  KIC 10661783 is an eclipsing binary that shows Delta Sct-like oscillations.
More than 60 pulsation frequencies have been detected in its light curve as
observed by the Kepler satellite. We want to determine the fundamental stellar
and system parameters of the eclipsing binary as a precondition for
asteroseismic modelling of the pulsating component and to establish whether the
star is a semi-detached Algol-type system. We measured the radial velocities of
both components from new high-resolution spectra using TODCOR and compute the
orbit using PHOEBE. We used the KOREL program to decompose the observed spectra
into its components, and analysed the decomposed spectra to determine the
atmospheric parameters. For this, we developed a new computer program for the
normalisation of the KOREL output spectra. Fundamental stellar parameters are
determined by combining the spectroscopic results with those from the analysis
of the Kepler light curve. We obtain Teff, logg, vsini, and the absolute masses
and radii of the components, together with their flux ratio and separation.
Whereas the secondary star rotates synchronously with the orbital motion, the
primary star rotates subsynchronously by a factor of 0.75. The newly determined
mass ratio of 0.0911 is higher than previously thought and means a detached
configuration is required to fit the light curve. With its low orbital period
and very low mass ratio, the system shows characteristics of the R CMa-type
stars but differs from this group by being detached. Its current state is
assumed to be that of a detached post-Algol binary system with a pulsating
primary component.
