Astrophysical Bulletin最新文献

We present an analysis of the relative abundance features of a number of chemical elements in the atmospheres of metal-rich (({textrm{[Fe/H]}}>-1)) Galactic-field RR Lyrae variable stars and the kinematic characteristics of these stars. We have previously shown that the relative abundances of some (alpha) elements: magnesium, silicon, calcium, and to a greater extent of titanium, as well as yttrium and scandium in such stars are lower than in most other types of stars bearing similar metallicity. It is found here that some of these metal-rich RR Lyrae stars also have very low relative abundances of sodium, aluminum, and nickel. The orbital parameters of all the metal-rich RR Lyrae variables studied in this paper are typical of the Galactic thin or thick disk objects, however, the unusual chemical composition let us to suggest a possible extragalactic origin for some of them.

The structure of sound waves in baryonic gas generated during the evolution of spherically symmetric dark matter halos with a mass less than the Jeans mass has been calculated. In this case, the source of the gravitational field that creates the wave can be at both the linear stage (evolving perturbation in dark matter) and the nonlinear stage (separated and virialized object). Peculiar motions of baryons in a sound wave in the second order in speed cause the absorption of relict radiation in the 21 cm line. It is shown that this additional absorption on sound waves is a fraction of a percent at redshifts (zsim 15{-}20) of the absorption value in the model of a homogeneous Universe, however, the additional absorption can be larger in the case of a non-standard spectrum of cosmological perturbations of matter density on small scales.

The rest wavelengths of diffuse interstellar bands (DIBs) are parameters of fundamental importance owing to the lack of unambiguous identification for these mysterious features. Usually the wavelengths of DIBs are estimated using known interstellar atomic or molecular lines serving to shift the spectrum to the rest wavelengths velocity scale. However, the latter may not share in fact the same parts of a cloud which the carriers of diffuse bands occupy. Here we argue that the narrowest known diffuse interstellar band 6196 Å is the best reference feature for building the ‘‘interstellar’’ wavelength scale. Also, we offer the geometrical center of gravity (the effective wavelength) of the diffuse bands as a rest wavelength measurer for these generally asymmetric features. We assessed the magnitude of variation of the center of gravity of the diffuse bands at 5780, 5797, 6284, and 7224 Å measured in 41 lines of sight in the broad range of interstellar reddening ((E_{B-V}) varies in the range of 0.13–1.06 stellar magnitudes) with the lack of evident Doppler-split in the profiles of interstellar atomic/molecular lines. We demonstrated that diffuse bands show gradual broadening of their profile widths, accompanied with the red-shift of the center of gravity, i.e., the red wing of the profiles is their most variable part. To estimate the width of the diffuse bands, we offer to apply an ‘‘effective width’’ parameter (W_{textrm{eff}}), which is the relation of the equivalent width ((EW)) to the depth of the feature. In contrast to habitual half width at half maximum ((FWHM)), the parameter originally introduced by us in 2008 (Galazutdinov, LoCurto, Krełowski) is not sensitive to the profile shape irregularities. (W_{textrm{eff}}) provides lower measurement uncertainties than the (FWHM) does. The gradual increase of (W_{textrm{eff}}), accompanied with the red-shift of the center of gravity of the profile, may suggest populating of higher transitions of the P branch of the bands of molecules, assuming the latter are DIB carriers. It is also shown, that diffuse bands are broader although more shallow in the harsh conditions of (sigma)-clouds, where atomic and molecular lines are weakened and/or totally absent. The difference of the effective width of DIBs in (zeta) and (sigma) clouds is discussed as well.

We report the results of laboratory studies of the main optical properties of the slitless spectrograph developed for a small telescope with a 0.5 m-diameter primary mirror and a focal ratio of (1:6.8). The spectrograph operates in the 450–950 nm wavelength interval and has a field of (35overset{prime}{.}6times 7overset{prime}{.}2). Its distinctive feature is the use of a composite grism subdivided into two subapertures with independently optimized parameters. Measurements show that the use of such a grism makes it possible to achieve a spectral resolving power (R) from 461 to 1041 with the grating diffraction efficiency as high as 45(%). We demonstrate that our solution provides better optical characteristics compared to the classical grism and that our measurements agree well with the results of modeling.

The structure of a solar coronal filament with plasma parameters typical for quiescent solar prominences (particle concentration (10^{10}{-}10^{12}) cm({}^{-3}) and temperature in the coldest part ranging from 4000 to 20 000 K), located horizontally in the corona at heights of several tens of thousands of kilometers has been calculated. The filament is considered as the upper part of a slightly curved twisted magnetic loop, the legs of which are anchored in the photosphere. The magnetic field of the filament is helical (twisted). To maintain transverse equilibrium, an external longitudinal field is necessary. There is also a weak transverse magnetic field, which has a significant effect on the distribution of pressure and gas density in the filament. A characteristic feature of the model, reproduced theoretically for the first time, is the presence of a rarefaction (cavity) outside the filament. The fine filamentary structure of the prominence, consisting of dense and cold fibrils immersed in a weak uniform horizontal magnetic field, has been modeled. It is shown that the observed vertical movements of plasma elements in the prominence, usually interpreted as manifestations of ‘‘thermal convection’’ in its body, can be due to vertical mechanical displacements of individual magnetic fibrils that make up the body of the prominence. Shear (slip) plasma movements on the photosphere can change the sign of the weak transverse field and thus reduce the plasma density on the filament axis, i.e., bring the density of the electric current on its axis closer to the critical value at which the drift velocity of electrons equals the ion sound speed.

