Main Astronomical Observatory of NAS of Ukraine

Kiev, Ukraine

Main Astronomical Observatory of NAS of Ukraine

Kiev, Ukraine
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Vasylenko A.A.,Main Astronomical Observatory of NAS of Ukraine | Zhdanov V.I.,Taras Shevchenko National University | Fedorova E.V.,Taras Shevchenko National University
Journal of Physical Studies | Year: 2016

Active galactic nuclei (AGN) are the brightest objects in the Universe and their brightness is mainly caused by accretion of matter onto supermassive black holes (SMBH). This is the common reason of the AGN activity. However, every AGN has differences and fine features, which are the subject of an intensive investigation. The occurrence of such highly-relativistic objects as SMBH residing at the AGN core makes them an excellent laboratory for testing the fundamental physical theories. The X-rays and gamma-rays generated in a corona of an accretion disc around SMBH yield valuable information for these tests, the radiation in the range of 1-100 keV being at present the most informative source. However, there are a number of obstacles for such a study due to different physical processes that complicate the interpretation of observations in different bands of the electromagnetic radiation. In this paper, we review the current concepts concerning the structure of AGNs with a focus on the central part of these objects that require relativistic theories for their understanding. The basic notions of the unified AGN schemes are considered; some modifications are reviewed. The paper contains the following sections. I. Introduction; II. Observational manifestations and classification of galaxies with active nuclei (II.A. Optical observations; II.B. Radio observations; II.C. X-ray data; II.D Infrared data; II.E. AGN anatomy with multywave data); III. AGN “central machine”; III.A. Black holes; III.B. Accretion disc types; III.C. Corona; III.D. AGN unified scheme); IV. Simulation X-ray AGN spectra (IV.A. The power-law contimuum and the exponential cut-off; IV.B. The absorption of X-rays; IV.C. Reflection; IV.D. Fe Kα line; IV.E. Spin paradigm); V. AGN as a laboratory to test the fundamental interactions (V.A. Strong gravitational fields; V.B. Dynamic dark energy near compact astrophysical objects. © 2016, Ivan Franko National University of Lviv. All Rights Reserved.

Neslusan L.,Slovak Academy of Sciences | Ivanova O.,Main Astronomical Observatory of NAS of Ukraine | Husarik M.,Slovak Academy of Sciences | Svoren J.,Slovak Academy of Sciences | Krisandova Z.S.,Slovak Academy of Sciences
Planetary and Space Science | Year: 2016

Photometric observations of asteroid (596) Scheila were obtained during and after its 2010 outburst. The estimated radius of the body (spherical approximation of the asteroidal body) was 51.2±3.0. km and 50.6±3.0. km for different methods. The ejected dust mass from the asteroid ranged from 2.5×107 to 3.4×107kg for different methods. An impact mechanism for triggering Scheila's activity is discussed. A few days before the impact, Scheila passed through the corridors of two potential cometary streams. © 2016 Elsevier Ltd.

Ivanova O.V.,Main Astronomical Observatory of NAS of Ukraine | Neslusan L.,Slovak Academy of Sciences | Svoren J.,Slovak Academy of Sciences | Seman Krisandova Z.,Slovak Academy of Sciences
Icarus | Year: 2015

We attempt to answer two questions concerning the impacts of stream meteoroids on the nuclei of Comets 9P/Tempel 1 and 81P/Wild 2: firstly, how many streams cross the orbits of both comets and, secondly, what is the index of the differential mass distribution of impactors, s, when we assume that a prevailing number of the craters on the surfaces of cometary nuclei were created by stream meteoroids? We found that 110 and 129 potential streams originating from comets likely cross the orbits of 9P and 81P, respectively (and 103 potential streams cross the orbit of 1P/Halley, for comparison). If we consider the more compact streams originating from asteroids, the 9P and 81P pass through such streams 15 664 and 65 368 times. Neither these large numbers of passages imply, however, enough large impactors to excavate the whole observed variety of craters on studied comets. For all craters on 9P and 81P, s=. 2.09. ±. 0.01 and s=. 2.25. ±. 0.03, respectively. The craters on 81P seem to be, however, excavated by the impactors from four discernible sources. For two numerous enough sources we find s=. 5.6. ±. 0.2 and s=. 5.2. ±. 0.5. The difference between the indices for the set of all craters and the sets of their partial groups obviously implies an unknown cosmogonic consequence. © 2015 Elsevier Inc.

