Abstract
Among presolar grains, oxide ones are made of oxygen, aluminum, and a small fraction of magnesium, produced by the 26Al decay. The largest part of presolar oxide grains belong to the so-called group 1 and 2, which have been suggested to form in Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, respectively. However, standard stellar nucleosynthesis models cannot account for the 17O/16O, 18O/16O, and 26Al/27Al values recorded in those grains. Hence, for more than 20 years, the occurrence of mixing phenomena coupled with stellar nucleosynthesis have been suggested to account for this peculiar isotopic mix. Nowadays, models of massive AGB stars experiencing Hot Bottom Burning or low mass AGB stars where Cool Bottom Process, or another kind of extra-mixing, is at play, nicely fit the oxygen isotopic mix of group 2 oxide grains. The largest values of the 26Al/27Al ratio seem somewhat more difficult to account for.
Highlights
Dust is an alternative probe, with respect to direct astronomical observations, to explore stars and their nucleosynthesis
We review the possibility of reproducing the isotopic abundances of oxygen and aluminum recorded in group 2 grains with low and intermediate mass Asymptotic Giant Branch (AGB) models by adopting the 17O+p reaction rates proposed by different authors
Trippella et al (2016) have shown that such a mechanism can induce the formation of a 13C-pocket suitable to address the observational constrains to s-process nucleosynthesis in low mass AGB stars, but our interest in the magnetic induced mixing is due to the possibility of reproducing the isotopic composition recorded in both SiC and oxide presolar grains of AGB origin (Palmerini et al, 2017, Palmerini et al, 2018)
Summary
Oxide ones are made of oxygen, aluminum, and a small fraction of magnesium, produced by the 26Al decay. The largest part of presolar oxide grains belong to the so-called group 1 and 2, which have been suggested to form in Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, respectively. Standard stellar nucleosynthesis models cannot account for the 17O/16O, 18O/16O, and 26Al/27Al values recorded in those grains. For more than 20 years, the occurrence of mixing phenomena coupled with stellar nucleosynthesis have been suggested to account for this peculiar isotopic mix. Models of massive AGB stars experiencing Hot Bottom Burning or low mass AGB stars where Cool Bottom Process, or another kind of extramixing, is at play, nicely fit the oxygen isotopic mix of group 2 oxide grains.
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