Astronomy Reports最新文献

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%.

The results of the study of the correlation between the Doppler widths (FWHM) of emission lines in the spectra of close and some wide binary systems of the WR + OB type and the system’s orbit inclination are presented in order to search for the effects of the orientation of the WR stellar wind. The widths of the studied lines do not show a correlation with the orbital inclination, and no significant orientation effects for the WR wind were detected.

This work continues the analysis of the model for calculating the thermal structure of an axisymmetric protoplanetary disk, initiated in the paper by Pavlyuchenkov (2024). The model is based on the well-known Flux-Limited Diffusion (FLD) approximation with separate calculation of heating by direct stellar radiation (hereinafter referred to as the FLD^s method). In addition to the previously described FLD^s model with wavelength-averaged opacities, we present a multiband model mFLD^s, where the spectrum of thermal radiation is divided into several frequency bands. The model is based on an implicit finite-difference scheme for the equations of thermal radiation diffusion, which reduces to a system of linear algebraic equations written in hypermatrix form. A modified Gauss method for inverting the sparse hypermatrix of the original system of linear equations is proposed. The simulation results described in the article show that the midplane radial temperature profile obtained with the mFLD^s method has a variable slope in accordance with the reference Monte Carlo radiative transfer simulations. The mFLD^s model also qualitatively reproduces the non-isothermality of the temperature distribution along the angular coordinate near the midplane, which is not provided by the FLD^s method. However, quantitative differences remain between the reference temperature values and the results of mFLD^s. These differences are likely due to the diffusive nature of the FLD approximation. It is also shown that the characteristic times for the disk to reach thermal equilibrium within the mFLD^s model can be significantly shorter than in FLD^s. This property should be taken into account when modeling non-stationary processes in protoplanetary disks within FLD-based models.

The paper presents an analysis of high-precision satellite light curves of exoplanets HD 189733b and HD 209458b. The dependence of the exoplanet radius on the wavelength caused by scattering in the planetary atmosphere is determined using a four-parameter limb darkening law based on a three-dimensional model of the stellar atmosphere. It is shown that when using the same exoplanet system characteristics for all wavelengths, primarily the orbital inclination, as well as when using a four-parameter law with a refined radius of the star, the change in the radius of the exoplanet HD 189733b with increasing corresponds to the model of an exponential Rayleigh atmosphere with a characteristic height of 380–400 km. At the same time, the characteristics of the atmosphere of HD 209458b largely depend on the adopted eccentricity of the system.

This paper is considers the structure of atmospheric optical turbulence using both measurements in the atmospheric surface layer and modeling data for the entire optically active atmosphere. Estimates of the structural characteristics of Kolmogorov and non-Kolmogorov atmospheric optical turbulence are presented. Approaches to calculating atmospheric coherence lengths are discussed, including the Fried parameter, the Bump length, and the coherence lengths of non-Kolmogorov optical turbulence sensitive to deformations of the energy spectrum of turbulent air temperature fluctuations. Estimates of the atmospheric angular resolution in the daytime for the location of the Large Solar Vacuum Telescope are given. The developed methodological foundations for calculating the characteristics of optical turbulence and atmospheric angular resolution can be applied to other astronomical observatories (both solar and stellar).

The physical mechanism responsible for the photometric period changes in chemically peculiar star 56 Ari was searched. It was previously shown that rate of the star’s period increase is several orders of magnitude larger than the rates expected from the evolutionary changes of the angular momentum or due to magnetic braking. Also no secular changes were detected in the surface structure or visibility of chemical spots which are responsible for the rotational modulation of stellar brightness. We hypothesize that period changes in 56 Ari are caused by the drift of surface magnetic and associated abundance structures as a result of the kink-type (Tayler) instability of the background magnetic field in the radiative zone of the star. Results of the numerical simulation presented in the paper yield growth and drift rates of the most rapidly developing non-axisymmetric mode of the instability, consistent with the observed rate of period changes in 56 Ari. The surface geometry of the 56 Ari magnetic field is also reproduces in the calculations. The proposed mechanism may also be used to explain the character of period changes in other Ap/Bp stars demonstrating such an effect.

