The intense extreme ultraviolet radiation heats the upper atmosphere of close-in exoplanets and drives the atmospheric escape. The escaping process determines the planetary evolution of close-in planets. The mass loss rate depends on the UV flux at the planet. We introduce the relevant physical quantities which describe the dominant physics in the atmosphere. We find that the equilibrium temperature and the characteristic temperature determine whether the system becomes energy-limited or recombination-limited. We classify the observed close-in planets using the physical conditions. We also find that many of the Lyman-α absorptions detected planets receive intenser flux than the critical flux which can be determined from physical conditions. Our classification method can quantitatively reveal whether the EUV is not strong enough to drive the outflow or the Lyman- α absorption is not detected for some reason (e.g. stellar wind confinement). We also discuss the thermo-chemical structure of hydrodynamic simulations with the relevant physics.

Planets that orbit low- to intermediate mass main sequence (MS) stars will experience vigorous star-planet interactions when the host star evolves through the giant branches, including the asymptotic giant branch (AGB) phase, due to extreme luminosities and stellar outflows. In this work, we take the first steps towards understanding how a planet’s temperature profile and chemical composition is altered when the host star evolves from the MS to the AGB phase. We used a 1D radiative transfer code to compute the temperature-pressure profile and a 1D chemical kinetics code to simulate the disequilibrium chemistry. We consider a Jupiter-like planet around a Solar-type star in two evolutionary stages (MS and AGB planet) by only varying the stellar luminosity. We find that the temperature throughout the AGB planet’s atmosphere is increased by several hundreds of Kelvin compared to the MS planet. We also find that CO joins H2O and CH4 as a prominent constituent in the AGB planet’s atmospheric composition.

High-energy stellar irradiation can photoevaporate planetary atmospheres, which can be observed in spectroscopic transits of hydrogen lines. Here, we investigate the effect of planetary magnetic fields on the observational signatures of atmospheric escape in hot Jupiters.

Transit observations have revealed the existence of atmospheric escape in several hot Jupiters. High energy photons from the host star heat the upper atmosphere and drive the hydrodynamic escape. The escaping atmosphere can interact with the stellar wind from the host star. We run radiation hydrodynamics simulations with non-equilibrium chemistry to investigate the wind effects on the escape and the transit signature. Our simulations follow the planetary outflow driven by the photoionization heating and the wind interaction in a dynamically coupled, self-consistent manner. We show that the planetary mass-loss rate is almost independent of the wind strength, which however affects the Ly-α transit depth considerably. But the Hα transit depth is almost independent of the wind strength because it is largely caused by the lower hot layer. We argue that observations of both lines can solve the degeneracy between the EUV flux from the host and the wind strength.

Wasp-31b is a planet of 0.48 Jupiter masses and 1.55 Jupiter radii, with orbital period of 3.4-days around a metal-poor, late-F-type, V = 11.7 dwarf star. The planet has a large atmospheric scale height that makes it a good target for transmission spectroscopy. Sing et al (2014) presented an optical and near-IR transmission spectrum of the atmosphere of WASP-31b obtained with the HST and show the presence of a strong potassium line. In contrast, Gibson et al. (2017) reports a spectrum of the atmosphere of WASP-31b, obtained with the FORS2 instrument on the VLT and find that there is no strong potassium line. Here, we take those two datasets and, using models, we try to find a case where both solutions are correct by considering different cloud scenarios.

Variability has now been robustly observed in a range of L and T type field brown dwarfs, primarily at near-IR and mid-IR wavelengths. The probable cause of this variability is surface inhomogeneities in the clouds of these objects, causing a semi-periodic variability signal when combined with the rotational modulation from the 3-12 hour period expected for these objects. Variability at similar or even higher amplitudes may be expected for young brown dwarfs and giant exoplanets, which share similar Teff as field brown dwarfs, but have considerably lower surface gravities. Variability studies of these objects relative to old field objects is then a direct probe of the effects of surface gravity on atmospheric structure. Here I discuss ongoing efforts to detect variability from these young objects, both for free-floating objects and companions to stars, including preliminary results from an ongoing survey of young, low surface gravity objects with NTT SOFI.

Past analysis of HD 189733b's atmosphere has been a cause for some debate, with conflicting findings regarding water and sodium abundances and the presence of a high altitude haze. We present our models of HD 189733b's atmospheric composition using VSTAR (Versatile Software for Transfer of Atmospheric Radiation). Since the effective temperature of the planet is expected to be approximately 5000K, newly available high-temperature spectral line lists were used.

The ExoMol project aims at providing comprehensive line lists of molecular transitions which are likely to be important in the atmospheres of extra-solar planets and cool stars, including brown dwarfs. The physics of the molecules involved varies and can be categories according to the number atoms in the species. Thus the molecules can be grouped as diatomics, both closed and open and shell, triatomics, tetratomics, methane and larger species. Progress in providing complete sets of line list for the molecules in each of these categorizes is considered. The latest line lists and related data for each of the species can be found on the project website www.exomol.com.

Clouds play a significant role for the energy budget in planetary atmospheres. They can scatter incident stellar radiation back to space, effectively cooling the surface of terrestrial planets. On the other hand, they may contribute to the atmospheric greenhouse effect by trapping outgoing thermal radiation. For exoplanets near the outer boundary of the habitable zone, condensation of CO2 can occur due to the low atmospheric temperatures. These CO2 ice clouds may play an important role for the surface temperature and, therefore, for the question of habitability of those planets. However, the optical properties of CO2 ice crystals differ significantly from those of water droplets or water ice particles. Except for a small number of strong absorption bands, they are almost transparent with respect to absorption. Instead, they are highly effective scatterers at long and short wavelengths. Therefore, the climatic effect of a CO2 ice cloud will depend on how much incident stellar radiation is scattered to space in comparison to the amount of thermal radiation scattered back towards the planetary surface. This contribution aims at the potential greenhouse effect of CO2 ice particles. Their scattering and absorption properties are calculated for assumed particle size distributions with different effective radii and particle densities. An accurate radiative transfer model is used to determine the atmospheric radiation field affected by such CO2 particles. These results are compared to less detailed radiative transfer schemes employed in previous studies.