GJ 436b and the stellar wind interaction: simulations constraints using Ly α and H α transits

The GJ 436 planetary system is an extraordinary system. The Neptune-sized planet that orbits the M3 dwarf revealed in the Ly alpha line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 h 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 similar to 56 per cent absorption found in Ly alpha transits, simultaneously with the lack of absorption in H alpha 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 Ly a 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] x 10(5) K. The stellar and planetary mass-loss rates are found to be 2 x 10(-15) M-circle dot yr(-1) and similar to[6-10] x 10(9) g s(-1), respectively, for a stellar EUV luminosity of [0.8-1.6] x 10(27) erg s(-1). For the parameters explored in our simulations, none of our models present any significant absorption in the H alpha line in agreement with the observations.

Automated summary

The GJ 436 planetary system is remarkable, with simulations suggesting a set of parameters that best fit observational data regarding the interaction of the stellar wind and the escaping planetary atmosphere. Absorption in the H α line was not significant in any models explored, consistent with observations.