  We compare the predictions of simple models for the radio emission from
classical novae with the MERLIN radio observations of nova V723 Cas (Nova Cas
1995). Spherically symmetric and ellipsoidal radiative transfer models are
implemented in order to generate synthetic emission maps. These are then
convolved with an accurate representation of the uv coverage of MERLIN. The
parameters and geometry of the shell model are based on those returned by
fitting models to the observed light curve. This allows direct comparison of
the model images with the nine 6-cm MERLIN images of V723 Cas. It is found that
the seemingly complex structure (clumping, apparent rotation) evident in the
observations can actually be reproduced with a simple spherical emission model.
The simulations showthat a 24-h track greatly reduces the instrumental effects
and the synthetic radio map is a closer representation of the true (model) sky
brightness distribution. It is clear that interferometric arrays with sparse uv
coverage (e.g. MERLIN, VLBA) will be more prone to these instrumental effects
especially when imaging ring-like objects with time-dependent structure
variations. A modelling approach such as that adopted here is essential when
interpreting observations.
