Group II Oxide Grains: How Massive Are Their AGB Star Progenitors?

Presolar grains and their isotopic compositions provide valuable constraints to AGB star nucleosynthesis. However, there is a sample of O- and Al-rich dust, known as group 2 oxide grains, whose origin is difficult to address. On the one hand, the O-17/O-16 isotopic ratios shown by those grains are similar to the ones observed in low-mass red giant stars. On the other hand, their large O-18 depletion and Al-26 enrichment are challenging to account for. Two different classes of AGB stars have been proposed as progenitors of this kind of stellar dust: intermediate mass AGBs with hot bottom burning, or low mass AGBs where deep mixing is at play. Our models of low-mass AGB stars with a bottom-up deep mixing are shown to be likely progenitors of group 2 grains, reproducing together the O-17/O-16, O-18/O-16 and Al-26/Al-27 values found in those grains and being less sensitive to nuclear physics inputs than our intermediate-mass models with hot bottom burning.

Automated summary

Research suggests that models of low-mass AGB stars are likely progenitors of group 2 oxide grains, being more reliable than intermediate-mass models with hot bottom burning.