Author:

Keywords:

stars : binaries : close, stars : binaries : eclipsing, stars : binaries : spectroscopic, stars : fundamental parameters, stars : oscillations, stars : individual : en lac, line-profile variability, cephei star 16-lacertae, long-term behavior, forced-oscillations, beta, pulsation, amplitudes, system, parameters, search, Science & Technology, Physical Sciences, Astronomy & Astrophysics, stars : individual : EN Lac, LINE-PROFILE VARIABILITY, CEPHEI STAR 16-LACERTAE, LONG-TERM BEHAVIOR, FORCED-OSCILLATIONS, BETA, PULSATION, AMPLITUDES, SYSTEM, PARAMETERS, SEARCH, 0201 Astronomical and Space Sciences, 5101 Astronomical sciences, 5107 Particle and high energy physics, 5109 Space sciences

Abstract:

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 P-1 = 0(d).16916703 was found to vary with a 74 year cycle. The amplitudes of the two other RV oscillations, having periods of P-3 = 0(d).18173256 and P-2 = 0(d).17085554, vary on much shorter time scales of 674 d and 331 d, respectively. The value of P-1 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 P-1 and P-3 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 A to P-3 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**.