Asteroseismic signatures of the helium-core flash

Abstract

All evolved stars with masses $M_{\star }\lesssim 2M_{\odot }$ undergo a helium(He)-core flash at the end of their first stage as a giant star. Although theoretically predicted more than 50 years ago, this core-flash phase has yet to be observationally probed. We show here that gravity modes (g modes) stochastically excited by He-flash driven convection are able to reach the stellar surface, and induce periodic photometric variabilities in hot-subdwarf stars with amplitudes of the order of a few mmag. As such they can now be detected by space-based photometry with the Transiting Exoplanet Survey Satellite (TESS) in relatively bright stars (e.g. magnitudes $I_C\lesssim 13$). The range of predicted periods spans from a few thousand seconds to tens of thousand seconds, depending on the details of the excitation region. In addition, we find that stochastically excited pulsations reproduce the pulsations observed in a couple of He-rich hot subdwarf stars. These stars, and in particular the future TESS target Feige 46, are the most promising candidates to probe the He-core flash for the first time.

14 Figures including Supplementary Information. Letter to Nature Astronomy

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Cited by in corpus (8)

• A helium-flash-induced mixing event can explain the lithium abundances of red clump stars
• Evolutionary modelling of subdwarf B stars using MESA with the predictive mixing and convective premixing schemes
• An evolutionary channel for CO-rich and pulsating He-rich subdwarfs
• A Plague of Magnetic Spots Among the Hot Stars of Globular Clusters
• Rapid expansion of red giant stars during core helium flash by waves propagation to the envelope and implications to exoplanets
• Neutrinos and Asteroseismology of Stars over the Helium Flash
• Onset of common envelope evolution during a core helium flash by rapid envelope expansion
• Detection horizon for the neutrino burst from the stellar helium flash