Suchergebnisse

A Li-rich red giant (RG) star (2M19411367+4003382) recently discovered in the direction of NGC 6819 belongs to the rare subset of Li-rich stars that have not yet evolved to the luminosity bump, an evolutionary stage where models predict Li can be replenished. The currently favored model to explain Li enhancement in first-ascent RGs like 2M19411367+4003382 requires deep mixing into the stellar interior. Testing this model requires a measurement of C-12/C-13, which is possible to obtain from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. However, the Li-rich star also has abnormal asteroseismic properties that call into question its membership in the cluster, even though its radial velocity and location on color-magnitude diagrams are consistent with membership. To address these puzzles, we have measured a wide array of abundances in the Li-rich star and three comparison stars using spectra taken as part of the APOGEE survey to determine the degree of stellar mixing, address the question of membership, and measure the surface gravity. We confirm that the Li-rich star is a RG with the same overall chemistry as the other cluster giants. However, its log g is significantly lower, consistent with the asteroseismology results and suggestive of a very low mass if the star is indeed a cluster member. Regardless of the cluster membership, the C-12/C-13 and C/N ratios of the Li-rich star are consistent with standard first dredge-up, indicating that Li dilution has already occurred, and inconsistent with internal Li enrichment scenarios that require deep mixing. ; National Science Foundation AST1109888 ; NSF AST-1358862, AST 1109718, AST 1312863 ; Alfred P. Sloan Foundation ; National Science Foundation ; U.S. Department of Energy Office of Science ; University of Arizona ; Brazilian Participation Group ; Brookhaven National Laboratory ; Carnegie Mellon University ; University of Florida ; French Participation Group ; German Participation Group ; Harvard University ; Instituto de Astrofisica de Canarias ; Michigan State/NotreDame/JINA Participation Group ; 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 ; Spanish Participation Group ; University of Tokyo ; University of Utah ; Vanderbilt University ; University of Virginia ; University of Washington ; Yale University ; National Aeronautics and Space Administration ; Two Micron All Sky Survey ; University of Massachusetts ; Infrared Processing and Analysis Center/California Institute of Technology ; U.S. Government NAG W-2166 ; Astronomy

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