Chromospheric emission and rotation of the Hyades lower main sequence

Abstract

The identity of chromospheric Ca II H- and K-line emission has been monitored for two seasons in a large sample of Hyades F and G dwarfs. Mean emission levels vary smoothly with spectral type, suggesting that the rotation rate at a given spectral type varies relatively little, and that the rotation rate decreases smoothly as a function of mass. In this case the mechanism which controls pre-main-sequence angular momentum loss in late-type stars must be self-regulating to a high degree.