ON THE ROTATION-ACTIVITY CORRELATION FOR ACTIVE BINARY STARS

We present an investigation of rotation-activity correlations using In ternational Ultraviolet Explorer (IUE) SWP measurements of the C IV em ission line at 1550 Angstrom for 72 active binary systems. We use a st andard stellar evolution code to derive non-empirical Rossby numbers, R-0, for each star in our sample and compare the resulting C IV rotati on-activity correlation to that found for empirically derived values o f the Rossby number and that based on rotation alone. For dwarf stars our values of R-0 do not differ greatly from empirical ones and we fin d a corresponding lack of improvement in correlation. Only a marginal improvement in correlation is found for evolved components in our samp le. We discuss possible additional factors, other than rotation or con vection, that may influence the activity levels in active binaries. Ou r observational data imply, in contrast to the theoretical predictions of convective motions, that activity is only weakly related to mass i n evolved stars. We conclude that current dynamo theory is limited in its application to the study of active stars because of the uncertaint y in the angular velocity-depth profile in stellar interiors and the u nknown effects of binarity and surface gravity.