Tuesday

Red giants experience recurrent mixing events that significantly alter the chemical composition of their envelopes. Inspecting changes in surface abundances allows us to probe the physical processes happening in the deep stellar interiors. Of particular importance are the three main oxygen isotopes which are altered in the course of the CNO-cycle and serve as indicators of the nucleosynthesis and mixing taking place.

In this contribution, I show that the predicted 16O/17O and 16O/18O from stellar models of red giants are at variance with observations (Halabi et al. 2015). This discrepancy puts two main uncertainties in stellar evolution models in the spotlight: convective boundary mixing and relevant nuclear reaction rates.
Owing to the steep profile of the 17O isotope inside the star, 16O/17O is very sensitive to the depth of convective mixing. On the other hand, the 17O destruction rates have been recently re-measured by the LUNA collaboration (Bruno et al. 2016).

I will discuss whether extra mixing or the new nuclear reaction rates can resolve the discrepancy between theory and observations.
Another suggested possible solution to match observations is assuming slightly supersolar initial 17O and 18O abundances instead of the solar values, combined with a subsolar initial 16O abundance (Lebzelter et al. 2015). I will show whether this agrees with predictions from galactic chemical evolution models and how exploring such significant deviations from model predictions may provide insight into the cosmic recycling of matter.