Toward fully compressible numerical simulations of stellar magneto-convection with the RAMSES code

TL;DR

This paper demonstrates the feasibility of fully compressible 3D magneto-hydrodynamical simulations of stellar interiors using the RAMSES code, capturing turbulent convection and magnetic field amplification relevant for stellar magnetism studies.

Contribution

It adapts the RAMSES code for highly subsonic turbulence and performs the first proof-of-concept 3D simulations of stellar magneto-convection with magnetic field effects.

Findings

Successful modeling of low Mach number flows (~10^{-3})

Observation of exponential magnetic energy growth indicating a small-scale dynamo

Development of a quasi-steady turbulent convection layer

Abstract

Numerical simulations of magneto-convection have greatly expanded our understanding of stellar interiors and stellar magnetism. Recently, fully compressible hydrodynamical simulations of full-star models have demonstrated the feasibility of studying the excitation and propagation of pressure and internal gravity waves in stellar interiors, which would allow for a direct comparison with asteroseismological measurements. However, the impact of magnetic fields on such waves has not been taken into account yet in three-dimensional simulations. We conduct a proof of concept for the realization of three-dimensional, fully compressible, magneto-hydrodynamical numerical simulations of stellar interiors with the RAMSES code. We adapted the RAMSES code to deal with highly subsonic turbulence, typical of stellar convection, by implementing a well-balanced scheme in the numerical solver. We then ran and analyzed three-dimensional hydrodynamical and magneto-hydrodynamical simulations with different resolutions of a plane-parallel convective envelope on a Cartesian grid. Both hydrodynamical and magneto-hydrodynamical simulations develop a quasi-steady, turbulent convection layer from random density perturbations introduced over the initial profiles. The convective flows are characterized by small-amplitude fluctuations around the hydrodynamical equilibrium of the stellar interior, which is preserved over the whole simulation time. Using our compressible well-balanced scheme, we were able to model flows with Mach numbers as low as $\mathcal{M} \sim 10^{-3}$, but even lower Mach number flows are possible in principle. In the magneto-hydrodynamical runs, we observe an exponential growth of magnetic energy consistent with the action of a small-scale dynamo. (Abridged)