Rotation and Activity in Late-type M Dwarfs

TL;DR

This study investigates the relationship between rotation and magnetic activity in late-type M dwarfs, revealing that rotation does not always correlate with activity, challenging previous assumptions.

Contribution

It provides new observational evidence that rotation and activity are not always linked in late-type M dwarfs, suggesting alternative mechanisms or thresholds.

Findings

Some rapidly rotating stars show no H-alpha emission.

Rotation and activity are not always correlated in late-type M dwarfs.

Possible existence of a rotation-dependent activity threshold or Maunder-minimum states.

Abstract

We have examined the relationship between rotation and activity in 14 late-type (M6-M7) M dwarfs, using high resolution spectra taken at the Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey. Most are inactive at a spectral type where H-alpha emission has previously seen to be very common. We used the cross-correlation technique to quantify the rotational broadening; six of the stars in our sample have vsini>3.5 km/s. Three of these stars do not exhibit H-alpha emission, despite rotating at velocities where previous work has observed strong levels of magnetic field and stellar activity. Our results suggest that rotation and activity in late-type M dwarfs may not always be linked, and open several additional possibilities including a rotation dependant activity threshold, or a Maunder-minimum phenomenon in fully convective stars.