2001A&A...367..236L

An analysis of 1236 new electronic spectra of the eclipsing binary EN Lac from four observatories and of 994 radial velocities (RV hereafter) from photographic spectra, published by several authors, has allowed us to disentangle the RV variations due to orbital motion and due to pulsations of the star. New, accurate orbital elements as well as precise values of the three pulsation periods, already known from the previous studies, were derived. The accuracy of the orbital solution has been substantially improved after the observed RV changes were properly prewhitened for the short-term oscillations. The amplitude of the dominant RV oscillation with a period of P₁=0.16916703d was found to vary with a 74 year cycle. The amplitudes of the two other RV oscillations, having periods of P₃=0.18173256d and P₂=0.17085554d, vary on much shorter time scales of 674d and 331d, respectively. The value of P₂ derived here does not correspond to a one year alias of the value found by several authors from photometry but appears to be an intrinsic period. The time scales of the amplitude modulations found for P₁ and P₃ are in good agreement with previous photometric results. For the first time we present evidence of line profile variations of EN Lac. They correlate well with the short-term RV variations but they alternatively occur with periods corresponding either to the fundamental periods or to the first harmonics of P₁ to P₃. An analysis of the RV scatter along the orbital phase curve for the new spectra, obtained over a relatively short interval of time, gives some indication of a sharp increase of this scatter when the stars are approaching periastron. Since this could be a signature of forced oscillations, the effect is worth further study, though it appears rather marginal at present.