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

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.

The results of a study of the short gamma-ray burst GRB 231115A in the X-ray and gamma-ray ranges are presented, based on data from the INTEGRAL and Fermi space observatories. The source of the burst is localized by the IBIS/ISGRI telescope of INTEGRAL observatory with an accuracy of ({leq}1.!!^{prime}5), it is located in the Cigar Galaxy (M 82). Early follow-up observations of the burst localization region were carried out in the optical range with the 36-cm telescope of the ISON-Kitab observatory and the 70-cm telescope AS-32 of the Abastumani Astrophysical Observatory. The optical emission has not been detected. The proximity of the host galaxy ((D_{L}simeq 3.5) Mpc) significantly limits energetics of the event ((E_{textrm{iso}} sim 10^{45}) erg) and allows us to interpret the burst as a giant flare of a previously unknown soft gamma repeater (SGR) which is an extreme manifestation of the activity of a highly magnetized neutron star (magnetar). This conclusion is confirmed by the energy spectrum atypically hard for cosmological gamma-ray bursts, as well as the absence of optical afterglow and gravitational wave signal, which should have been detected in the LIGO/Virgo/KAGRA experiments if the burst was caused by a merger of binary neutron stars. The location of the burst in the (E_{p,i}{-}E_{textrm{iso}}) and (T_{90,i}{-}EH) diagrams also suggests that GRB 231115A was a magnetar giant flare. This is the first well-localized giant flare of an extragalactic SGR.

We present the results of the infrared photometric observations in the (JHKLM) bands and infrared spectroscopic observations in the range 1–2.5 (mu)m for the carbon Mira star T Dra performed from 2019 to 2023. An analysis of the photometric observations shows the presence of both pulsational brightness fluctuations with an amplitude falling from (1.2^{m}) in the (J) band to (0.84^{m}) in the (L) and (M) bands and a linear trend in the mean brightness with a value of (0.0007^{m}/d) in the (J) band. In the infrared spectrum of T Dra we have identified the absorption bands of C({}_{2})H({}_{2}), HCN, CN, CO, and C({}_{2}) molecules. The depth of the absorption band at 1.53 (mu)m has been found to depend on the star’s brightness. We show that the CO (lambda 2.29) (mu)m bands have a high contrast, suggesting their formation not in the stellar atmosphere but in the circumstellar dust envelope. We present the spectral energy distribution of T Dra in a wide spectral range from which the bolometric fluxes at maximum and minimum brightness have been estimated: (4.8times 10^{-10}) and (2.5times 10^{-10}) W m({}^{-2}), respectively. For the distance to T Dra of 944 pc they correspond to the star’s luminosity at maximum brightness (L_{textrm{max}}approx 13,300;L_{odot}) and at minimum brightness (L_{textrm{min}}approx 6900;L_{odot}). We have modeled the radiative transfer in the circumstellar envelope of T Dra and estimated the parameters of the star and the envelope: (T_{textrm{eff}}=2400) K, (R_{*}=670R_{odot}), (R_{textrm{in}}=5{-}6) AU, (R_{textrm{out}}sim 50,000) AU, (tau_{V}=3.5), (M_{textrm{dust}}=4{-}8times 10^{-5};M_{odot}), and (dM/dtsim 1.5times 10^{-6}) (M_{odot}) yr({}^{-1}).

We present the results of our study of the influence of stellar activity on the efficiency of the plasma radio emission generation mechanism and the properties of this emission in the atmospheres of exoplanets with a weak magnetic field. The plasma generation mechanism can be efficiently realized in the case where the Langmuir frequency exceeds the electron gyrofrequency, and the electron cyclotron maser is inefficient. This mechanism, which depends significantly on plasma parameters, suggests the generation of plasma (quasi-static) waves by energetic electrons followed by their conversion into electromagnetic radiation. The stellar wind, depending on its intensity, can modify significantly the plasmasphere of an exoplanet and change its parameters. Using the interaction of the exoplanet HD 189733b with a stellar wind of various intensities from the central star as an example, we show that the plasma mechanism can be realized at any stellar wind intensity, only the requirements for the parameters of the plasma mechanism change. In particular, the plasma wave energy density needed to generate a radio flux accessible to detection by modern radio-astronomical means changes, and its frequency range changes. The latter will allow the detected radio emission to be used as an indicator of the activity of the parent star.

The flute instability at the inner edge of a thin diamagnetic accretion disk is analyzed. The magnetic field configuration model from Aly (1980) is used. We have analyzed a modified dispersion relation for the flute instability that takes into account the Keplerian disk rotation. We have derived the inner radius of the accretion disk within our analysis of the flute instability. We show that the inner radius does not differ from the Alfvén radius for spherical accretion to within a dimensionless coefficient, with the proportionality coefficient depending only on the turbulence alpha parameter and the relative disk thickness ((h/r)).

Superbursts of neutron stars are rare but powerful events explained by the explosive burning of carbon in the deep layers of the outer envelope of the star. In this paper we perform a simulation of superbursts and propose a simple method for describing the neutrino stage of their cooling, as well as a method for describing the evolution of the burst energy on a scale of several months. We note a universal relation for the temperature distribution in the burnt layer at its neutrino cooling stage, as well as the unification of bolometric light curves and neutrino heat loss rates for deep and powerful bursts. We point out the possibility of long-term retention of the burst energy in the star’s envelope. The results can be useful for interpretation of superburst observations.