  Binary post-asymptotic giant branch (post-AGB) stars are thought to be the
products of a strong but poorly-understood interaction during the AGB phase.
The aim of this contribution is to update the orbital elements of a sample of
galactic post-AGB binaries observed in a long-term radial-velocity monitoring
campaign. Radial velocities are computed from high signal-to-noise spectra by
use of a cross-correlation method. The radial-velocity curves are fitted by
using both a least-squares algorithm and a Nelder-Mead simplex algorithm. We
use a Monte Carlo method to compute uncertainties on the orbital elements. The
resulting mass functions are used to derive a companion mass distribution by
optimising the predicted to the observed cumulative mass-function
distributions, after correcting for observational bias. As a result, we derive
and update orbital elements for 33 galactic post-AGB binaries, among which 3
are new orbits. The orbital periods of the systems range from 100 to about 3000
days. Over 70 percent (23 out of 33) of our binaries have significant non-zero
eccentricities ranging over all periods. Their orbits are non-circular despite
the fact that the Roche-lobe radii are smaller than the maximum size of a
typical AGB star and tidal circularisation should have been strong when the
objects were on the AGB. We derive a distribution of companion masses that is
peaked around 1.09 $M_\odot$ with a standard deviation of 0.62 $M_\odot$. The
large spread in companion masses highlights the diversity of post-AGB binary
systems. Furthermore, we find that only post-AGB stars with high effective
temperatures (> 5500 K) in wide orbits are depleted in refractory elements,
suggesting that re-accretion of material from a circumbinary disc is an ongoing
process. It appears, however, that chemical depletion is inefficient for the
closest orbits irrespective of the actual surface temperature.