This paper is devoted to studying the variability of the (gamma) Cas variable star SAO 49725. We analyze both the optical and X-ray spectra of the star. The line profile variability in the spectrum of SAO 49725 was discovered on short (70–223 minutes) scales. Regular variations of the SAO 49725 light curves with a period of 1.1989 days are detected using the photometric light curves obtained with the TESS satellite, identified with the rotation period of the star. The pattern of the photometric variability of SAO 49725 according to the TESS data significantly varies at different observational epochs. The TESS components of the SAO 49725 light curves with the periods of about (3{-}21) days may be instrumental. The presence of variations with the period (P=230pm 178) minutes in the SAO 49725 X-ray light curves, obtained by the XMM-Newton telescope, is suspected.

We have selected candidate massive stars in the galaxy IC 342 based on archival images from the Hubble Space Telescope and images from the 2-m telescope at the National Astronomical Observatory, Rozhen, Bulgaria. Spectral observations of 24 out of 27 selected stars are carried out with the 6-m BTA telescope of SAO RAS and with the 3.5-m Apache Point Observatory telescope (USA) as part of the program for searching for bright massive stars in galaxies outside the Local Group. Our analysis reveals that 12 objects have spectra lacking prominent features, except for the emission lines of the surrounding nebulae and are identified as single supergiants of classes O9 to F5 or spatially unresolved young compact clusters. One source with an absorption spectrum probably belongs to our Galaxy. The spectra of seven other objects show features typical of Wolf–Rayet stars or compact clusters containing Wolf–Rayet stars. Another source is a compact supernova remnant. Two other objects are tentatively classified as cold LBV candidates, and one object is classified as a B[e]-supergiant candidate.

We present a refined speckle-interferometric orbit of a binary system (mu) Cet, with the main component studied based on the analysis of photometric and spectroscopic data, obtained with the SAO RAS 6-m telescope. The object was initially classified as a giant with chemical composition anomalies. As a result of our analysis, we conclude that the star belongs to the Main Sequence, to the class of non-peculiar stars. Analysis of photometric data from the TESS mission indicates that the main component of the system belongs to the (gamma) Dor pulsators.

The paper presents and analyzes a summary of magnetometric studies of single white dwarfs (WD) conducted at SAO RAS jointly with a number of other observatories. The goals of the studies are to search for regular large-scale magnetic fields in these stars and to construct a probability distribution of WD occurrence depending on the strength of these fields. Based on the analysis, the WDs were determined whose magnetospheres do not change their configurations for a long time, from several tens to hundreds of years at least, and possibly more. These stars can be used as standards of circular polarization. Using data from modern surveys and SAO RAS observations, versions of the observed probability distributions of WDs by their surface magnetic fields in the range of (10^{3}{-}10^{9}) G were constructed. The distribution of WDs with fields from (10^{6}) G to (10^{9}) G is well described by a power-law dependence. In the region of smaller fields the dependence is violated, demonstrating a selection ‘‘dip’’. The selection is caused by the technical complexity of magnetometric studies of WDs. The paper also discusses the physical nature of the selection associated with the complication of the interaction of global magnetic fields of low intensity (less than 10 kG) with dynamic processes in the surface layers of WDs. In particular, convection is capable of destroying the global symmetry of the surface magnetic field with an intensity of several kilogauss. Based on the analysis of the obtained distributions, it is concluded that all WDs with surface fields above several tens of kilogauss are carriers of regular global fields damped on times of (10^{10}) years. Magnetic fields with intensities of several kilogauss and lower lose their global structure, fragmenting into spots, which complicates and even makes impossible their detection by standard spectropolarimetric methods. Confirming examples and recommendations for improving the methodology of magnetometric observations of degenerate stars with weak magnetic fields are given.

We continue to study the ultra-luminous X-ray source NGC 7793 P13 in the optical range. In this work, we are testing the model of a spherically symmetric wind atmosphere of the donor star, previously identified as a B9 Ia supergiant. The model spectrum has shown good agreement with the observed one at a relatively high mass loss rate of (dot{M}approx 6times 10^{-6}M_{odot}text{ yr}^{-1}); other parameters turned out to be close to those expected for late B-supergiants. The increased mass loss rate can be explained by the high rotation velocity of the star. In addition, we have qualitatively demonstrated the effect of X-ray irradiation on the observed spectrum and discuss the fundamental possibility of wind acceleration under conditions of powerful irradiation.