Speaker
Maria Lugaro
(University of Utrecht)
Description
Presolar spinel (MgAl2O4) grains have been recently discovered in meteorites and
represent the most abundant type of presolar oxides. The O, Mg and Al isotopic
compositions of the vast majority of presolar oxide grains indicate that these grains
originated in red giant and asymptotic giant branch (AGB) stars of masses lower than
approximately 3 solar masses. Grain OC2 has a unique composition, showing most
extreme O and Mg isotopic ratios among presolar oxide grains: O17/O16 three times
higher than solar, O18/O16 26 times lower than solar, and excesses in Mg25 and Mg26
of (43+/-1)% and (117+/-1)%, respectively, with respect to solar. Its origin has thus
been tentatively attributed to an AGB star of intermediate mass, around 5 solar
masses. In intermediate-mass AGB stars the heavy Mg isotopes are produced in the He
intershell by alpha-capture reactions on Ne22, while the O and Al compositions are
mostly determined by proton captures at the base of the convective envelope (hot
bottom burning). Using detailed models of AGB stars of different masses and
metallicities that include Vassiliadis & Wood mass-loss rates and time-dependent
convective mixing during the nucleosynthesis postprocessing, we analyse the O, Mg
and Al compositions in AGB stars and discuss them in the light of the extremely
precise measurements of the composition of grain OC2.
Primary author
Maria Lugaro
(University of Utrecht)
Co-authors
Dr
Amanda Karakas
(McMaster University)
Dr
Larry Nittler
(Carnegie Institution of Washington)
