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

Based on data from the ZTF photometric survey, we have revealed asynchrony of the polar SDSS J085414.02+390537.3. A beat period (P_{textrm{beat}}=24.6pm 0.1) days, during which the system changes its brightness by ({approx}3^{m}), is distinguished in the light curves. Power peaks at the white-dwarf rotation period (P_{textrm{spin}}=113.197pm 0.001) min and orbital period (P_{textrm{orb}}=113.560pm 0.001) min are revealed in the periodograms, with the corresponding polar asynchrony being (1-P_{textrm{orb}}/P_{textrm{spin}}=0.3{%}). The photometric behavior of the polar points to a change of the main accreting pole during the beat period. Based on the Zeeman splitting of the H(beta) line, we have estimated the mean magnetic field strength of the white dwarf to be (B=28.5pm 1.5) MG. The magnetic field strength near the magnetic pole has been found by modeling the cyclotron spectra to be (B=34pm 2) MG. The Doppler tomograms in the H(beta) line exhibit a distribution of emission sources typical for polars in velocity space with evidence of the transition of the accretion stream from the ballistic trajectory to the magnetic one.

We explain the anomalous outburst activity of comet 29P/Schwassmann–Wachmann 1 by the existence of satellites touching the surface of the comet nucleus at the pericenters of their orbits. It is assumed that the satellites move in eccentric orbits and a large amount of dust, the reflection of light from which causes periodic outbursts in brightness (BAA 2023), is ejected as a result of their collisions with the dust layer of the nucleus. Depending on the depth of penetration of the satellites into the dust layer, outbursts in comet brightness of various intensities occur. An improvement of the comet orbit by invoking positional observations allows the preferred direction of the ejection of material to be determined from the photocenter offset, which we interpret as the direction of the velocity vector of the largest satellite at the pericenter. The results of our numerical simulations of the ejection and subsequent motion of dust particles caused by the contact of the satellite with the dust layer of the comet nucleus explain the formation of the structures observed in the comet: the dust jets and their mirror symmetry as well as the extent of the region of material ejection from the surface of the comet nucleus.

We discuss an algorithm whereby the massive galaxy clusters detected in the SRG/eROSITA all-sky survey are identified and their photometric redshifts are estimated. For this purpose, we use photometric redshift estimates for galaxies and WISE forced photometry. To estimate the algorithm operation quality, we used a sample of 634 massive galaxy clusters from the Planck survey with known spectroscopic redshifts in the range (0.1<z_{textrm{spec}}<0.6). The accuracy of the photometric redshift estimates for this sample is (delta z_{textrm{phot}}/(1+z_{textrm{phot}})approx 0.5{%}), the fraction of large deviations is 1.3({%}). We show that these large deviations arise mainly from the projections of galaxy clusters or other large-scale structures at different redshifts in the X-ray source field. Measuring the infrared (IR) luminosities of galaxy clusters allows one to estimate the reliability of the optical identification of the clusters detected in the SRG/eROSITA survey and to obtain an additional independent measurement of their total gravitational masses, (M_{500}). We show that the masses (M_{500}) of the galaxy clusters estimated from their IR luminosity measurements have an accuracy (sigma_{log M_{500}}=0.124), comparable to the accuracy of the mass estimation for the galaxy clusters from their X-ray luminosities.

This paper is an extension of the study by Khamitov et al. (2022) with regard to the catalog and the astrophysical interpretation of the imitation of significant proper motions in active galactic nuclei (AGNs) and quasars based on data from the Gaia space observatory. We present a sample of SRG/eROSITA X-ray sources in the eastern Galactic hemisphere (({0^{circ}<l<180^{circ}})) having significant proper motions in the Gaia EDR3 measurements with the confirmed extragalactic nature of the objects. The catalog consists of 248 extragalactic sources with spectroscopically measured redshifts. The catalog includes all of the objects available in the SIMBAD database and coincident with the identified optical counterpart within 0.5 arcsec. Eighteen sources with spectroscopically measured redshifts from observations with the Russian–Turkish 1.5-m telescope RTT-150 (Khamitov et al. 2022) have been additionally included in the catalog. The sources in the catalog are AGNs of various types (Sy1, Sy2, LINER), quasars, radio galaxies, and star-forming galaxies. The imitation of significant proper motions can be explained (by the VIM effect previously known in astrometry) by the presence of transient events on the line of sight in the vicinity of AGNs and quasars (within the Gaia optical resolution element). Among such astrophysical events are supernova outbursts, tidal disruption events in binary AGNs, the variability of high-mass supergiants, the presence of OB associations against the background of AGNs with a variable brightness, etc. The model of outbursts with a fast rise–exponential decay profile allows the variable positional parameters of most sources observed in Gaia to be described. This approach can be used as an independent way of detecting transient events in the vicinity of AGNs (on scales of several hundred parsecs in the plane of the sky) based on data from the SRG/eROSITA catalogs of X-ray sources and the optical Gaia catalog.

