ACTIVITY-RELATED CHARACTERISTICS OF THE CONVECTIVE ENVELOPES IN EVOLVING LOW-MASS STARS

Convective envelope structures have been computed for the post-main-sequence evolutionary phases of 0.7-1.6 M⊙ model stars having initial mass-fraction abundances of helium and heavier elements equal to Y = 0.25 and Z = 0.0169 (solar), respectively. Two types of quantities as a function of the basic stellar parameters have been studied. The first of these is relevant to the theory of stellar dynamos and includes estimates of the convective turnover time, various dynamo number parameters, and the maximum non thermal energy which is available for the dynamo action. The other is related to the expected sizes of inhomogeneities on the stellar surfaces and comprises the determination of the depth of the convective zone, the pressure scale height at the outer edge of the convective region, and the thicknesses of the shells where the super-adiabatic gradient is large and where the opacity is within 10% of its maximum. All of the above properties, which are fully discussed, are extensively tabulated and their variations as a function of evolutionary state are conveniently displayed in a number of contour plots to facilitate comparisons with observations.