  This paper is part of an effort to correct the transmission spectra of a
transiting planet orbiting an active star. In Paper I (Cracchiolo et al. 2020)
we have demonstrated a methodology to minimize the potential bias induced by
unocculted star spots on the transmission spectrum, assuming a spot model
parameterized by filling factor and temperature. In this work we introduce the
limb darkening effect, therefore the position of the spot in the stellar disk
and the impact parameter of the transiting planet now play a key role. The
method is tested on simulations of planetary transits of three representative
kinds of planetary systems, at ARIEL resolution. We find that a realistic
treatment of the limb darkening is required to reliably estimate both the spots
parameters and the transmission spectrum of the transiting planet. Furthermore,
we show that the influence of the spots onthe retrieval of the planetary
transmission spectrum is significant for spots close to the center of the star,
covering a fraction greater than 0.05 and with a temperature contrast greater
than 500 K, and that for these cases our method can confidently extract the
transmission spectrum and the impact parameter of the transiting planet for
both cases of occulted and not occulted spots, provided that we have an
accurate characterization of the stellar parameters and a reliable simulator of
the instrument performances.
