Time filter

Source Type

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.

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 3 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.

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.

Discover hidden collaborations