  Context: Some secondary effects are known to introduce variations in spectra
of massive binaries. These phenomena (such as the Struve--Sahade effect,
difficulties to determine properly the spectral type,...) have been reported
and documented in the literature. Aims: We simulate the spectra of circular
massive binaries at different phases of the orbital cycle and accounting for
the gravitational influence of the companion star on the shape and physical
properties of the stellar surface. Methods: We use the Roche potential to
compute the stellar surface, von Zeipel theorem and reflection effects to
compute the surface temperature. We then interpolate in a grid of NLTE
plan-parallel atmosphere model spectra to obtain the local spectrum at each
surface point. We finally sum all the contributions (accounting for the Doppler
shift, limb-darkening, ...) to obtain the total spectrum. The computation is
done for different orbital phases and for different sets of physical and
orbital parameters. Results: Our first models reproduce the Struve--Sahade
effect for several lines. Another effect, surface temperature distribution is
visible but the distribution predicted by our current model is not yet
consistent with observations. Conclusions: In some cases, the Struve--Sahade
effect as well as more complex line intensity variations could be linked to
blends of intrinsically asymmetric line profiles that are not appropriatly
treated by the deblending routine. Systematic variations of lines for (nearly)
contact systems are also predicted by the model.
