Deciphering Long-Term Photospheric and Chromospheric Activity on the Contact Binary VW Cephei

Abstract

During 1987, 1988, and 1989 we have been conducting a coordinated effort of ground-based photometry and UV spectroscopy of the bright W UMa contact binary VW Cephei. The photometry has indicated the presence of large, cool starspot regions on the larger, cooler star of the system. IUE observations were conducted to search for possible phase dependent variations of the strong chromospheric and transition region emission lines that could correlate with the location and extent of the starspots deduced from the light curves. From these data we found strong but not conclusive evidence to support the physical and geometrical connection between the photospheric starspots and the overlying chromospheric and transition region emissions. In addition, we have completed the measurements of all useable archival spectra of VW Cep back to 1978 to investigate the long-term variations of the UV line emissions. This work indicates systematic seasonal changes in the UV emission level with a time-scale of a few years which could be attributed to an activity cycle. From high dispersion spectra obtained in 1988 and 1989 we detected a sharp apparently stationary emission feature superimposed over the broad Mg II h + k emission line profiles of the two stars. VW Cep represents an extreme case for studying stellar dynamo theory and long-term ground based photometry coupled with IUE observations should play a crucial role in the understanding of magnetic fields and activity cycles in rapidly rotating solar-like stars.