Three-Dimensional Simulations of Massive Stars: II. Age Dependence

TL;DR

This study uses 3D simulations to analyze how age affects internal wave dynamics and overshooting in 7 solar mass stars at different evolutionary stages, revealing significant changes in wave trapping and spectral properties.

Contribution

It provides the first detailed 3D simulation comparison of convective overshooting and internal gravity wave behavior across stellar ages in intermediate-mass stars.

Findings

Overshooting layers are mostly confined above the convective boundary.

Older stars exhibit more complex internal gravity wave trapping.

Surface frequency spectra become steeper with stellar age.

Abstract

We present 3D full star simulations, reaching up to 90% of the total stellar radius, for three $7M_\odot$ stars of different ages (ZAMS, midMS and TAMS). A comparison with several theoretical prescriptions shows the generation spectra for all three ages are dominated by convective plumes. Two distinct overshooting layers are observed, with most plumes stopped within the layer situated directly above the convective boundary (CB); overshooting to the second, deeper layer becomes increasingly more infrequent with stellar age. Internal gravity wave (IGW) propagation is significantly impacted in the midMS and TAMS models as a result of some IGWs getting trapped within their Brunt-V\"{a}is\"{a}l\"{a} frequency spikes. A fundamental change in the wave structure across radius is also observed, driven by the effect of density stratification on IGW propagation causing waves to become evanescent within the radiative zone, with older stars being affected more strongly. We find that the steepness of the frequency spectrum at the surface increases from ZAMS to the older models, with older stars also showing more modes in their spectra.