Enrichment of very metal poor stars with both -process and -process elements from stars

Wanajo, Shinya*; Nomoto, Kenichi*; Iwamoto, Nobuyuki  ; Ishimaru, Yuri*; Beers, T. C.*

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.