Astronomy Reports最新文献

A new method is used to study a current version of the two-planet problem on the secular evolution of planetary orbits with small eccentricities and mutual inclinations, having an arbitrary orientation relative to the main (picture) plane. A model has been developed that describes a wide class of exoplanetary systems with an inclination angle of orbits different from (pi {text{/}}2.) The orbits of the planets are modeled by the Gaussian rings, the perturbing function is represented by the mutual gravitational energy of these rings in the form of a series up to terms of second order of smallness. To describe the evolution of orbits, instead of osculating Keplerian elements, a new set of variables is introduced: the unit vector ({mathbf{R}}) of normal to the plane of the ring and two Poincaré variables (left( {p,q} right);) for eight independent variables, a system of differential equations is obtained and analytically solved. The method is applied to study the secular evolution of the two-planet system Kepler-117 (KOI-209) with non-resonant orbits of exoplanets. It has been established that in this system the oscillations of the same components of the orientation vector ({mathbf{R}}) for each of the orbits, as well as the values (left( {e,i,{{Omega }}} right),) occur strictly in antiphase. The eccentricities of both orbits oscillate with the period ({{T}_{kappa }} approx 182.3;{text{years}},) and the inclinations of the orbits and the longitudes of the ascending nodes change in the libration mode with the same period ({{T}_{g}} approx {text{174}}.5;{text{years}}.) The lines of the orbital apsides rotate unevenly counterclockwise with the periods of secular rotation ({{T}_{{{{g}_{2}}}}} approx 178.3;{text{years}}) (for a light planet), and ({{T}_{{{{g}_{1}}}}} approx 8140;{text{years}}) (for a more massive planet).

The study of the existence of the quadratic local integral in stationary two-dimensional potential fields that was initiated in the first part of the work, is continued. New mathematical relationships that deepen the understanding of the structure of functions describing the behavior of potential fields under arbitrary mass distribution have been proposed. The rotation of the coordinate system to simplify the equations and emphasize key features of the functional dependencies has been employed. Particular attention has been paid to arbitrary functions defining the potential and its derivatives under specific conditions. Their properties and possible solutions have been analyzed. Besides, linear differential equations with polynomial and periodic solutions have been studied. Theoretical results, which can be used for further analysis of quadratic integrals and for clarifying the differences between polynomials and other types of functions in broader mathematical models, have been formulated. The paper is partially based on a report presented at the Modern Stellar Astronomy 2024 conference.

High-precision photometric measurements of the unexplored eclipsing star V1141 Cas (P = 6.909^d, (V{{ = 12.02}^{m}}), (e = 0.37), Sp B1 V) have shown that the apsidal rotation velocity, ({{dot {omega }}_{{{text{obs}}}}} = 0.127^circ )/yr, is two times slower than the theoretical value under the synchronism condition, ({{dot {omega }}_{{{text{theor}}}}} = 0.235^circ )/yr. The physical parameters of the component stars were obtained: ({{T}_{1}} = 23,500 pm 400) K, ({{M}_{1}} = 8.4 pm 0.5{kern 1pt} {{M}_{ odot }}), ({{R}_{1}} = 4.24 pm 0.08{kern 1pt} {{R}_{ odot }}), ({{T}_{2}} = 22,000 pm 400) K, ({{M}_{2}} = 7.0 pm 0.5{kern 1pt} {{M}_{ odot }}), and ({{R}_{2}} = 3.38 pm 0.08{kern 1pt} {{R}_{ odot }}). The age of the system is determined to   be 7.5 million years with a solar chemical composition. The measured photometric parallax, (pi =0.00031^{primeprime} pm 0.00004^{primeprime} ), is very close to the Gaia value. The interstellar extinction, ({{A}_{{text{V}}}} = {{2.2}^{m}}), is 40 percent higher than the survey’s data.

We report on the discovery of rare emergence (31 nights from 363 nights of observations) of narrow absorption features in hydrogen and helium lines in stationary SS 433 spectra with velocities ranging from ‒650 to –1900 km/s. The components arise independently of the appearance of P Cygni line profiles which are frequently observed in the SS 433 stationary spectra with terminal velocities ranging from –200 to ( sim {kern 1pt} - {kern 1pt} 2500) km/s. The characteristic rising time of the transient absorptions is about one day and the decay time is about two days. The phenomenology of the absorptions suggests their origin due to hydrodynamic instabilities of wind outflows from a supercritical accretion disk in SS 433.

