  Hundreds of candidate hybrid pulsators of intermediate type A-F were revealed
by the recent space missions. Hybrid pulsators allow to study the full stellar
interiors, where p- and g-modes are simultaneously excited. The true hybrid
stars must be identified since other processes, due to stellar multiplicity or
rotation, might explain the presence of (some) low frequencies observed in
their periodograms. We measured the radial velocities of 50 candidate Delta Sct
- Gamma Dor hybrid stars from the Kepler mission with the Hermes/Ace
spectrographs over a span of months to years. We aim to derive the fraction of
binary and multiple systems and to provide an independent and homogeneous
determination of the atmospheric properties and vsini for all targets. The
objective is to identify the physical cause of the low frequencies. We computed
1-D cross-correlation functions (CCFs) in order to find the best parameters in
terms of the number of components, spectral type and vsini for each target.
Radial velocities were measured from spectrum synthesis and by using a 2-D
cross-correlation technique in the case of double- and triple-lined systems.
Fundamental parameters were determined by fitting (composite) synthetic spectra
to the normalised median spectra corrected for the appropriate Doppler shifts.
We report on the analysis of 478 high-resolution Hermes and 41 Ace spectra of
A/F-type candidate hybrid pulsators from the Kepler field. We determined their
radial velocities, projected rotational velocities, atmospheric properties and
classified our targets based on the shape of the CCFs and the temporal
behaviour of the radial velocities. We derived orbital solutions for seven new
systems. Three long-period preliminary orbital solutions are confirmed by a
photometric time-delay analysis. Finally, we determined a global multiplicity
fraction of 27% in our sample of candidate hybrid stars.
