Probability distributions of initial rotation velocities and core-boundary mixing efficiencies of γ Doradus stars

¹ IRAP, Université de Toulouse, CNRS, UPS, CNES, 14 Avenue Édouard Belin, 31400 Toulouse, France
e-mail: jmombarg@irap.omp.eu
² Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
³ Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010 6500 GL Nijmegen, The Netherlands
⁴ Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany
⁵ I-BioStat, Universiteit Hasselt, Martelarenlaan 42, 3500 Hasselt, Belgium
⁶ I-BioStat, KU Leuven, Kapucijnenvoer 7, 3000 Leuven, Belgium

Received: 11 January 2024
Accepted: 7 February 2024

Abstract

Context. The theory of rotational and chemical evolution is incomplete, thereby limiting the accuracy of model-dependent stellar mass and age determinations. The γ Doradus (γ Dor) pulsators are excellent points of calibration for the current state-of-the-art stellar evolution models, as their gravity modes probe the physical conditions in the deep stellar interior. Yet, individual asteroseismic modelling of these stars is not always possible because of insufficient observed oscillation modes.

Aims. This paper presents a novel method to derive distributions of the stellar mass, age, core-boundary mixing efficiency, and initial rotation rates for γ Dor stars.

Methods. We computed a grid of rotating stellar evolution models covering the entire γ Dor instability strip. We then used the observed distributions of the luminosity, effective temperature, buoyancy travel time, and near-core rotation frequency of a sample of 539 stars to assign a statistical weight to each of our models. This weight is a measure of how likely the combination of a specific model is. We then computed weighted histograms to derive the most likely distributions of the fundamental stellar properties.

Results. We find that the rotation frequency at zero-age main sequence follows a normal distribution, peaking at around 25% of the critical Keplerian rotation frequency. The probability-density function for extent of the core-boundary mixing zone, given by a factor of f_CBM times the local pressure scale height (assuming an exponentially decaying parameterisation), decreases linearly with increasing f_CBM.

Conclusions. Converting the distribution of fractions of critical rotation at the zero-age main sequence to units of d⁻¹, we find most F-type stars start the main sequence with a rotation frequency between 0.5 d⁻¹ and 2 d⁻¹. Regarding the core-boundary mixing efficiency, we find that it is generally weak in this mass regime.