The Lithium-, r- and s-Enhanced Metal-Poor Giant HK-II 17435-00532

Details The Lithium-, r- and s-Enhanced Metal-Poor Giant HK-II 17435-00532 The Lithium-, r- and s-Enhanced Metal-Poor Giant HK-II 17435-00532

Apr 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc.1001..169r&link_type=abstract

IXTH TORINO WORKSHOP ON EVOLUTION AND NUCLEOSYNTHESIS IN AGB STARS AND THE IIND PERUGIA WORKSHOP ON NUCLEAR ASTROPHYSICS. AIP C

Astronomy and Astrophysics

Astrophysics

Population Ii Stars, Stellar Structure, Interiors, Evolution, Nucleosynthesis, Ages, Abundances, Chemical Composition, S-Process

Scientific paper

We present the first detailed abundance analysis of the metal-poor giant HK-II 17435-00532. This star was observed as part of the University of Texas Long-Term Chemical Abundances of Stars in the Halo (CASH) Project. A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R~15000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = -2.2) star has an unusually high lithium abundance (logɛ(Li) = +2.1), mild carbon ([C/Fe] = +0.7) and sodium ([Na/Fe] = +0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = +0.8) and r-process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing mechanisms that connect the convective envelope with the outer regions of the H-burning shell. If so, HK-II 17435-00532 is the most metal-poor starin which this short-lived phase of Li enrichment has been observed. The r- and s-process material was not produced in this star but was either present in the gas from which HK-II 17435-00532 formed or was transferred to it from a more massive binary companion. Despite the current non-detection of radial velocity variations (over a time span of ~180 days), it is possible that HK-II 17435-00532 is in a long-period binary system, similar to other stars with both r and s enrichment.

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