Issue A&A Volume 367, Number 1, February III 2001 Page(s) 236 - 249 Section Formation, structure and evolution of stars DOI http://dx.doi.org/10.1051/0004-6361:20000344

A&A 367, 236-249 (2001)
DOI: 10.1051/0004-6361:20000344

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

H. Lehmann¹, P. Harmanec^{2, 3}, C. Aerts⁴, H. Bozic^{5, 3}, P. Eenens⁶, G. Hildebrandt⁷, D. Holmgren⁸, P. Mathias⁹, G. Scholz⁷, M. Slechta³ and S. Yang<sup>10

1</sup>  Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany
    e-mail: lehm@tls-tautenburg.de
²  Institute of Astronomy of the Charles University, V Holesovickách 2, 180 00 Praha 8, Bohemia, Czech Republic
³  Astronomical Institute, Academy of Sciences, 251 65 Ondrejov, Bohemia, Czech Republic
    e-mail: hec(bozic, slechta)@sunstel.asu.cas.cz
⁴  Institute of Astronomy, Celestijnenlaan 200 B, 3001 Leuven, Belgium
    e-mail: Conny.Aerts@ster.kuleuven.ac.be
⁵  Hvar Observatory, Faculty of Geodesy, University of Zagreb, Kaciceva 26, 10000 Zagreb, Croatia
    e-mail: hbozic@geodet.geof.hr
⁶  Departamento de Astronomia, Universidad de Guanajuato, Apartado 144, 36000 Guanajuato, GTO, Mexico
    e-mail: eenens@carina.astro.ugto.mx
⁷  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: ghildebrandt(gscholz)@aip.de
⁸  Dept. of Physics & Astronomy, Brandon University, Brandon, Manitoba, R7A 6A9, Canada
    e-mail: holmgren@brandonu.ca
⁹  Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
    e-mail: mathias@obs-nice.fr
¹⁰  Dept. of Physics & Astronomy, University of Victoria, PO Box 3055, Victoria, B.C., V8W 3P6, Canada
    e-mail: yang@beluga.phys.uvic.ca

(Received 9 October 2000 / Accepted 17 November 2000 )

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 was found to vary with a 74 year cycle. The amplitudes of the two other RV oscillations, having periods of and , 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.

Key words: stars: binaries: close -- stars: binaries: eclipsing -- stars: binaries: spectroscopic -- stars: fundamental parameters -- stars: oscillations -- stars: individual: EN Lac

Offprint request: H. Lehmann

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