We report the discovery of a cool metal-poor, main-sequence star exhibiting large excesses of r -process elements. This star is one of the two newly discovered cool subdwarfs (effective temperatures of 5000 K) with extremely low metallicity ([Fe/H] < −3) identified from follow-up high-resolution spectroscopy of metal-poor candidates from the Sloan Digital Sky Survey. SDSS J2357−0052 has [Fe/H] = −3.4 and [Eu/Fe] = +1.9, and exhibits a scaled solar r -process abundance pattern of heavy neutron-capture elements. This is the first example of an extremely metal-poor, main-sequence star showing large excesses of r -process elements; all previous examples of the large r -process-enhancement phenomena have been associated with metal-poor giants. The metallicity of this object is the lowest, and the excess of Eu ([Eu/Fe]) is the highest, among the r -process-enhanced stars found so far. We consider possible scenarios to account for the detection of such a star and discuss techniques to enable searches for similar stars in the future.
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Aoki et al. (2010) studied this question.
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