  We present a 3D hydrodynamic study of the effects that different stellar wind
conditions and planetary wind structures have on the calculated Ly-$\alpha$
absorptions produced during the transit of HD 209458b. Considering a range of
stellar wind speeds $\sim$[350-800] km s$^{-1}$, coronal temperature
$\sim$[3-7] $\times10^{6}$ K and two values of the polytropic index $\Gamma$
$\sim$[1.01-1.13], while keeping fixed the stellar mass loss rate, we found a
that a $\dot M_p$ range between $\sim$[3-5] $\times 10^{10}$g s$^{-1}$ give
account for the observational absorption in Ly-$\alpha$ measured for the
planetary system. Also, several models with anisotropic evaporation profiles
for the planetary escaping atmosphere were carried out, showing that both, the
escape through polar regions and through the night side yields larger
absorptions than an isotropic planetary wind.
