Other
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005phdt.........2t&link_type=abstract
Thesis (PhD). Open University (United Kingdom), England, DAI-C 66/04, p. 825, Winter 2005
Other
10
Radial Velocity, Carbon-Enhanced, Metal-Poor, Stars
Scientific paper
We report the first results of a spectroscopic effort to understand the nucleosynthetic histories of carbon-enhanced, metal-poor (CEMP) stars. We observed 27 candidate CEMP stars with high-resolution echelle spectrographs at S/N ~ 35-45. We calculate 1D, LTE atmospheric parameters and C, N, Ti, Fe, Zn, Sr, Y, Zr, Ba, La, Eu and Pb abundances for 10 stars from this sample. We identify 5 CEMP stars with enhancements in the elements produced by slow neutron captures (CEMP-s) and 1 CEMP star with unspectacular neutron-capture element abundances (CEMP-no). Among the 4 remaining stars, we find a possible "mild" CH star; a metal-rich, C-normal object and 2 metal-poor stars with unspectacular C abundances.
In addition, we obtained multi-epoch radial velocities, using spectrum cross- correlation techniques, for these 27 targets, 4 additional candidate CEMP stars and 14 candidate and confirmed CEMP stars analysed by other groups. Supplementing these data with velocities from the literature, we discover 13 spectroscopic binaries, 3 low-amplitude velocity-variable objects, 10 stars which may exhibit radial-velocity variation with longer sampling intervals, and 15 stars which exhibit no variation over their observational baseline.
We find that 5 of our 12 confirmed CEMP-s stars are binaries, and demonstrate that this binary fraction (~42%) implies that all our CEMP-s stars are binaries. Therefore, we conclude that CEMP-s stars most likely received their C and s-process element overabundances from a now extinct, formerly more massive companion when the latter was in its thermally-pulsing phase on the asymptotic giant branch (TP-AGB). Low-mass (1.5 and 3 [Special characters omitted.] ) AGB models successfully reproduce the observational scatter in the Pb abundances and ratios, but fail to predict the observed range in the lighter s-process elements. (Abstract shortened by UMI.)
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