  We describe the incorporation of polarized radiative transfer into the
atmospheric radiative transfer modelling code VSTAR (Versatile Software for
Transfer of Atmospheric Radiation). Using a vector discrete-ordinate radiative
transfer code we are able to generate maps of radiance and polarization across
the disc of a planet, and integrate over these to get the full-disc
polarization. In this way we are able to obtain disc-resolved, phase-resolved
and spectrally-resolved intensity and polarization for any of the wide range of
atmopsheres that can be modelled with VSTAR. We have tested the code by
reproducing a standard benchmark problem, as well as by comparing with classic
calculations of the polarization phase curves of Venus. We apply the code to
modelling the polarization phase curves of the hot Jupiter system HD 189733b.
We find that the highest polarization amplitudes are produced with optically
thick Rayleigh scattering clouds and these would result in a polarization
amplitude of 27 ppm for the planetary signal seen in the combined light of the
star and planet. A more realistic cloud model consistent with the observed
transmission spectrum results is an amplitude of ~20 ppm. Decreasing the
optical depth of the cloud, or making the cloud particles more absorbing, both
have the effect of increasing the polarization of the reflected light but
reducing the amount of reflected light and hence the observed polarization
amplitude.
