The interior angular momentum of core hydrogen burning stars from gravity-mode oscillations

TL;DR

This study uses gravity-mode oscillations to measure the internal angular momentum distribution in 67 core-hydrogen burning stars, revealing moderate differential rotation and significant core spin-down before the helium-burning phase.

Contribution

It provides the first comprehensive asteroseismic analysis of internal rotation in a large, diverse sample of intermediate-mass main-sequence stars, linking core rotation to stellar evolution stages.

Findings

Core rotation rates are moderate and show deviations from rigid rotation.

Significant core spin-down occurs before the transition to core-helium burning.

Most gravity modes are in the sub-inertial regime, indicating strong rotational influence.

Abstract

A major uncertainty in the theory of stellar evolution is the angular momentum distribution inside stars and its change during stellar life. We compose a sample of 67 stars in the core-hydrogen burning phase with a $\log\,g$ value from high-resolution spectroscopy, as well as an asteroseismic estimate of the near-core rotation rate derived from gravity-mode oscillations detected in space photometry. This assembly includes 8 B-type stars and 59 AF-type stars, covering a mass range from 1.4 to 5\,M$_\odot$, i.e., it concerns intermediate-mass stars born with a well-developed convective core. The sample covers projected surface rotation velocities $v\sin\,i \in[9,242]\,$km\,s$^{-1}$ and core rotation rates up to $26\mu$Hz, which corresponds to 50\% of the critical rotation frequency. We find deviations from rigid rotation to be moderate in the single stars of this sample. We place the near-core rotation rates in an evolutionary context and find that the core rotation must drop drastically before or during the short phase between the end of the core-hydrogen burning and the onset of core-helium burning. We compute the spin parameter, which is the ratio of twice the rotation rate to the mode frequency (also known as the inverse Rossby number), for 1682 gravity modes and find the majority (95\%) to occur in the sub-inertial regime. The ten stars with Rossby modes have spin parameters between 14 and 30, while the gravito-inertial modes cover the range from 1 to 15.