Bibcode
DOI
Roederer, Ian U.; Frebel, Anna; Shetrone, Matthew D.; Allende Prieto, Carlos; Rhee, Jaehyon; Gallino, Roberto; Bisterzo, Sara; Sneden, Christopher; Beers, Timothy C.; Cowan, John J.
Bibliographical reference
The Astrophysical Journal, Volume 679, Issue 2, pp. 1549-1565.
Advertised on:
6
2008
Journal
Citations
49
Refereed citations
45
Description
We present the first detailed abundance analysis of the metal-poor giant
HKII 17435-00532. This star was observed as part of the University of
Texas long-term project Chemical Abundances of Stars in the Halo (CASH).
A spectrum was obtained with the High Resolution Spectrograph (HRS) on
the Hobby-Eberly Telescope with a resolving power of R~15,000. 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 that
connects the convective envelope with the outer regions of the H-burning
shell. If so, HKII 17435-00532 is the most metal-poor star in which this
short-lived phase of Li enrichment has been observed. The Na and
n-capture enrichment can be explained by mass transfer from a companion
that passed through the thermally pulsing AGB phase of evolution with
only a small initial enrichment of r-process material present in the
birth cloud. Despite the current nondetection of radial velocity
variations (over ~180 days), it is possible that HKII 17435-00532 is in
a long-period or highly inclined binary system, similar to other stars
with similar n-capture enrichment patterns.
Based on observations obtained with the Hobby-Eberly Telescope, which is
a joint project of the University of Texas at Austin, the Pennsylvania
State University, Stanford University,
Ludwig-Maximilians-Universität München, and
Georg-August-Universität Göttingen.