Mind the Gap. I. Ha activity for M-Dwarfs

These unstable M-dwarfs provide new laboratories in which to understand how changing interior structures can produce potentially observable activity at the surface. In this work, we report the results of the largest high-resolution spectroscopic H{alpha} emission survey to date spanning this transition region, including 480 M-dwarfs observed using the CHIRON spectrograph at CTIO/SMARTS 1.5m.

We find that M dwarfs with H{alpha} in emission are almost entirely found 0-0.5mag above the top edge of the gap in the HRD, whereas effectively no stars in and below the gap show emission. Thus, the top edge of the gap marks a relatively sharp activity transition, and there is no anomalous H{alpha} activity for stars in the gap. We also identify a new region at 10.3<MG<10.8 on the main sequence where fewer M-dwarfs exhibit H{alpha} emission compared to M dwarfs above and below this magnitude range.