Distributions and evolution of the equatorial rotation velocities of 2937 BAF-type main-sequence stars from asteroseismology

A break in the specific angular momentum at M ≃ 2.5 M_⊙

¹ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
² Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010 6500 GL Nijmegen, The Netherlands
³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 8 August 2025
Accepted: 20 October 2025

Abstract

Context. Studies of the rotational velocities of intermediate-mass main-sequence stars are crucial for testing stellar evolution theory. They often rely on spectroscopic measurements of the projected rotation velocities, V_eqsin i. These not only suffer from the unknown projection factor sin i but tend to ignore additional line-profile broadening mechanisms aside from rotation, such as pulsations and turbulent motions near the stellar surface. This limits the accuracy of V_eq distributions derived from V_eqsin i measurements.

Aims. We use asteroseismic measurements to investigate the distribution of the equatorial rotation velocity V_eq, its ratio with respect to the critical rotation velocity, V_eq/V_crit, and the specific angular momentum, J/M, for several thousands of BAF-type stars, covering a mass range from 1.3 M_⊙ to 8.8 M_⊙ and almost the entire core-hydrogen burning phase.

Methods. We rely on high-precision model-independent internal rotation frequencies, as well as on masses and radii from asteroseismology to deduce V_eq, V_eq/V_crit, and J/M for 2937 gravity-mode pulsators in the Milky Way. The sample stars have rotation frequencies between almost zero and 33 μHz, corresponding to rotation periods above 0.35 d.

Results. We find that intermediate-mass stars experience a break in their J/M occurring in the mass interval [2.3, 2.7] M_⊙. We establish unimodal V_eq and V_eq/v_crit distributions for the mass range [1.3, 2.5]  M_⊙, while stars with M ∈ [2.5, 8.8] M_⊙ reveal some structure in their distributions. We find that the near-core rotation slows down as stars evolve, pointing to very efficient angular momentum transport.

Conclusions. The kernel density estimators of the asteroseismic internal rotation frequency, equatorial rotation velocity, and specific angular momentum of this large sample of intermediate-mass field stars can conveniently be used for population synthesis studies and to fine-tune the theory of stellar rotation across the main sequence evolution.