Origin of radio-quiet coronal mass ejections in flare stars

TL;DR

This paper proposes that the absence of Type II radio bursts in flare stars is due to their strong magnetic fields increasing Alfven speeds, making it difficult for such bursts to form, thus explaining their radio-quiet nature.

Contribution

It introduces a hypothesis that high magnetic field strengths in flare stars prevent Type II burst formation, challenging the direct scaling from solar to stellar flares.

Findings

Type II bursts are rarely observed in flare stars.

High Alfven speeds in flare star coronae inhibit Type II burst generation.

Scaling solar flare models to stars may be ineffective for predicting radio emissions.

Abstract

Type II radio bursts are observed in the Sun in association with many coronal mass ejections (CME's. In view of this association, there has been an expectation that, by scaling from solar flares to the flares which are observed on M dwarfs, radio emission analogous to solar Type II bursts should be detectable in association with M dwarf flares. However, several surveys have revealed that this expectation does not seem to be fulfilled. Here we hypothesize that the presence of larger global field strengths in low-mass stars, suggested by recent magneto-convective modeling, gives rise to such large Alfven speeds in the corona that it becomes difficult to satisfy the conditions for the generation of Type II radio bursts. As a result, CME's propagating in the corona/wind of a flare stars are expected to be "radio-quiet" as regards Type II bursts. In view of this, we suggest that, in the context of Type II bursts, scaling from solar to stellar flares is of limited effectiveness.