  We studied the polarised spectrum of the post-AGB binary system 89\,Herculis
on the basis of data collected with the high resolution \emph{Catania
Astrophysical Observatory Spectropolarimeter}, \emph{HArps-North POlarimeter}
and \emph{Echelle SpectroPolarimetric Device for the Observation of Stars}. We
find the existence of linear polarisation in the strongest metal lines in
absorption and with low excitation potentials. Signals are characterized by
complex Q and U morphologies varying with the orbital period. As possible
origin of this "Second Solar Spectrum"-like behaviour, we rule out magnetic
fields, continuum depolarisation due pulsations and hot spots. { The linear
polarisation we detected also in the Ca{\sc ii}\,8662\AA\, line is a clear
evidence of optical pumping polarisation and it rules out the scattering
polarisation from free electrons of the circumbinary environment.} In the
framework of optical pumping due to the secondary star, the observed periodic
properties of the spectral line polarisation can be justied by two jets, flow
velocity of few tens of km\,s$^{-1}$, at the basis of that hour-glass structure
characterising 89\,Herculis. We also discovered linear polarisation across the
emission profile of metal lines. Numerical simulations show that these
polarised profiles could be formed in an undisrupted circumbinary disk rotating
at $\le$10 km\,s$^{-1}$ and whose orientation in the sky is in agreement with
optical and radio interferometric results. We conclude that the study of those
aspherical enevlopes, whose origin is not yet completely understood, of PNe and
already present in the post-AGB's, can benefit of high resolution
spectropolarimetry and that this technique can shape envelopes still too far
for interferometry.

Solar and Stellar Astrophysics