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Kovacevic A.,University of Belgrade | Popovic L.C.,Astronomical Observatory | Shapovalova A.I.,Special Astrophysical Observatory of the Russian AS | Ilic D.,University of Belgrade | And 2 more authors.
Advances in Space Research | Year: 2014

We used the Z-transformed Discrete Correlation Function (ZDCF) and the Stochastic Process Estimation for AGN Reverberation (SPEAR) methods for the time series analysis of the continuum and the Hα and Hβ line fluxes of a sample of well known type 1 active galactic nuclei (AGNs): Arp 102B, 3C 390.3, NGC 5548, and NGC 4051, where the first two objects are showing double-peaked emission line profiles. The aim of this work is to compare the time lag measurements from these two methods, and check if there is a connection with other emission line properties. We found that the obtained time lags from Hβ are larger than those derived from the Hα analysis for Arp 102B, 3C 390.3 and NGC 5548. This may indicate that the Hβ line originates at larger radii in these objects. Moreover, we found that the ZDCF and SPEAR time lags are highly correlated (r∼0.87), and that the error ranges of both ZDCF and SPEAR time lags are correlated with the FWHM of used emission lines (r∼0.7). This increases the uncertainty of the black hole mass estimates using the virial theorem for AGNs with broader lines. © 2014 Published by Elsevier Ltd.


Kulyk I.,Ukrainian Academy of Sciences | Korsun P.,Ukrainian Academy of Sciences | Rousselot P.,University of Burgundy | Afanasiev V.,Special Astrophysical Observatory of the Russian AS | Ivanova O.,Ukrainian Academy of Sciences
Icarus | Year: 2016

Based on spectroscopic and photometric observations we analyzed the dust environment of two minor distant objects, P/2008 CL94 (Lemmon) and P/2011 S1 (Gibbs). Both targets demonstrated the comet-like activity beyond the "zone of water-ice sublimation". Meanwhile the spectrum of P/2008 CL94 (Lemmon) did not reveal molecular emission features above reflected continuum in a spectral region of 4100-6800Å. Reddening of the continuum is linear along the dispersion with the mean normalized reflectivity gradient equals to 2.0%. ±. 0.4%. The normalized reflectivity of P/2011 S1 (Gibbs) derived from the V-R and R-I color indices equals 11%. ±. 9% and 26%. ±. 6% respectively. Both objects have likely small nuclei (about 2 and 4. km in the radii for P/2008 CL94 and P/2011 S1 respectively), which are consistent with nucleus sizes of 'Jupiter-family' comets. The level of physical activity of P/2008 CL94 and S/2011 S1 is characterized by R-Afρ quantity of 106. ±. 3. cm and 76. ±. 8. cm respectively. The Afρ values are resulted in dust production rates of about 1-2. kg/s, assuming the average geometric albedo of grains of 0.1 and the dust outflow velocities between 1 and 10. m/s. © 2016 Elsevier Inc.


Jovanovic P.,Astronomical Observatory | Jovanovic P.,Isaac Newton Institute of Chile | Popovic L.C.,Astronomical Observatory | Popovic L.C.,Isaac Newton Institute of Chile | And 4 more authors.
Astrophysical Journal | Year: 2010

Here we show that in the case when double-peaked emission lines originate from outer parts of the accretion disk, their variability could be caused by perturbations in the disk emissivity. In order to test this hypothesis, we introduced a model of the disk perturbing region in the form of a single bright spot (or flare) by a modification of the power-law disk emissivity in an appropriate way. The disk emission was then analyzed using numerical simulations based on the ray-tracing method in the Kerr metric and the corresponding simulated line profiles were obtained. We applied this model to the observed Hβ line profiles of 3C 390.3 (observed in the period 1995-1999) and estimated the parameters of both the accretion disk and the perturbing region. Our results show that two large amplitude outbursts of the Hβ line observed in 3C 390.3 could be explained by successive occurrences of two bright spots on the approaching side of the disk. These bright spots are either moving, originating in the inner regions of the disk and spiralling outward by crossing small distances during the period of several years, or stationary. In both cases, their widths increase with time, indicating that they most likely decay. © 2010. The American Astronomical Society. All rights reserved.


