Evidence for dynamo bistability among very low mass stars

TL;DR

This study provides evidence that very low mass stars exhibit bistability in their magnetic dynamo processes, with two distinct magnetic states coexisting among similar stars, challenging current understanding of stellar magnetism.

Contribution

It presents the first spectropolarimetric evidence of dynamo bistability in fully convective late M dwarfs, suggesting two separate magnetic regimes.

Findings

Detection of two distinct magnetic field types among similar stars.

Evidence supporting the existence of dynamo bistability in low-mass stars.

Implications for magnetic field generation theories in fully convective stars.

Abstract

Dynamo action in fully convective stars is a debated issue that also questions our understanding of magnetic field generation in partly convective Sun-like stars. During the past few years, spectropolari- metric observations have demonstrated that fully convective objects are able to trigger strong large-scale and long-lived magnetic fields. We present here the first spectropolarimetric study of a sample of active late M dwarfs (M5-M8) carried out with ESPaDOnS@CFHT. It reveals the co-existence of two distinct types of magnetism among stars having similar masses and rotation rates. A possible explanation for this unexpected discovery is the existence of two dynamo branches in this parameter regime, we discuss here the possible identification with the weak vs strong field bistability predicted for the geodynamo.