Astronomy Reports最新文献

In the paper, the structure of the hydrogen–helium upper atmosphere of hot Jupiter depending on the flux of extreme ultraviolet radiation from the host star has been studied. An aeronomic 1D model based on the approximation of single-fluid multicomponent hydrodynamics has been used for calculations. The numerical model has taken into account chemical reactions, heating-cooling processes, tidal action from the star, diffusion, and thermal conductivity. Calculations have been performed for hot Jupiter HD 209458b. In all the obtained solutions, a transonic planetary wind has been formed leading to a hydrodynamic outflow of the atmosphere. Taking into account the tidal force has led to increase the outflow of atmosphere by 2.5 times compared to the case, in which only the gravity of the planet has been considered. The dependence of the mass loss rate of the planet on the flux of extreme ultraviolet radiation has been found 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 δLib and SXLyn were analyzed. It was 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 δLib 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 SXLyn, 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.

In the paper, a model for simulating the non-stationary thermal structure of protoplanetary disk in axial symmetry has been provided. The model has been based on the widely used approach of splitting the radiation field into stellar and intrinsic thermal radiation of the medium. The heating by stellar radiation has been calculated by the ray tracing method while the well-known diffusion approximation with a flux limiter (FLD approach) has been used to treat the thermal radiation. To solve the resulting system of linear equations, a modification to Gauss method has been proposed, which has made it possible to speed up the calculations by a factor of ten compared to the widely adopted GMRES method. This model has been used to calculate the steady-state thermal structure of two disks, including those with the parameters of the EX Lup system. A detailed analysis of the simulation results has been performed. Comparison with the results of more accurate methods has made it possible to identify the main shortcomings of the model related to the ignoring of light scattering and to the diffusion nature of the FLD approximation. It has been shown that the disk thermal structure calculated with the FLD approximation has evolved according to analytical estimates of the characteristic thermal time.

In this paper, we have provided 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, Russian Academy of Sciences (IAA RAS). The methods and observational data sets used in constructing each of the theories have been described. A comparison of the ephemerides computed within these theories has been made using examples from future space missions. It has been 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 has been that none of the considered options (JPL DE, EPM, and INPOP) has an advantage in terms of accuracy. All three options have been equally valid, and any of the three ephemeris options can be used in practice.

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 (Delta {{f}_{{{text{dif}}}}}) and the scintillation time (Delta {{t}_{{{text{dif}}}}}). We have found that these parameters vary significantly over time. For PSR B1133+16, the decorrelation bandwidth (Delta {{f}_{{{text{dif}}}}}) varied from 100 to 350 kHz for the period of 2014 to 2018. For PSR B0919+06 (Delta {{f}_{{{text{dif}}}}}) varied from 36 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. The mean value is (n = 3.40 pm 0.11) for PSR B1133+16 and (n = 3.90 pm 0.04) for PSR B0919+06. We have also measured the angular diameter of the average scattering disks, ({{theta }_{{text{H}}}}), for these two pulsars. For PSR B0919+06, ({{theta }_{{text{H}}}} = 26{kern 1pt} - {kern 1pt} 28) mas, and for B1133+16, ({{theta }_{{text{H}}}} = 12.0 pm ) 1.6 mas. We provide the estimates of the distance to the scattering screens. All measured parameters have been compared with previously published data.

Solar flares can be accompanied by high plasma velocities exceeding several hundred km/s. Detection and measurement of such velocities is limited by narrow-band and small wavelength range in most solar instruments. However, similar events with Doppler velocities exceeding two hundred km/s have been detected by the solar optical spectrographs at the Ondřejov Observatory. The results of the analysis of our multi-wavelength observation performed during the solar flare of June 7, 2011 and the calculation of several physical parameters of the coronal mass ejection fragments following the flare have been present. The calculation of the radiation of heated gas have been performed with allowance for self-absorption in the spectral lines of hydrogen and calcium. All the crucial processes of discrete level populating and depopulating have been taken into account in the balance equations. The theoretical radiation fluxes in the lines have coincided with those observed in the temperature range of 6300–10000 K at a gas concentration of  ~((3{kern 1pt} - {kern 1pt} 5) times {{10}^{{10}}} {text{c}}{{{text{m}}}^{{ - 3}}}), a gas layer thickness of (6800{kern 1pt} - {kern 1pt} 7000) km, and a linear concentration of ((2{kern 1pt} - {kern 1pt} 4) times {{10}^{{19}}} {text{c}}{{{text{m}}}^{{ - 3}}}).

