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Title: Normal and outlying populations of the Milky Way stellar halo at [Fe/H] <–2

From detailed abundance analysis of >100 Hamburg/ESO candidate extremely metal-poor (EMP) stars we find 45 with [Fe/H] < –3.0 dex. We identify a heretofore unidentified group: Ca-deficient stars with sub-solar [Ca/Fe] ratios and the lowest neutron-capture abundances; the Ca-deficient group comprises ∼10% of the sample, excluding Carbon stars. Our radial velocity distribution shows that the carbon-enhanced stars with no s-process enhancements, CEMP-no, and which do not show C{sub 2} bands are not preferentially binary systems. Ignoring Carbon stars, approximately 15% of our sample are strong (≥5σ) outliers in one or more elements between Mg and Ni; this rises to ∼19% if very strong (≥10σ) outliers for Sr and Ba are included. Examples include: HE0305–0554 with the lowest [Ba/H] known; HE1012–1540 and HE2323–0256, two (non-velocity variable) C-rich stars with very strong [Mg,Al/Fe] enhancements; and HE1226–1149, an extremely r-process rich star.
Authors:
 [1] ;  [2] ; ; ;  [3] ;  [4] ;  [5] ;  [6]
  1. Palomar Observatory, Mail Stop 249-17, California Institute of Technology, Pasadena, CA 91125 (United States)
  2. Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117, Heidelberg (Germany)
  3. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  4. Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg (Germany)
  5. Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)
  6. University of California, Department of Physics and Astronomy, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States)
Publication Date:
OSTI Identifier:
22342020
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; APPROXIMATIONS; CAPTURE; CARBON; CARBON STARS; DISTRIBUTION; ELECTROMAGNETIC PULSES; METALS; MILKY WAY; NEUTRON REACTIONS; R PROCESS; RADIAL VELOCITY; S PROCESS; TRITIUM