Rotation and Activity in Late-type M Dwarfs.

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 Hα 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 v sin i>=3.5 kms^-1. Three of these stars do not exhibit Hα 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 addtional possibilities including a rotation dependant activity threshold, or a Maunder-minimum phenomenon in fully convective stars. [ABSTRACT FROM AUTHOR]