  The first results of radiative transfer calculations on decretion discs of
binary Be stars are presented. A smoothed particle hydrodynamics code computes
the structure of Be discs in coplanar circular binary systems for a range of
orbital and disc parameters. The resulting disc configuration consists of two
spiral arms, and can be given as input into a Monte Carlo code, which
calculates the radiative transfer along the line of sight for various
observational coordinates. Making use of the property of steady disc structure
in coplanar circular binaries, observables are computed as functions of the
orbital phase. Orbital-phase series of line profiles are given for selected
parameter sets under various viewing angles, to allow comparison with
observations. Flat-topped profiles with and without superimposed multiple
structures are reproduced, showing, for example, that triple-peaked profiles do
not have to be necessarily associated with warped discs and misaligned
binaries. It is demonstrated that binary tidal effects give rise to
phase-locked variability of the violet-to-red (V/R) ratio of hydrogen emission
lines. The V/R ratio exhibits two maxima per cycle; in certain cases those
maxima are equal, leading to a clear new V/R cycle every half orbital period.
This study opens a way in identifying binaries and in constraining the
parameters of binary systems that exhibit phase-locked variations induced by
tidal interaction with a companion star.
