  The growth of spectroscopic observations of exoplanetary systems allows the
possibility of testing theoretical models and studying the interaction that
exoplanetary atmospheres have with the wind and the energetic photons from the
star. In this work, we present a set of numerical 3D simulations of HD 209458b
for which spectral lines observations of their evaporative atmosphere are
available. The different simulations aim to reproduce different scenarios for
the star-planet interaction. With our models, we reconstruct the Ly$\alpha$
line during transit and compare with observations. The results allow us to
analyse the shape of the line profile under these different scenarios and the
comparison with the observations suggests that HD209458b may have a magnetic
field off less than 1 G. We also explore the behaviour of the magnesium lines
for models with and without magnetic fields.
