Vol 101, No 11 (2024)

In the paper the structure of the hydrogen-helium upper atmosphere of hot Jupiter depending on the flux of hard ultraviolet radiation from the parent star is investigated. Aeronomic 1D model based on the approximation of single-fluid multicomponent hydrodynamics is used for calculations. The numerical model takes into account chemical reactions, heating-cooling processes, tidal action from the star, diffusion and thermal conductivity. Calculations were performed for the hot Jupiter HD 209458b. In all the solutions obtained a transonic planetary wind is formed leading to a hydrodynamic outflow of the atmosphere. Taking into account the tidal force leads to increase the outflow of atmosphere by 2.5 times compared to the case in which only the gravity of the planet is considered. The dependence of mass loss rate of the planet on the flux of hard ultraviolet radiation turned out to be nonlinear. This may be due to a different dominant mechanism of conversion of absorbed radiant energy in the upper atmosphere within the limits of weak and strong ultraviolet fluxes.

Variations in the orbital period of eclipsing binaries δ Lib and SX Lyn are studied. It is shown that these variations can be represented with equal accuracy in two ways: either in the form of a superposition of secular decrease and cyclic variations or only in the form of cyclic fluctuations. Cyclic variations in the period of δ Lib in both cases can be due to the presence of a third body in the system. In the case of a quadratic representation, they can be also a consequence of the magnetic activity of the secondary component. For SX Lyn a superposition of two cyclic variations is found for both linear and quadratic representation. The lower-period variations in both cases can be due to the presence of a third body in the system. The longer-period variation can be a consequence of the magnetic activity of the secondary component. The secular decrease in the periods of both systems could be due to a loss of angular momentum due to magnetic braking.

We present the analysis of observations of three pulsars at a frequency of 327 MHz with the ground-space interferometer RadioAstron. The main scintillation parameters were measured: the decorrelation bandwidth ∆f_dif and the scintillation time ∆t_dif. We have found that these parameters vary significantly over time. For PSR B1133+16, the decorrelation bandwidth ∆f_dif varied from 100 kHz to 350 kHz from 2014 to 2018. For PSR B0919+06 ∆f_dif varied from 36 kHz to 195 kHz over approximately the same time period. In the direction of the observed pulsars, the power-law indices for the spatial inhomogeneity spectrum of the scattering plasma were estimated. The characteristic frequency and time scales of the diffractive scintillations for PSR B0809+74 are comparable to the receiver bandwidth and observation time, respectively. Therefore, only a lower limit for n can be obtained for this pulsar. For PSR B1133+16, the mean value is n = 3.40 ± 0.11, and n = 3.90 ± 0.04 for PSR B0919+06. We have also measured the angular diameter of the average scattering disks, θ_H , for these two pulsars. For PSR B0919+06, θ_H = 26 – 28 mas, and for B1133+16, θ_H = 12.0 ± 1.6 mas. We provide the estimates of the distance to the scattering screens. All measured parameters have been compared with previously published data.

This paper provides an overview and description of three leading sources of planetary ephemerides: the ephemerides from the Jet Propulsion Laboratory (JPL) and their developed ephemeris theory DE; the ephemerides from the Institute of Celestial Mechanics and Ephemeris Calculation (IMCCE) and their developed theory INPOP; and the ephemeris theory EPM developed at the Institute of Applied Astronomy of the Russian Academy of Sciences (IAA RAS). The methods and observational data sets used in constructing each of the theories are described. A comparison of the ephemerides computed within these theories is made using examples from future space missions. It is shown that the differences in computed positions do not exhibit systematic characteristics and represent rather random discrepancies caused by variations in dynamic models and the observational data taken into account. The overall conclusion from the comparison of the ephemerides is that none of the considered options (JPL DE, EPM, and INPOP) has an advantage in terms of accuracy. All three options are equally valid, and any of the three ephemeris options can be used in practice.