Astronomy Letters-A Journal of Astronomy and Space Astrophysics最新文献

The consequences of a protoplanetary disk collision with a gas stream are being studied using three-dimensional numerical gas-dynamic simulation. The influence of orbital parameters and the stream mass on the accretion activity of the star is examined. It is shown that the orbital inclination and the initial mass of the infalling material are the most influential parameters in determining the accretion rate. The obtained accretion rate dependencies are compared with actual observational data for two FU Ori type stars. It turns out that not only is the maximum accretion rate consistent with observational estimates, but the behavior of the accretion rate over time is very similar to available long-term light curves.

Based on a sample of masers, we have solved the basic kinematic equations with the inclusion of the Galactic rotation parameters and the peculiar solar velocity as the sought-for unknowns. Based on a spectral analysis, we have obtained the following estimates: (|f|_{R,theta}=(7.0,5.1)pm(1.2,1.4)) km s({}^{-1}), the corresponding wavelengths (lambda_{R,theta}=(1.9,1.7)pm(0.4,0.7)) kpc, and (chi_{odot}={-}140^{circ}pm 15^{circ}). We have confirmed the presence of periodic perturbations in the vertical maser velocities with an amplitude (|f|_{W}=3.1pm 1.4) km s({}^{-1}) and a wavelength (lambda=1.9pm 0.8) kpc. We show that the velocity perturbations (f_{R}) and (f_{theta}) can have both the same and opposite signs. Therefore, we have obtained a large spread of estimates. For example, if (f_{R}) and (f_{theta}) have the same signs, then (Omega_{p}=25.8pm 2.0) km s({}^{-1}) kpc({}^{-1}) and (R_{textrm{cor}}=9.1pm 0.8) kpc, while if (f_{R}) and (f_{theta}) have opposite signs, then (Omega_{p}=35.4pm 2.0) km s({}^{-1}) kpc({}^{-1}) and (R_{textrm{cor}}=6.8pm 0.8) kpc.

We describe the scientific and technological goals of the ‘‘Monitor Vsego Neba’’ (MVN, All-Sky Monitor) space experiment and present its first results. This experiment began to operate onboard the International Space Station (ISS) on December 19, 2024. An analysis of the first results of its observations and the in-orbit operation of the equipment has shown that the basic MVN characteristics correspond to the declared ones in sensitivity, spatial, energy, and time resolution. We have obtained observational data for the brightest sources that can be used for the further calibration of the instrument. We have also determined the particle background of the Earth’s radiation belts and the constraints that are imposed by the enhanced background in the regions of the South Atlantic Anomaly and high latitudes on the observations of celestial sources. We have revealed a problem of the thermal regime of the detectors due to the off-design additional heat flow from the ISS surface that reduces the effective exposure time of observations. The technological goals of the experiment are successfully accomplished. An analysis of the operation of the equipment has shown the validity of the underlying software and hardware solutions. We present the possibility of extending the scientific part of the research with regard to direct X-ray observations of the Sun.

The recurrence times RT (also known as waiting times) of solar flares in active regions in soft X-rays are studied using GOES satellite data from 1998 to 2025. It is shown that the RT distribution is fairly well approximated by a lognormal distribution. Based on grouped samples, changes in three types of average values of log RT distributions over time are studied. From these studies, it can be concluded that the average logarithms of recurrence times, regardless of the method of calculation, show variations similar to variations in sunspot numbers SSN; mean RT values vary between 110 and 280 min.

The origin of the circumstellar (CS) shell of the unusual SN Ia 2020aeuh is explored using a light curve model and observational constraints. The synthesized ({}^{56})Ni mass (({approx}1) (M_{odot})), the mass of the CS shell (0.04–0.2 (M_{odot})), the radius ((2times 10^{16}) cm), and its expansion velocity (({lesssim}200) km s({}^{-1})) have been estimated. The large ({}^{56})Ni mass and the properties of the CS shell are consistent with the scenario of a massive binary C/O white dwarf merger that was accompanied by the loss of ({sim}0.1) (M_{odot}) of matter. The supernova is shown to have exploded ({gtrsim}30) years after the white dwarf merger.

We have simulated the recording of one of the brightest gamma-ray bursts, GRB 221009A, with a segmented scintillation detector. Based on the analysis of Konus-WIND observations, we reproduced the spectral characteristics of the burst in our simulation. Particular attention was given to the influence of instrumental (dead time and pile-up) effects on the accuracy of reconstructing the energy spectrum and polarization of the emission at extremely high fluxes. Detector segmentation was shown to reduce significantly the distortion of the recorded spectrum. We found that a reliable polarization measurement is possible at fluxes up to ({sim}10^{-5}) erg cm({}^{-2}) s({}^{-1}), whereas at fluxes ({sim}10^{-2}) erg cm({}^{-2}) s({}^{-1}) (the main peak of the burst light curve) a polarization measurement is impossible due to the significant influence of the dead time and pile-up effects.

