Asteroseismic masses, ages, and core properties of γ Doradus stars using gravito-inertial dipole modes and spectroscopy

Abstract

The asteroseismic modelling of period spacing patterns from gravito-inertial modes in stars with a convective core is a high-dimensional problem. We utilise the measured period spacing pattern of prograde dipole gravity modes (acquiring Π 0 ), in combination with the effective temperature (T eff ) and surface gravity (log g) derived from spectroscopy, to estimate the fundamental stellar parameters and core properties of 37 γ Doradus (γ Dor) stars whose rotation frequency has been derived from Kepler photometry. We make use of two 6D grids of stellar models, one with step core overshooting and one with exponential core overshooting, to evaluate correlations between the three observables Π 0 , T eff , and log g and the mass, age, core overshooting, metallicity, initial hydrogen mass fraction and envelope mixing. We provide multivariate linear model recipes relating the stellar parameters to be estimated to the three observables (Π 0 , T eff , log g). We estimate the (core) mass, age, core overshooting and metallicity of γ Dor stars from an ensemble analysis and achieve relative uncertainties of ∼ 10 per cent for the parameters. The asteroseismic age determination allows us to conclude that efficient angular momentum transport occurs already early on during the main sequence. We find that the nine stars with observed Rossby modes occur across almost the entire main-sequence phase, except close to core-hydrogen exhaustion. Future improvements of our work will come from the inclusion of more types of detected modes per star, larger samples, and modelling of individual mode frequencies.

The first view of δ Scuti and γ Doradus stars with the TESS mission

“…Ouazzani, Dupret & Reese (2012) and Hatta et al (2019) are required. Furthermore, the large number of excited g modes in these stars allow the physics of convective core overshooting and chemical mixing to be probed, as well as accurate determinations of stellar masses and ages using forward seismic modelling (Schmid & Aerts 2016;Aerts et al 2018;Mombarg et al 2019). These studies clearly demonstrate the asteroseismic potential of high-quality space-based observations of intermediate-mass stars.…”

Period spacings of γ Doradus pulsators in the Kepler field: Rossby and gravity modes in 82 stars

“…Our 'standard model' at each mass had X = 0.71, Z = 0.014 (corresponding to [M/H] = 0.036), α MLT = 1.8, exponential core overshooting of 0.015 Hp, exponential H-burning shell over-and undershooting of 0.015 Hp, exponential envelope overshooting of 0.025 Hp, diffusive mixing log D mix = 0 (in cm −2 s −1 ), OPAL opacities, and theAsplund et al (2009) solar abundance mixture. The parameters were chosen to be close to solar values, in agreement with observed metallicity values from spectroscopy and with the values from previously published asteroseismic modelling studies of g-mode pulsators (e.g Schmid & Aerts 2016;Mombarg et al 2019)…”

Rotational and pulsational variability in the TESS light curve of HD 27463

“…Similar studies of a magnetic B-type star (HD 43317) found a much lower convective overshoot (f ov = 0.004) and the authors conclude that convective mixing is suppressed by the magnetic field (Buysschaert et al 2018). More recently, Mombarg et al (2019) performed ensemble asteroseismic modelling of gravity modes in 37 γ Doradus stars observed by the Kepler space mission. Mombarg et al (2019) found best-fitting diffusive exponential overshooting values that range between 0 and 0.03 for these main-sequence intermediate-mass stars.…”

“…More recently, Mombarg et al (2019) performed ensemble asteroseismic modelling of gravity modes in 37 γ Doradus stars observed by the Kepler space mission. Mombarg et al (2019) found best-fitting diffusive exponential overshooting values that range between 0 and 0.03 for these main-sequence intermediate-mass stars.…”