Ansgar Reiners, Nandan Joshi, Bertrand Goldman
We present a catalogue of rotation and chromospheric activity in a sample of
334 M dwarfs of spectral types M0--M4.5 populating the parameter space around
the boundary to full convection. We obtained high-resolution optical spectra
for 206 targets and determined projected rotational velocity, vsini, and Halpha
emission. The data are combined with measurements of vsini in field stars of
the same spectral type from the literature. Our sample adds 157 new rotation
measurements to the existing literature and almost doubles the sample of
available vsini. The final sample provides a statistically meaningful picture
of rotation and activity at the transition to full convection in the solar
neighborhood. We confirm the steep rise in the fraction of active stars at the
transition to full convection known from earlier work. In addition, we see a
clear rise in rotational velocity in the same stars. In very few stars, no
chromospheric activity but a detection of rotational broadening was reported.
We argue that all of them are probably spurious detections; we conclude that in
our sample all significantly rotating stars are active, and all active stars
are significantly rotating. The rotation-activity relation is valid in
partially and in fully convective stars. Thus, we do not observe any evidence
for a transition from a rotationally dominated dynamo in partially convective
stars to a rotation-independent turbulent dynamo in fully convective stars;
turbulent dynamos in fully convective stars of spectral types around M4 are
still driven by rotation. Finally, we compare projected rotational velocities
of 33 stars to rotational periods derived from photometry in the literature and
determine inclinations for a few of them.
View original:
http://arxiv.org/abs/1201.5774
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