The Spatial Association of Spots and Plages

C.J. Butler

Proceedings IAU Symposium 176, 'Stellar Surface Structure' Vienna. 1995. Kluwer

We review the evidence, from rotational modulation, for association of plages and spots on active binaries. We find reasonably convincing support for such an association from IUE SWP observations of RS CVn stars, but little or no evidence from MgII line fluxes. There is a similar lack of evidence for BY Dra systems. The results can be interpreted as evidence for: (a) the presence of active longitudes which persist on some RS CVn stars for several years, (b) high filling factors in MgII emission and (c) lower filling factors, and therefore greater contrast, in SWP emission. There is a suggestion that the association between plages and spots are more clearly seen in longer period RS CVn stars than the very active, short period, systems favoured by IUE observers.