GRB nucleosynthesis in dwarf galaxies

Recent observations with large telescopes have revealed that stars in nearby dwarf spheroidal galaxies (dSph stars) have elemental abundances distinct from metal poor stars in our galaxy [7, 8, 9]. This indicates that the chemical evolution of these dwarf galaxies was dominated by supernovae that have not mainly contributed to the chemical evolution of our galaxy. On the other hand, the identification of host galaxies of gamma-ray bursts (GRBs) suggests that GRBs may preferentially occur in low luminosity metal-poor galaxies [6]. Supernovae associated with GRBs might have exclusively imprinted their nucleosynthesis on the elemental abundances of stars in dwarf galaxies while these supernovae were too rare to contribute to the chemical evolution of our galaxy. To test this conjecture, we have planned to perform nucleosynthesis calculations in aspherical supernovae and investigate the elemental abundance patterns of stars inheriting the nucleosynthesis products by taking into account ejecta with different abundance patterns moving in different directions. As a consequence, we found that aspherical supernovae could be responsible for low α/Fe ratios (except for Ca/Fe) and/or large scatter of the abundance ratios seen in dSph stars. The abundance ratios of O/Mg are found to be a good indicator to identify the progenitor stars that have supplied heavy elements to dSph stars.