[P-AE18] Exoplanets

[PAE18-04] Characterization of upper atmospheres of hot exoplanets by multi-line observations
and complex numerical simulations

*Ildar Shaikhislamov¹ (1.Institute of Laser Physics Siberian Branch of Russian Academy of Sciences)

Keywords:hot exoplanets, atmospheres

Close orbiting hot exoplanets form a sub-class among a very diverse population. They possess a unique feature of a bulk outflow of upper atmospheres. The multicomponent and partially ionized atmospheric material heated by intense ionizing radiation of a host star overflows with a supersonic velocity the Roche lobe and collides with the stellar wind plasma. This kind of material dynamics differs principally from the processes in tenuous planetary exospheres in the Solar system. The observational evidence of such atmospheric escape was revealed for a number of hot Jupiters and warm Neptunes via measurement of their transit absorption in VUV lines of such elements as H, C, O, Mg, Si, Fe. Recently, a wealth of information was provided by the analysis of exoplanets’ transit absorption in the infra-red line of metastable helium triplet. Moreover, the first detection of transit absorption by Oxygen atom at 777.4 nm at Kelt-9b promises new possibilities. The escape of upper atmospheres of hot exoplanets is a complex phenomenon influenced by a number of physical processes, and quantitative interpretation of observational data requires special numerical simulations. The comparison of spectrally resolved transit measurements of particular exoplanets and 3D simulations of their dynamical environments gives tantalizing evidence of interaction between the planetary and stellar winds, enabling important conclusions about exoplanetary atmospheres and parameters of the stellar wind plasmas. In this talk, we present some results obtained by our 3D aeronomy multi-fluid MHD model which includes radiation transfer and kinetic simulation of excited levels. We studied several hot Jupiters and warm Neptunes, for which transit observations were made with different spectral resolutions - HD209458b, HD189733b, Wasp107b, Wasp80b, GJ436b, GJ3470b, TOI421b&c, PiMenC. For two of them (GJ436b [1], GJ3470b [2]), the modeling revealed that the observed strong absorption in the Lyα line can only be explained if the corresponding stellar winds interacting with the escaping planetary atmospheric flows, have parameters comparable to the Solar Wind. Simulations of HD189733b [3] confirmed that the existing variability in the transit spectral measurements can be explained by varying space weather conditions. Transit absorptions in the HI, OI, CII, and HeI lines measured for HD209458b made it possible to estimate an upper limit of possible magnetic field of this planet [4]. For the binary planetary system TOI421, we predicted [5] a strong in-transit absorption in the blue wing of the Lyα line and relatively weak absorption in the metastable helium line. Such studies of various stellar-planetary systems provide a basis for remote sensing of the varying space weather conditions of different stars. The progress of quality and quantity of observations, new instruments, new approaches to the probing of planetary winds, including the new spectral windows, multi-spectral and multi-instrumental observations of targets require further development of the modeling tools capable of complex simulation and interpretation of all available observations.
The research is carried out under RSF project 23-12-00134.
[1] Shaikhislamov I. F., Khodachenko M. L., Lammer H., et al. // ApJ 2019, 885(1), 67.
[2] Shaikhislamov I. F., Khodachenko M. L., Lammer H., et al. // MNRAS 2021. 500(1). 1404.
[3] Rumenskikh M. S., Shaikhislamov I. F., Khodachenko M. L., et al. // ApJ. 2022. 927(2). 238.
[4] Khodachenko M. L., Shaikhislamov I. F., Lammer H., et al. // MNRAS 2021. 507(3). 3626.
[5] Berezutsky A. G., Shaikhislamov I. F., Rumenskikh M. S., et al. // MNRAS. 2022. 515(1), 706.