Carbon-enhanced metal-poor stars: CEMP-s and CEMP-no subclasses in the halo system of the Milky Way

Daniela Carollo, Ken Freeman, Timothy C. Beers, Vinicius M. Placco, Jason Tumlinson, Sarah L. Martell

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Abstract

We explore the kinematics and orbital properties of a sample of 323 very metal-poor stars in the halo system of the Milky Way, selected from the high-resolution spectroscopic follow-up studies of Aoki et al. and Yong et al. The combined sample contains a significant fraction of carbon-enhanced metal-poor (CEMP) stars (22% or 29%, depending on whether a strict or relaxed criterion is applied for this definition). Barium abundances (or upper limits) are available for the great majority of the CEMP stars, allowing for their separation into the CEMP-s and CEMP-no subclasses. A new method to assign membership to the inner- and outer-halo populations of the Milky Way is developed, making use of the integrals of motion, and applied to determine the relative fractions of CEMP stars in these two subclasses for each halo component. Although limited by small-number statistics, the data suggest that the inner halo of the Milky Way exhibits a somewhat higher relative number of CEMP-s stars than CEMP-no stars (57% versus 43%), while the outer halo possesses a clearly higher fraction of CEMP-no stars than CEMP-s stars (70% versus 30%). Although larger samples of CEMP stars with known Ba abundances are required, this result suggests that the dominant progenitors of CEMP stars in the two halo components were different; massive stars for the outer halo, and intermediate-mass stars in the case of the inner halo.

Original languageEnglish
Article number180
Pages (from-to)1-19
Number of pages19
JournalAstrophysical Journal
Volume788
Issue number2
DOIs
Publication statusPublished - 20 Jun 2014

Bibliographical note

Copyright 2014 The American Astronomical Society. First published in the Astrophysical journal, 788(2), 180, 2014, published by IOP Publishing. The original publication is available at http://www.doi.org/10.1088/0004-637X/788/2/180. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • Galaxy: evolution
  • Galaxy: formation
  • Galaxy: halo
  • Galaxy: structure
  • stars: abundances
  • surveys

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