Probable past and future close encounters of open clusters with known characteristics over 64 m-illion years have been calculated by integrating the orbits of cluster centers in the Galactic potential using the galpy package. It has been shown that in the Galactic neighborhood of the Sun, pairwise cluster encounters at distances comparable to or smaller than their sizes occur at a characteristic rate of 35–40 events per 1 Myr. Close encounters between open clusters with a significant age difference occur at a rate of 15 events per Myr. It can be expected that in the Galaxy as a whole, such events occur an order of magnitude more frequently per unit time. Thus, dynamical interactions between stellar ensembles of different ages may not be too rare and could influence the properties of stellar populations. A pair of clusters with similar ages: HSC 1428 and Gulliver 22 was identified as a likely physically bound binary cluster system. A forecast of expected close encounters over the next 32 Myr has been provided for 490 pairs of clusters. Currently, 29 pairs of clusters are at their closest approach. The paper has been partially based on a report presented at the Modern Stellar Astronomy 2024 conference.

Interplanetary coronal mass ejections (ICMEs) are among the main drivers of major geomagnetic storms. The recovery phase of such storms, characterized by a return of geomagnetic indices to pre-disturbance levels, is primarily governed by the decay of the ring current and the cessation of solar wind energy input. This study examines how the characteristics of the recovery phase, specifically the exponential decay time constant ((tau )) of key geomagnetic indices, depend on the polarity configuration of the interplanetary magnetic field (IMF) of the ICMEs. A total of 163 ICME-driven storms from 1995 to 2015 were analyzed using hourly OMNI data. The recovery phase of each storm was modeled with an exponential decay to extract (tau ) for the Disturbance Storm Time (Dst) index, Planetary amplitude (ap) index, and Auroral Electrojet (AE) index. Events were categorized into eleven distinct IMF polarity and flux rope configurations to evaluate polarity-dependent recovery behavior. Correlation analyses were also conducted to assess the relationship between (tau ) of geomagnetic indices and various solar wind parameters, including IMF ({{B}_{z}}), solar wind speed, and coupling functions. Results reveal significant differences in recovery durations across ICME polarity groups. The SN polarity exhibited the fastest Dst recovery ((tau = 18.68 pm 0.80) h), whereas SNS and ({{F}^{ + }}) configurations exhibited the slowest recoveries ((tau = 43.95 pm 1.27) and (50.97 pm 1.58) h, respectively). For the ap and AE indices, the fastest recovery occurred in NSN ((tau = 4.02 pm 0.46) h) and SNN ((tau = 4.33 pm 0.61) h) configurations, while prolonged recovery was associated with (Fr) (ap) and NSS (AE) events ((tau > 29.90) h). Events dominated by northward magnetic fields recovered significantly faster than those with prolonged southward IMF orientations. Strong statistical coupling was found between (tau )(Dst) and (tau )(ap) ((r = 0.87)), while (tau )(AE) was most sensitive to (n{{E}_{y}}) ((r = - 0.52)). Additionally, configurations with small rotation angles (({{F}^{ - }})) recovered more rapidly than those with complex rotations (({{F}^{ + }})), reflecting the role of magnetic structure in sustaining energy input. These findings enhance predictive models of magnetospheric recovery by linking IMF polarity and flux rope topology to the timescales of geomagnetic relaxation.

Orbital-period variations of the eclipsing binaries GI Cep and V548 Cyg are analyzed. The period variations in both systems can be described as a superposition of secular decrease and two cyclic variations of the period. The rate of decrease of the period dP/dt = 3.73 × 10^–7 day/yr for GI Cep and 2.38 × 10^–7 day/yr for V548 Cyg. A superposition of two types of cyclic variations is observed for GI Cep and V548 Cyg: with periods 14.4 years and 33.7 years for GI Cep, and 5.4 and 43.8 years for V548 Cyg. The observed cyclic variations in the period of GI Cep can occur due to the presence of a third body in the system or due to the magnetic activity of the secondary component. The system can be triple or quadruple. The hypothesis of magnetic activity is not suitable for V548 Cyg. Apparently, this is quadruple system.

