Magnetic field generation in PMS stars with and without radiative core

TL;DR

This study uses MHD simulations to explore how magnetic fields in pre-main sequence stars evolve differently depending on whether they are fully convective or have developed a radiative core, revealing differences in magnetic topology.

Contribution

The paper presents the first MHD simulation comparison of magnetic field generation in PMS stars at different evolutionary stages with and without a radiative core.

Findings

Fully convective star rotates almost rigidly.

Partially convective star exhibits differential rotation.

Magnetic field topology differs between the two stages.

Abstract

Recent observations of the magnetic field in pre-main sequence stars suggest that the magnetic field topology changes as a function of age. The presence of a tachocline could be an important factor in the development of magnetic field with higher multipolar modes. In this work we performed MHD simulations using the EULAG-MHD code to study the magnetic field generation and evolution in models that mimic stars at two evolutionary stages. The stratification for both stellar phases was computed by fitting stellar structure profiles obtained with the ATON stellar evolution code. The first stage is at $1.1 \mathrm{Myr}$, when the star is completely convective. The second stage is at $14 \mathrm{Myrs}$, when the star is partly convective, with a radiative core developed up to $30\%$ of the stellar radius. In this proceedings we present a preliminary analysis of the resulting mean-flows and magnetic field. The mean-flow analysis shown that the star rotate almost rigidly on the fully convective phase, whereas at the partially convective phase there is differential rotation with conical contours of iso-rotation. As for the mean magnetic field both simulations show similarities with respect to the field evolution. However, the topology of the magnetic field is different.