Article open access publication

AN ELEMENTAL ASSAY OF VERY, EXTREMELY, AND ULTRA-METAL-POOR STARS*

The Astrophysical Journal, IOP Publishing, ISSN 1538-4357

Volume 807, 2, 2015

DOI:10.1088/0004-637x/807/2/173, Dimensions: pub.1058945807,

Affiliations

Organisations

  1. (1) Landessternwarte, ZAH, Königstuhl 12, D-69117 Heidelberg, Germany
  2. (2) University of Copenhagen, grid.5254.6, KU
  3. (3) University of Notre Dame, grid.131063.6
  4. (4) Australian National University, grid.1001.0
  5. (5) Massachusetts Institute of Technology, grid.116068.8
  6. (6) Instituto de Astrofísica de Canarias, grid.17423.33

Description

We present a high-resolution elemental-abundance analysis for a sample of 23 very metal-poor ([Fe/H] < −2.0) stars, 12 of which are extremely metal-poor ([Fe/H] < −3.0), and 4 of which are ultra-metal-poor ([Fe/H] < −4.0). These stars were targeted to explore differences in the abundance ratios for elements that constrain the possible astrophysical sites of element production, including Li, C, N, O, the α-elements, the iron-peak elements, and a number of neutron-capture elements. This sample substantially increases the number of known carbon-enhanced metal-poor (CEMP) and nitrogen-enhanced metal-poor (NEMP) stars—our program stars include eight that are considered "normal" metal-poor stars, six CEMP-no stars, five CEMP-s stars, two CEMP-r stars, and two CEMP-r/s stars. One of the CEMP-r stars and one of the CEMP-r/s stars are possible NEMP stars. We detect lithium for three of the six CEMP-no stars, all of which are Li depleted with respect to the Spite plateau. The majority of the CEMP stars have [C/N] > 0. The stars with [C/N] < 0 suggest a larger degree of mixing; the few CEMP-no stars that exhibit this signature are only found at [Fe/H] < −3.4, a metallicity below which we also find the CEMP-no stars with large enhancements in Na, Mg, and Al. We confirm the existence of two plateaus in the absolute carbon abundances of CEMP stars, as suggested by Spite et al. We also present evidence for a "floor" in the absolute Ba abundances of CEMP-no stars at A(Ba) ~ −2.0.

Research Categories

Main Subject Area

Fields of Research

Links & Metrics

NORA University Profiles

University of Copenhagen

Dimensions Citation Indicators

Times Cited: 63

Field Citation Ratio (FCR): 17.61

Open Access Info

Green, Published