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

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.

We have studied the kinematics of a unique sample of young open star clusters (OSCs) with high vertical velocities, (15<W<40) km s({}^{-1}). The characteristics of these clusters were taken from the catalogue by Hunt and Reffert (2023), where their mean proper motions, line-of-sight velocities, and distances were calculated using Gaia DR3 data. These OSCs are located within 0.6 kpc of the Sun and form two clumps: one in the region of the Sco–Cen OB association and the other one in the region of the Per OB3–Per OB2 associations. The OSC group of 47 members in the region of the Sco–Cen association is shown to expand along the (y) axis, (partial V/partial y=51pm 12) km s({}^{-1}) kpc({}^{-1}). This group also has a positive rotation around the (z) axis with an angular velocity of (71pm 11) km s({}^{-1}) kpc({}^{-1}) and a negative rotation around the (x) axis with an angular velocity of (-35pm 5) km s({}^{-1}) kpc({}^{-1}). Based on the velocities of 27 OSCs from the region of the Per OB3–Per OB2 associations, we have found no gradients differing significantly from zero. We have studied the kinematics of more than 1700 stars selected by Luhman (2022) as probable members of the Sco–Cen OB association. These stars are shown to have no high vertical velocities. The expansion coefficient of the stellar system in the (xy) plane has been found from all stars to be (K_{xy}=43.2pm 2.2) km s({}^{-1}) kpc({}^{-1}). Based on stars from the three UCL, LCC, and V1062 Sco groups with a mean age ({sim}20) Myr, for the first time we have found a volume expansion coefficient of the stellar system differing significantly from zero, (K_{xyz}=43.2pm 3.4) km s({}^{-1}) kpc({}^{-1}).