KITP Conference: White Dwarfs from Physics to Astrophysics

At the KITP conference White Dwarfs from Physics to Astrophysics, I gave a talk entitled Ashes to Ashes: White Dwarfs from Double White Dwarf Mergers.

UFRGS Astronomy Seminar

I am “visiting” Universidade Federal do Rio Grande do Sul to give the Astronomy Seminar. A recording of my talk is available on YouTube.

Northwestern CIERA Seminar

I am “visiting” Northwestern University to give the CIERA Astro Seminar. A recording of my talk is available on YouTube.

A Helium-flash-induced Mixing Event Can Explain the Lithium Abundances of Red Clump Stars

This research was featured in AAS Nova.

The Astrophysical Journal Letters, Volume 901, Issue 1, id. L18, 5 pp.

Josiah Schwab

Observations demonstrate that the surface abundance of ${}^{7}\mathrm{Li}$ in low-mass stars changes dramatically between the tip of the red giant branch and the red clump. This naturally suggests an association with the helium core flash, which occurs between these two stages. Using stellar evolution models and a simple, ad hoc mixing prescription, we demonstrate that the ${}^{7}\mathrm{Li}$ enhancement can be explained by a brief chemical mixing event that occurs at the time of the first, strongest He subflash. The amount of ${}^{7}\mathrm{Be}$ already present above the H-burning shell just before the flash, once it mixes into the cooler envelope and undergoes an electron capture converting it to ${}^{7}\mathrm{Li}$ , is sufficient to explain the observed abundance at the red clump. We suggest that the excitation of internal gravity waves by the vigorous turbulent convection during the flash may provide a physical mechanism that can induce such mixing.

AAS Author Series

I participated in the AAS Journal Author Series and chatted with Frank Timmes about the ApJ article Mixing via Thermocompositional Convection in Hybrid C/O/Ne White Dwarfs.