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Kolotkov D.Y.,University of Warwick | Smirnova V.V.,University of Turku | Smirnova V.V.,Central Pulkovo Astronomical Observatory | Strekalova P.V.,Central Pulkovo Astronomical Observatory | And 3 more authors.
Astronomy and Astrophysics | Year: 2017

Aims. Long-period quasi-periodic variations of the average magnetic field in a small-scale magnetic structure on the Sun are analysed. The structure is situated at the photospheric level and is involved in a facula formation in the chromosphere. Methods. The observational signal obtained from the SDO/HMI line-of-sight magnetograms of the target structure has a non-stationary behaviour, and is therefore processed with the Hilbert-Huang Transform spectral technique. Results. The empirical decomposition of the original signal and subsequent testing of the statistical significance of its intrinsic modes reveal the presence of the white and pink noisy components for the periods shorter and longer than 10 min, respectively, and a significant oscillatory mode. The oscillation is found to have a non-stationary period growing from approximately 80 to 230 min and an increasing relative amplitude, while the mean magnetic field in the oscillating structure is seen to decrease. The observed behaviour could be interpreted either by the dynamical interaction of the structure with the boundaries of supergranula cells in the region of interest or in terms of the vortex shedding appearing during the magnetic flux emergence. © 2017 ESO.

Makarenko N.G.,Institute for Problems of Informatics and Control | Nagovitsyn Y.A.,Central Pulkovo Astronomical Observatory | Karimova L.M.,Institute for Problems of Informatics and Control | Kruglun O.A.,Institute for Problems of Informatics and Control
Geomagnetism and Aeronomy | Year: 2013

The possibility to apply long-term regional series to reconstruct the Earth's global temperature in the past is considered. It is shown using symbolic analysis methods that significant (on the so-called order patterns) are relations of time series of St. Petersburg temperature with certain regional and global series. New sets of global temperature reconstructions, starting from the mid-18th century, are constructed on the basis of the previously proposed MSR and DPS methods. © 2013 Pleiades Publishing, Ltd.

Bobylev V.V.,Saint Petersburg State University | Bajkova A.T.,Central Pulkovo Astronomical Observatory
Astronomische Nachrichten | Year: 2013

We tested distances derived from the equivalent widths of interstellar Ca II spectral lines by Megier et al. (2009). To this end, we used a sample of nearby 126 young OB3 stars (r < 1 kpc) with known proper motions and line-of-site velocities. We shown that these stars are closely associated with the Gould Belt structure. The bulk of the sample (about 100 stars) shows the same kinematics as the sample of distant OB3 stars. Their galactocentric radial velocities agree well with the following spiral density wave parameters: the amplitude of radial perturbations fR ≈ 12 km s-1, wavelength λ ≈ 2.3 kpc, and phase of the Sun in spiral wave χ⊙ ≈ -90°. However, we revealed 20 stars with absolutely unusual kinematical features. Their galactocentric radial velocities show a wave shifted by ≈180° with respect to the wave found from the entire sample. The superposition of two spiral patterns seems to be a likely explanation. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bajkova A.T.,Central Pulkovo Astronomical Observatory | Bobylev V.V.,Saint Petersburg State University
Astronomische Nachrichten | Year: 2013

The parameters of the Galactic spiral wave are re-determined using a modified periodogram (spectral) analysis of the galactocentric radial velocities of 58 masers with known trigonometric parallaxes, proper motions, and line-of-site velocities. The masers span a wide range of galactocentric distances, 3 < R < 14 kpc, which, combined with a large scatter of position angles θ of these objects in the Galactic plane required an accurate account of logarithmic dependence of spiral-wave perturbations on both the galactocentric distance and position angle. A periodic signal was detected corresponding to a spiral density wave with wavelength of λ = 2.4 ± 0.4 kpc, peak velocity of wave perturbations of fR = 7.5 ± 1.5 km s-1, phase of the Sun of χ⊙ = -160 ± 15°, and pitch angle of -5.5 ± 1°. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tsap Y.T.,Crimean Astrophysical Observatory | Tsap Y.T.,Central Pulkovo Astronomical Observatory | Stepanov A.V.,Central Pulkovo Astronomical Observatory
Proceedings of the International Astronomical Union | Year: 2010

Based on the three-fluid approximation the influence of the neutral component of hydrogen plasma on Joule dissipation of electric currents are considered. As distinguished from Mestel & Spitzer (1956) and Parker (1963) it has been shown that the magnetic flux may be not conserved in the case of the "ambipolar diffusion" due to collisions between ions and neutrals. This is explained by the ion acceleration under the action of Ampere's force. Joule dissipation is determined by electron and ion collisions in a partially ionized plasma. Plasma evacuation from current sheets is the effective mechanism of its cooling. Thickness of a current sheet can achieve up to hundreds of kilometers in the solar chromosphere. The origin of the solar chromospheric jets observed with the Hinode satellite are discussed. © 2011 International Astronomical Union.

