Large-scale magnetic topologies of M dwarfs

TL;DR

This study uses spectropolarimetry to analyze magnetic field topologies in about 20 M dwarfs, revealing differences in magnetic structures and dynamo processes between fully and partly convective stars.

Contribution

First spectropolarimetric analysis of a small M dwarf sample providing new insights into magnetic topologies and dynamo mechanisms in fully-convective stars.

Findings

Distinct magnetic topologies in fully vs. partly convective stars

Differences in differential rotation patterns

Evidence for different dynamo processes in fully convective stars

Abstract

We present here the first results of a spectropolarimetric analysis of a small sample (about 20) of active stars ranging from spectral type M0 to M8, which are either fully-convective or possess a very small radiative core. This study aims at providing new constraints on dynamo processes in fully-convective stars. Results for stars with spectral types M0-M4 -- i.e. with masses above or just below the full convection threshold (about 0.35Msun) -- are presented. Tomographic imaging techniques allow us to reconstruct the surface magnetic topologies from the rotationally modulated time-series of circularly polarised profiles. We find strong differences between partly and fully convective stars concerning magnetic field topology and characteristic scales, and differential rotation. Our results suggest that magnetic field generation in fully convective stars relies on different dynamo processes than those acting in the Sun and other partly convective stars, in agreement with theoretical expectations.