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Transit observations of exoplanets make it possible to measure temperature and relative abundance of various elements in their atmospheres. The infrared line of metastable helium HeI 10 830 Å is widely used to study the atmospheres of exoplanets by the transit absorption method. The emission spectra of stars have a significant impact on the physical and chemical parameters of the upper layers of the atmospheres. In this paper, we consider the features of absorption in the helium line for stars of different spectral classes by numerical simulation. The results show the key role of the star's emission spectrum in the formation of the upper atmosphere and in the amplitude of transit absorption of exoplanets in the HeI 10 830-Å line. [ABSTRACT FROM AUTHOR]

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]

The laboratory experiment on modeling a sub-Alfvénic interaction of expanding plasma cloud with vacuum magnetic field is described. We produce spherically symmetric cloud by 4-beam laser irradiation of the pellet. The presented data reveal complex dynamic of cloud deceleration and formation of two field aligned jets, development of the flute instability and rapid collapse of the diamagnetic cavity. It is shown that cavity collapse can't be explained by plasma motion or anomalous diffusion and requires for explanation a new mechanism. [ABSTRACT FROM AUTHOR]

Structural instabilities that develop during pulsed injection of dense plasma jets into vacuum in the presence of an external quasi-homogeneous magnetic field are studied by high-speed photography using ICCD cameras. The experiments are carried out in the chamber of the "Krot" stand, which has record-breaking dimensions in its class of installations (diameter—3 m, length of the working section—10 m), and makes it possible to study plasma dynamics by various diagnostic methods at scales of more than 1 m both along the magnetic field and in the direction transverse to the magnetic field. During injection along the magnetic field, a transverse collimation of the flow of ionized matter and the development of a flute instability of the plasma boundary are observed, which, at the late stages of expansion, leads to the plasma leaving the injection region in the form of several jets across the field. During transverse injection, the formation of a collimated flow, a "plasma sheet," is observed, in which, as the plasma moves across the field, inhomogeneous structures develop in the direction of injection. [ABSTRACT FROM AUTHOR]

The paper presents the results of laboratory experiment modeling the interaction between Lunar magnetic anomalies and Solar wind. To model the LMA we use quadrupole magnetic field. The main dimensionless parameter of the problem, the ion inertia length relative to the mini-magnetosphere size, well corresponds between experiment and LMA conditions. The main result is measurement of the magnetically reflected proton fluxes, which show qualitative agreement to available satellite data. [ABSTRACT FROM AUTHOR]

An experiment to model a system of field-aligned currents in a dense inner magnetospheric plasma is performed under laboratory conditions for the first time. The magnitude and length of the flow of field-aligned currents were measured as a function of the magnetic field. [ABSTRACT FROM AUTHOR]