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

Journal Article · Fri Jul 10 00:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/807/2/173· OSTI ID:22522180

Hansen, T.; Christlieb, N. ^[1]; Hansen, C. J. ^[2]; Beers, T. C.; Placco, V. M. ^[3]; Yong, D.; Bessell, M. S.; Norris, J. E.; Asplund, M. ^[4]; Frebel, A. ^[5]; Pérez, A. E. García, ^[6]

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1. Landessternwarte, ZAH, Königstuhl 12, D-69117 Heidelberg (Germany)
2. Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø (Denmark)
3. Department of Physics and JINA-CEE: Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556 (United States)
4. Research School of Astronomy and Astrophysics, The Australian National Univeristy, Weston, ACT 2611 (Australia)
5. Kavli Institute for Astrophysics and Space Research and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
6. Instituto de Astrofísica de Canarias, E38205 La Laguna, Tenerife, Spain and Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife (Spain)

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.

• OSTI ID: 22522180
• Journal Information: Astrophysical Journal, Vol. 807, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
CAPTURE
CARBON
ELEMENT ABUNDANCE
GALAXIES
HYDROGEN
IRON
LITHIUM
METALLICITY
NEUTRON REACTIONS
NITROGEN
NUCLEOSYNTHESIS
RESOLUTION
STARS