Spectral behavior of 44 (iota) Bootis and VW Cephei in the ultraviolet

We present ultraviolet spectra of two W UMa-type binary systems, 44 (iota) Boo and VW Cep, with good coverage over their 0.268-day and 0.278-day periods, respectively, using observations obtained with the International Ultraviolet Explorer (IUE) during the period of 1978-1989 and 1978-1992. Three profiles of 44 (iota) Boo and VW Cep showing variations of line fluxes at three orbital phases are presented. This paper focuses on the calculated spectral line fluxes for the O I emission line at 1306 Å, C II emission line at 1336 Å, C IV emission line at 1550 Å and the He II emission line at 1640 Å, produced in the transition region and chromosphere. Our results show that there are variations of line fluxes with time, similar to the light curves found for both 44 (iota) Boo and VW Cep. We attribute these spectral variations in line fluxes to the variations of both density and temperature in the line-emitting region as a result of the intermediate-scale magnetic field responsible for stellar activity leading to these spectral variations. The ultraviolet luminosities indicate that 44 (iota) Boo and VW Cep have active chromospheres and transition regions.