Korsun P.P.,Main Astronomical Observatory of NAS of Ukraine | Rousselot P.,University of Franche Comte | Kulyk I.V.,Main Astronomical Observatory of NAS of Ukraine | Afanasiev V.L.,Special Astrophysical Observatory of the Russian AS | Ivanova O.V.,Main Astronomical Observatory of NAS of Ukraine
Icarus | Year: 2014

Spectrophotometric monitoring of distant Comet C/2002 VQ94 (LINEAR) was performed with the 6-m telescope of SAO RAS (Special Astrophysical Observatory of Russian Academy of Sciences) and with the 2.5-m Nordic Optical Telescope (Observatory del Roque de los Muchachos, Canarias, Spain) between 2008 and 2013. During this period the comet was on the outbound segment of its orbit, between heliocentric distances of 8.36au and 16.84au. Analysis of the spectra revealed the presence of the CO+ and N2+ emissions in the cometary coma at a distance of 8.36au from the Sun. This distance is larger than ionic emissions have been detected in any previous objects. Only continuum, with no traces of emissions, was detected in the spectrum obtained in 2009 when the comet was at a distance of 9.86au. From the spectra obtained in 2008, average column densities of 2.04×109molcm-2 for N2+ and 3.26×1010molcm-2 for CO+ were measured in the cometary coma. The derived values correspond to N2+/CO+=0.06 within the projected slit. Images obtained through a red continuum filter in 2008 showed a bright, dust coma, indicating a high level of physical activity. A considerably lower level of activity was observed in 2009 and 2011 at distances of 9.86au and 13.40au respectively. No noticeable activity was detected in 2013 at a heliocentric distance of 16.84au. The Afρ parameter, which is used as an indicator of cometary activity, was measured as 2000cm in 2008, and 800cm in 2009 and 2011. The Afρ values correspond to dust production rates between 10-20kgs-1, 4-6kgs-1 and 3-5kgs-1 at 8.36, 9.86, and 13.40au respectively. There is an obvious correlation between the decrease of the dust production rate of the nucleus and the disappearance of the emissions in the spectrum of C/2002 VQ94 (LINEAR) at heliocentric distances greater than 9au. The colors and size of the nucleus of C/2002 VQ94 (LINEAR) were estimated from the images obtained during the late stage at a heliocentric distance of 16.84au, when the activity had probable ceased. The B-V and V-R colors were estimated to be 1.07±0.05 and 0.54±0.03 respectively. The effective nucleus radius of 48±2km is in agreement with the previously published results, obtained from the observations of the comet during its early inactive stage (Jewitt, D. [2005]. Astron. J. 129, 530-538; Weiler, M., Rauer, H., Sterken, C. [2011]. Icarus 212, 351-366). © 2014 Elsevier Inc.

Kostogryz N.M.,Kiepenheuer Institute for Solar Physics | Kostogryz N.M.,Main Astronomical Observatory of NAS of Ukraine | Yakobchuk T.M.,Kiepenheuer Institute for Solar Physics | Yakobchuk T.M.,Main Astronomical Observatory of NAS of Ukraine | Berdyugina S.V.,Kiepenheuer Institute for Solar Physics
Astrophysical Journal | Year: 2015

We present results of numerical simulations of flux and linear polarization variations in transiting exoplanetary systems, caused by host star disk symmetry breaking. We consider different configurations of planetary transits depending on orbital parameters. The starspot contribution to the polarized signal is also estimated. Applying the method to known systems and simulating observational conditions, a number of targets is selected where transit polarization effects could be detected. We investigate several principal benefits of the transit polarimetry, particularly for determining orbital spatial orientation and distinguishing between grazing and near-grazing planets. Simulations show that polarization parameters are also sensitive to starspots, and they can be used to determine spot positions and sizes. © 2015. The American Astronomical Society. All rights reserved.

Ivanova O.V.,Main Astronomical Observatory of NAS of Ukraine | Skorov Y.V.,TU Braunschweig | Skorov Y.V.,Max Planck Institute for Solar System Research | Korsun P.P.,Main Astronomical Observatory of NAS of Ukraine | And 2 more authors.
Icarus | Year: 2011

We investigated three comets, which are active at large heliocentric distances, using observations obtained at the 6-m BTA telescope (SAO RAS, Russia) in the photometric mode of the focal reducer SCORPIO. The three comets, 29P/Schwassmann-Wachmann 1, C/2003 WT42 (LINEAR), and C/2002 VQ94 (LINEAR), were observed after their perihelion passages at heliocentric distances between 5.5 and 7.08. AU. The dust production rates in terms of Afρ was measured for these comets. Using the retrieved values, an average dust production rate was derived under different model assumptions. A tentative calculation of the total mass loss of the comet nucleus within a certain observation period was executed. We calculated the corresponding thickness of the depleted uppermost layer where high-volatile ices completely sublimated. The results obtained in our study strongly support the idea that the observed activity of Comet SW1 requires a permanent demolition of the upper surface layers. © 2010 Elsevier Inc.

