Degenerate Thermal Pulses in Asymptotic Giant Branch Stars

Abstract

We report on the discovery of a new kind of thermal pulse in intermediate-mass asymptotic giant branch (AGB) stars. Deep dredge-up during normal thermal pulses on the AGB leads to the formation of a long unburnt tail in the helium profile. Eventually, the tail ignites under partially degenerate conditions, producing a strong shell flash with very deep subsequent dredge-up. The carbon content of the intershell convective region (XC ~ 0.6) is substantially higher than in a normal thermal pulse (XC ~ 0.25), and about 4 times more carbon is dredged up than in a normal pulse.