To be published in:
Astronomy and Astrophysics
The Struve-Sahade effect in the optical spectra of O-type binaries I.
M. De Becker1,** and
1 Institut d'Astrophysique et de Géophysique - Université de Liège, Allée du 6 Août, Bât B5c, B-4000 Liège (Sart Tilman), Belgium
2 European Southern Observatory, Alonso de Cordova 3107, 19 Vitacura, Santiago, Chile
* Research Associate FNRS, Belgium
** Postdoctoral Researcher FNRS, Belgium
+ Based on observations made at the European Southern Observatory (La Silla, Chile) and at the Observatoire de Haute-Provence (France).
Aims. We present a spectroscopic analysis of four massive binary systems
that are known or are good candidates to display the Struve-Sahade effect
(defined as the apparent strengthening of the secondary spectrum of the
binary when the star is approaching, and the corresponding weakening of
the lines when it is receding).
Stars: individual: HD100213, HD159176, HD165052, DHCep binaries: spectroscopic stars: fundamental parameters
Methods. We use high resolution optical spectra to determine new orbital
solutions and spectral types of HD 165 052, HD 100 213, HD 159 176 and
DH Cep. As good knowledge of the fundamental parameters of the considered
systems is necessary to examine the Struve-Sahade effect. We then study
equivalent width variations in the lines of both components of these
binaries during their orbital cycle.
Results. In the case of these four systems, variations appear in the
equivalent widths of some lines during the orbital cycle, but the definition
given above can any longer be valid, since it is now clear that the effect
modifies the primary spectrum as much as the secondary spectrum.
Furthermore, the lines affected, and the way in which they are affected,
depend on the considered system. For at least two of them (HD 100 213 and
HD 159 176) these variations probably reflect the ellipsoidal variable
nature of the system.