Both solar and stellar average temporal profiles of emission demonstrate general laws of evolution of such complex and diverse phenomenon as flare. Empirically obtained average profiles for events with simple dynamic make it possible both to analyze the emission mechanisms of solar and stellar flares and to help to divide complex events into discrete acts of energy release. Microwave emission is of particular interest, since it can reflect the precipitation dynamics of accelerated electrons. For the reconstruction of average time profiles. We selected 116 observed with the Siberian Radioheliograph observations in the range of 3‒24 GHz. These profiles have demonstrated a simple time structure and a broadband gyrosynchrotron spectrum of non-thermal nature. The wide spectral range allowed to divide emission into emission of optically thick and optically thin sources. The time profiles that describe the emission from different regions of the flare loop have been summed within the respective spectral band, after which for each event, normalization and time scaling have been applied. The average time profiles have been obtained as the median value for each time bin (step). As a result, it has been shown that the microwave average time profiles for the microwave optically thick and thin sources are identical for a solar flare with simple dynamics. This indicates the dominance of accelerated electron precipitation processes in the emission of such events. Also, the dominance of non-thermal processes for this type of event has been confirmed by a comparison with the results of a solar-flare dynamics modelling in the 304 Å line obtained in studies of other authors and an analysis of the dynamics of microwave emission during the decay phase. Analytical functions that describe the rise and decay phases of microwave emission of solar-flare have been obtained. The use of analytical functions in combination with the average time profile for the analysis of the February 3, 2022 event has shown the possibility of using this method to separate the acts of energy release associated with the precipitation of accelerated electrons. The obtained average time profiles, as well as analytical functions describing the behaviour of simple solar-flare microwave emission, can be used both to analyze the emission of solar events in the microwave range and to study the processes occurring during stellar flares.

We performed star counts in the region of the open cluster NGC 3532. The ranges of trigonometric parallaxes and proper motions containing all the stars of the cluster were determined using the stars with 5‑and 6-parameter Gaia DR3 solutions. The estimated radius of the cluster was ({{R}_{c}} = 178{'} pm 3{'} ) and the number of cluster stars was ({{N}_{c}} = 2200 pm 40). We estimate the number of stars with poor astrometric solutions that may be members of the cluster. For this purpose, we analyze the surface density distribution of stars with two-parameter Gaia DR3 solutions, stars with the parameter (operatorname{RUWE} > 1.4), and stars with large relative errors of trigonometric parallaxes in the vicinity of the cluster. We are looking for stars that fall within the area of the color–magnitude diagram occupied by probable members of the NGC 3532 cluster from the Hant–Reffert sample. The radial surface density profile plotted with such stars shows the concentration of stars toward the cluster center. An analysis of the profile yields an estimate of (2150 pm 230) stars that may be cluster members. Thus, nearly one half of cluster members can be lost when the probable members are selected only by exact astrometric data of Gaia DR3. Among these lost stars, there may be a significant number of unresolved binary and multiple systems.

A high-precision algorithm for interpreting transit light curves in the model of an eclipsing classical binary star–exoplanet system for interpretation moving from the eccentricity ((e))–periastron longitude ((omega )) variables to the ((ecos omega ,;{kern 1pt} esin omega )) eccentricity components has been improved. The possibilities of interpretation by eccentricity components have been studied. It has been shown that the dependence of the minimum’s shape on (esin omega ) alone is clearly expressed at small e values and weakens with increasing (e). The linear correlation between the radius value, which is characteristic of any e values, has been shown.

Dust growth is one of the key processes leading to planet formation in protoplanetary disks. Centimeter-sized dust grains, pebbles, are essential for the formation of planetesimals through streaming instability and play a crucial role in the formation of protoplanetary cores, giant planets, and the enrichment of their atmospheres with chemical elements. In this paper, the impact of luminosity outbursts on the amount of pebbles and icy mantles in a protoplanetary disk has been studied. We have performed global simulations of the formation and evolution of a self-gravitating, viscous protoplanetary disk using the two-dimensional thin-disk hydrodynamic code FEOSAD, which self-consistently produces luminosity outbursts. The model includes thermal balance, dust evolution and its interaction with gas, the development of magnetorotational instability, adsorption and desorption of four volatile species (H₂O, CO₂, CH₄, and CO), and the effect of icy mantles on the fragmentation properties of dust aggregates. Our results have shown that luminosity outbursts have a stronger impact on the CO₂, CH₄, and CO ice lines than on the water ice line. This is because the H₂O ice line resides in a region dominated by viscous heating during the early stages of disk evolution, whereas the ice lines of the other molecules lie in regions where stellar irradiation dominates the thermal structure, making them more sensitive to temperature variations induced by the outbursts. Nevertheless, luminosity outbursts lead to a twofold reduction in the total amount of pebbles in the disk due to the disintegration of dust aggregates into monomers following the loss of water ice, which acts as a binding agent. The reformation of pebbles occurs over several thousand years after the outburst, primarily through collisional coagulation. The characteristic timescales for pebble recovery significantly exceed the freezing timescales of water ice. The desorption of icy mantles occurs in a highly non-axisymmetric and intrinsically two-dimensional region of the disk due to the formation of spiral substructures during the early evolution of a gravitationally unstable disk.