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Abstract
The ϵ mechanism is a self-excitation mechanism of pulsations which acts on the regions where nuclear burning takes place. It has been shown that the ϵ mechanism can excite pulsations in models of hot helium-core flash, and that the pulsations of LS IV-14· 116, a He-enriched hot subdwarf star, could be explained that way. We aim to study the ϵmechanism effects on models of hot pre-horizontal branch stars and determine, if possible, a domain of instability in the log g — log T eff plane. We compute non-adiabatic non-radial pulsations on such stellar models, adopting different values of initial chemical abundances and mass of the hydrogen envelope at the time of the main helium flash. We find an instability domain of long-period (400 s ≲ P ≲ 2500 s) g -modes for models with 22000K ≲ Teff ≲ 50000K and 4.67 ≲ log g ≲ 6.15.
Highlights
Hot horizontal branch (HB) stars are core helium-burning low-mass stars (∼ 0.5 M )
extreme horizontal branch (EHB) stars are identified with the hot subdwarf B stars in the field
We aim to extend the study of the -mechanism effects on stellar models appropriate for pre-blue horizontal branch (BHB) and pre-EHB stars
Summary
Hot horizontal branch (HB) stars are core helium-burning low-mass stars (∼ 0.5 M ). Before settling in this phase, low-mass stars undergo a helium-core flash and subsequent subflashes. The position of stars in the BHB or the EHB depends mainly on their hydrogen-rich envelope mass. The pre-EHB and pre-BHB stars are going through He-subflashes. There are some sdBs with mild helium enrichment These stars could be at the pre-EHB phase where the ongoing diffusion has had no time to turn the envelope hydrogen pure ([2]). It has been shown that the -mechanism can excite pulsations in models of hot helium-core flash, and in the subsequent subflashes ([2]). We aim to extend the study of the -mechanism effects on stellar models appropriate for pre-BHB and pre-EHB stars
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