Synchronous UBV observations of UV Ceti flares. II     

N. N. Kilyachkov  N. D. Melikyan  L. V. Mirzoyan  S. S. Shevchenko 《Astrophysics》1979,15(4):405-410

  相似文献   

The well-known Herbig AE star AB Aur. I. Investigation of variability of the emission lines in the region 0.37–0.88 μm     

V. S. Shevchenko 《Astrophysics》1987,27(3):606-614

  相似文献   

Polarization and brightness opposition effects for the E-type Asteroid 44 Nysa     

Vera K. Rosenbush  Vasilij G. Shevchenko  Alexander V. Sergeev  Feodor P. Velichko  Nikolai V. Karpov 《Icarus》2009,201(2):655-665

We present new polarimetric and photometric observations of high-albedo E-type Asteroid 44 Nysa in the BVRI wavebands at phase angles ranging from 0.41° to 7.49° during the 2005 opposition. A bimodal phase-angle dependence of polarization was found for Nysa in the V band. The polarization opposition effect was revealed in the form of a secondary minimum of negative polarization with amplitude ∼0.3% centered at a phase angle ∼0.8°. It is superimposed on the regular negative polarization branch with minimal polarization −0.30% at a phase angle 5.8°. We analyzed all available polarimetric data for E-type Asteroids 44 Nysa, 64 Angelina, and 214 Ashera and confirmed the presence of the polarization opposition effect for high-albedo asteroids at phase angle ∼1° with an amplitude ∼0.35%. The magnitude-phase curves reveal the presence of spike-like opposition effect of brightness for 44 Nysa in the BVRI spectral bands. 44 Nysa is the second high-albedo asteroid after 64 Angelina for which both the polarization opposition effect and the brightness opposition effect are detected. The differences between the parameters of the opposition effects for silicate surfaces (44 Nysa, 64 Angelina, Io) and icy surfaces (Europa, Ganymede, Iapetus, Saturn's rings) are discussed. The specific morphological parameters of opposition effects, in particular the angular width of the polarization opposition effect is comparable to that of the brightness opposition effect, provide almost unequivocal evidence that they are caused by coherent backscattering. One of unexpected results of our investigation is that 44 Nysa becomes bluer with increasing phase angle, while 64 Angelina shows phase reddening.  相似文献   

CCD-photometry and pole coordinates for eight asteroids     

Vasilij G. Shevchenko  N. Tungalag  Ninel M. Gaftonyuk  Alan W. Harris 《Planetary and Space Science》2009,57(12):1514-1520

The long time photometric observations were carried out for eight asteroids: (122) Gerda, (153) Hilda, (190) Ismene, (221) Eos, (411) Xanthe, (679) Pax, (700) Auravictrix, (787) Moskva. New rotation periods have been determined for the asteroids (153) Hilda (5.959 h) and (411) Xanthe (11.408 h), and known rotation periods for some of the others have been confirmed. Using our data and others data we have estimated new pole coordinates for the observed asteroids.  相似文献   

Planetary dynamics in the system α Centauri: The stability diagrams     

E. A. Popova  I. I. Shevchenko 《Astronomy Letters》2012,38(9):581-588

The stability of the motion of a hypothetical planet in the binary system ?? Cen A?CB has been investigated. The analysis has been performed within the framework of a planar (restricted and full) three-body problem for the case of prograde orbits. Based on a representative set of initial data, we have obtained the Lyapunov spectra of the motion of a triple system with a single planet. Chaotic domains have been identified in the pericenter distance-eccentricity plane of initial conditions for the planet through a statistical analysis of the data obtained. We have studied the correspondence of these chaotic domains to the domains of initial conditions that lead to the planet??s encounter with one of the binary??s stars or to the escape of the planet from the system. We show that the stability criterion based on the maximum Lyapunov exponent gives a more clear-cut boundary of the instability domains than does the encounterescape criterion at the same integration time. The typical Lyapunov time of chaotic motion is ??500 yr for unstable outer orbits and ??60 yr for unstable inner ones. The domain of chaos expands significantly as the initial orbital eccentricity of the planet increases. The chaos-order boundary has a fractal structure due to the presence of orbital resonances.  相似文献   

Adiabatic chaos in the Prometheus–Pandora system     

Ivan I. Shevchenko 《Monthly notices of the Royal Astronomical Society》2008,384(3):1211-1220

