Astrophysical Bulletin最新文献

The unequal distribution of the position angles of 3733 extended radio sources from the F1912 catalog in the range of redshifts up to 5.56 allows one to assert that the anisotropy of the spatial orientation of objects is real and not local.

We present the results of spectropolarimetric observations of 107 chemically peculiar (CP) stars carried out in 2017 with the SAO RAS 6-m telescope using the Main Stellar Spectrograph and a circular polarization analyzer. For each object, we measured the longitudinal magnetic field (B_{e}) (using both the classical and regression methods) and radial velocity (V_{r}), and estimated its fundamental parameters ((T_{textrm{eff}}), (log g), and (v_{e}sin i)). Observations of standard stars with zero or well-known magnetic field confirmed the stability of the instruments and data reduction techniques. As a result of this analysis, a magnetic field was detected for the first time in 11 stars: HD 16145, HD 22032, HD 34889, HD 37333, HD 37808, HD 112118, HD 180058, HD 188862, HD 294046, BD +45({}^{circ}) 4114, and BD +80({}^{circ}) 87. Thus, the total number of magnetic CP stars discovered at the BTA between 2007 and 2017 reached 75. The complete measurement results are published in the paper’s tables and are available online in the VizieR database.

In this paper, we consider one possible mechanism leading to the ultra-slow rotation of individual magnetic stars called super-slowly rotating Ap stars (ssrAp stars). The periods of such objects sometimes exceed hundreds of years. It is believed that they acquired their slow rotation even before the stars entered the main sequence (MS). To explain this phenomenon, we turned to a propeller mechanism model for a magnetic star moving in the interstellar medium. As an example of the potential efficiency of the proposed mechanism, we considered the typical ssrAp star, 33 Lib (HD 137949). A detailed justification using modeling requires solving a multiparameter problem. At the same time, it can be argued that in certain cases, the considered version of ‘‘magnetic’’ braking is capable of effectively slowing the rotation of a star.

We present the results of analyzing the radio variability of the source S255IR NIRS3 following an accretion event. The source was observed at two epochs: in January–March 2017 at frequencies of 0.3–10 GHz and in March 2019 at 1.32–1.42 GHz using the GMRT and VLA observatories. The 2017 data show that the spectrum is well described by a power-law dependence, (F_{nu}simnu^{0.50pm 0.02}), over the entire frequency range. Such a spectral index is typically attributed to a combination of thermal bremsstrahlung emission from the ionized gas with both optically thick and optically thin components. No evidence for nonthermal emission or emission solely from an optically thick component is found at the low-frequency end of the spectrum. In contrast, the 2019 observations in the range of 1.32–1.42 GHz yield a spectral index of (1.58pm 0.03), which is characteristic of predominantly optically thick thermal emission from the ionized gas. This change in behavior may be explained by a transition from jet-dominated emission in 2017 to emission dominated by an ultracompact H II region in 2019. The observed flux density is (3.93pm 0.10) mJy in 2017 (at 1.42 GHz) and (3.58pm 0.16) mJy in 2019 (1.37 GHz). The emission measured in 2017 is (EMgtrsim 3times 10^{8}) pc cm({}^{-6}).

We constructed 2D model of the Galaxy which initially included an analytical bar, bulge, disk and halo. The model disk formed the outer elliptical resonance rings (textrm{R}_{1}) and (textrm{R}_{2}) located near the Outer Lindblad Resonance (OLR) of the bar, as well as an inner resonance ring r located near the corotation radius (CR). As the density of stars in the elliptical rings increased, we introduced additional gravitational perturbations created by the rings. The radial component of gravitational perturbations from the elliptical rings, (F_{R}), at a point with the Galactocentric coordinates ((R), (theta)) was represented as a combination of three polynomials in powers of (R/R_{e}) or (R_{e}/R), where (R_{e}) is the distance to the midline (middle) of the ring at a given angle (theta). The azimuthal component of the disturbances, (F_{T}), was calculated from the force (F_{R}). The difference between the values of the force (F_{R}) ((F_{T})) calculated using the numerical differentiation of the potential and using the analytical representation does not exceed 5.7(%) (1.3(%)) of the maximum value of the force (F_{R}) produced by the elliptical rings. In general, the gravity of the elliptical rings had little effect on the process of adjustment of epicyclic motions near the bar’s OLR.

