The activity and rotation limit in the Hyades

TL;DR

This study investigates the rotation and activity limits of K to M stars in the Hyades cluster, revealing that the onset of activity occurs at earlier spectral types compared to field stars, with a relation similar to field star activity-rotation patterns.

Contribution

It provides new measurements of stellar rotation and activity in the Hyades, highlighting a shifted activity threshold and comparing it to field stars.

Findings

Fast rotators exist at spectral types where activity increases.

The activity and rotation threshold is shifted to earlier types in the Hyades.

The activity-rotation relation is similar to that of field stars.

Abstract

We conduct a study of K to M type stars to investigate the activity and the rotation limit in the Hyades. We use a sample of 40 stars in this intermediate-age cluster (~625 Myr) to probe stellar rotation in the threshold region where stellar activity becomes prevalent. Here we present projected equatorial velocities (vsin i) and chromospheric activity measurements (H{\alpha}) that indicate the existence of fast rotators in the Hyades at spectral types where also the fraction of stars with H{\alpha} emission shows a rapid increase ("H{\alpha} limit"). The locus of enhanced rotation (and activity) thus seems to be shifted to earlier types in contrast to what is seen as the rotation limit in field stars. The relation between activity and rotation appears to be similar to the one observed in fields stars.