H$\boldmath{\alpha}$ variations of the RS CVn type binary ER Vulpeculae

We present the results of spectroscopic observations of the active eclipsing binary ER Vul in the 5860–6700 Å spectral range carried out at the Catania Astrophysical Observatory. Accurate measurements of radial velocities by using the cross-correlation technique have been made and a new orbital solution is given. All spectra display chromospheric emission which fills in the Hα absorption lines of both components. The equivalent width (EW) of the Hα emission has been measured by subtraction of a synthetic spectrum built up with spectra of inactive standard stars. The EW of total Hα emission, arisen from both components, shows a phase-dependent variation. It reaches its maximum value just before the primary eclipse. We were able to separate the contributions to the Hα emission from the individual components at phases far from the eclipses. We have found that the secondary, cooler component is the most active and its Hα residual emission shows the same trend as the total Hα emission, along orbital phase. This Hα equivalent width variation can be due to plage-like structures on the chromosphere of secondary star. In addition, a decrease of the Hα EW around the ingress phase of the primary eclipse is apparent.