~(41) Ca IN PRESOLAR GRAPHITE OF SUPERNOVA ORIGIN

摘要

Five low-density graphite grains from the Murchison meteorite have large ~(41)K excesses that can be attributed to the decay of ~(41)Ca. The inferred ~(41)Ca/~(40)Ca ratios, which range up to 1.7 X 10~(-2), and other isotopic signatures, ~(15)N, ~(18)O, and ~(28)Si excesses and high ~(26)Al/~(27)Al ratios, indicate a Type II supernova origin for these grains and are evidence for heterogeneous mixing of supernova ejecta.~(41)Ca seems to mainly originate from neutron capture in the C-rich and O-rich supernova zones, with only minor contributions from the O-burning zone. Admixture of material from the O-rich zone to outer C-rich layers is required to explain the abundance patterns of the stable Ca isotopes. In contrast, the Ti isotopic compositions reflect that of the C-rich zone and do not require substantial amounts of material from the O-rich zone.