A preliminary interpretation of stellar chromospheric CA II emission variations within the framework of stellar dynamo theory

Abstract

Recent stellar chromospheric Ca II emission data are analyzed and interpreted within the framework of simple concepts of dynamo theory. From an examination of the rotation rates and B-V indexes of 26 stars as presented by Vaughn at el. (1981) and the background flux values derived by Wilson (1978) for 18 reference stars, an empirical relation is derived between dynamo number, calculated from the B-V index and rotation rate, and stellar chromospheric emission flux. The Ca-emission cycle morphology of the sample stars is then examined, and differences between the four morphological classes identified are explained in terms of the correlation of large dynamo numbers with the presence of several interfering magnetic modes of different spatial scales, which do not exhibit a marked cyclic behavior, and small numbers with the excitation of only a single mode. The gap noted by Vaughn and Preston (1980) in the relation between the log of the emission flux with (B-V) is then interpreted as representing a transition from a multiple-mode dynamo to a single-mode dynamo as the dynamo number decreases.