Numerical simulations of the kappa-mechanism with convection

TL;DR

This paper uses 2-D direct numerical simulations to study the interaction between convection and pulsations driven by the kappa-mechanism, providing insights into mode stability and nonlinear saturation in stellar layers.

Contribution

It introduces a novel approach combining linear stability analysis and DNS to explore convection-pulsation coupling in stellar models.

Findings

Identification of conditions for kappa-mechanism instability in radiative layers

Confirmation of nonlinear saturation of unstable modes via DNS

Analysis of convection and acoustic mode coupling using projections

Abstract

A strong coupling between convection and pulsations is known to play a major role in the disappearance of unstable modes close to the red edge of the classical Cepheid instability strip. As mean-field models of time-dependent convection rely on weakly-constrained parameters, we tackle this problem by the means of 2-D Direct Numerical Simulations (DNS) of kappa-mechanism with convection. Using a linear stability analysis, we first determine the physical conditions favourable to the kappa-mechanism to occur inside a purely-radiative layer. Both the instability strips and the nonlinear saturation of unstable modes are then confirmed by the corresponding DNS. We next present the new simulations with convection, where a convective zone and the driving region overlap. The coupling between the convective motions and acoustic modes is then addressed by using projections onto an acoustic subspace.