Asteroseismic analysis of variable hot subdwarf stars observed with TESS I. The mean g-mode period spacings in hot subdwarf B stars

Abstract

We present photometric and spectroscopic analyses of gravity (g-mode) long-period pulsating hot subdwarf B (sdB) stars. We perform a detailed asteroseismic and spectroscopic analysis of five pulsating sdB stars observed with {\it TESS} aiming at the global comparison of the observations with the model predictions based on our stellar evolution computations coupled with the adiabatic pulsation computations. We apply standard seismic tools for mode identification, including asymptotic period spacings and rotational frequency multiplets. We calculate the mean period spacing for $l=1$ and $l=2$ modes and estimate the errors by means of a statistical resampling analysis. For all stars, atmospheric parameters were derived by fitting synthetic spectra to the newly obtained low-resolution spectra. We have computed stellar evolution models using {\tt LPCODE} stellar evolution code, and computed $l=1$ g-mode frequencies with the adiabatic non-radial pulsation code {\tt LP-PUL}. Derived observational mean period spacings are then compared to the mean period spacings from detailed stellar evolution computations coupled with the adiabatic pulsation computations of g-modes. The atmospheric parameters derived from spectroscopic data are typical of long-period pulsating sdB stars with the effective temperature ranging from 23\,700\,K to 27\,600\,K and surface gravity spanning from 5.3\,dex to 5.5\,dex. In agreement with the expectations from theoretical arguments and previous asteroseismological works, we find that the mean period spacings obtained for models with small convective cores, as predicted by a pure Schwarzschild criterion, are incompatible with the observations. We find that models with a standard/modest convective boundary mixing at the boundary of the convective core are in better agreement with the observed mean period spacings and are therefore more realistic.

Accepted for publication in A&A

References in corpus (16)

• Astrophysics Source Code Library
• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
• On the proper use of the Schwarzschild and Ledoux criteria in stellar evolution computations
• A brief introductory guide to TLUSTY and SYNSPEC
• New binaries among UV-selected, hot subdwarf stars and population properties
• Asteroseismology revealing trapped modes in KIC 10553698A
• Signatures of nonlinear mode interactions in the pulsating hot B subdwarf star KIC 10139564
• KIC7668647: a 14 day beaming sdB+WD binary with a pulsating subdwarf
• The discovery of differential radial rotation in the pulsating subdwarf B star KIC 3527751
• Evolutionary modelling of subdwarf B stars using MESA with the predictive mixing and convective premixing schemes
• TESS first look at evolved compact pulsators : Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018
• Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS: I. Asteroseismology of the GW Vir stars RX J2117+3412, HS 2324+3944, NGC 6905, NGC 1501, NGC 2371, and K 1-16
• Hot UV-bright stars of galactic globular clusters
• A search for variable subdwarf B stars in TESS Full Frame Images -- I. Variable objects in the southern ecliptic hemisphere
• The effects of near-core convective shells on the gravity modes of the subdwarf B pulsator KIC 10553698A

Cited by in corpus (3)

• New Variable Hot Subdwarf Stars Identified from Anomalous Gaia Flux Errors, Observed by TESS, and Classified via Fourier Diagnostics
• Pulsating subdwarf B stars observed with K2 during Campaign 7 and an examination of seismic group-properties
• Discovery and analysis of three magnetic hot subdwarf stars: evidence for merger-induced magnetic fields