X-Rays, Color, and the Vaughan-Preston Gap

Stellar activity is a function both of stellar mass (or color) and rotation period. If the period dependence in a plot of normalized x-ray luminosity vs. B-V color is accounted for, the remaining color dependence strongly resembles the convective turnover time. A connection is suggested between this color dependence and the existence of regions of lower star density in activity-color diagrams.