A Multi-fluid Model for Escaping Atmosphere and Mg Absorption Line for WASP-12b
Multi-fluid numerical modeling is used to discuss the observed absorption profile of MgII resonance lines during the transit of WASP-12b and quantifies the crucial mechanisms responsible for the generation of energetic neutral atoms. The hydrodynamic model includes the hydrogen chemistry and the expansion of upper atmosphere due to stellar XUV radiation and its interaction with the stellar wind. The model describes the mass loss process and escaping planetary wind in a self-consistent manner. The simulation is performed with sets different stellar wind parameters, and the obtained results show that in case of fast stellar wind a shock is formed around the planet.
However, in the case of slow stellar wind, the planetary wind is dragged towards the tail side, and the thermal pressure of the stellar wind compresses the planetary material from the lateral side leading to the formation of ionopause boundary. The dynamics of MgII ions are estimated and the results with a sets of different stellar wind parameters and XUV flux values under a realistic Sun-like star condition showed that for stellar wind density, Nsw=1x105, and stellar wind velocity, Vsw=30 (in the unit of 9.01 Kms-1) 3-4% absorption in MgII resonance lines.