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

We present the observations of the carbon-rich post-AGB object IRAS 22272(+)5435 performed in the 550, 625, and 880 nm bands by the method of differential speckle polarimetry with the 2.5-m telescope of the Caucasus Mountain Observatory. A shell has been detected at an angular distance of (1^{primeprime}) from the star in all bands. The infrared (IR) source IRAS 22272(+)5435 is associated with the semiregular variable star V354 Lac. Apart the quasi-periodic variability caused by pulsations, an increase in the near-IR ((KLM)) brightness due to an additional dust ejection was observed in the period from 1996 to 2004 (Ikonnikova et al. 2025). We have constructed a model of the circumstellar dust shell that reproduces well (within the adopted model assumptions) the observed spectral energy distribution and the polarized flux distribution in the visible range. The model is consistent with the observations performed by the method of differential speckle polarimetry in 2020. We have obtained the following parameters of the star and its dust shell. For the distance (d=1410) pc derived from the Gaia DR3 parallax the luminosity of the star is (L=6600,L_{odot}). The dust shell in our model consists of four components formed by the isotropic wind and the superwind at the AGB stage as well as by the isotropic wind and the equatorial ejection at the post-AGB phase. The dust masses in these shells are (3times 10^{-9}), (6.9times 10^{-7}), (3times 10^{-4}), and (1.3times 10^{-4},M_{odot}), respectively. The increase in the IR flux in 1996–2004 is explained in the model by the separate ejection of a dust cloud with a mass of (6times 10^{-10},M_{odot}) whose velocity is estimated to be 60 km s({}^{-1}).

The Spectrum-Roentgen-Gamma (SRG) observatory continues to operate successfully in orbit at the Lagrange point L2. The Mikhail Pavlinsky ART-XC telescope has demonstrated high efficiency in conducting X-ray surveys both over large sky regions and the entire celestial sphere. A recently published source catalog, based on data from the first four and partially completed fifth sky scans, contains 1545 objects detected in the 4–12 keV energy range. In this work, using the same sky survey data, we assess the sensitivity to point source detection across the celestial sphere based on X-ray aperture photometry—that is, we calculate the upper flux limit in the 4–12 keV band at any given significance level. The method is implemented using both Poisson statistics and Bayesian inference, with consistent results between the two approaches. This information is important for studying variable and transient X-ray sources, as well as sources that are not detected with sufficient statistical significance in the ART-XC all-sky survey. The ART-XC upper limit service is available at https://www.srg.cosmos.ru/uplim.

Recently, a series of long-term reconstructions of the total solar irradiance (TSI) has been obtained. They indicate that the amplitude of its secular variations does not exceed 1 W/m({}^{2}). Such a small amplitude suggests a very weak influence of TSI on the Earth’s climate change both in the past and in the future. In this paper it is shown that the data on the concentration of cosmogenic beryllium in Central Antarctica ices fit poorly into the small-amplitude scenario. The ({}^{10})Be concentration variations in Antarctic ice indicate that the increase in TSI can reach 1.4–2.7 W/m({}^{2}) after the end of the Maunder minimum (the end of the 17th century) and up to 3.4 W/m({}^{2}) after the Spörer minimum (the first half of the 15th century). The causes of the remaining uncertainties and the direction of further studies are discussed.

The process of long-duration stable mass transfer (or stripping) in a close neutron star binary system is possible at a sufficiently large initial asymmetry of the component masses. At the final stage of the evolution of such systems the low-mass neutron star fills its Roche lobe, whereupon its mass is gradually transferred to the more massive component. At some instant of time the transfer stability is lost, causing the minimum-mass neutron star to explode. In the stripping calculations the effect of non-conservative mass transfer has been taken into account for the first time, leading to an increase in the duration of stable mass transfer from a few tenths of a second to a few seconds. This allows the time delay of 1.7 s between the loss of the gravitational-wave signal and the detection of the gamma-ray burst from the multimessenger event GW170817–GRB170817A to be naturally explained. The interaction of the envelope of the exploded minimum-mass neutron star with the matter ejected during non-conservative mass transfer may explain two episodes in the light curve of this gamma-ray burst.

