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Vol 49, No 6 (2023)
Articles
Transient Events in the Circumnuclear Regions of AGNs and Quasars As Sources of Imitations of Proper Motions
Abstract
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
369-398
What Can We Learn about Compton-thin AGN Tori from Their X-Ray Spectra?1
Abstract
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), \(\langle N\rangle\), 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 keV and 2–7 keV energy bands), the high-energy hardness ratio (ratio of the continuum fluxes in the 10–100 keV 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.
399-400
Determination of the Spiral Pattern Speed in the Milky Way from Young Open Star Clusters
Abstract
We have estimated the spiral pattern speed in the Galaxy Ωp 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 Ωp. They all are based on the linear Lin–Shu spiral density wave theory. We have obtained an estimate of Ωp = 24.26 ± 0.52 km s-1 kpc-1 by the first method, which is most reliable in our view, using the velocity perturbations fR and fθ found through a spectral analysis of the radial, VR, and residual rotation, ΔVcirc , velocities. Using the second method, we have found the velocity perturbations fR and fθ by solving the basic kinematic equations together with the Galactic rotation parameters and obtained an estimate of Ωp = 23.45±0.53 km s-1 kpc-1. We have found Ωp = 28.9 ± 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 θbirth.
401-411
Determination of the Parameters of a Nonlinear Kinematic Galactic Rotation Model Based on the Proper Motions and Radial Velocities of Stars from the Gaia DR3 Catalogue
Abstract
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.
412-425
Azimuthal Patterns in Planetesimal Circumstellar Disks
Abstract
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 + 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 m (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.
426-438