Pulsational instabilities driven by the $\epsilon$ mechanism in hot pre-horizontal branch stars I. The Hot-Flasher Scenario

Abstract

The $\epsilon$ mechanism is a self-excitation mechanism of stellar pulsations which acts in regions inside the star where nuclear burning takes place. It has been shown that the $\epsilon$ mechanism can excite pulsations in models of hot pre-horizontal branch stars, and that the shortest periods of LS IV-14${}^{\circ }$116 could be explained that way. We aim to study the $\epsilon$ mechanism in stellar models appropriate for hot pre-horizontal branch stars to predict their pulsational properties and the instability domain in the $\log g-\log T_{\mathrm{eff}}$ plane. We perform detailed computations of non-adiabatic non-radial pulsations on stellar models during the helium subflashes just before the helium-core burning phase. We find an instability domain of long-period gravity modes due to the $\epsilon$ mechanism in the $\log g-\log T_{\mathrm{eff}}$ plane at roughly $22000\mathrm{K}\lesssim T_{\mathrm{eff}}\lesssim 50000$K and $4.67\lesssim \log g\lesssim 6.15$. Consequently, we find instabilities due to the $\epsilon$ mechanism on pre-extreme horizontal branch stellar models ($T_{\mathrm{eff}}\gtrsim 22000$K), but not on pre-blue horizontal branch stellar models ($T_{\mathrm{eff}}\lesssim 21000$K). The periods of excited modes range between $\sim 200$ and $\sim 2000$s. Comparison with the three known pulsating He-rich subdwarfs shows that $\epsilon$ mechanism can excite gravity modes in stars with similar surface properties, but in our models it is only able to excite modes in the range of the shortest observed periods. We predict a new instability strip for hot-subdwarf stars of which LS IV-14${}^{\circ }$116 could be the first inhabitant. Based on simple estimates we expect 1 to 10 stars in the current samples of hot-subdwarf stars to be pulsating by the $\epsilon$ mechanism. Our results could constitute a theoretical basis for future searches of pulsators in the Galactic field.

13 pages, 11 figures, accepted for publication in A&A

References in corpus (19)

• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• Modeling He-rich subdwarfs through the hot-flasher Scenario
• New nonadiabatic pulsation computations on full PG1159 evolutionary models: the theoretical GW Vir instability strip revisited
• First full evolutionary computation of the He-flash induced mixing in Population II stars
• SDSS J160043.6+074802.9: a very rapid sdO pulsator
• Discovery of a variable lead-rich hot subdwarf: UVO 0825+15
• Abundance analyses of helium-rich subluminous B stars
• Subdwarf B stars from the common envelope ejection channel
• Rapidly rotating second-generation progenitors for the blue hook stars of ω Cen
• KIC 1718290: A Helium-rich V1093-Her-like Pulsator on the Blue Horizontal Branch
• Short-period $g$-mode pulsations in low-mass white dwarfs triggered by H shell burning
• The enigmatic He-sdB pulsator LS IV$-$14${}^{\circ }$116: new insights from the VLT
• The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars
• Stellar Evolution and Variability in the Pre-ZAHB Phase
• Asteroseismology of hybrid $\delta$ Scuti--$\gamma$ Doradus pulsating stars
• Two candidate brown dwarf companions around core helium-burning stars
• On the possible existence of short-period g-mode instabilities powered by nuclear burning shells in post-AGB H-deficient (PG1159-type) stars
• Hot Flashers and He Dwarfs in Galactic Globulars
• Pulsations of Pre-White Dwarfs with Hydrogen-dominated Atmospheres

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