Efremov V.I.,Central Pulkovo Astronomical Observatory | Parfinenko L.D.,Central Pulkovo Astronomical Observatory | Solov'ev A.A.,Central Pulkovo Astronomical Observatory | Kirichek E.A.,Central Pulkovo Astronomical Observatory
Solar Physics | Year: 2014

We processed magnetograms that were obtained with the Michaelson Doppler Imager onboard the Solar and Heliospheric Observatory (SOHO/MDI). The results confirm the basic properties of long-period oscillations of sunspots that have previously been established and also reveal new properties. We show that the limiting (lowest) eigenmode of low-frequency oscillations of a sunspot as a whole is the mode with a period of 10 - 12 up to 32 - 35 hours (depending on the sunspot's magnetic-field strength). This mode is observed consistently throughout an observation period of 5 - 7 days, but its amplitude is subject to quasi-cyclic changes, which are separated by about 1.5 - 2 days. As a result, the lower mode with a period of about 35 - 48 hours appears in the power spectrum of sunspot oscillations. But this lowest mode is apparently not an eigenmode of a sunspot because its period does not depend on the magnetic field of the sunspot. Perhaps the mode reflects the quasi-periodic sunspot perturbations caused by supergranulation cells that surround it. We also analyzed SOHO/MDI artifacts, which may affect the low-frequency power spectra of sunspots. © 2013 Springer Science+Business Media Dordrecht.

Kouprianov V.,Central Pulkovo Astronomical Observatory
Proceedings of the International Astronautical Congress, IAC | Year: 2015

Ground-based optical measurements remain the most comprehensive and reliable source of high-orbit space debris data. International Scientific Optical Network (ISON) collaboration, a joint effort of several dozen optical facilities spread over the globe and coordinated by Keldysh Institute for Applied Mathematics (KIAM), provides millions of measurements for the various classes of medium-And high-orbit space objects per year. The range of instruments scales from 0.2 meter wide-field survey sensors to 2 meter class telescopes for tracking faint debris. An important part of each sensor is the software for real-Time detection of space objects. Each ISON facility is driven by a common image acquisition and space object detection pipeline based on the Apex II astronomical image analysis platform. 10 years of successful operation made the pipeline mature and stable, and most of the recent developments are aimed at further increasing its sensitivity and reliability, in particular for faint space debris observations. Here we concentrate on such developments, including an improved moving object detection algorithm and a new method for increasing signal-To-noise ratio involving grayscale morphology. Copyright © (2015) by International Astronautical Federation All rights reserved.

Efremov V.I.,Central Pulkovo Astronomical Observatory | Parfinenko L.D.,Central Pulkovo Astronomical Observatory | Solov'ev A.A.,Central Pulkovo Astronomical Observatory
Solar Physics | Year: 2010

We applied special data-processing algorithms to the study of long-period oscillations of the magnetic-field strength and the line-of-sight velocity in sunspots. The oscillations were investigated with two independent groups of data. First, we used an eight-hour-long series of solar spectrograms, obtained with the solar telescope at the Pulkovo Observatory. We simultaneously measured Doppler shifts of six spectral lines, formed at different heights in the atmosphere. Second, we had a long time series of full-disk magnetograms (10 - 34 hour) from SOHO/MDI for the line-of-sight magnetic-field component. Both ground- and space-based observations revealed long-period modes of oscillations (40 - 45, 60 - 80, and 160 - 180 minutes) in the power spectrum of the sunspots and surrounding magnetic structures. With the SOHO/MDI data, one can study the longer periodicities. We obtained two new significant periods (> 3σ) in the power spectra of sunspots: around 250 and 480 minutes. The power of the oscillations in the lower frequencies is always higher than in the higher ones. The amplitude of the long-period magnetic-field modes shows magnitudes of about 200 - 250 G. The amplitude of the line-of-sight velocity periodicities is about 60 - 110 m s -1. The absence of low-frequency oscillations in the telluric line proves their solar nature. Moreover, the absence of low-frequency oscillations of the line-of-sight velocity in the quiet photosphere (free of magnetic elements) proves their direct connection to magnetic structures. Long-period modes of oscillation observed in magnetic elements surrounding the sunspot are spread over the meso-granulation scales (10″ - 12″), while the sunspot itself oscillates as a whole. The amplitude of the long-period mode of the line-of-sight velocity in a sunspot decreases rapidly with height: these oscillations are clearly visible in the spectral lines originating at heights of approximately 200 km and fade away in lines originating at 500 km. We found a new interesting property: the low-frequency oscillations of a sunspot are strongly reduced when there is a steady temporal trend (strengthening or weakening) of the sunspot's magnetic field. Another important result is that the frequency of long-period oscillations evidently depends on the sunspot's magnetic-field strength. © 2010 Springer Science+Business Media B.V.

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