Insights from Asteroseismology of Massive Stars: The Need for Additional Angular Momentum Transport Mechanisms

Ehsan Moravveji,M.J.P.F.G Monteiro,M.S Cunha,J.M.T.S Ferreira

doi:10.1051/epjconf/201716002004

Ehsan Moravveji, M.J.P.F.G Monteiro + Show 2 more

Open Access

https://doi.org/10.1051/epjconf/201716002004

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Abstract

In massive stars, rotation and oscillatory waves can have a tight interplay. In order to assess the importance of additional angular momentum transport mechanisms other than rotation, we compare the asteroseismic properties of a uniformly rotating model and a differentially rotating one. Accordingly, we employ the observed period spacing of 36 dipole g-modes in the Kepler $\sim3.2$ M$_\odot$ target KIC 7760680 to discriminate between these two models. We favor the uniformly rotating model, which fully satisfies all observational constraints. Therefore, efficient angular momentum transport by additional mechanisms such as internal gravity waves, heat-driven modes and magnetic field is needed during early main sequence evolution of massive stars.

Highlights

Introduction and objectiveMassive stars are moderate to fast rotators [6]
Because the nuclear timescale τnuc is much longer than the dynamical timescale, the oscillatory motions in stars have sufficient time to interact with the background star
One critical interaction is an efficient redistribution of angular momentum inside stars by non-radial oscillations [1, 8, 9, 25, 28], or through internal gravity waves [20, 21]

Summary

Introduction and objective

Massive stars are moderate to fast rotators [6]. Rotation modifies the thermal and structural equilibrium in stars, launches meridional circulation currents [29], and triggers a handful of hydrodynamical instabilities (Maeder 2009, [11]). The other model has a differential rotation (abbreviated as DR) The latter represents ignoring the angular momentum flux carried by waves F = 0, and obeys the standard angular momentum transport by rotation in a diffusion approximation [5, 19]. The high-precision Kepler observations of pulsating stars has opened a unique window to empirically constrain the angular momentum distribution inside heat-driven pulsators. The radiative envelopes of three evolved γ Dor stars – near the end of core H burning phase – were shown to rotate almost uniformly [7, 14, 22] The descendant of these stars are the red giants which are shown to have a core-to-surface rotation rate slower than the model predictions [2].

Observational constraints

Uniform versus differential rotation

The asteroseismic test

Discussion and conclusions