  Radiative shocks are shocks in a gas where the radiative energy and flux
coming from the very hot post-shock material are non-negligible in the shock's
total energy budget, and are often large enough to heat the material ahead of
the shock. Many simulations of radiative shocks, both in the contexts of
astrophysics and laboratory experiments, use a grey treatment of radiative
transfer coupled to the hydrodynamics. However, the opacities of the gas show
large variations as a function of frequency and this needs to be taken into
account if one wishes to reproduce the relevant physics. We have performed
radiation hydrodynamics simulations of radiative shocks in Ar using multigroup
(frequency dependent) radiative transfer with the HERACLES code. The opacities
were taken from the ODALISC database. We show the influence of the number of
frequency groups used on the dynamics and morphologies of subcritical and
supercritical radiative shocks in Ar gas, and in particular on the extent of
the radiative precursor. We find that simulations with even a low number of
groups show significant differences compared to single-group (grey)
simulations, and that in order to correctly model such shocks, a minimum number
of groups is required. Results appear to eventually converge as the number of
groups increases above 50. We were also able to resolve in our simulations of
supercritical shocks the adaptation zones which connect the cooling layer to
the final post-shock state and the precursor. Inside these adaptation zones, we
find that the radiative flux just ahead of the shock in one or several
high-opacity groups can heat the gas to a temperature higher than the
post-shock temperature. Through the use of Hugoniot curves, we have checked the
consistency of our radiation hydrodynamics scheme by showing that conservation
of mass, momentum and energy (including radiative flux) holds. ABRIDGED.
