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

We propose a model of deep and prolonged eclipses in young UX Ori stars. Some of these events last for decades and existing models cannot explain them. We show that such eclipses can be caused by the infall of gas and dust clumps from the remnants of the protostellar cloud onto the protoplanetary disk. The perturbation in the disk caused by the infall of a clump leads to a burst of accretional stellar activity and, as a consequence, to a strengthening of the disk wind. If the circumstellar disk is tilted at a small angle to the line of sight, then the dust raised by the wind from the disk surface can cause a dramatic decrease in the stellar brightness that can last for decades.

We have developed the method of periodic principal components for signals with a quasi-periodic dynamic spectrum characteristic of radio pulsars. The method is based on an analysis of the eigenvectors and eigenvalues of the signal frequency–time correlation matrix averaged over many pulsar rotation periods. Using the observations of PSR B0329(+)54 with the radio telescope at Pushchino Radio Astronomy Observatory near a frequency of 111 MHz in a 2.5 MHz band as an example, we show that even for short data intervals (a few minutes) the developed method allows one to identify up to nine pulse components of the pulsar, to estimate the correlation between them, and to find the period of Faraday modulation for each component as well as its relative phase and frequency–time chirp rate, i.e., it allows the structure of the emission source to be judged.

Based on the speckle observations of the wide double star ADS 15571 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences in 2014, we have confirmed the existence of a close companion to component A that was previously detected from astrometric observations at the Pulkovo Observatory. An extension of the BTA observations from 2014 to 2022 has allowed 28 positions of the companion relative to the primary star to be obtained. From this series we have constructed the relative orbit of the companion and determined the sum of the masses of subsystem A ((1.686pm 0.014) (M_{odot})). A comparison of this orbit with the orbit of the photocenter of component A constructed from Pulkovo photographic observations has also allowed the mass ratio of the primary star and the companion and their individual masses to be estimated: (M_{textrm{Aa}}=(1.10pm 0.07)) (M_{odot}) and (M_{textrm{Ab}}=(0.59pm 0.07)) (M_{odot}). Based on the estimates of the magnitude difference between the two stars of the system ADS 15571A, we have estimated the spectral types of the components: ADS 15571Aa—F8V; ADS 15571Ab—K5V–K5.5V. The speckle observations of component B have shown that it has no resolvable companions.

We have constructed a model for the passage of gamma-ray burst radiation through a dense molecular cloud. In our calculations we take into account the main radiation–cloud material interaction processes: the ionization of H and He atoms, the ionization of metal ions with the emission of Auger electrons, the ionization and photodissociation of H({}_{2}) molecules, the absorption of ultraviolet radiation in the H({}_{2}) lines of the Lyman and Werner bands, and the vaporization of dust grains. The ionization of metal ions by X-ray radiation determines the gas ionization fraction in the region where the gas is predominantly neutral. The photoionization of the inner electron shells of ions is accompanied by the emission of Auger electrons, giving rise to metal ions in a high ionization state. In particular, the column densities of Mg, Si, and Fe ions in the ionization states I–IV are much lower than the column densities of these ions in the ionization state V or higher. The photoionization of metal ions by ultraviolet radiation occurs only at distances smaller than the dust vaporization radius and for neutral atoms with an ionization threshold below 13.6 eV. The results of our calculations have confirmed the previously made assumption that the ionization of He atoms plays an important role in the absorption of radiation in the X-ray wavelength range. For a low metallicity, (textrm{[M/H]}leq{-}1), the role of helium atoms is dominant.

Based on published data, we have constructed models for the magnetic structures of three stars with a relatively strong magnetic field. They all have a dipolar structure and do not differ in their properties from the bulk of the magnetic stars. However, they, as well as some other objects with a strong magnetic field, do not obey the direct dependence of the rotation period on the stellar magnetic field strength that is expected from the hypothesis about the loss of angular momentum by its transfer to the surrounding protostellar clouds through magnetic field lines.

