A new analysis of the radial velocity variations of the eclipsing and spectroscopic binary EN Lacertae

Abstract

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 P1 = 0.d 16916703 was found to vary with a 74 year cycle. The amplitudes of the two other RV oscillations, having periods of P3 = 0.d 18173256 and P2 = 0. d 17085554, vary on much shorter time scales of 674 d and 331 d, 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 .

A new version of the moment method, optimized for mode identification in multiperiodic stars

“…EN (16) The first spectroscopic mode identification for this star was recently done by who considered a subset of 940 high-resolution high S /N spectra gathered by Lehmann et al (2001). Our mode identification presented here, which was done using K 1 = 0.0824, K 2 = 0.0841 and K 3 = 0.0951, is one of the identification results adapted by , who considered also other spectroscopic diagnostics for identification.…”

Metallicities of theβCephei stars from low-resolution ultraviolet spectra

“…BW Vul is a binary system (P orb = 33.3 ± 0.3 y, Pigulski 1992) with the secondary component 6−10 mag fainter than the primary. EN Lac is an eclipsing binary with orbital period 12.0968 d (Pigulski & Jerzykiewicz 1988;Lehmann et al 2001, and references therein). The secondary component is fainter than the primary by about 5 mag.…”

A photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere

“…This star has been studied by many authors. We refer to Chapellier et al (1995) and Lehmann et al (2001) for a summary of the observational studies and to Dziembowski & Jerzykiewicz (1996) for the first seismic study of this β Cephei star. In this section, we illustrate the process we term non-adiabatic asteroseismology, by deriving constraints on the metallicity of the star.…”

“…In this section, we illustrate the process we term non-adiabatic asteroseismology, by deriving constraints on the metallicity of the star. The three observed frequencies used in our study were taken from Lehmann et al (2001) and the photometric amplitudes obtained with Johnson filters were derived by Jerzykiewicz (1993). Aerts et al (2002) showed convincingly that the spectroscopic mode identification is fully compatible with the photometric one for this star, and points towards a radial mode for the first frequency ( f 1 = 5.9112 c d −1 ), an = 2 mode for the second frequency ( f 2 = 5.8551 c d −1 ) and an = 1 mode for the third frequency ( f 3 = 5.5033 c d −1 ).…”