ULTRAVIOLET VARIATIONS IN THE SPECTRUM OF THE VISIBLE CENTRAL STAR OFABELL 35

We report on simultaneous IUE and photometric observations carried out in March 1992 of the G8IV star BD-22-degrees 3467 located at the cent re of the planetary nebula Abell 35. The main feature of the IUE low r esolution spectra is a strong Mg II emission, which is common in fairl y close binaries. Meanwhile no variations of the hot companion were de tected in the SWP spectrum, variations were detected in the intensity of the MgII line arising from the G-star; these variations, like those of the CaII measured by us previously (Jasniewicz et al. 1992), seem to be in antiphase with the visible V-light curve. From 4 LWP spectra extracted from the archive ULDA we also show the existence of long-ter m variations of the Mg II line possibly linked with the mean brightnes s of the star. Thus the present material reinforces the idea that chro mospheric activity occurs at the surface of die rapidly rotating G-sta r and that the visible light is modulated by dark spots.