More than half of currently known stars have nearby exoplanets with size between Earth and Neptune, called super-Earths and mini-Neptunes. The California–Kepler Survey (CKS) studied data from NASA’s Kepler mission and revealed a bimodal distribution of planets with (R < 3.5{kern 1pt} {{R}_{{text{E}}}}) by radius (({{R}_{{text{E}}}}) is the radius of the Earth). It occurred that there was a lack of planets with radii (1.5{kern 1pt} {{R}_{{text{E}}}} < R < 2{{R}_{{text{E}}}}). The CKS did not take into account data from other missions and exoplanets discovered by non-transit methods. All data from this mission were limited to 2022. This article examines the distribution of super-Earths and mini-Neptunes, taking into account all data on exoplanets known by 2024 from the NASA catalog. Mini-Neptunes and super-Earths with known radii were selected. There were 937 such planets, including 366 planets with known mass. Since the radius of a planet can only be determined by the transit method, the distribution by radii is built using the data of transit planets, but, unlike CKS, not only the data of the Kepler mission are taken. The data for the remaining distributions are selected regardless of the method of their detection and the telescope used. We show that the current data are best fitted by a double-peaked Gaussian distribution, which describes two populations of planets: rocky (hereinafter super-Earths) and exoplanets with gas envelopes (exoplanets surrounded by hydrogen–helium atmospheres, but consisting mainly of heavy elements—ice and rock, hereinafter mini-Neptunes). The magnitude of the gap between populations at present is analyzed. It is shown that the gap is filled evenly on both sides; in CKS, the first peak is significantly smaller than the second, that is, there were fewer super-Earths than mini-Neptunes. Perhaps more super-Earths have been discovered recently, which is why there was a shortage of them in the CKS. The composition of some exoplanets was determined using theoretical models of the dependence of mass on radius.

Rope flux models of solar flares associate the phenomenon of quasi-periodic pulsations of flare radiation with a parametric catastrophe that occurs when the top of a twisted magnetic loop enters the corona. A sharp decrease in external pressure leads to the longitudinal magnetic field of a force-free flux rope tending to zero on the magnetic surface where the current changes sign, and the density of the azimuthal current and the force-free parameter begin to grow indefinitely near this surface, approaching a break. The current velocity of electrons here will inevitably exceed the speed of ion sound, and plasma instability will arise. Scattering of electrons on ion-acoustic plasmons will sharply decrease the plasma conductivity and cause rapid, flare dissipation of the magnetic energy of the rope, i.e., decrease in the amplitude of the field and currents and expansion of the rope cross-section. This is how the first peak of the flare radiation will be formed. In this case, the torque applied to each section of the rope will be greatly weakened in the energy release region. In equilibrium, the torque should be the same along the entire length of the loop, so there will be a transfer of the azimuthal flux by Alfvén waves from the loop legs to the top. Alignment of the torque along the rope axis will return the rope to its original state, after which the second peak of the flare radiation is formed, and the process is repeated several times until the reserve of free magnetic energy associated with the currents in the entire loop decreases significantly. The oscillations of the rope cross-section accompanying the peaks of its radiation represent a specific type of fluctuations of a system with time-varying rigidity: in them the magnetic field intensity, providing the restoring force, changes greatly. Calculation of such oscillations allows achieving not only qualitative but also quantitative correspondence between the theoretical results and observational data.

Stellar models are calculated in the approximation of a uniform density distribution. Variational method was used for determination of the boundary of a stability loss, for stellar masses in the range from 2 up to ({{10}^{5}}{kern 1pt} {{M}_{ odot }}). The effects of the general relativity had been taken into account. The equation of state in the temperature and density ranges ({{10}^{9}} < T{{ < 10}^{{10}}}) K, ({{10}^{5}} < rho {{ < 10}^{{10}}}) g/cm³ had been taken from the work of Imshennik and Nadyozhin (1965). The critical parameters for the values of entropy and stellar masses differ from more accurate values, obtained using a more complicated variant of accepted density distribution, not more than 12%.