Types of gaseous envelopes of “hot Jupiter” exoplanets

Abstract

As a rule, the orbital velocities of "hot Jupiters," i.e., exoplanets with masses comparable to the mass of Jupiter and orbital semi-major axes less than 0.1 AU, are supersonic relative to the stellar wind, resulting in the formation of a bow shock. Gas-dynamical modeling shows that the gaseous envelopes around "hot Jupiters" can belong to two classes, depending on the position of the collision point. if the collision point is inside the Roche lobe of the planet, the envelopes have the almost spherical shapes of classical atmospheres, slightly distorted by the influence of the star and interactions with the stellar-wind gas; if the collision point is located outside the Roche lobe, outflows from the vicinity of the Lagrangian points L 1 and L 2 arise, and the envelope becomes substantially asymmetrical. The latter class of objects can also be divided into two types. If the dynamical pressure of the stellar-wind gas is high enough to stop the most powerful outflow from the vicinity of the inner Lagrangian point L 1 , a closed quasi-spherical envelope with a complex shape forms in the system. If the wind is unable to stop the outflow from L 1 , an open aspherical envelope forms. The possible existence of atmospheres of these three types is confirmed by 3D numerical modeling. Using the typical "hot Jupiter" HD 209458b as an example, it is shown that all three types of atmospheres could exist within the range of estimated parameters of this planet. Since different types of envelopes have different observational manifestations, determining the type of envelope in HD 209458b could apply additional constrains on the parameters of this exoplanet.

Investigation of the environment around close-in transiting exoplanets using cloudy

“…We find that no lines or continuum absorption sources appear in the NUV (NUVA, NUVB, NUVC filters) space-based wavelengths unless the cloud temperatures are below 10,000 K ( Figure 6). This suggests that whatever caused the early ingress in WASP-12b (Fossati et al 2010;Haswell et al 2012;Nichols et al 2015) was not from shocked stellar wind gas but is more likely planetary gas as has been previously suggested (Lanza 2009;Lai, Helling & van den Heuvel 2010;Bisikalo et al 2013a;Bisikalo et al 2013b;Cherenkov, Bisikalo & Kaigorodov 2014;Lanza 2015). An escaping atmosphere of WASP-12b would also explain the variability in the complete set of near-UV observations (Fossati et al 2010;Haswell et al 2012;Sing et al 2013;Nichols et al 2015).…”

“…Our conclusions add to a body of theoretical work suggesting that UV asymmetry observations are not suitable approach for exoplanet magnetic field detection (Ben-Jaffel & Ballester 2014;Grießmeier 2015;Alexander et al 2015). Additionally, our modeling of lower temperature clouds suggests that the UV and optical observations are likely caused by gas from the planetary atmosphere (Lai, Helling & van den Heuvel 2010;Bisikalo et al 2013a;Bisikalo et al 2013b;Cherenkov, Bisikalo & Kaigorodov 2014). Therefore, any future models attempting to explain the early UV observation need to include planetary gas in their simulations.…”

“…Using the plasma photoionization and microphysics code CLOUDY (Ferland et al 1998;Ferland et al 2013) we explore whether there is a UV absorbing species in the stellar wind that can cause an early UV ingress in the transits of closein exoplanets due to the presence of a magnetic (Vidotto, Jardine & Helling 2011a) or non-magnetic (Lai, Helling & van den Heuvel 2010;Bisikalo et al 2013a;Bisikalo et al 2013b) bow shock compressing the coronal plasma. We find under realistic physical conditions for the corona (Table 1; § 3) that there aren't any species that can cause an absorption with sufficient opacity for all UV wavelengths and also for all other wavelengths between X-ray and radio (Figures 4 and 5).…”

“…A model ignoring magnetic fields has recently been proposed to explain the WASP-12b HST observations (Bisikalo et al 2013a;Bisikalo et al 2013b; see also Lai, Helling & van den Heuvel 2010). These authors perform hydrodynamic simulations in 3-D and looked at the interaction between the stellar wind and the escaping planetary atmosphere.…”

Major prospects of exoplanet astronomy with the World Space Observatory–UltraViolet mission

“…The filling of their Roche lobes results in a powerful outflow of material from the close-in planet towards the host star. As a consequence, the gaseous envelopes around these planets may be significantly nonspherical and, at the same time, stationary and long-lived (Bisikalo et al 2013a(Bisikalo et al , 2013b(Bisikalo et al , 2013c. Non-thermal particles are also believed to play a significant role in the energy balance of a planet upper atmosphere.…”