A CATALOG OF ROTATION AND ACTIVITY IN EARLY-M STARS

Abstract

We present a catalogue of rotation and chromospheric activity in a sample of\n334 M dwarfs of spectral types M0--M4.5 populating the parameter space around\nthe boundary to full convection. We obtained high-resolution optical spectra\nfor 206 targets and determined projected rotational velocity, vsini, and Halpha\nemission. The data are combined with measurements of vsini in field stars of\nthe same spectral type from the literature. Our sample adds 157 new rotation\nmeasurements to the existing literature and almost doubles the sample of\navailable vsini. The final sample provides a statistically meaningful picture\nof rotation and activity at the transition to full convection in the solar\nneighborhood. We confirm the steep rise in the fraction of active stars at the\ntransition to full convection known from earlier work. In addition, we see a\nclear rise in rotational velocity in the same stars. In very few stars, no\nchromospheric activity but a detection of rotational broadening was reported.\nWe argue that all of them are probably spurious detections; we conclude that in\nour sample all significantly rotating stars are active, and all active stars\nare significantly rotating. The rotation-activity relation is valid in\npartially and in fully convective stars. Thus, we do not observe any evidence\nfor a transition from a rotationally dominated dynamo in partially convective\nstars to a rotation-independent turbulent dynamo in fully convective stars;\nturbulent dynamos in fully convective stars of spectral types around M4 are\nstill driven by rotation. Finally, we compare projected rotational velocities\nof 33 stars to rotational periods derived from photometry in the literature and\ndetermine inclinations for a few of them.\n