A NEW APPROACH TO DETERMINE THE INITIAL MASS FUNCTION IN THE SOLAR NEIGHBORHOOD

摘要

Oxygen to iron abundance ratios of metal-poor stars provide information on nucleosynthesis yields from massive stars that end in Type Ⅱ supernova (SN Ⅱ) explosions. Using a standard model of chemical evolution of the Galaxy we have reproduced the solar neighborhood abundance data and estimated the oxygen and iron yields of genuine SN Ⅱ origin. The estimated yields are compared with the theoretical yields to derive the relation between the lower and upper mass limits in each generation of stars and the initial mass function (IMF) slope. Independent of this relation, we furthermore derive the relation between the lower mass limit and the IMF slope from the stellar mass-to-light ratio in the solar neighborhood. These independent relations unambiguously determine the upper mass limit of m_u = 50 ± 10 solar mass and the IMF slope index of 1.3-1.6 above 1 solar mass. This upper mass limit corresponds to the mass beyond which stars end as black holes without ejecting processed matter into the interstellar medium. We also find that the IMF slope index below 0.5 solar mass cannot be much shallower than 0.8.