log Z vs. log P_rot for our sample stars shown with the squares. The colour coding denotes the B−V colour of the stars. The fit to our results (Eq. (11)) is shown with the solid line. For comparison we plot the stars from Donahue et al. (1996) as grey points and the fit to these stars with the dashed line. We also show the fit to the stars of Henry et al. (1995a) with the dotted line for the log P_rot range covered by our work and that of Donahue et al. (1996).