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

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 $^\circ$14 116 has been found to show multiperiodic luminosity variations. The variability of LS IV $^\circ$14 116 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 $^\circ$14 116 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 $^\circ$14 116.