Polosukhina N.,Crimean Astrophysical Observatory | Shavrina A.,Main Astronomical Observatory of NAS of Ukraine | Drake N.A.,State University of Rio de Janeiro | Smirnova M.,Crimean Astrophysical Observatory
Memorie della Societa Astronomica Italiana, Supplementi - Journal of the Italian Astronomical Society, Supplement | Year: 2012

We discuss lithium abundance and 6Li/7Li isotopic ratio in atmospheres of some magnetic roAp stars. Overabundances of the lithium were found in atmospheres of some roAp stars based on the analysis of both lithium lines at 6104 Å and 6708 Å as well as the high values of the 6Li/7Li isotopic ratio (0.2-0.5). These facts can be explained by lithium production in spallation reactions on stellar surface and by preserving 7Li and 6Li isotopes to be destroyed in the inner layers of stellar atmospheres by strong magnetic fields near magnetic poles. Our synthetic spectrum calculations take into account magnetic line broadening effects. © SAIt 2012.

Kostogryz N.M.,Kiepenheuer Institute for Solar Physics | Kostogryz N.M.,Main Astronomical Observatory of NAS of Ukraine | Berdyugina S.V.,Kiepenheuer Institute for Solar Physics | Berdyugina S.V.,University of Hawaii at Manoa
Astronomy and Astrophysics | Year: 2015

Scattering and absorption processes in stellar atmosphere affect the center-to-limb variations of the intensity (CLVI) and the linear polarization (CLVP) of stellar radiation. Aims. There are several theoretical and observational studies of CLVI using different stellar models, however, most studies of CLVP have concentrated on the solar atmosphere and have not considered the CLVP in cooler non-gray stellar atmospheres at all. In this paper, we present a theoretical study of the CLV of the intensity and the linear polarization in continuum spectra of different spectral type stars. Methods. We solve the radiative transfer equations for polarized light iteratively assuming no magnetic field and considering a plane-parallel model atmospheres and various opacities. Results. We calculate the CLVI and the CLVP for Phoenix stellar model atmospheres for the range of effective temperatures (4500 K-6900 K), gravities (log g = 3.0-5.0), and wavelengths (4000-7000 Å), which are tabulated and available at the CDS. In addition, we present several tests of our code and compare our results with measurements and calculations of CLVI and the CLVP for the Sun. The resulting CLVI are fitted with polynomials and their coefficients are presented in this paper. Conclusions. For the stellar model atmospheres with lower gravity and effective temperature the CLVP is larger. © 2015 ESO.

Babyk I.,Taras Shevchenko National University | Babyk I.,Main Astronomical Observatory of NAS of Ukraine
Journal of Physical Studies | Year: 2012

This paper presents a study of X-ray Abell 13 (kT = 5.76 ± 0.15 keV) cluster located at the distance of 400 Mpc (z = 0.0943) from us. The data on cluster was obtained from Chandra X-ray Observatory. We used numerical simulations and the hydrostatic equilibrium condition on the intracluster gas for determining the total mass of the cluster. We used the Navarro-Frenk-White model and spherically symmetry assumption for modeling the density profile of a dark matter, and also the β-model to study a central region of the cluster in detail. As a result, the following parameters of the β-model were obtained after getting fit to the surface brightness: β = 0.87 ± 0.07 and r0 = 134 ± 22 kpc. We used the DSDEPROJ method of deprojection for getting more accurate parameters to determine the density profile and mass of Abell 13. Thus, the total mass of the cluster was obtained as M200 = 4.69+0.51-0.44 1014M for the radius R200 = 1.51+0.41 -0.33 Mpc. The fraction of a dark matter in the total mass is ~ 90%, while the gas is ~ 10%. We did not take into account the galactic component, so, the "total" mass is the sum of masses of a dark matter and intercluster gas.

Ivanova O.,Main Astronomical Observatory of NAS of Ukraine | Borysenko S.,Main Astronomical Observatory of NAS of Ukraine | Golovin A.,Main Astronomical Observatory of NAS of Ukraine
Icarus | Year: 2014

We present an analysis of the photometric data of Comet C/2011 L4 (PANSTARRS) observed at heliocentric distance of 4.4-4.2. AU. The Comet C/2011 L4 (PANSTARRS) shows one significant activity, despite of its quite large heliocentric distance. The color indexes, dust mass-loss rates and radius of the comet are measured. © 2013 Elsevier Inc.

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