CA-41 IN PRESOLAR GRAPHITE OF SUPERNOVA ORIGIN

Five low-density graphite grains from the Murchison meteorite have lar ge K-41 excesses that can be attributed to the decay of Ca-41. The inf erred Ca-41/(40)CA ratios, which range up to 1.7 x 10(-2), and other i sotopic signatures, N-15, O-18, and Si-28 excesses and high Al-26/Al-2 7 ratios, indicate a Type II supernova origin for these grains and are evidence for heterogeneous mixing of supernova ejecta. Ca-41 seems to mainly originate from neutron capture in the C-rich and O-rich supern ova zones, with only minor contributions from the O-burning zone. Admi xture of material from the O-rich zone to outer C-rich layers is requi red to explain the abundance patterns of the stable Ca isotopes. In co ntrast, the Ti isotopic compositions reflect that of the C-rich zone a nd do not require substantial amounts of material from the O-rich zone .