Bon E.,Astronomical Observatory | Bon E.,Isaac Newton Institute of Chile | Jovanovic P.,Astronomical Observatory | Jovanovic P.,Isaac Newton Institute of Chile | And 12 more authors.
Astrophysical Journal | Year: 2012

One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole (BH) system in their cores. Here, we present an observational evidence for the first spectroscopically resolved sub-parsec orbit of a such system in the core of Seyfert galaxy NGC4151. Using a method similar to those typically used for spectroscopic binary stars, we obtained radial velocity curves of the supermassive binary system, from which we calculated orbital elements and made estimates about the masses of the components. Our analysis shows that periodic variations in the light and radial velocity curves can be accounted for by an eccentric, sub-parsec Keplerian orbit with a 15.9 year period. The flux maximum in the light curve corresponds to the approaching phase of the secondary component toward the observer. According to the obtained results, we speculate that the periodic variations in the observed Hα line shape and flux are due to shock waves generated by the supersonic motion of the components through the surrounding medium. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion, we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into the BH mass growth process. © 2012. The American Astronomical Society. All rights reserved.


Shapovalova A.I.,Special Astrophysical Observatory of the Russian AS | Popovic L.C.,Astronomical Observatory | Popovic L.C.,Isaac Newton Institute of Chile | Burenkov A.N.,Special Astrophysical Observatory of the Russian AS | And 17 more authors.
Astrophysical Journal, Supplement Series | Year: 2012

We present the results of a long-term (1999-2010) spectral optical monitoring campaign of the active galactic nucleus (AGN) Ark 564, which shows a strong Fe II line emission in the optical. This AGN is a narrow-line Seyfert 1 (NLS1) galaxy, a group of AGNs with specific spectral characteristics. We analyze the light curves of the permitted Hα, Hβ, optical Fe II line fluxes, and the continuum flux in order to search for a time lag between them. Additionally, in order to estimate the contribution of iron lines from different multiplets, we fit the Hβ and Fe II lines with a sum of Gaussian components. We find that during the monitoring period the spectral variation (F max/F min) of Ark 564 is between 1.5 for Hα and 1.8 for the Fe II lines. The correlation between the Fe II and Hβ flux variations is of higher significance than that of Hα and Hβ (whose correlation is almost absent). The permitted-line profiles are Lorentzian-like and do not change shape during the monitoring period. We investigate, in detail, the optical Fe II emission and find different degrees of correlation between the Fe II emission arising from different spectral multiplets and the continuum flux. The relatively weak and different degrees of correlations between permitted lines and continuum fluxes indicate a rather complex source of ionization of the broad-line emission region. © 2012. The American Astronomical Society. All rights reserved.


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.


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.


Arshakian T.G.,Max Planck Institute for Radio Astronomy | Leon-Tavares J.,Max Planck Institute for Radio Astronomy | Leon-Tavares J.,National Institute of Astrophysics, Optics and Electronics | Lobanov A.P.,Max Planck Institute for Radio Astronomy | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

The mechanism and the region of generation of variable continuum emission are poorly understood for radio-loud active galactic nuclei because of the complexity of the nuclear region. High-resolution radio very long baseline interferometry (VLBI) observations have allowed us to zoom into a subparsec-scale region of the jet in the radio-loud galaxy 3C 390.3. We have combined the radio VLBI and the optical data covering the time period of 14 yr in order to look for a link between the optical flares and the parsec-scale jet. We have identified two stationary and nine moving radio features in the innermost subparsec-scale region of the jet. All nine ejections are associated with optical flares. We have found a significant correlation (at a confidence level of >99.99 per cent) between the ejected jet components and the optical continuum flares. The epochs at which the moving knots pass through the location of a stationary radio feature and at which the optical light curve reaches maximum are correlated. The radio events follow the maxima of optical flares with a mean time delay of 0.10 ± 0.04 yr. This correlation can be understood if the variable optical continuum emission is generated in the innermost part of the jet. A possible mechanism of the energy release is the ejection of knots of high-energy electrons that are accelerated in the jet flow and generate flares of synchrotron continuum emission in the wide range of frequencies from radio to X-ray bands. In this scenario, the beamed optical continuum emission from the jet and counterjet ionizes a gas in a subrelativistic outflow surrounding the jet. This results in the formation of two outflowing conical regions with broad emission lines (in addition to the conventional broad-line region around the central nucleus). © 2009 RAS.