This paper investigates the impact of triaxiality and mass variations of the primaries on motion around the triangular equilibrium points (TEPs) of the restricted three-body problem (R3BP). The motion of the primaries takes place within the framework of the Gylden–Mestschersky problem while their mass variation occur in accordance with the unified Mestschersky law and the bigger primary is a triaxial body. The dynamical equations of the time-dependent system are derived and transformed to a system of equations with constant coefficients. The solutions of the equations with constant coefficients were explored, and it was seen that there exists analytically a pair of TEPs. The stability of the TEPs is investigated and it is seen that the points can be stable and unstable, depending on the variable mass parameters, critical mass parameters, triaxiality of the bigger primary and the constant (kappa ) of mass variation. The region of stability increases and decreases depending on the stabilizing or destabilizing behaviors of the triaxiality of the bigger primary and the variable mass parameter. The stability of the TEPs of the time-dependent system are unstable as solutions do not converge but tend to infinity with time. Numerically, we explore the study for the general case of a particle in the gravitational field of the bigger triaxial primary and a smaller spherical body using the mass parameters which covers for most astronomical systems to demonstrate the applications of our problem in astronomy. It is seen that there can be finitely many pairs of TEPs for variable mass parameters, and the region of stability of the TEPs for different mass parameters was explored. Further, the zero velocity curves unveiled more interesting scenarios that could not have been observed analytically. It is observed that an increasing mass parameter of the binary gives a larger region where motion of the particle is allowed and vice versa, while the departure of the bigger primary to a triaxial body always reduces region of allowed motion and the variation constant can increase or decrease region where motion is allowed. The study can be applied to provide insights into the dynamics of an infinitesimal mass around variable mass primaries coupled with variations in shape.

We present the results of our monitoring of Giant Radio Pulses (GRPs) of pulsar B0531+21 (J0534+2200) in the Crab Nebula. Observations has been carried in the Pushchino Radio Astronomy Observatory (PRAO) of the Astro Space Center (ASC) of the Lebedev Physical Institute (LPI) using the LPI Large Phased Array (LPA) radio telescope at 111 MHz frequency at band with 2.5 MHz with a 128-channel spectrum analyzer and PRAO Digital Pulsar Receiver in 2002–2024. We show that the dependence between the scattering time (tau ) and the dispersion measure (DM) of GRPs in the time interval 2010–2021 differs significantly from that before 2010 and after 2021. In 2010–2021, the values of (tau ) and (DM) demonstrated significant growth and instability, and the functional relationship between them changes rapidly. The data for the entire observation interval forms on plot of {(tau ,dm)} (where (dm = (DM - 56.7) times {{10}^{3}})) three main and one transitional branches, formed by 14 different time segments. That may be well approximated by power functions (tau propto d{{m}^{n}}) with values (n = 0.7), 1.1, and 1.86 for the main and 2.1 for the transitional branches. This behavior of (tau ) and (DM) is explained by anomalous variations in the density and turbulence of magnetically active plasma in the Crab Nebula and the interstellar medium in 2010–2021. Comparing the data at 111 and 610 MHz in the MJD interval 55000–56500 (June 2009–July 2013), we obtained an estimate (beta = 3.4 pm 0.2) for the dependence of observed scattering on the frequency (tau propto {{nu }^{{ - beta }}}). This value is close to the previously published, but significantly differs from the dependencies for both Kolmogorov ((beta = 4.4)) and normal distribution ((beta = 4)) of spatial inhomogeneities of the interstellar medium.

We searched for a rapprochement in space between a star cluster and an extrasolar planetary system in past epochs. We have found that a host star TOI-2796 is a candidate for such an encounter with the cluster NGC 1977. We estimated time and distance between the objects of such a rapprochement. These parameters allowed us to estimate the gravitational effect on the loss of comets from a hypothetical analogue of the Oort cloud of the TOI-2796. The place of the encounter in the sky is shown. This point can be considered to be the place of appearance of interstellar comets. We confirm and suggest that there is possibility of past and future stellar close encounters of stars with star clusters which can perturb the analogue of the Oort cloud’s stability and triggering cometary showers in the vicinity of giant planets. The orbital parameters for the sample are calculated using the galpy package. The MWPotential14 gravitational potential is used, composed of a power law, exponentially cut-off bulge, Miyamoto–Nagai potential disc, and Navarro–Frenk–White dark matter halo. Time calculations were carried out within the age limits of the objects considered. The color-absolute magnitude diagram and the isochron system were used to calculate the age of the cluster. By extending the tracks of the cluster and stars’ motion in past epochs (~5.4 Myr), the time of the maximum approach (≈30 pc) of the TOI-2796 star, hosting a planetary system, with NGC 1977 has been found. As a result of our research, we derived that the host star’s approach with the cluster might entail effects related with the cluster’s gravitational pull on the nuclei of comets located in the outer border of the planetary system’s Oort cloud. The impact of approach on Oort cloud comets has been estimated.

The problem of the formation of exoplanets in inclined orbits relative to the equatorial plane of the parent star or the main plane of the protoplanetary disk can be solved by introducing a smaller inclined disk. However, the question of the nature of such an internal disk remains open. In the paper, we successfully tested the hypothesis about the formation of an inclined inner disk in a protoplanetary disk near a T Tau type star as a result of a gas stream falling on it. To test the hypothesis, three-dimensional gas-dynamic calculations were performed taking into account viscosity and thermal conductivity using the PLUTO package. In the course of the analysis of calculations, it was shown that a single intersection of the matter stream with the plane of the disk cannot ensure the formation of an inclined disk near the star, while a double intersection can. In addition, in the case of a retrograde fall of matter, the angle of inclination of the resulting inner disk is significantly greater. An analysis of the observational manifestations of this event was also carried out: the potential change in the brightness of the star, the distribution of optical thickness in angles, the evolution of the accretion rate. It is shown that the decrease in brightness can reach up to ({{5}^{m}}), taking into account scattered light, and such a decrease in brightness will last several decades. In addition, a sharp increase in the accretion rate by two orders of magnitude could potentially trigger an FU Ori-like outburst.