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-element-enhanced metal-poor star BS 16934-002Aoki, Wako*; Honda, Satoshi*; Beers, T. C.*; Hidai, Masahide*; Iwamoto, Nobuyuki; Tominaga, Nozomu*; Umeda, Hideyuki*; Nomoto, Kenichi*; Norris, J. E.*; Ryan, S. G.*
Astrophysical Journal, 660(1, Part1), p.747 - 761, 2007/05
Times Cited Count：45 Percentile：72.28(Astronomy & Astrophysics)A detailed elemental abundance analysis has been carried out for the very metal-poor ([Fe/H] = -2.7) star BS 16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD 122563 indicates excesses of O, Na, Mg, Al, and Sc in BS 16934-002. Of particular interest, no excess of C or N is found in this object, in contrast to CS 22949-037 and CS 29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the elements. No established nucleosynthesis model exists that explains the observed abundancepattern. A supernova model, including mixing and fallback, assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS 16934-002.
Sadakane, Kozo*; Arai, Akira*; Aoki, Wako*; Arimoto, Nobuo*; Hidai, Masahide*; Onishi, Takashi*; Tajitsu, Akito*; Beers, T. C.*; Iwamoto, Nobuyuki; Tominaga, Nozomu*; et al.
Publications of the Astronomical Society of Japan, 58(3), p.595 - 604, 2006/06
Times Cited Count：11 Percentile：31.92(Astronomy & Astrophysics)We report detailed spectroscopic studies performed for the secondary star in the black hole binary (micro-quasar) V4641 Sgr in order to examine its surface chemical composition and to see if its surface shows any signature of pollution by ejecta from a supernova explosion. We obtain abundances of 10 elements and find definite over-abundances of N (by 0.8 dex or more) and Na (by 0.8 dex) in V4641 Sgr. From line-by-line comparisons of eight other elements (C, O, Mg, Al, Si, Ti, Cr, Fe) between V4641 Sgr and the two normal late B-type stars, which have been reported to have solar abundances. An evolutionary model of a massive close binary system has been constructed to explain the abundances observed in V4641 Sgr. The model suggests that the BH forming supernova in this system was a dark one.
-process and 
-process elements from 
starsWanajo, Shinya*; Nomoto, Kenichi*; Iwamoto, Nobuyuki; Ishimaru, Yuri*; Beers, T. C.*
Astrophysical Journal, 636(2, Part1), p.842 - 847, 2006/01
Times Cited Count：36 Percentile：64.57(Astronomy & Astrophysics)Recent spectroscopic studies have revealed the presence of numerous carbon-enhanced, metal-poor stars with [Fe/H]
that exhibit enhancements of -process elements. These stars are believed to be the result of a binary mass-transfer episode from a former asymptotic giant-branch (AGB) companion that underwent -process nucleosynthesis. However, several such stars exhibit significantly lower Ba/Eu ratios than solar -process abundances. We propose a model in which the double enhancements of - and -process elements originate from a former companion in a wide binary system, which may undergo -processing during an AGB phase, followed by -processing during its subsequent supernova explosion. The mass of Eu captured by the secondary through the wind from the supernova is estimated. We find that the estimated mass is in good agreement with a constraint on the Eu yield per supernova event, when the initial orbital separation is taken to be 
1 year.