We have estimated the spiral pattern speed in the Galaxy (Omega_{p}) from a large sample of young open star clusters (OSCs). For this purpose, we have used 2494 OSCs younger than 50 Myr. Their mean proper motions, line-of-sight velocities, and distances were calculated by Hunt and Reffert (2023) based on data from the Gaia DR3 catalogue. Three methods have been applied to estimate (Omega_{p}). They all are based on the linear Lin–Shu spiral density wave theory. We have obtained an estimate of (Omega_{p}=24.26pm 0.52) km s({}^{-1}) kpc({}^{-1}) by the first method, which is most reliable in our view, using the velocity perturbations (f_{R}) and (f_{theta}) found through a spectral analysis of the radial, (V_{R}), and residual rotation, (Delta V_{rm circ}), velocities. Using the second method, we have found the velocity perturbations (f_{R}) and (f_{theta}) by solving the basic kinematic equations together with the Galactic rotation parameters and obtained an estimate of (Omega_{p}=23.45pm 0.53) km s({}^{-1}) kpc({}^{-1}). We have found (Omega_{p}=28.9pm 2.8) km s({}^{-1}) kpc({}^{-1}) by the third method based on an analysis of the position angles of OSCs at their birth time (theta_{rm birth}).

We have developed a Monte Carlo code for simulation of X-ray spectra of active galactic nuclei (AGN) based on a model of a clumpy obscuring torus. Using this code, we investigate the diagnostic power of X-ray spectroscopy of obscured AGN with respect to the physical properties and orientation of the torus, namely: the average column density, (langle N_{textrm{H}}rangle), the line-of-sight column density, (N_{textrm{H}}), the abundance of iron, (A_{textrm{Fe}}), the clumpiness (i.e., the average number of gas clouds along the line of sight), (langle Nrangle), and the viewing angle, (alpha). In this first paper of a series, we consider the Compton-thin case, where both (langle N_{textrm{H}}rangle) and (N_{textrm{H}}) do not exceed (10^{24}) cm({}^{-2}). To enable quantitative comparison of the simulated spectra, we introduce five measurable spectral characteristics: the low-energy hardness ratio (ratio of the continuum fluxes in the 7–11 and 2–7 keV energy bands), the high-energy hardness ratio (ratio of the continuum fluxes in the 10–100 and 2–10 keV energy bands), the depth of the iron K absorption edge, the equivalent width of the Fe K(alpha) line, and the fraction of the Fe K(alpha) flux contained in the Compton shoulder. We demonstrate that by means of X-ray spectroscopy it is possible to tightly constrain (langle N_{textrm{H}}rangle), (N_{textrm{H}}), and (A_{textrm{Fe}}) in the Compton-thin regime, while there is degeneracy between clumpiness and viewing direction.

We have solved the Ogorodnikov–Milne stellar-kinematics equations in the Galactic rectangular coordinate system based on the total velocities for a special sample of stars with radial velocities from the final Gaia Data Release 3 catalogue. We have found the region of applicability of the linear model and the regions that it describes poorly. We have constructed a second-order model that takes into account the peculiarities of stellar kinematics more accurately and showed its applicability for stars at distances up to 5 kpc.

