Abstract
We present a 3D hydrodynamic study of the effect that different stellar wind conditions and planetary wind structures have on the calculated Lyα absorptions during the transit of HD209458b. We approach the problem using 3D hydrodynamic simulations. Considering a range of stellar wind speeds ∼ [350-800] km s^{-1}, coronal temperature ∼ [3-7] × 10^{6} K and two values of the polytropic index Γ ∼ [1.01-1.13], while keeping fixed the stellar mass loss rate, we found a that a M_{p} range between ∼ [3-5] × 10^{10}g s^{-1} give account for the observational absorption in Lyα 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, resembling the emission associated with reconnection processes, and through the night side, produced by a strong stellar wind that compresses the planetary atmosphere and inhibits its escape from the day hemisphere yields larger absorptions than an isotropic planetary wind.
