Ultraviolet variations in the spectrum of the visible central star of Abell 35.

Abstract

We report on simultaneous IUE and photometric observations carried out in March 1992 of the G8IV star BD-22 3467 located at the centre of the planetary nebula Abell 35. The main feature of the IUE low resolution spectra is a strong Mg II emission, which is common in fairly close binaries. Meanwhile no variations of the hot companion were detected 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-term variations of the Mg II line possibly linked with the mean brightness of the star. Thus the present material reinforces the idea that chromospheric activity occurs at the surface of the rapidly rotating G-star and that the visible light is modulated by dark spots.