Glitch analysis and asteroseismic modelling of subgiant $\mu$ Herculis: confirming and interpreting the ${\Gamma }_1$ peak as the helium glitch

Abstract

The measurements of pressure-mode and mixed-mode oscillation frequencies in subgiant stars offer a unique opportunity to probe their internal structures -- from the surface to the deep interior -- and to precisely determine their global properties. We have conducted a detailed asteroseismic analysis of the benchmark subgiant $\mu$ Herculis using eight seasons of radial velocity observations from the SONG-Tenerife, and have determined its mass, radius, age, and surface helium abundance to be $1.105_{-0.024}^{+0.058}$ M${}_{\odot }$, $1.709_{-0.015}^{+0.030}$ R${}_{\odot }$, $8.4_{-0.1}^{+0.4}$ Gyr, and $0.242_{-0.021}^{+0.006}$, respectively. We have demonstrated that simultaneously fitting the helium glitch properties, oscillation frequencies, and spectroscopic observables yields a more accurate inference of the surface helium abundance and hence stellar age. A significant discrepancy between the observed extent of the helium ionization zone and that predicted by stellar models is identified and examined, underscoring potential limitations in the current modelling of stellar interiors. Our analysis confirms that the helium glitch originates from the region between the two stages of helium ionisation, i.e. from the ${\Gamma }_1$ peak, rather than from the second helium ionisation zone itself. Within the conventional formalism, this implies that the glitch analysis characterises the region located between the two helium ionisation zones.

16 pages, 15 figures (including 4 in the appendix), 6 tables (including 1 in the appendix), accepted for publication in MNRAS

References in corpus (19)

• The K2 Mission: Characterization and Early results
• Helioseismology and Solar Abundances
• ADIPLS -- the Aarhus adiabatic oscillation package
• Correcting stellar oscillation frequencies for near-surface effects
• A new correction of stellar oscillation frequencies for near-surface effects
• Asteroseismology for "à la carte" stellar age-dating and weighing: Age and mass of the CoRoT exoplanet host HD 52265
• An asteroseismic signature of helium ionization
• Stellar parameters and chemical abundances of 223 evolved stars with and without planets
• A Stellar Model-fitting Pipeline for Asteroseismic Data from the Kepler Mission
• First Results From The Hertzsprung Song Telescope: Asteroseismology Of The G5 Subgiant Star {\Mu}Her
• Age dating of an early Milky Way merger via asteroseismology of the naked-eye star $\nu$ Indi
• Asteroseismic estimate of helium abundance of a solar analog binary system
• The BAyesian STellar Algorithm (BASTA): a fitting tool for stellar studies, asteroseismology, exoplanets, and Galactic archaeology
• Seismic measurement of the locations of the base of convection zone and helium ionization zone for stars in the {\it Kepler} seismic LEGACY sample
• Prospects for asteroseismic inference on the envelope helium abundance in red giant stars
• A Theoretical Study of Acoustic Glitches in Low-Mass Main-Sequence Stars
• Properties of the ionisation glitch: I. Modelling the ionisation region
• Asteroseismology of the G8 subgiant beta Aquilae with SONG-Tenerife, SONG-Australia and TESS
• Properties of the ionisation glitch II. Seismic signature of the structural perturbation