The first determination of the actinide Th abundance for a red giant of the Ursa Minor dwarf galaxy

Wako Aoki; Satoshi Honda; Kozo Sadakane; Nobuo Arimoto

doi:10.1093/pasj/59.3.l15

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arXiv · 0704.3104

The first determination of the actinide Th abundance for a red giant of the Ursa Minor dwarf galaxy

Wako Aoki·Satoshi Honda·Kozo Sadakane·Nobuo Arimoto

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Abstract

The Thorium abundance for the red giant COS82 in the Ursa Minor dwarf spheroidal galaxy is determined based on a high resolution spectrum. This is the first detection of actinides in an extra Galactic object. A detailed abundance pattern is determined for 12 other neutron-capture elements from the atomic number 39 to 68. These elements are significantly over-abundant with respect to other metals like Fe (> 1 dex) and their abundance pattern agrees well with those of the r-process-enhanced, very metal-poor stars known in the Galactic halo, while the metallicity of this object ([Fe/H] ~ -1.5) is much higher than these field stars ([Fe/H] ~ -3.0). The results indicate that the mechanism and the astrophysical site that are responsible for neutron-capture elements in COS82 is similar to that for field r-process-enhanced stars, while the condition of low mass star formation is quite different. An estimate of the age of this object based on the Th abundance ratio is discussed.

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Wako Aoki, Satoshi Honda, Kozo Sadakane, Nobuo Arimoto. 2007-04-24. The first determination of the actinide Th abundance for a red giant of the Ursa Minor dwarf galaxy. https://doi.org/10.1093/pasj%2F59.3.l15

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