Rousselot P.,University of Franche Comte | Korsun P.P.,Ukrainian Academy of Sciences | Kulyk I.V.,Ukrainian Academy of Sciences | Afanasiev V.L.,Special Astrophysical Observatory of the Russian AS | And 5 more authors.
Astronomy and Astrophysics | Year: 2014

Context. The study of small bodies that have a cometary activity at a large heliocentric distance (larger than 5 au) is important for a better understanding of the physical properties of comets and their origin. Such studies require long-term monitoring and a significant observational effort. Aims. Our goal is to monitor the cometary activity and search for possible emission lines of C/2006 S3 (LONEOS), which is a distant comet that was discovered in 2006 and passed perihelion at 5.13 au in April 2012. Methods. We performed different observing runs with telescopes, ranging from 2 m to 6 m both in imaging and spectroscopic modes in the optical range, between 2006 and 2014. Results. The comet C/2006 S3 (LONEOS) was a very active object with Afρ ~ 4000 cm at its maximum of activity, corresponding to a dust production rate of 82 kg s-1, considering a mean geometric albedo of 0.1 and grain outflow velocities in the range 2-22 m s-1. It appeared to be more active after its perihelion than before and we did not manage to detect any emission lines. Upper limits for the main cometary species that have emission bands in the optical range are provided. Our dust environment modeling is in agreement with a collimated source of dust that appeared in 2013. © 2014 ESO.


Neustroev V.V.,National University of Ireland | Suleimanov V.F.,University of Tübingen | Suleimanov V.F.,Kazan Federal University | Borisov N.V.,Special Astrophysical Observatory of the Russian AS | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present an analysis of time-resolved, medium-resolution optical spectroscopic observations of UX Ursae Majoris (UX UMa) in the blue (3920-5250 Å) and red (6100-7200 Å) wavelength ranges that were obtained in 1999 April and 2008 March, respectively. The observed characteristics of our spectra indicate that UX UMa has been in different states during those observations. The blue spectra are very complex. They are dominated by strong and broad single-peaked emission lines of hydrogen. The high-excitation lines of He ii λ4686 and the Bowen blend are quite strong as well. All the lines consist of a mixture of absorption and emission components. Using Doppler tomography, we have identified four distinct components of the system: the accretion disc, the secondary star, the bright spot from the gas stream/disc impact region and the unique compact area of absorption in the accretion disc seen as a dark spot in the lower left-hand quadrant of the tomograms. In the red wavelength range, both the hydrogen (Hα) and neutral helium (He i λ6678 and He i λ7065) lines were observed in emission and both exhibited double-peaked profiles. Doppler tomography of these lines reveals spiral structure in the accretion disc, but in contrast to the blue wavelength range, there is no evidence for either the dark spot or the gas stream/disc impact region emission, while the emission from the secondary star is weak. During the observations in 1999, UX UMa showed many of the defining properties of the SW Sextantis stars. However, all these features almost completely disappeared in 2008. We have also estimated the radial velocity semi-amplitudes K 1 and K 2 and evaluated the system parameters of UX UMa. These estimates are inconsistent with previous values derived by means of analysis of white dwarf eclipse features in the light curve in different wavelength ranges. © 2010 The Authors. Journal compilation © 2010 RAS.

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