Chromospheric activity in δ Scuti stars: the suspected variable τ Cygni.

Abstract

High-resolution IUE spectra of the suspected variable τ Cyg were obtained to search for a possible variability of the Mg II h, k double-peaked emission. The observations, spanning an interval of about 6.3 h, have shown flux excursions within or just near 15%, value suggested by some authors as limit to detect actual variations with IUE spectra. A variability, difficult to explain, could be present in the ratios F_k2v/F_k2r. The emission fluxes seem to be higher than those of the δ Scuti variables ρ Pup and β Cas. This comparison could give some insights on the possible role of the convection on the pulsational and chromospheric activities of τ Cyg. A positive correlation between the total emission fluxes and the rotational velocities of these stars was found.