We present the implementation of a nested meshes hierarchy for the FARGO3D code,
as well as the implementation of the resulting code in the numerical study of
the dynamical friction exerted over a massive and luminous perturber moving at
constant velocity in an opaque and homogeneous gas medium. In this scenario, we
consider thermal diffusion for the gas and the feedback of the heat emitted by
the perturber on the force that it experiences from its surroundings. The force
that arises in response to the heat irradiated by the perturber, dubbed heating
force, is directed along the direction of motion of the perturber, therefore
inducing an acceleration on it. We compared the value of said force with the
analytic estimates in the low and high Mach number limits, and found an accurate
match. The drag force exerted on a non-luminous perturber in a thermally
diffusive medium is significantly different from the drag force of the adiabatic
case. In the limit of a vanishing velocity, this drag force tends to a finite
value which we determine using linear perturbation theory and corroborate with
numerical simulations. We find a threshold in the luminosity needed to get a
net acceleration of the perturber and find it to be generally much smaller than
the luminosity of accreting low-mass planetary embryos embedded in a gaseous
protoplanetary disc.