Results of spectro-photometric monitoring of the classical T Tauri star RY Tau are presented. The observation series span 220 nights from 2013 to 2024. During the observation period, the stellar brightness varied within the range of (V=9^{textrm{ m}}{-}11^{textrm{m}}). The rotation axis of the ‘‘star + accretion disk’’ system is tilted at a large angle, so the line of sight intersects the wind region and accreting flows in the stellar magnetosphere. Variability in the short-wavelength wing of the H(alpha) emission line and the profile of the D Na I resonance doublet are analyzed. It is shown that the wind and accretion flows vary on a time scale of approximately 20 days. When the predominant flow direction changes, a time lag is observed: initially, accretion increases, and after two days, absorption in the line-of-sight wind decreases. It is concluded that the spectral line profiles are formed in the magnetospheric accretion flows and the conical wind originating from the boundary of the stellar magnetosphere. The time lag is determined by the tilt of the magnetic dipole and the opening angle of the conical wind. It is assumed that RY Tau operates in an unstable propeller mode, and fluctuations in the accretion and wind flows are caused by density waves in the accretion disk.

We present here the results of analyzing the activity of the young solar-type star (spectral class G4 V) TIC 434398831 belonging to the Moving Group Theia 116 aged approximately 61 Myr. The atmospheric mass loss estimates of the TIC 434398831 b and c planets are also found. Using the data from the TESS mission, the rotation period of the star ((Papprox 1overset{textrm{d}}{.}75)) is determined, and a hypothesis is put forward regarding the possible evolution of spots (cool regions) on its surface. For TIC 434398831, the differential rotation parameter of the star is found to be (DeltaOmega=0.081) rad/day. The areas of cool spots on the surface of the star are estimated to exceed manifold the maximum area of spots on the Sun varying for different sectors in the range of 47 140–103 090 MSH. In addition, the properties of the TIC 434398831 flare activity are studied. For the most reliable event, the relative duration of the flare is measured (about 50 s), the emitted energy was (2.1times 10^{33}) erg. According to the Kamogata Wide-field Survey (KWS), the long-term activity cycle of the star is found to be 2500 days (6.8 years). The results of calculations of the atmospheric mass loss values for the planets TIC 434398831 b and c ((dot{M})) are presented using two atmospheric loss models: with an energy constraint (EC) and with a hydrodynamic approximation (HA) for two values of the (log R^{prime}_{HK}) parameter (the XUV photon-flux values). Calculations with the HA model yield lower estimates of the (dot{M}) parameter. The ranges of the (dot{M}) parameter variations for TIC 434398831 b lie in the interval from (1.8times 10^{10}) to (1.7times 10^{9}) g s({}^{-1}) (the model with EC) and from (5.1times 10^{9}) to (4.8times 10^{8}) g s({}^{-1}) (the model with HA), and for TIC 434398831 c they are from (1.7times 10^{10}) to (1.6times 10^{9}) g s({}^{-1}) (the model with EC) and from (4.3times 10^{9}) to (4.0times 10^{8}) g s({}^{-1}) (the model with HA).

