiased sample of the LMC spans a large range in metallicity, from [Fe/H] = -0.2 to very metal-poor stars with [Fe/H] -2.5, the most metal-poor Magellanic Cloud (MC) stars detected to date. The LMC [alpha/Fe]-[Fe/H] distribution is very flat over a large metallicity range but rises by similar to 0.1 dex at -1.0 < [Fe/H] less than or similar to -0.5. We interpret this as a sign of the known recent increase in MC star formation activity and are able to reproduce the pattern with a chemical evolution model that includes a recent "starburst." At the metal-poor end, we capture the increase of [alpha/Fe] with decreasing [Fe/H] and constrain the "alpha-knee" to [Fe/H] less than or similar to -2.2 in both MCs, implying a low star formation efficiency of similar to 0.01 Gyr(-1). The MC knees are more metal-poor than those of less massive MW dwarf galaxies such as Fornax, Sculptor, or Sagittarius. One possible interpretation is that the MCs formed in a lower-density environment than the MW, a hypothesis that is consistent with the paradigm that the MCs fell into the MW's gravitational potential only recently. ; State Research Agency (AEI) of the Spanish Ministry of Science, Innovation and Universities (MCIU) European Union (EU) AYA2017-88254-P National Science Foundation (NSF) AST-1801940 Crafoord Foundation Swedish Research Council Ruth och Nils-Erik Stenbacks stiftelse Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE) - US National Science Foundation PHY 14-30152 Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT FONDECYT 3180210 1170364 Becas Iberoamerica Investigador 2019, Banco Santander Chile Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT PIA/BASAL AFB-170002 Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT) Universidad Nacional Autónoma de México IN109919 Alfred P. Sloan Foundation United States Department of Energy (DOE) Center for High-Performance Computing at the University of Utah

The Sloan Digital Sky Survey III's Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution near-infrared spectroscopic survey covering all of the major components of the Galaxy, including the dust-obscured regions of the inner Milky Way disk and bulge. Here we present a sample of 10,341 likely red-clump stars (RC) from the first two years of APOGEE operations, selected based on their position in color-metallicity-surface-gravity-effective-temperature space using a new method calibrated using stellar evolution models and high-quality asteroseismology data. The narrowness of the RC locus in color-metallicity-luminosity space allows us to assign distances to the stars with an accuracy of 5%-10%. The sample extends to typical distances of about 3 kpc from the Sun, with some stars out to 8 kpc, and spans a volume of approximately 100 kpc(3) over 5 kpc less than or similar to R less than or similar to 14 kpc, vertical bar Z vertical bar less than or similar to 2 kpc, and -15 degrees less than or similar to Galactocentric azimuth less than or similar to 30 degrees. The APOGEE red-clump (APOGEE-RC) catalog contains photometry from the Two Micron All Sky Survey, reddening estimates, distances, line-of-sight velocities, stellar parameters and elemental abundances determined from the high-resolution APOGEE spectra, and matches to major proper motion catalogs. We determine the survey selection function for this data set and discuss how the RC selection samples the underlying stellar populations. We use this sample to limit any azimuthal variations in the median metallicity within the approximate to 45 degrees azimuthal region covered by the current sample to be <= 0.02 dex, which is more than an order of magnitude smaller than the radial metallicity gradient. This result constrains coherent non-axisymmetric flows within a few kiloparsecs from the Sun. ; NASA through Space Telescope Science Institute HST-HF-51285.01 ; NASA NAS5-26555, NNX13AE70G ; McLaughlin Fellowship at the University of Michigan ; European Research Council under the European Union 321035 ; NSF AST-1105930, AST-1311835 ; CNPq-Brazil ; Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) - U.S. National Science Foundation PHY 08-22648 ; Danish National Research Foundation DNRF106 ; Spanish Ministry of Economy and Competitiveness AYA-2011-27754 ; European Research Council under the European Community 338251 ; Deutsche Forschungsgemeinschaft (DFG) SFB 963/1 ; ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) - European Research Council 267864 ; MICINN AYA2011-24704 ; Alfred P. Sloan Foundation ; U.S. Department of Energy Office of Science ; University of Arizona ; Brookhaven National Laboratory ; Carnegie Mellon University ; University of Florida ; Harvard University ; Instituto de Astrofisica de Canarias ; Johns Hopkins University ; Lawrence Berkeley National Laboratory ; Max Planck Institute for Astrophysics ; Max Planck Institute for Extraterrestrial Physics ; New Mexico State University ; New York University ; Ohio State University ; Pennsylvania State University ; University of Portsmouth ; Princeton University ; University of Tokyo ; University of Utah ; Vanderbilt University ; University of Virginia ; University of Washington ; Yale University ; McDonald Observatory