Rotation-Activity Correlations in K-M dwarfs II.

Although these results are preliminary and will need confirmation, the data suggest that these distinct RACs may be associated with different dynamo regimes. We also study R'_HK_ as a function of the Rossby number R_0_. We find (i) for dK4 stars, R'_HK_ as a function of R_0_ agrees well with previous results for F-G-K stars and (ii) in dK6, dM2, dM3, and dM4 stars, at a given R_0_, the values of R'_HK_ lie at a factor of 3, 10, 20, and 90, respectively, below the F-G-K RAC.

Our results suggest a significant decrease in the efficiency of the dynamo mechanism(s) as regards chromospheric heating before and at dM3, i.e., before and at the transition to complete convection. We also show that the ratio of coronal heating to chromospheric heating L_X_/L_HK_ increases by a factor of 100 between dK4 and dM4 stars.