  Carbon-enhanced metal-poor stars, CH stars and barium stars, among other
classes of chemically peculiar stars, are thought to be products of the
interaction of low- and intermediate-mass binaries which occurred when the most
evolved star was in the asymptotic giant branch (AGB) phase. Binary evolution
models predict that if the initial orbital periods of such systems are shorter
than a few thousand days, their orbits should have circularised due to tidal
effects. However, observations of the progeny of AGB binaries show that many of
these objects have substantial eccentricities, up to about 0.9. In this work we
explore the impact of wind mass transfer on the orbits of AGB binaries by
performing numerical simulations in which the AGB wind is modelled using a
hydrodynamical code and the stellar dynamics is evolved using an N-body code.
We find that in most models wind mass transfer contributes to the
circularisation of the orbit, but on longer timescales than tidal
circularisation if the eccentricity is less than about 0.4. For low initial
wind velocities and pseudo-synchronisation of the donor star, we find a
structure resembling wind Roche-lobe overflow near periastron. In this case,
the interaction between the gas and the stars is stronger than for high initial
wind velocities and the orbit shrinks while the eccentricity decreases. In one
of our models wind interaction is found to pump the eccentricity on a similar
timescale as tidal circularisation. Although our study is based on a small
sample of models, it offers some insight into the orbital evolution of
eccentric binaries interacting via winds. A larger grid of numerical models for
different binary parameters is needed to test if a regime exists where
hydrodynamical eccentricity pumping can effectively counteract tidal
circularisation, and if this can explain the puzzling eccentricities of the
descendants of AGB binaries.