A kinematic analysis of the young stellar association TW Hya has been performed. The components of the displacement matrix in the Ogorodnikov–Milne linear model have been estimated both graphically and by solving the basic kinematic equations. The association’s volume expansion with the coefficient (K_{xyz}=103pm 9) km s({}^{-1}) kpc({}^{-1}) was confirmed, which yields a dynamical age estimate of (t=9.7pm 0.8) Myr. Using the graphical method, estimates of the association proper rigid-body rotation parameters (omega) around the galactic axes (x) and (y) have been obtained for the first time, with velocity values in the range of 50–70 km s({}^{-1}) kpc({}^{-1}) and errors in their determination of 14–19 km s({}^{-1}) kpc({}^{-1}). However, these values are not confirmed by another method. For example, when solving kinematic equations using only proper motions, all three components of the rigid body rotation do not differ significantly from zero, ((omega_{x},omega_{y},omega_{z})=(4,7,11)pm(5,5,5)) km s({}^{-1}) kpc({}^{-1}).

We present a sample of High-Frequency Peaked Radio Source (HFP) candidates from the AT20G catalog with spectral indices of the optically thick emission region (alpha_{textrm{below}}) exceeding (+0.5), aimed to study their spectral properties. The sample includes 269 objects, about 70(%) of which are quasars. Using the CATS database, we construct the spectra of the sources and determine their main parameters: the spectral indices below and above the peak ((alpha_{textrm{below}}), (alpha_{textrm{above}})), the peak frequencies (nu_{textrm{obs}}), the flux densities at the peak frequency (S_{textrm{peak}}), and the half-widths of the peak in the radio spectra. The spectral flux densities of the sources were obtained at different telescopes and often over different observation epochs. The spectral analysis shows that we are dealing with a sample consisting of HFP sources, whose properties are fairly uniform and whose peak frequencies are (nu_{textrm{obs}}>5) GHz. Most of the sources (67(%)) have no data at the frequencies below 0.8 GHz. One hundred eighty-seven sources have ultra-inverted spectra ((alpha_{textrm{below}}>+0.7)), which make up 3.2(%) of all the sources in the AT20G catalog and 70(%) of all the sources in our sample. The calculations show that the sample consists of compact objects, whose radio luminosity at the frequency of 20 GHz lies in the range of (10^{23}{-}10^{30}) W Hz({}^{-1}), the angular sizes of the emitting regions of the sources are 0.002–0.25 mas, the linear sizes are from 0.2 to 30 pc. The dependence of the intrinsic peak frequencies of radio sources from their angular sizes is in a good agreement with the previously discovered relation for CSS and GPS objects. Based on the information provided by the CATS database, the radio source variability indices are estimated. A variability of 25(%) or higher was found for seven quasars, five of which are blazars. A comparison of the redshift dependences ((z)) of (R)-band magnitudes reveals that most of the HFP galaxies in our sample follow the Hubble relation earlier obtained for the GPS galaxies, and can hence be candidates ‘‘young’’ radio source candidates.

The increase of metallicity in the galactic interstellar medium occurs via the interaction of many physical processes. These processes differ by mass and chemical composition of the matter delivered into the interstellar medium. Massive supernovae have masses from 8 to 100 (M_{odot}) and, during their explosions, eject the maximum amount of heavy elements into the surrounding space. The consequences of such outbursts are most easily detected in galaxies having the lowest masses. Based on the relationship between the luminosities of galaxies and their brightest stars, as well as theoretical models of massive supernovae and isochrones of stars with masses of 8.3–8.7 (M_{odot}), we determined that galaxies with luminosities below (M_{B}geq-12overset{textrm{m}}{.}5) should be devoid of stars with masses greater than 8 (M_{odot}). This means that massive supernovae cannot form in such galaxies. Hence, the galaxies are deprived of their main source of metal enrichment. This constraint should be observed as a metallicity drop in galaxies at (M_{B}=-12overset{textrm{m}}{.}5). Based on the published data, a ‘‘luminosity–metallicity’’ diagram has been constructed, which indeed shows a metallicity jump at luminosities above (M_{B}=-12overset{textrm{m}}{.}5). In galaxies of even lower luminosity, massive supernovae never flare up and the metallicity of the interstellar medium increases due to the stellar wind and thermal pulsations of AGB (TP-AGB) stars.