The results of photometric UBV monitoring of open clusters NGC 2266 and NGC 7762 are presented. 2... more The results of photometric UBV monitoring of open clusters NGC 2266 and NGC 7762 are presented. 2MASS JH photometry is additionally used to determine the parameters of both clusters. For NGC 2266 the following parameters are obtained: the limiting radius 6.2 arcmin, log (age [yr]) = 9.08 ± 0.04, metallicity Z = 0.004 ([Fe/H] = -- 0.68), interstellar reddening EB-V = 0.17 and a distance of 2.80 ± 0.15 kpc. No evidence for the existence of an extended corona was found. As a result of 45 hour monitoring of 7200 stars in the cluster field, 12 were found to be variable. All of them are located outside the cluster radius. For NGC 7762 the following parameters are obtained: limiting radius 23.5 arcmin (including an extended corona), log (age [yr]) = 9.38 ± 0.04, interstellar reddening EB-V = 0.59 and a distance of 0.8 ± 0.25 kpc; solar metallicity is accepted. The near-IR data suggest EJ-H = 0.11 and a peculiar interstellar reddening law. As a result of 55 hour monitoring of 5500 stars in ...
Monthly Notices of the Royal Astronomical Society, 2015
ABSTRACT We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.93... more ABSTRACT We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006–2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the Gamma-Ray Large Area Space Telescope (GLAST)-AGILE Support Program of the Whole Earth Blazar Telescope, as well as data from the Swift (optical–UV and X-rays) and Fermi (γ-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman α intervening system at z = 0.525. Two major outbursts were observed in 2006–2007 and in 2012–2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio–optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the γ-ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches ∼19 per cent during the early stage of the 2012–2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarization angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour/structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg ii broad emission line with an essentially stable flux of 6.2 × 10− 15 erg cm− 2 s− 1 and a full width at half-maximum of 2053 km s− 1.
Monthly Notices of the Royal Astronomical Society, 2013
ABSTRACT Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-ray... more ABSTRACT Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily γ-ray observations by Fermi. Discrete correlation analysis between the optical and γ-ray emission reveals correlation with a time lag of 0 ± 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time-scales than corresponding γ-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and γ-ray-emitting zone in the jet. The mean optical degree of polarization slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarization angle (EVPA) shows a preferred orientation of about 15°, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011-2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarization. A helical magnetic field model predicts an evolution of the mean polarization that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model.
ABSTRACT We present new photometric data for an EW-type binary star -- MM Dra. Light curve data i... more ABSTRACT We present new photometric data for an EW-type binary star -- MM Dra. Light curve data in B and R colors for a total of 37 hours of observation have been analyzed. We obtained a new period of the binary -- 0.26548 (0.00001) days, slightly larger than previous estimates, but broadly consistent with the previously reported minima epochs. The presence of O'Connel effect in the light curve is noted.
The results of photometric UBV monitoring of open clusters NGC 2266 and NGC 7762 are presented. 2... more The results of photometric UBV monitoring of open clusters NGC 2266 and NGC 7762 are presented. 2MASS JH photometry is additionally used to determine the parameters of both clusters. For NGC 2266 the following parameters are obtained: the limiting radius 6.2 arcmin, log (age [yr]) = 9.08 ± 0.04, metallicity Z = 0.004 ([Fe/H] = -- 0.68), interstellar reddening EB-V = 0.17 and a distance of 2.80 ± 0.15 kpc. No evidence for the existence of an extended corona was found. As a result of 45 hour monitoring of 7200 stars in the cluster field, 12 were found to be variable. All of them are located outside the cluster radius. For NGC 7762 the following parameters are obtained: limiting radius 23.5 arcmin (including an extended corona), log (age [yr]) = 9.38 ± 0.04, interstellar reddening EB-V = 0.59 and a distance of 0.8 ± 0.25 kpc; solar metallicity is accepted. The near-IR data suggest EJ-H = 0.11 and a peculiar interstellar reddening law. As a result of 55 hour monitoring of 5500 stars in ...
Monthly Notices of the Royal Astronomical Society, 2015
ABSTRACT We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.93... more ABSTRACT We present an analysis of the multiwavelength behaviour of the blazar OJ 248 at z = 0.939 in the period 2006–2013. We use low-energy data (optical, near-infrared, and radio) obtained by 21 observatories participating in the Gamma-Ray Large Area Space Telescope (GLAST)-AGILE Support Program of the Whole Earth Blazar Telescope, as well as data from the Swift (optical–UV and X-rays) and Fermi (γ-rays) satellites, to study flux and spectral variability and correlations among emissions in different bands. We take into account the effect of absorption by the Damped Lyman α intervening system at z = 0.525. Two major outbursts were observed in 2006–2007 and in 2012–2013 at optical and near-IR wavelengths, while in the high-frequency radio light curves prominent radio outbursts are visible peaking at the end of 2010 and beginning of 2013, revealing a complex radio–optical correlation. Cross-correlation analysis suggests a delay of the optical variations after the γ-ray ones of about a month, which is a peculiar behaviour in blazars. We also analyse optical polarimetric and spectroscopic data. The average polarization percentage P is less than 3 per cent, but it reaches ∼19 per cent during the early stage of the 2012–2013 outburst. A vague correlation of P with brightness is observed. There is no preferred electric vector polarization angle and during the outburst the linear polarization vector shows wide rotations in both directions, suggesting a complex behaviour/structure of the jet and possible turbulence. The analysis of 140 optical spectra acquired at the Steward Observatory reveals a strong Mg ii broad emission line with an essentially stable flux of 6.2 × 10− 15 erg cm− 2 s− 1 and a full width at half-maximum of 2053 km s− 1.
Monthly Notices of the Royal Astronomical Society, 2013
ABSTRACT Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-ray... more ABSTRACT Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved by the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope in collaboration with the Steward Observatory allows us to perform a detailed comparison with the daily γ-ray observations by Fermi. Discrete correlation analysis between the optical and γ-ray emission reveals correlation with a time lag of 0 ± 1 d, which suggests cospatiality of the corresponding jet emitting regions. A better definition of the time lag is hindered by the daily gaps in the sampling of the extremely fast flux variations. In general, optical flares present more structure and develop on longer time-scales than corresponding γ-ray flares. Observations at X-rays and at millimetre wavelengths reveal a common trend, which suggests that the region producing the mm and X-ray radiation is located downstream from the optical and γ-ray-emitting zone in the jet. The mean optical degree of polarization slightly decreases over the considered period and in general it is higher when the flux is lower. The optical electric vector polarization angle (EVPA) shows a preferred orientation of about 15°, nearly aligned with the radio core EVPA and mean jet direction. Oscillations around it increase during the 2011-2012 outburst. We investigate the effects of a geometrical interpretation of the long-term flux variability on the polarization. A helical magnetic field model predicts an evolution of the mean polarization that is in reasonable agreement with the observations. These can be fully explained by introducing slight variations in the compression factor in a transverse shock waves model.
ABSTRACT We present new photometric data for an EW-type binary star -- MM Dra. Light curve data i... more ABSTRACT We present new photometric data for an EW-type binary star -- MM Dra. Light curve data in B and R colors for a total of 37 hours of observation have been analyzed. We obtained a new period of the binary -- 0.26548 (0.00001) days, slightly larger than previous estimates, but broadly consistent with the previously reported minima epochs. The presence of O'Connel effect in the light curve is noted.
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Papers by E. Ovcharov