The chaotic orbital motion of Prometheus and Pandora, the 16th and 17th satellites of Saturn, is studied. Chaos in their orbital motion, as found by Goldreich & Rappaport and Renner & Sicardy, is due to interaction of resonances in the resonance multiplet corresponding to the 121:118 commensurability of the mean motions of the satellites. It is shown rigorously that the system moves in adiabatic regime. The Lyapunov time (the 'time horizon of predictability' of the motion) is calculated analytically and compared to the available numerical–experimental estimates. For this purpose, a method of analytical estimation of the maximum Lyapunov exponent in the perturbed pendulum model of non-linear resonance is applied. The method is based on the separatrix map theory. An analytical estimate of the width of the chaotic layer is made as well, based on the same theory. The ranges of chaotic diffusion in the mean motion are shown to be almost twice as big compared to previous estimates for both satellites.  相似文献   

On reverberation and cross-correlation estimates of the size of the broad-line region in active galactic nuclei     

A. V. Melnikov  I. I. Shevchenko 《Monthly notices of the Royal Astronomical Society》2008,389(1):478-488

It is known that the dependence of the emission-line luminosity of a typical cloud in the active galactic nuclei (AGN) broad-line regions (BLRs) upon the incident flux of ionizing continuum can be non-linear. We study how this non-linearity can be taken into account in estimating the size of the BLR by means of the 'reverberation' methods. We show that the BLR size estimates obtained by cross-correlation of emission-line and continuum light curves can be much (up to an order of magnitude) less than the values obtained by reverberation modelling. This is demonstrated by means of numerical cross-correlation and reverberation experiments with model continuum flares and emission-line transfer functions and by means of practical reverberation modelling of the observed optical spectral variability of NGC 4151. The time behaviour of NGC 4151 in the Hα and Hβ lines is modelled on the basis of the observational data by Kaspi et al. and the theoretical BLR model by Shevchenko. The values of the BLR parameters are estimated that allow to judge on the size and physical characteristics of the BLR. The small size of the BLR, as determined by the cross-correlation method from the data of Kaspi et al., is shown to be an artefact of this method. So, the hypothesis that the BLR size varies in time is not necessitated by the observational data.  相似文献   

On the rotational dynamics of Prometheus and Pandora     

A. V. Melnikov  I. I. Shevchenko 《Celestial Mechanics and Dynamical Astronomy》2008,101(1-2):31-47

Possible rotation states of two satellites of Saturn, Prometheus (S16) and Pandora (S17), are studied by means of numerical experiments. The attitude stability of all possible modes of synchronous rotation and the motion close to these modes is analyzed by means of computation of the Lyapunov spectra of the motion. The stability analysis confirms that the rotation of Prometheus and Pandora might be chaotic, though the possibility of regular behaviour is not excluded. For the both satellites, the attitude instability zones form series of concentric belts enclosing the main synchronous resonance center in the phase space sections. A hypothesis is put forward that these belts might form “barriers” for capturing the satellites in synchronous rotation. The satellites in chaotic rotation can mimic ordinary regular synchronous behaviour: they preserve preferred orientation for long periods of time, the largest axis of satellite’s figure being directed approximately towards Saturn.  相似文献   

Co,Hf, Ce,Cr, Th,and REE Charateristics of Modern Bottom Sediments of the Barents Sea     

Maslov  A. V.  Politova  N. V.  Shevchenko  V. P.  Kozina  N. V.  Novigatsky  A. N.  Kravchishina  M. D. 《Doklady Earth Sciences》2019,485(1):298-302

Doklady Earth Sciences - The Co, Hf, Ce, Cr, Th, and REE characteristics are analyzed for modern sediments collected by a bottom grab during the 67th and 68th cruises of R/V Akademik Mstislav...  相似文献   

Experience of Studying the Turbulent Structure of the Atmospheric Boundary Layer Using an Unmanned Aerial Vehicle     

Chechin  D. G.  Artamonov  A. Yu.  Bodunkov  N. E.  Zhivoglotov  D. N.  Zaytseva  D. V.  Kalyagin  M. Yu.  Kouznetsov  D. D.  Kounashouk  A. A.  Shevchenko  A. M.  Shestakova  A. A. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(5):526-532

Izvestiya, Atmospheric and Oceanic Physics - The growing relevance of the use of unmanned aerial vehicles (UAVs) for studying turbulence in the atmospheric boundary layer (ABL) is associated with...  相似文献