The Ca II H&K Rotation-Activity Relation in 53 mid-to-late type M-Dwarfs

TL;DR

This study investigates the relationship between stellar rotation and magnetic activity in 53 mid-to-late M-dwarfs, revealing a consistent power-law and saturated regime with a mass dependence in magnetic activity indicators.

Contribution

It provides new empirical measurements of the Ca II H&K flux and rotation periods for a sample of M-dwarfs, extending understanding of the rotation-activity relation in fully convective stars.

Findings

Power-law and saturated regimes consistent with previous studies.

Observed a mass dependence in the magnetic activity indicator $R'_{HK}$.

Data spans rotation periods from hours to months.

Abstract

In the canonical theory of stellar magnetic dynamo, the tachocline in partially convective stars serves to arrange small-scale fields, generated by stochastic movement of plasma into a coherent large-scale field. Mid-to-late M-dwarfs, which are fully convective, show more magnetic activity than classical magnetic dymano theory predicts. However, mid-to-late M-dwarfs show tight correlations between rotation and magnetic activity, consistent with elements of classical dynamo theory. We use data from Magellan Inamori Kyocera Echelle (MIKE) Spectrograph to detail the relation between Ca II H\&K flux and rotation period for these low-mass stars. We measure $R'_{HK}$ values for 53 spectroscopically identified M-dwarfs selected from the MEarth survey; these stars span spectral classes from M5.0 to M3.5 and have rotation periods ranging from hours to months. We present the rotation--activity relationship as traced through these data. We find power law and saturated regimes consistent to within one sigma of previously published results and observe a mass dependence in $R'_{HK}$.