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The results of modeling the Hα absorption spectrum of the atmosphere of the hot Jupiter WASP‑52b are presented. The atmosphere was modeled with a three-dimensional hydrodynamic code. Several different values of the XUV ionizing radiation were considered. The Lyα-photon transfer in the atmosphere was simulated by the Monte Carlo method. Spatial distributions of the volume density of hydrogen atoms excited to the second energy level H(2) were obtained, and absorption spectra in the Hα line were calculated. It was also shown that absorption takes place in a layer with a thickness of about 1.5 times the planetary radius, while the greatest influence on absorption is exerted by Lyα photons produced due to recombination of electrons and protons. [ABSTRACT FROM AUTHOR]

Simulation results are presented for the Lyα flux impact from the parent star on the Hα absorption spectrum in the atmospheres of the hot Jupiters HD189733b and HD 209458b. The atmosphere is simulated using a three-dimensional hydrodynamic code. Several options are considered for the upper atmospheric composition, including variations in the XUV parameter. The Lyα photon transfer in the atmosphere is simulated by the Monte Carlo method. Spatial distributions are obtained for the bulk density of hydrogen atoms excited to the second energy level; absorption spectra in the Hα line are calculated. It is shown that the transit absorption of the hot Jupiters in the Hα line can be described by a relatively simple model of the Lyα photon transfer in the upper atmosphere. [ABSTRACT FROM AUTHOR]

The studies of close-orbit gaseous exoplanets—hot Jupiters and warm Neptunes—are reviewed. Transit spectral observations of the Hubble Space Telescope stimulated the numerical modeling of these objects. The supersonic outflow of the upper atmosphere of hot exoplanets and its interaction with the stellar plasma flow is a newly-discovered phenomenon in plasma physics and astrophysics that pools photo- and plasma-chemistry, collision-induced gas-dynamics, and collisionless space plasma. Starting from 2003, the modeling of physical processes in this field has considerably developed from simple quasi-empiric analytical formulas to global three-dimensional magnetic hydrodynamic (3D MHD) codes. The attained level makes it possible to interpret the in-transit measurements in absorption lines of different elements and estimate the parameters of both the planetary atmospheres and the stellar plasma wind. [ABSTRACT FROM AUTHOR]

As is known, the influence of the ionizing radiation and the gravity of a star on a hot Jupiter results in the outflow of its atmosphere. Due to the gravity of the planet, the outflowing matter acquires angular momentum, after which it is accumulated on a higher circular orbit around the star and forms a disk or a torus. The angular momentum interexchange between the torus and the planet induces the migration of the planet to the star. In this paper, we consider the effectiveness of this migration mechanism by the example of the HD 209458 system. It turns out that, after 4.5 × 109 years since the evaporation of the protoplanetary disk, the planet might migrate from an orbit at ≳0.67 AU to its current orbit at 0.045 AU. [ABSTRACT FROM AUTHOR]

The absorption of stellar radiation observed at transits of HD 209458b in resonant lines of O  i and C  ii has not yet been satisfactorily modelled. In our previous two-dimensional (2D) simulations, we have shown that the hydrogen-dominated upper atmosphere of HD 209458b, heated by extreme ultraviolet radiation, expands supersonically beyond the Roche lobe and drags heavier species along with it. Assuming solar abundances, O  i and C  ii particles accelerated by tidal forces to velocities up to 50  |${\rm km}\,{\rm s}^{-1}$| should produce the absorption due to Doppler resonance at the level of 6–10 per  cent, consistent with the observations. Since the 2D geometry does not take into account the Coriolis force in a planet reference frame, the question remains to what extent the spiralling of escaping planetary material and actually achieved velocity may influence the conclusions made on the basis of 2D modelling. In this paper, we apply for the first time in studies of HD 209458b a global 3D hydrodynamic multifluid model. The results confirm our previous findings that the velocity of the planetary flow is sufficiently high to match the widths of O  i and C  ii resonant lines. To match the absorption in those lines, including H  i , with observations, the mass-loss rate of HD 209458b should be about |$2.5\times10^{11}\,{\rm g\,s^{-1}}$|⁠ , which is 3.5 times larger than that revealed by the 2D model. The other novel finding is that matching of the absorption measured in Mg  ii and S  iii lines requires at least 10 times lower abundances of these elements than the solar values. [ABSTRACT FROM AUTHOR]

We present two-dimensional multifluid numerical modelling of the upper atmosphere of the hot Jupiter WASP-12b. The model includes hydrogen chemistry, and self-consistently describes the expansion of the planetary upper atmosphere and mass-loss due to intensive stellar irradiation, assuming a weakly magnetized planet. We simulate the planetary upper atmosphere and its interaction with the stellar wind (SW) with and without the inclusion of tidal force and consider different XUV irradiation conditions and SW parameters. With the inclusion of tidal force, even for a fast SW, the escaping planetary material forms two streams, propagating towards and away from the star. The atmospheric escape and related mass-loss rate reaching the value of 1012 g s−1 appear to be mostly controlled by the stellar gravitational pull. We computed the column density and dynamics of Mg  ii ions considering three different sets of SW parameters and XUV fluxes. The simulations enable to compute the absorption at the position of the Mg h line and to reproduce the times of ingress and egress. In case of a slow SW and without accounting for tidal force, the high orbital velocity leads to the formation of a shock approximately in the direction of the planetary orbital motion. In this case, mass-loss is proportional to the stellar XUV flux. At the same time, ignoring of tidal effects for WASP-12b is a strong simplification, so the scenario with a shock, altogether is an unrealistic one. [ABSTRACT FROM AUTHOR]

Results of a study of the influence of solar-type host stars superflares on the gas dynamics of the extended envelopes of giant exoplanets are presented. During flare events, the radiation intensity of the host star in the extreme ultraviolet and soft X-ray can increase by several orders of magnitude for a short time, leading to strong local heating of the exoplanet atmosphere on the side facing the star, with the formation of shocks in the atmosphere. Computations of the gas-dynamical response of the atmosphere of the hot Jupiter HD 209458b to characteristic superflares of solar-like stars were carried out earlier in [1] using a one-dimensional aeronomical model correctly taking into account heating and chemical processes in the atmosphere. To investigate the outflow of atmospheric gas, the results obtained with this onedimensional model were used as simple boundary conditions for computations of the three-dimensional flow structure after a flare. The results of these three-dimensional gas-dynamical computations show that the mass ejection of the flare increases the size of the envelope over several hours, which could be detected with existing observing facilities. It is shown that the mass-loss rates for the most powerful superflare considered could be enhanced by an order of magnitude over several tens of hours after the flare. [ABSTRACT FROM AUTHOR]

Self-Consistent 2D modelling of stellar wind interaction with the upper atmosphere of WASP-12b has been performed. The two case-scenarios of the planetary material escape and interaction with the stellar wind, namely the 'blown by the wind' (without the inclusion of tidal force) and 'captured by the star' (with the tidal force) have been modelled under different stellar XUV radiations and stellar wind parameters. In the first scenario, a shock is formed around the planet, and the planetary mass loss is controlled completely by the stellar radiation energy input. In the second scenario, the mass loss is mainly due to the gravitational interaction effects. The dynamics of MG II and related absorption were modelled with three sets of different stellar wind parameters and XUV flux values. [ABSTRACT FROM AUTHOR]