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.

arXiv comment14 Figures including Supplementary Information. Letter to Nature Astronomy

References in corpus (27)

• The Transiting Exoplanet Survey Satellite: Simulations of planet detections and astrophysical false positives
• Ultraviolet Radiation from Evolved Stellar Populations -- I. Models
• New models for the evolution of Post-Asymptotic Giant Branch stars and Central Stars of Planetary Nebulae
• Post-Asymptotic Giant Branch Evolution of Low- and Intermediate-Mass Stars. Preliminary Results
• Hot subluminous stars
• Ensemble Asteroseismology of Solar-Type Stars with the NASA Kepler Mission
• Internal Gravity Waves in Massive Stars: Angular Momentum Transport
• Red-giant seismic properties analyzed with CoRoT
• Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808
• Modeling He-rich subdwarfs through the hot-flasher Scenario
• Internal Gravity Wave Excitation by Turbulent Convection
• 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
• Flash Mixing on the White Dwarf Cooling Curve: FUSE Observations of three He-rich sdB Stars
• The Observational Signatures of Convectively Excited Internal Gravity Modes in Main Sequence Stars
• Acoustic Signatures of the Helium Core Flash
• Discovery of a variable lead-rich hot subdwarf: UVO 0825+15
• Abundance analyses of helium-rich subluminous B stars
• Rapidly rotating second-generation progenitors for the blue hook stars of ω Cen
• The mysterious cut-off of the Planetary Nebula Luminosity Function
• KIC 1718290: A Helium-rich V1093-Her-like Pulsator on the Blue Horizontal Branch
• The energy flux spectrum of internal waves generated by turbulent convection
• The enigmatic He-sdB pulsator LS IV$-$14${}^{\circ }$116: new insights from the VLT
• Pulsational instabilities driven by the $\epsilon$ mechanism in hot pre-horizontal branch stars I. The Hot-Flasher Scenario
• The inside-out planetary nebula around a born-again star
• Discovery of a second pulsating intermediate helium-enriched sdOB star
• Seismic characterization of red giants going through the Helium-core flash

Cited by in corpus (10)

• 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
• Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV -14 116 revisited
• A Plague of Magnetic Spots Among the Hot Stars of Globular Clusters
• PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data
• 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