Astrophysical Bulletin最新文献

Chemically peculiar (CP) stars of early spectral types are the only Main-Sequence objects of the Hertzsprung–Russel diagram that have strong magnetic fields covering the entire surface of a star and maintaining a stable structure on a scale of at least decades. The origin and evolution of magnetic fields of CP stars are still a subject of discussion, despite significant progress in the field of observation of stellar magnetic fields and their theoretical description. This situation has developed not least because of the problem of accurately determining the age of CP stars. We performed a review of magnetic fields of CP stars in the Orion OB1 association and five intermediate-age clusters ((alpha) Per, Pleiades, NGC 7092, and IC 4756) and found evidence of a strong decrease in the proportion and strength of magnetic fields of CP stars relative to normal stars of the same spectral types. The found dependences can serve as confirmation of the fossil nature of large-scale magnetic fields of stars. The conclusions of this paper are based on the measurements of more than 800 spectra obtained in the period from 2013 to 2023 with the Main Stellar Spectrograph of the 6-m BTA Telescope for about 100 stars.

All available photometry for the Cepheid KN Cen is analyzed to construct its ((O-C)) diagram spanning a 134-year long time interval. This made it possible for the first time to compute the rate of evolutionary period increase of the Cepheid, (dP/dt=+2.91(pm{1.68})) s yr({}^{-1}), which is consistent with the results of model computations for the third crossing of the instability strip. The test for stability of pulsations proposed by Lombard and Koen confirmed the reality of the evolutionary period change.

In this paper, we analyze the apparent surface density observations of 81 globular clusters provided by Gaia DR2. The problems of analyzing these observations and their differences from similar data obtained using the HST are discussed. Based on the results of this analysis of the quality of observational data and a number of physical considerations, we separate globular clusters into three classes and then consider the issues of modeling the apparent surface density versus distance. The values of the free parameters of the model are found by the symplectic minimization method. The free parameters including the concentration parameter are for the first time found using the 4-parameter generalized model we propose.

We present the results of analyzing the activity manifestations of the K3 V spectral type dwarf HIP 113103 (HD 216530) and estimate the matter loss from the atmospheres of two of its planets. HIP 113103 can be classified as a relatively young object with an age of about 470 million years—1 billion years. Using the standard method, based on the observed data from the TESS mission, we estimated the areas of spots on the surface of the star, which exceed the maximum area of spots on the Sun and are 6100 and 4950 MSH for sectors 1 and 28, respectively. According to the data from the observation archive of the All Sky Automated Survey, the activity cycles of HIP 113103 have been established to last about 610, 825, and 1030 days (1.7, 2.3, and 2.8 years, respectively). Both planets in the stellar system HIP 113103 are characterized as objects with radii of 1.829(R_{oplus}) and 2.400(R_{oplus}), with periods of 7.6 and 14.2 days, respectively, lying on opposite sides of the Fulton Gap in the ‘‘Period—Radius’’ diagram. The loss of matter from the planetary atmospheres was calculated using an approximation formula corresponding to the energy-limited atmospheric loss model. To estimate the flux of XUV photons, analytical dependences were used connecting flux values and the (log R^{prime}_{textrm{HK}}) parameter. It was found that the values (dot{M}) values for planets b and c are equal to (2.8times 10^{8}) g s({}^{-1}) and (1.9times 10^{8}) g s({}^{-1}), respectively. The planet HIP 113103 b attracts special attention because, with its radius (R_{p}=1.829R_{oplus}), it belongs to a small population of planets with the radii (1.5R_{oplus}<R_{p}<2.0R_{oplus}), which characterizes the evolution of super-Earths and mini-Neptunes. HIP 113103 c has a radius of (R_{p}=2.40R_{oplus}) and an equilibrium temperature of (585pm 10) K which characterizes the object as an already established warm mini-Neptune. A comparison of the properties of planets b and c is of interest, since they belong to the same system, are irradiated by the same star, probably have similar ages and conditions of formation, etc.

The age estimates of magnetic stars obtained from the ages of clusters and associations are compared with those determined using the grids of evolutionary paths and isochrones separately for each star. Large deviations between the age systems have been discovered. Analysis of the studies that use ‘‘cluster’’ ages shows that they differ significantly from those obtained using individual estimates.

A local integral that allows us to immediately determine the velocity field for certain specific initial conditions was introduced by Antonov and Shamshiev in 1992. We consider cases where the integrability of the trajectory can be advanced further. We then obtain an analytical relationship between (x), (y), (z), (t) on a given trajectory. Possible cases are classified and one of them is analyzed.

