{
  "id": "1409.3566",
  "version": "v1",
  "published": "2014-09-11T20:00:01.000Z",
  "updated": "2014-09-11T20:00:01.000Z",
  "title": "Tracing chemical evolution over the extent of the Milky Way's Disk with APOGEE Red Clump Stars",
  "authors": [
    "David L. Nidever",
    "Jo Bovy",
    "Jonathan C. Bird",
    "Brett H. Andrews",
    "Michael Hayden",
    "Jon Holtzman",
    "Steven R. Majewski",
    "Verne Smith",
    "Annie C. Robin",
    "Ana E. Garcia Perez",
    "Katia Cunha",
    "Carlos Allende Prieto",
    "Gail Zasowski",
    "Ricardo P. Schiavon",
    "Jennifer A. Johnson",
    "David H. Weinberg",
    "Diane Feuillet",
    "Donald P. Schneider",
    "Matthew Shetrone",
    "Jennifer Sobeck",
    "D. A. Garcia-Hernandez",
    "O. Zamora",
    "Hans-Walter Rix",
    "Timothy C. Beers",
    "John C. Wilson",
    "Robert W. O'Connell",
    "Ivan Minchev",
    "Cristina Chiappini",
    "Friedrich Anders",
    "Dmitry Bizyaev",
    "Howard Brewington",
    "Garrett Ebelke",
    "Peter M. Frinchaboy",
    "Jian Ge",
    "Karen Kinemuchi",
    "Elena Malanushenko",
    "Viktor Malanushenko",
    "Moses Marchante",
    "Szabolcs Meszaros",
    "Daniel Oravetz",
    "Kaike Pan",
    "Audrey Simmons",
    "Michael F. Skrutskie"
  ],
  "comment": "18 pages, 17 figures. Accepted for publication in ApJ",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We employ the first two years of data from the near-infrared, high-resolution SDSS-III/APOGEE spectroscopic survey to investigate the distribution of metallicity and alpha-element abundances of stars over a large part of the Milky Way disk. Using a sample of ~10,000 kinematically-unbiased red-clump stars with ~5% distance accuracy as tracers, the [alpha/Fe] vs. [Fe/H] distribution of this sample exhibits a bimodality in [alpha/Fe] at intermediate metallicities, -0.9<[Fe/H]<-0.2, but at higher metallicities ([Fe/H]=+0.2) the two sequences smoothly merge. We investigate the effects of the APOGEE selection function and volume filling fraction and find that these have little qualitative impact on the alpha-element abundance patterns. The described abundance pattern is found throughout the range 5<R<11 kpc and 0<|Z|<2 kpc across the Galaxy. The [alpha/Fe] trend of the high-alpha sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (~10%). Using simple galactic chemical evolution models we derive an average star formation efficiency (SFE) in the high-alpha sequence of ~4.5E-10 1/yr, which is quite close to the nearly-constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the early evolution of the Milky Way disk was characterized by stars that shared a similar star formation history and were formed in a well-mixed, turbulent, and molecular-dominated ISM with a gas consumption timescale (1/SFE) of ~2 Gyr. Finally, while the two alpha-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track this cannot hold in the outer Galaxy, requiring instead a mix of two or more populations with distinct enrichment histories.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-09-11T20:00:01.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "apogee red clump stars",
      "milky ways disk",
      "tracing chemical evolution",
      "galactic chemical evolution models",
      "milky way disk"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/796/1/38",
      "journal": "The Astrophysical Journal",
      "year": 2014,
      "month": "Nov",
      "volume": 796,
      "number": 1,
      "pages": 38
    },
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2014ApJ...796...38N"
    }
  }
}