The GJ 436 planetary system is an extraordinary system. The Neptune-size planet that orbits the M3 dwarf revealed in the Lyα line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 hours after the planetary transit. Here, we carry out a series of 3D radiation hydrodynamic simulations to model the interaction of the stellar wind with the escaping planetary atmosphere. With these models, we seek to reproduce the ∼56% absorption found in Lyα transits, simultaneously with the lack of absorption in Hα transit. Varying the stellar wind strength and the EUV stellar luminosity, we search for a set of parameters that best fit the observational data. Based on Lyα observations, we found a stellar wind velocity at the position of the planet to be around [250-460] km s−1 with a temperature of [3−4]×105 K. The stellar and planetary mass loss rates are found to be 2×10−15 M⊙ yr−1 and ∼[6−10]×109 g s−1, respectively, for a stellar EUV luminosity of [0.8−1.6]×1027 erg s−1. For the parameters explored in our simulations, none of our models present any significant absorption in the Hα line in agreement with the observations.
@article{arxiv.2012.05128,
title = {GJ 436b and the stellar wind interaction: simulations constraints using Ly$\alpha$ and H$\alpha$ transits},
author = {C. Villarreal D'Angelo and A. A. Vidotto and A. Esquivel and G. Hazra and A. Youngblood},
journal= {arXiv preprint arXiv:2012.05128},
year = {2021}
}