Hiroko Ito et al 2009 ApJ 698 L37 doi:10.1088/0004-637X/698/1/L37
Hiroko Ito1,2, Wako Aoki1,2, Satoshi Honda3 and Timothy C. Beers4
Show affiliationsWe present a one-dimensional LTE chemical abundance analysis of the very bright (V = 9.1) carbon-enhanced metal-poor (CEMP) star BD+44°493, based on high-resolution, high signal-to-noise spectra obtained with Subaru/HDS. The star is shown to be a subgiant with an extremely low iron abundance ([Fe/H] = –3.7), while it is rich in C ([C/Fe] = +1.3) and O ([O/Fe] = +1.6). Although astronomers have been searching for extremely metal-poor stars for decades, this is the first star found with [Fe/H] <–3.5 and an apparent magnitude V < 12. Based on its low abundances of neutron-capture elements (e.g., [Ba/Fe] =–0.59), BD+44°493 is classified as a "CEMP-no" star. Its abundance pattern implies that a first-generation faint supernova is the most likely origin of its carbon excess, while scenarios related to mass loss from rapidly rotating massive stars or mass transfer from an asymptotic giant branch companion star are not favored. From a high-quality spectrum in the near-UV region, we set an very low upper limit on this star's beryllium abundance (A(Be) = log(Be/H) + 12 < –2.0), which indicates that the decreasing trend of Be abundances with lower [Fe/H] still holds at [Fe/H] <–3.5. This is the first attempt to measure a Be abundance for a CEMP star, and demonstrates that high C and O abundances do not necessarily imply high Be abundances.
Galaxy: abundances; stars: abundances; stars: individual (BD+44° 493); stars: Population II
97.20.Tr Population II stars (horizontal branch, metal poor, etc.)
97.10.Me Mass loss and stellar winds
97.20.Li Giant and subgiant stars
Issue 1 (2009 June 10)
Received 2009 March 19, accepted for publication 2009 April 30
Published 2009 May 21
Hiroko Ito et al 2009 ApJ 698 L37
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