Thermohaline mixing in low-mass giants: RGB and beyond

TL;DR

This study investigates thermohaline mixing in low-mass red giants, confirming its significant role in altering chemical yields and its persistence beyond the RGB phase, while assessing the impact of rotation and magnetic fields.

Contribution

It demonstrates that thermohaline mixing can destroy helium-3 in stars below 1.5 solar masses and persists during core helium burning, with minimal influence from rotation and magnetic fields.

Findings

Thermohaline mixing destroys helium-3 in stars below 1.5 Msun.

Mixing continues during core helium burning and beyond.

Rotational and magnetic mixing are negligible compared to thermohaline mixing.

Abstract

Thermohaline mixing has recently been proposed to occur in low mass red giants, with large consequence for the chemical yields of low mass stars. We investigate the role of thermohaline mixing during the evolution of stars between 1 Msun and 3 Msun. We use a stellar evolution code which includes rotational mixing and internal magnetic fields. We confirm that thermohaline mixing has the potential to destroy most of the helium 3 which is produced earlier on the main sequence during the red giant stage, in stars below 1.5Msun. We find this process to continue during core helium burning and beyond. We find rotational and magnetic mixing to be negligible compared to the thermohaline mixing in the relevant layers, even if the interaction of thermohaline motions with the differential rotation may be essential to establish the time scale of thermohaline mixing in red giants.