| | 3 | |
| | 4 | = Christie paper = |
| | 5 | 2.5D spherical simulations of planetary and stellar wind interactions, including charge exchange, were performed. Hydrodynamic simulations were performed, with density fixed at the base of the planetary wind and an inflow boundary condition on one half of the simulation serving to emulate the stellar wind. In addition to charge exchange, advection, photoionization and recombination, and collisional ionization were included. The escape parameter lambda was used to categorize the models; it was found that there were two distinct regimes, with a transition region between. With lambda <= 4 (high planetary temp), the planetary wind becomes transonic before colliding with the stellar wind, creating a large tail that takes a significant amount of time to mix. With lambda >= 6 (low planetary temp), the planetary wind has no chance to become transonic before it encounters the stellar wind, and the winds mix turbulently rather than collide, resulting in a well-mixed, barely evident tail. The transition region between these is also shown clearly in the calculated mass-loss rates of the simulations. |
| | 6 | |
| | 7 | = Schneiter paper (2016) = |
| | 8 | Paper makes synthetic observations of Lyman-alpha absorption in tails created by interacting solar and planetary winds. Simulations are performed in 3d spherical coordinates, using the Guacho hydrodynamics code, with photoionization of hydrogen included (no magnetism). They have nineteen models of varying stellar UV flux (photoionization rate), stellar wind conditions, and the mass-loss rate of the planet. The planetary wind is initialized self-consistently in order to obtain the desired mass-loss rate, at 3R,,p,,. Both the stellar and planetary winds are isotropic, ignoring effects of tidal locking and atmospheric mixing. They approximate the radiation pressure from the star by reducing stellar gravity. |
| | 9 | |
| | 10 | They find that by including photoionization, a smaller neutral tail is formed, leading to less absorption; they also find a lower time to a stationary state than in previous models without photoionization. By numerically integrating to determine the optical depth, it is seen that the most absorption in in the blue-shifted side, between -130 and -40 km/s. This absorption is most dependent on the mass loss rate of the planet (with more material, there is more absorption) and on the ionizing flux (more ionization, less absorption, in an approximately linear relationship). By comparing their models to observation, the heat efficiency of HD 209458b (the planet modelled for simulations) can be predicted to be less than 50%. In addition, it can be seen that the observed Lyman-alpha absorption does not necessarily require charge exchange to accelerate the neutral hydrogen sufficiently. |