A method for radiometer-noise generation and its software implementation in the form of a Python library module is proposed. The method can be used to simulate radiometer noise with variable component properties: Gaussian white noise and flicker noise (random drift) with a power spectrum linearly increasing with decreasing frequency. The method is based on the transformation of spectral properties of Gaussian noise via sequential filtering by a differentiator, nonlinear threshold switch, and subsequent integration. By changing the integrator accumulation time constant and the threshold level relative to noise intensity (sigma) one can change the resulting form of the spectrum and the corresponding statistical parameters of the output noise over a wide range: from stationary white noise to noise dominated by a (1/f)-type spectrum component. Empirical polynomial approximation formulas for the dependence of the spectral index of the resulting noise records on the nonlinear threshold switch level in the 0.0–(3.5sigma) interval are derived based on numerical simulations using a software implementation of the model. Examples of noise-record implementations, their spectra, and autocorrelation functions are demonstrated. The generated noise is shown to be similar to the noise observed on radio telescopes of the Institute of Applied Astronomy of the Russian Academy of Sciences.

Based on archival images from the Hubble Space Telescope, stellar photometry of the galaxy NGC 4068 was carried out. The resulting Hertzsprung-Russell diagram (CM diagram) shows branches of young and old stars. To estimate the metallicity of young stars, isochrones of different ages and metallicities were used. A combination of isochrones and the CM diagram of stars shows that the young stars of NGC 4068 have high metallicity, up to the metallicity of the Sun ((Z=0.02)). Since stars of high metallicity are observed throughout the body of the galaxy, we can talk about high metallicity of the entire galaxy, and not just one local region. The position of NGC 4068 among 105 irregular galaxies of different metallicities is shown on a diagram of the dependence between the metallicities of old and young stars. The almost linear dependence between these parameters indicates the absence of processes of rapid enrichment of galaxies with metals at the present stage of their evolution. The obtained results do not confirm the conclusion about the low metallicity of NGC 4068 reported earlier. For direct measurements of the metallicity of NGC 4068, the coordinates and fields of identification of the three brightest red supergiants with a high color index ((V-I)), which indicates their high metallicity, are presented.

In this paper, the first in a series of four articles, the scientific goals of the Metron project are highlighted, and the characteristics of the cosmic objects available for study within its framework are provided. The Metron interferometer radio telescope should include arrays of meter-range dipole antennas placed on Earth, in outer space, or on the far side of the Moon (or a combination of these options). Working in the meter range will enable the study of the so-called cosmological epoch of the ‘‘Dark Ages’’, which is challenging to observe but highly interesting for understanding the origin of the first stars, galaxies, and black holes, as well as for the search for new cosmological objects and processes. One possibility is to search for absorption in the 21-cm line within the extended halos around early protogalaxies and supermassive primordial black holes, whose existence is predicted in a number of models. Another goal of Metron may be to clarify the anomalous absorption in the 21-cm line previously detected by the EDGES telescopes and to observe radio emissions from the magnetospheres of stars and exoplanets. The Metron project aims to achieve unprecedented resolution in the meter range, which is expected to yield new world-class scientific results. Meter-range antennas and receivers are relatively simple and inexpensive, and the construction of interferometric arrays from them can be accomplished in a relatively short period of time.

In the article, a method is developed for estimating the dynamic masses of the stellar and gas components of cluster-cloud systems under conditions of non-isolation and significant non-stationarity of stellar and gas subsystems in a regular field. A number of estimates of the dynamic masses of the stellar and gas components of the system are made without using the virial theorem for zero and positive values of the total energies (E) of the system as a whole and (E_{2}) of its gaseous subsystem. The well-known estimates of the free-fall time (tau_{textrm{ff}}) for fragments in the force field of a sphere of uniform and inhomogeneous density sphere simulating a system of gas and stars are refined. The estimates of the (tau_{textrm{ff}}) quantities are supplemented by estimates of the radial velocities (v_{r}) of the fragments in such systems. A number of relations between the parameters of the stellar and gas subsystems in the considered models of embedded clusters are obtained. It is shown that instead of one virial coefficient to describe the system, it is necessary to use three coefficients, the formulas for which are given. The relations make it possible to estimate the dynamic masses of non-isolated and non-stationary subsystems from data on the structural-dynamic characteristics of an embedded cluster. It is shown that the ratio ({overline{v}}_{c,1}^{2}/sigma_{1,v}^{2}>4), where (sigma_{1,v}^{2}) is the mean square of the velocities of the stellar subsystem in the case of its virial equilibrium, and ({overline{v}}_{c,1}^{2}) is the mean square of the critical velocities of the stars in this subsystem. It is shown that embedded clusters with parameters (x=R_{1}/R_{2}) and (mu=M_{1}/M_{2}) have maximum values ({overline{v}}_{c,1}^{2}/sigma_{1,v}^{2}) along some curve in the ((x,mu)) space ((M_{i}) and (R_{i}) are the mass and radius of the (i)th subsystem). The embedded clusters with parameters ((x,mu)) close to this curve are the least susceptible to destruction space relaxation processes. It is shown that, depending on the initial energies (E) and (E_{2}), the masses of a subsystem of stars in an embedded cluster can be much smaller than the virial masses of this subsystem. This result is also of particular interest for estimating the dynamic masses of galaxy clusters. It is noted that an increase in the degree of non-stationarity of the considered models of embedded clusters leads to a decrease in the periods of oscillations of the stellar subsystem.