Pulsations driven by the ε-mechanism in post-merger remnants: First results

Abstract

Helium-rich subdwarfs are a rare subclass of hot subdwarf stars which constitute a small and inhomogeneous group showing varying degrees of helium enrichment. Only one star, LS IV º14 116 has been found to show multiperiodic luminosity variations. The variability of LS IV º14 116 has been explained as the consequence of nonradial g-mode oscillations, whose excitation is difficult to understand within the frame of the standard κ-mechanism driving pulsations in sdBV stars. In a recent study, we have proposed that the pulsations of LS IV º14 116 might be driven through the ε-mechanism acting in unstable He-burning zones in the interior of the star, that appear before the quiescent He-burning phase. One of the few accepted scenarios for the formation of He-rich subdwarfs is the merger of two He-core white dwarfs. As part of this project, we present a study of the ε-mechanism in post-merger remnants, and discuss the results in the light of the pulsations exhibited by LS IV º14 116.