Rotation and Activity in Late-type M Dwarfs

摘要

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-calibratedspectra from the Sloan Digital Sky Survey. Most are inactive at a spectral type where Ha emissionhas previously seen to be very common. We used the cross-correlation technique to quantify therotational broadening; six of the stars in our sample have vsini>3.5 luns-1. Three of these stars donot exhibit Ha emission, despite rotating at velocities where previous work has observed stronglevels of magnetic field and stellar activity. Our results suggest that rotation and activity in late-typeM dwarfs may not always be linked, and open several addtional possibilities including a rotationdependant activity threshold, or a Maunder-minimum phenomenon in fully convective stars.