We discuss the difference between the traditional Waldmeier rule and its various modifications related to the fact that the height of the 11-year cycle maxima is conditioned by the activity growth rates on the rising branches. We consider the closeness of the correlations between the Waldmeier effect, on the one hand, and its modifications that consider the activity growth rate from minimum to maximum instead of the length of the rising branch, on the other hand. Using Fisher’s test, we show that the traditional Waldmeier effect describes the observational data more poorly than does the modified one (with the argument of the maximum growth rate on the rising branch): the residual dispersion of data points for it is significantly larger (the significance level is (alpha=0.01)). Based on a series of total sunspot areas on a 400-year time scale (Nagovitsyn and Osipova 2021), we consider the correlation of its values at activity maxima (AR_{M}) with the mean rate of its change on the rising branches (MAR), including that during the Maunder minimum. We show that this correlation is nonlinear and close: the correlation coefficients for two different nonlinear fits, a parabola and a power law, are fairly large: (R=0.97{-}0.98).

We have identified the radio and gamma-ray pulsars known in the eastern half of the sky in the soft X-ray band using data from the all-sky X-ray survey performed by the eROSITA telescope onboard the Spectrum–Roentgen–Gamma observatory. As a result, we have found new candidate counterparts for 12 pulsars of different ages and types at a confidence level ({gtrsim}3sigma). A comparable number has been previously identified in the western half of the sky. In total, this accounts for about 12(%) of the number of known pulsars that have already been detected in X-rays. We give estimates of the X-ray fluxes from the new counterparts, preliminary characteristics of their X-ray spectra, and brief descriptions of the properties of the pulsars themselves. The telescope has also detected 56 pulsars in the eastern half of the sky previously identified in X-rays by other observatories.

We investigate the relativistic effect of geodetic nutation in the rotation of Jupiter and its 94 satellites, for which the ephemerides are known, around their axes on an 800-year time interval. The most significant periodic terms of the geodetic rotation of these celestial bodies have been determined for the first time: (1) for Jupiter relative to the Solar System Barycenter and the plane of the mean orbit of Jupiter at epoch J2000.0 in the Euler angles, in the perturbing terms of the physical libration and in the absolute value of the angular rotation vector of the geodetic rotation of the body under study; (2) for eight regular (four inner (Metis J16, Adrastea J15, Amalthea J5, Thebe J14) and four Galilean (Io J1, Europa J2, Ganymede J3, Callisto J4)) satellites of Jupiter relative to: (a) the Solar System Barycenter and the plane of the mean orbit of the satellite under study at epoch J2000.0 in the Euler angles, in the perturbing terms of the physical libration and in the absolute value of the angular rotation vector of the geodetic rotation of the body under study; (b) the Solar System Barycenter and the plane of the mean orbit of the Jovian System Barycenter at epoch J2000.0 in the Euler angles, in the perturbing terms of the physical libration and in the absolute value of the angular rotation vector of the geodetic rotation of the body under study; (c) the Jovian System Barycenter and the plane of the mean orbit of the satellite under study at epoch J2000.0 in the perturbing terms of the physical libration and in the absolute value of the angular rotation vector of the geodetic rotation of the body under study; (3) for 86 irregular satellites (J6–J13, J17–J72, J5501–J5507, J5509–J5523) of Jupiter in the absolute value of the angular rotation vector of the geodetic rotation of the body under study relative to: (a) the Solar System Barycenter; (b) the Jovian System Barycenter. The calculated analytical values of the geodetic nutation of the celestial bodies under study can be used to numerically study the rotation of these bodies in the relativistic approximation.

Pulsar wind nebulae are the nearest space laboratories to Earth for studying a collisionless, strongly magnetized electron-positron plasma. One way to study this plasma is to construct relativistic magnetohydrodynamic (MHD) models of nebulae. These models aim to reveal, among other things, the nature of MHD structures in highly magnetized nebular flows responsible for the appearance of various features in X-ray images of nebulae—arcs, jets, tori, and so on. This paper examines the predictive potential of a recently constructed MHD model of a compact pulsar wind nebula with a double-torus X-ray morphology. The model predicts the following. Within the volume of a compact double-torus nebula, flows of highly magnetized plasma should be relativistic and quasi-laminar and may form regular folds. As they approach the outer boundary of the double torus, these flows should split into two parts. Large-scale plumes of magnetic plasma, splitting off from these flows toward the nebula’s equator, can sporadically penetrate into the opposite hemisphere of the nebula, where the plasma has reversed magnetic polarity. The base of the nebula’s leeward jet should be surrounded by a regular, toroidal magnetic vortex. We show that these predictions are supported by archival Chandra observations of Vela, the double-torus nebula of the pulsar PSR J0835–4510. The model also explains the origin of some of the diffuse X-ray emission around the double-torus of Vela.