Period-activity relations in close binaries.

Abstract

The chromosphere transition region and coronal emissions of late spectral type main sequence stars with rotational periods short enough to bridge the gap between rapidly rotating single stars and contact binaries are analyzed. It is found that very active sample stars do not follow the scaling laws of Ayres et al. (1981) for line intensities originating in the upper transition regions and coronae, but do follow these laws for the lower excitation lines. The region where the transition region fluxes are independent of the spectral type and rotational period is shown to start in the detached binary domain at a rotation period close to three days. The fractional fluxes for the chromospheres, transition regions, and coronae reveal different dependences on the rotational period, but the total losses seem to depend linearly on the angular velocity.