An H({}_{2})O maser flare detected in July 2023 in the star-forming region DR21OH when monitoring the continuum emission in DR21 with PRAO RT22 is reported. These observations were part of a program to study the characteristics of the antenna and the atmospheric absorption at a wavelength of 1.35 cm. Subsequent access to archival data and new measurements have shown that the detected flare in 2023 was not the only one in the source, and DR21OH is highly variable in the H({}_{2})O line at 22 GHz with a rather unpredictable character. Based on continuum measurements in DR21, we have estimated the effective area of RT22.

We present new radar images and polarimetric data for the candidate landing sites of the Russian Luna-25 spacecraft near the Manzinus and Boguslawsky craters in the south polar region of the Moon. The images were obtained with the 64-m TNA-1500 antenna at the Bear Lakes Satellite Communications Center of the Special Design Bureau of the Moscow Power Engineering Institute and the 13.2-m RT-13 radio telescope at the Svetloe Observatory of the Institute of Applied Astronomy of the Russian Academy of Sciences in a bistatic configuration at a wavelength of 4.2 cm. At this wavelength the radar signals can penetrate into the lunar regolith to a depth up to 1 m and are sensitive to surface and suspended rocks with a diameter of about 1 cm or more. A spatial resolution ({sim}80) m per pixel was achieved through the focused processing algorithm that avoids the radar image smearing at a long integration time. The receiving-system noise temperature measurements during the entire observation session provided a reliable estimate of the circular polarization ratio (CPR) of the echo signal. Analysis of the radar images obtained revealed regions with high radar backscatter and CPR. The number and distribution of rocks and irregularities with sizes comparable to the radar wavelength on the surface and in the near-surface layer of regolith were estimated. As a result of the radar data analysis, we conclude that the surface and the near-surface regolith layer of the main site are smoother than those of the reserved site, which makes it preferable for landing. Thus, the resulting new radar images and CPR maps can be used in planning future lunar missions.

We have carried out a deep survey of the M81 field in the 25–60 keV energy band based on long-term (2003–2023) INTEGRAL observations. A record sensitivity of 0.16 mCrab at a detection significance of (4sigma) has been achieved in the central part of the field owing to the long accumulated exposure (19.2 Ms). The total area of the survey is 1004 deg({}^{2}) at a sensitivity level better than 0.72 mCrab. We have produced a catalog of sources detected at a significance level higher than (4sigma). It contains 51 objects most of which are active galactic nuclei (AGNs). The median redshift of the Seyfert galaxies in the catalog is (z=0.0366). Six sources have not been detected previously in any of the X-ray surveys. According to the available indirect data, all of them and two more sources that have already been entered previously into the INTEGRAL survey catalogs can also be AGNs, including those with strong internal absorption.

We analyze the accuracy of estimating the stellar parameters (effective temperature (T_{textrm{eff}}), surface gravity log (g), metallicity [Fe/H], angular diameter (theta)) and the color excess (E(B-V)) obtained by the (chi^{2}) minimization method from broadband photometry using the Johnson–Cousins, 2MASS photometric systems, and ATLAS9 model stellar atmospheres as an example. The method has been tested for the internal accuracy and with real objects: isolated stars and stars from clusters. A high photometric accuracy ((sigma_{m}leq 0.01ldots 0.015^{m})), at which the errors are ({sigma}T_{textrm{eff}}approx 2{-}5{%}), (sigma) log (gapprox 0.6), (sigma[textrm{Fe/H}]approx 1), (sigmathetaapprox 2%), and ({sigma}E(B-V)approx 0.02{-}0.07^{m}) for stars with (T_{textrm{eff}}lesssim 8000) K, is required to obtain acceptable results. For hotter stars ({sigma}T_{textrm{eff}}) reaches (10%), (sigma) log (gapprox 0.6) dex, (sigmathetaapprox 3%), and ({sigma}E(B-V)approx 0.02{-}0.07^{m}), but the determination of the metallicity becomes impossible. We show that the method can be used to estimate the color excess in stellar fields. The limitations of the method are discussed.

Here we present the results of a numerical study of the main reactions that determine the methyl formate abundance under conditions of a low-mass protostellar object with both normal and enhanced cosmic-ray ionization rates. The estimations of the contribution that dust chemistry has on the gas-phase methyl formate abundance are made. The impact of the transition from the prestellar to protostellar phases on the methyl-formate chemistry is studied as well.