2007A&A...463..233A

Understanding large-scale mass exchange in binaries also requires studies of complicated objects in the rapid phases of the process. β Lyr is one such object. Our goals were to analyse 52 photographic and 651 electronic spectra of β Lyr to obtain additional information about circumstellar matter and to investigate spectrophotometric information for the first time. Improved quadratic ephemeris was derived via orbital solution with the FOTEL program. The spectra were disentangled using the KOREL program. Spectrophotometric quantities of 15 stronger absorption lines of the primary were measured and corrected for the orbital continuum variations using the fluxes calculated from a fit of the light curves with the BINSYN program. Central intensities of the V and R peaks of the Hα emission line were measured and corrected for the orbital light changes using the R-band light curve numerically modelled with the program PERIOD04. Disentangling of photographic and electronic spectra led to the detection of weak absorption lines originating from the pseudophotosphere of the accretion disc. This way, a rich line spectrum of the accretion disc, not limited to only two previously known SiII 6347 and SiII 6371 lines, was obtained. A projected rotational velocity of 180km/s was estimated for the disc spectrum. Such a value agrees well with the assumption of the Keplerian rotation of the outer layers of the accretion disc. After the correction, a pronounced increase of the strength of all absorption lines around phases of the primary eclipse was found. We argue that this is due to additional absorption of the light of the primary in one of the jets and/or scattering envelope above the accretion disc of the gainer. The net intensity of the V peak of Hα shows no orbital variation, but a possible 271-d periodicity. The net intensity of the R peak shows mild orbital changes and a slow change over a cycle of about 2780 days. These results seem to support the earlier conclusion that the Hα emission originates in the jet-like structures. All new findings support the current picture that the circumstellar structures of β Lyr consist of a thick accretion disc, bipolar jets, and a scattering envelope above the disc.