A Metal-poor Double-lined Spectroscopic Binary With C, Li, And S-process Overabundances

Details A Metal-poor Double-lined Spectroscopic Binary With C, Li, And S-process Overabundances A Metal-poor Double-lined Spectroscopic Binary With C, Li, And S-process Overabundances

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21113105s&link_type=abstract

American Astronomical Society, AAS Meeting #211, #131.05; Bulletin of the American Astronomical Society, Vol. 39, p.959

Astronomy and Astrophysics

Astronomy

Scientific paper

We present a detailed high-resolution spectroscopic analysis of the carbon-rich low metallicity Galactic halo object CS 22964-161. Our observations with the Magellan MIKE spectrograph reveal CS 22964-161 to be a double-lined spectroscopic binary. Using radial velocities from 31 MIKE spectra we derive accurate orbital parameters for the system (P = 252d, e = 0.66, Mpsin3i = 0.77M&sun;, Mssin3i = 0.68 M&sun;). From a model atmosphere analysis we show that both primary and secondary stars are near the metal-poor main-sequence turnoff (Teff,p = 6050K, log gp = 3.7, and Teff,s = 5850 K, log gs = 4.1), and have similar overall metallicities ([Fe/H] ≈ -2.4) and abundance ratios. The CS 22964-161 components are very enriched in carbon ([C/Fe] = +1.2) and in neutron-capture elements that can be created in the s-process (e.g., [Ba/Fe] = +1.3, [Pb/Fe] = +2.2). The primary star has a lithium abundance close to the "Spite-Plateau” value, log ɛ(Li) = 2.1. We believe that the binary members seen today received their anomalous abundances from a third star that underwent mass loss during its AGB evolution. We compare the observed CS 22964-161 abundance set with nucleosynthesis predictions of AGB stars, consider the outer envelope stability in the observed stars as they drew mass from the third (AGB) companion, and consider whether that third star is still a member of the CS 22964-161 system.
This work has been supported by the U.S. National Science Foundation through grants AST-0607708 to CS and AST-0507325 to IBT, and by the Italian MIUR-PRIN06 Project to RG.

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