Joint Astrophysics Colloquium

What do presolar grains tell us about what's happening inside low-mass stars?

Ken Nollet

Argonne National Laboratory

The isolation of presolar grains from meteorites in recent years presents both opportunities and challenges for models of astrophysical environments. A large fraction of these grains condensed as solids in the atmospheres of low-mass stars during the final phases of their evolution, as indicated by agreement between predicted and measured isotopic ratios. However, abundances of isotopes that participate in hydrogen-burning reactions do not agree with stellar-evolution models so exactly. This circumstance, along with related observations of stars that are active today, indicates that “standard” stellar evolution is missing some important mechanisms for mixing between different layers inside the stars. I will describe the data on presolar grains, concentrating on their relation to the properties of low-mass stars. Then I will describe a model of “extra mixing” in stars that can explain some of the differences from standard stellar evolution. Finally, I will discuss the stubborn problem of the nitrogen isotopic ratios in the grains, which remains unresolved even with the assumption of extra mixing.