出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We determined chemical abundances of extremely metal-poor (EMP) stars in the Sextans dwarf galaxy. The heavy element Ba is deficient in EMP stars in dwarf galaxies in general, while some fraction of EMP stars in the Milky Way halo show large excesses of this element. Sextans, however, we identified one object (S15-19) that shows exceptionally high Ba abundance ([Ba/Fe]~+0.4), which is as high as the values found in r-process enhanced stars in the Milky Way (so-called r-II stars). We recently conducted high resolution spectroscopy for this object to determine the origin of the heavy elements in this object. The low upper-limit of the Eu abundance indicates that the Ba of this object is not explained by the r-process, but s-process at least partially contributed to the enrichment of heavy elements. The carbon-excess and the radial velocity variation found for this object suggest that the Ba excess is attributed to the s-process in an AGB star and the mass transfer across the binary system.