Ways of formation of azimuthal resonant patterns in circumstellar planetesimal disks with planets are considered. Our analytical estimates and massive numerical experiments show that the disk particles that initially reside in zones of low-order mean-motion resonances with the planet may eventually concentrate into potentially observable azimuthal patterns. The structuring process is rapid, usually taking (sim)100 orbital periods of the planet. It is found that the relative number of particles that retain their resonant position increases with decreasing the mass parameter (mu) (the ratio of masses of the perturbing planet and the parent star), but a significant fraction of the particle population is always removed from the disk due to accretion of the particles onto the star and planet, as well as due to their transition to highly elongated and hyperbolic orbits. Expected radio images of azimuthally structured disks are constructed. In the considered models, azimuthal patterns associated with the (2:1) and (3:2) resonances are most clearly manifested; observational manifestations of the (1:2) and (2:3) resonances are also possible.

We describe the methods of the SRGz system for the physical identification of eROSITA point X-ray sources from photometric data in the DESI Legacy Imaging Surveys footprint. We consider the models included in the SRGz system (version 2.1) that have allowed us to obtain accurate measurements of the cosmological redshift and class of an X-ray object (quasar/galaxy/star) from multiwavelength photometric sky surveys (DESI LIS, SDSS, Pan-STARRS, WISE, eROSITA) for 87({%}) of the entire eastern extragalactic region ((0^{circ}<l<180^{circ}), (|b|>20^{circ})). An important feature of the SRGz system is that its data handling model (identification, classification, photo-z algorithms) is based entirely on heuristic machine learning approaches. For a standard choice of SRGz parameters the optical counterpart identification completeness (recall) in the DESI LIS footprint is (95{%}) (with an optical counterpart selection precision of (94{%})); the classification completeness (recall) of X-ray sources without optical counterparts in DESI LIS is (82{%}) ((85{%}) precision). A high quality of the photometric classification of X-ray source optical counterparts is achieved in SRGz: ({>}99{%}) photometric classification completeness (recall) for extragalactic objects (a quasar or a galaxy) and stars on a test sample of sources with SDSS spectra and GAIA astrometric stars. We present an analysis of the importance of various photometric features for the optical identification and classification of eROSITA X-ray sources. We have shown that the infrared (IR) magnitude (W_{2}), the X-ray/optical(IR) ratios, the optical colors (for example, ((g-r))), and the IR color ((W_{1}-W_{2})) as well as the color distances introduced by us play a significant role in separating the classes of X-ray objects. We use the most important photometric features to interpret the SRGz predictions in this paper. The accuracy of the SRGz photometric redshifts (from DESI LIS, SDSS, Pan-STARRS, and WISE photometric data) has been tested in the Stripe82X field on a sample of 3/4 of the optical counterparts of eROSITA point X-ray sources (for which spectroscopic measurements are available in Stripe82X): (sigma_{NMAD}=3.1{%}) (the normalized median absolute deviation of the prediction) and (n_{>0.15}=7.8{%}) (the fraction of catastrophic outliers). The presented photo-z results for eROSITA X-ray sources in the Stripe82X field are more than a factor of 2 better in both metrics ((sigma_{NMAD}) and (n_{>0.15})) than the photo-z results of other groups published in the Stripe82X catalog.

The extreme levels of solar activity on time scales of 300–400 and 9000 years are considered. The total sunspot area (AR), a physical index of solar activity, has been estimated using the sunspot number reconstruction from Wu et al. (2018). The main study has been carried out precisely in terms of this index. The variations in solar activity at the epoch of the last 300–400 years represent fairly well its variations on time scales of the order of nine millennia. The maximum level of solar activity for the yearly averages is (AR_{M}=2930pm 400) m.s.h. (millionths of the solar hemisphere). The upper limit for the daily values is (AR_{M}=7500pm 2200) m.s.h. for the traditional sunspot areas corrected for the perspective distortion and (AR_{OM}=11,400pm 3300) m.s.d. (millionths of the solar disk) for the so-called ‘‘observed’’ areas—the sunspot projections onto the visible solar disk. The maximum yearly averages of the sunspot number (SN_{M}=258pm 38) and the sunspot group number (GN_{M}=12.3pm 2.4) have also been estimated; 11.3({%}) of the time the solar activity is at an extremely high level; 8.5 and 4.5({%}) of the time its level corresponds to the Dalton minimum or lower and an extremely low one, respectively. Thus, extremely high levels are more likely for solar activity than extremely low ones.