Evolution of stars with initial masses (M_{textrm{ZAMS}}=1.1), (1.3), and (1.5;M_{odot}) and relative mass abundances of metals (Z=0.006) and 0.02 was computed from the main sequence up to the final AGB stage. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of hydrodynamics describing pulsations of red giants, whereas for each evolutionary sequence of Mira variables pulsating in the fundamental mode we determined the theoretical period–luminosity relation. A change in the metal abundance is shown to substantially affect the period–luminosity relation because of significant growth of the slope with decreasing (Z). In particular, Mira variables of the LMC ((Z=0.006)) with periods from 200 to 300 days are brighter by 0.2–0.5 mag than galactic Mira variables ((Z=0.02)) with same pulsation periods. The low boundary of fundamental mode pulsations changes from (Piapprox 70) day for (Z=0.02) to (Piapprox 120) day for (Z=0.006).

The cosmic microwave background absorption intensity in the 21 cm line of neutral hydrogen in the presence of additional power in the form of a ‘‘bump’’ in the spectrum of cosmological density perturbations is calculated. The main absorption-amplifying effect is the earlier birth of the first stars forming an ultraviolet radiation background. This radiation reduces the spin temperature of neutral hydrogen and, thus, amplifies the absorption in the 21 cm line. A comparison of various cosmological models (with and without a bump in the density perturbation spectrum) shows that it is possible to determine the probable position of the bump in the perturbation spectrum and, thus, to reconstruct the spectrum of cosmological perturbations on scales (k>1) Mpc({}^{-1}) from the position of the absorption frequency profile.

We discuss the possibility of the realization of the plasma generation mechanism in the source of decameter radio emission associated with Ganymede and the explanation of the formation of quasi-periodic sequences of bursts of this radiation based on this mechanism. According to the model being discussed, the recorded quasi-periodic sequences of radiation pulses are a consequence of the realization of a pulsating regime of plasma wave conversion into extraordinary electromagnetic waves with a small refractive index in the source. The negative radiation frequency drift observed in the frequency–time spectrogram is due to the group delay of waves with a small refractive index and the dispersion of the medium. Based on the plasma model, we have estimated the plasma parameters in the generation region, which are in agreement with the data obtained through satellite measurements.

We present results of hybrid particle-in-cell simulation of ions 1st order Fermi acceleration at a curvilinear shock front. Using the example of the global model of the Earth’s bow shock, the efficiency of particles injection into the Fermi acceleration process is investigated depending on their impact parameter. It is shown that Fermi acceleration and the formation of a foreshock occur only in quasi-parallel regions. Meanwhile, particles can be injected and gain initial energy in quasi-perpendicular regions through the shock drift acceleration mechanism, and then enter the Fermi acceleration region. Suprathermal particles generated near the quasi-parallel front regions can subsequently propagate along the front to quasi-perpendicular regions. The fraction of particles injected into the acceleration process near the subsolar point of the Earth’s bow shock reaches 20(%). The model allows for the identification of features of the Fermi acceleration process on curvilinear shocks that are significant for application to astrophysical shocks of various scales.

Emission of water molecules cannot be observed from Earth, less abundant isotopologues, such as H({}_{2}^{18})O and HDO, are used to trace water in star-forming regions. The main aim of this study is to determine HDO abundance in the hot core RCW 120 S2. We performed observations of the hot core in the 200–255 GHz range using the nFLASH230 receiver on the APEX telescope. Two HDO lines were detected toward RCW 120 S2. Their intensities are described by excitation temperature ({approx}290) K and gas number density ({geq}10^{9}) cm({}^{-3}). The emission originates from the hot core rather than the warm dense envelope surrounding a central young stellar object. The HDO column density ranges from ((3.9{-}7.9)times 10^{13}) cm({}^{-3}) with the best-fit model value of (5.6times 10^{13}) cm({}^{-3}). The HDO abundance relative to hydrogen is (1.7times 10^{-9}). This HDO abundance value is among the lowest reported for hot cores. Combined with the non-detection of the H({}_{2}^{18})O line, we conclude that protostellar heating in RCW 120 S2 is still in its early stages.

Using results of numerical simulations and galaxy clusters observations, it is shown that the transition from deterministic chaos to hard turbulence in the galaxy clusters magnetized plasmas occurs via a randomization process. The notion of distributed chaos has been used to describe the randomization process. The randomization can be quantified with the main parameter of the distributed chaos, which in turn can be related to magnetic helicity. Spontaneous breaking of local reflectional symmetry (an intrinsic property of chaotic/turbulent motions) generates local helicity even when the global helicity is negligible. It is shown that the magnetic fields can impose their level of randomization on the Faraday rotation maps. Results of the numerical simulations of the galaxy clusters dynamos are in good agreement with this approach, as well as with the results obtained using observations of the Faraday rotation sky.