Spectropolarimetric measurements of the mean longitudinal magnetic field of chemically peculiar stars II. Phase relating the magnetic and luminosity variabilities

For a sample of chemically peculiar stars! we report time-resolved measurem ents of the effective magnetic field which were obtained with the spectropo larimetry operating at the Catania Astrophysical Observatory. These observa tions are combined with data from the literature for better pointing out th at periodic magnetic variability which characterises this class of stars. P eriods given in the literature have been checked and, if possible, redeterm ined, not only by means of the magnetic measurements but referring also to the Hipparcos photometry. The variability of the effective magnetic field o f the already known magnetic star 25 Sex is pointed out for the first time. As to the suspected magnetic chemically peculiar star EP UMa, our measurem ents confirm that this is really a magnetic star and we indicate a possible variability period. The accuracy of the variability period for CS Vir and FF Vir is improved. The suggestion that light variability is due to the re- distribution of ultraviolet flux towards the visible wavelengths in metal r ich regions, which are not homogeneously distributed on the stellar surface , appears not always and straightly valid. Local line-blocking is certainly important in the case of CS Vir and a direct influence of the magnetic fie ld on the infrared photometric variability cannot be ruled out for 25 Sex.