Calibrating angular momentum transport in intermediate-mass stars from gravity-mode asteroseismology

Abstract

The physical mechanisms driving the transport of angular momentum in stars are not fully understood, as current models cannot explain the observed stellar rotation profiles across all stages of evolution. By making use of pulsating F-type dwarfs, this work aims at (i) observationally calibrating the efficiency of angular momentum transport, assuming a constant uniform viscosity, and (ii) testing how well state-of-the-art rotating stellar models with angular momentum (AM) transport by rotationally-induced processes can explain observed rotation profiles. In both cases, the aim is to simultaneously reproduce the measured near-core rotation and core-to-surface rotation ratio. Asteroseismic modelling is applied to a sample of seven slowly rotating pulsators, to derive (core) masses and ages from their gravity-mode oscillations. This work focuses on the main sequence, using models that start with an initial uniform rotation frequency at the start of core-hydrogen burning that is a free parameter. Two treatments of AM transport are considered: (i) a constant uniform viscosity, and (ii) rotationally-induced processes. Next, the initial rotation frequency of each star is derived from the observed present-day near-core rotation frequency for both treatments. To explain the near-core rotation rate at the inferred age, initial rotation frequencies at the zero-age main sequence need to be below 10 percent of the initial critical break-up frequency. A diffusive approximation of angular momentum transport can in general explain the observed rotation profiles of the six slowly-rotating F-type dwarfs, for average values of the viscosity between 2x10^5 and 5x10^7 cm^2/s or when the viscosity is computed from rotationally-induced mechanisms. Yet, for three stars in the sample, the core-to-surface rotation fraction from rotationally-induced mechanisms is predicted to be higher than observed.

Accepted for publication in Astronomy & Astrophysics, 13 pages

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