Central Astronomical Observatory at Pulkovo

Saint Petersburg, Russia

Central Astronomical Observatory at Pulkovo

Saint Petersburg, Russia
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Krasnikov S.,Central Astronomical Observatory at Pulkovo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2016

The "trousers" spacetime is a pair of flat two-dimensional cylinders ("legs") merging into a single one ("trunk"). In spite of its simplicity this spacetime has a few features (including, in particular, a naked singularity in the "crotch") each of which is presumably unphysical, but for none of which a mechanism is known able to prevent its occurrence. Therefore, it is interesting and important to study the behavior of the quantum fields in such a space. Anderson and DeWitt were the first to consider the free scalar field in the trousers spacetime. They argued that the crotch singularity produces an infinitely bright flash, which was interpreted as evidence that the topology of space is dynamically preserved. Similar divergencies were later discovered by Manogue, Copeland, and Dray who used a more exotic quantization scheme. Later yet the same result obtained within a somewhat different approach led Sorkin to the conclusion that the topological transition in question is suppressed in quantum gravity. In this paper I show that the Anderson-DeWitt divergence is an artifact of their choice of the Fock space. By choosing a different one-particle Hilbert space one gets a quantum state in which the components of the stress-energy tensor (SET) are bounded in the frame of a free-falling observer. © 2016 American Physical Society.

Tokovinin A.,Cerro Tololo Inter American Observatory | Kiyaeva O.,Central Astronomical Observatory at Pulkovo
Monthly Notices of the Royal Astronomical Society | Year: 2015

A sample of 477 solar-type binaries within 67 pc with projected separations larger than 50 au is studied by a new statistical method. Speed and direction of the relative motion are determined from the short observed arcs or known orbits, and their joint distribution is compared to the numerical simulations. By inverting the observed distribution with the help of simulations, we find that average eccentricity of wide binaries is 0.59 ± 0.02 and the eccentricity distribution can be modelled as f(e) ≈ 1.2e + 0.4. However, wide binaries containing inner subsystems, i.e. triple or higher order multiples, have significantly smaller eccentricities with the average e = 0.52±0.05 and the peak at e~0.5.We find that the catalogue of visual orbits is strongly biased against large eccentricities. A marginal evidence of eccentricity increasing with separation (or period) is found for this sample. Comparison with spectroscopic binaries proves the reality of the controversial period-eccentricity relation. The average eccentricity does increase with binary period, being 0.39 for periods from 102 to 103 d and 0.59 for the binaries studied here (105-106 d). © 2015 The Authors. Published by Oxford University Press.

Krasnikov S.,Central Astronomical Observatory at Pulkovo
Classical and Quantum Gravity | Year: 2014

The fact that the null generators of a future Cauchy horizon are past-complete was first proved by Hawking and Ellis (1973 The Large Scale Structure of Spacetime (Cambridge: Cambridge University Press)). Then, Budzyński, Kondracki and Królak outlined a proof free from the error found in the original one (2000 New properties of Cauchy and event horizons arXiv:gr-qc/0011033). Now, Minguzzi has published his version of the proof (2014 J. Math. Phys. 55 082503), patching a previously unnoticed hole in the preceding two. I am not aware of any flaws in that last proof, but it is quite difficult. In this note, I present a simpler one. © 2014 IOP Publishing Ltd.

Gnedin Y.N.,Central Astronomical Observatory at Pulkovo | Piotrovich M.Y.,Central Astronomical Observatory at Pulkovo
International Journal of Modern Physics A | Year: 2016

We discuss the astronomical methods of searching for light Goldstone bosons (axions and arions). The basic idea is to use processes of coupling between axions and photons: a) the axion decay into two photons; b) the transformation process of photons into axions (arions) in the magnetic fields of stars and also of interstellar and intergalactic media; c) the inverse process of transformations of axions (arions) which are generated into cores of stars into X-ray photons. The decaying axions affect upon the diffuse extragalactic background radiation, the brightness of the night sky and especially on the intergalactic light of clusters of galaxies due to generation of the axion radiative decay emission line. The processes (b) and (c) are strongly dependent on polarization state of photon and may produce a noticeable amount of linear polarization. © 2016 World Scientific Publishing Company.

Sokolov N.A.,Central Astronomical Observatory at Pulkovo
Astrophysics and Space Science | Year: 2010

The spectrophotometric variability of the magnetic CP star 56 Arietis (56 Ari) in the ultraviolet spectral region from 1950 to 3200 Å is investigated. This study is based on the archival International Ultraviolet Explorer data obtained at different phases of the rotational cycle. The brightness of 56 Ari is not constant in the investigated wavelengths over the whole rotational period. The monochromatic light curves continuously change their shape with wavelength. This indicates that we do not observe a truly 'null wavelength region' where the monochromatic light curve has a zero amplitude. Probably, an uneven surface distribution of silicon and iron mainly influences the flux redistribution from the far-UV to near-UV spectral regions, although additional sources of opacity may be involved. The redistribution of the flux at phase 0.25 is connected with the nonuniform distribution of silicon on the stellar surface of 56 Ari. On the other hand, the redistribution of the flux at phase 0.65 is quite complex, because there are additional blocking and redistribution of the flux by iron lines in the near-UV spectral region. © 2010 Springer Science+Business Media B.V.

Krasnikov S.,Central Astronomical Observatory at Pulkovo
Classical and Quantum Gravity | Year: 2015

General relativity lacks the notion of the speed of gravity. This is inconvenient, and the current paper is aimed at filling this gap. To that end I introduce the concept of the 'alternative' and argue that its variation, called the 'superluminal alternative', describes exactly what one understands by the 'superluminal gravitational signal'. Another, closely related, object called the 'semi-superluminal alternative' corresponds to the situation in which a massive (and therefore gravitating) body reaches its destination sooner than a photon would if the latter were sent instead of the body. I prove that in general relativity constrained by the condition that only globally hyperbolic spacetimes are allowed, (1) semi-superluminal alternatives are absent, and (2) under some natural conditions and conventions, admissible superluminal alternatives are absent too. © 2015 IOP Publishing Ltd.

Krasnikov S.,Central Astronomical Observatory at Pulkovo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The building of a time machine, if possible at all, requires the relevant regions of spacetime to be compact (that is, physically speaking, free from sources of unpredictability such as infinities and singularities). Motivated by this argument we consider the spacetimes with the compactly determined Cauchy horizons (CDCHs), the defining property of which is the compactness of J-(U)̄ J+(S0), where U is an open subset of the Cauchy horizon and S0 is a Cauchy surface of the initial globally hyperbolic region Min. The following two facts are established: (1) Min has no globally hyperbolic maximal extension. This means that, by shaping appropriately a precompact portion of a globally hyperbolic region, one can force the Universe to produce either a closed causal curve, or a quasiregular singularity, whichever it abhors less. (2) Before a CDCH is formed a null geodesic appears which infinitely approaches the horizon returning again and again in the same - arbitrarily small - region. The energy of the photon moving on such a geodesic increases with each passage, or at least falls insufficiently fast. As a result, an observer located in the mentioned region would see a bunch of photons passing through his laboratory with the arbitrarily large total energy. We speculate that this phenomenon may have observable consequences. © 2014 American Physical Society.

Ivanov V.G.,Central Astronomical Observatory at Pulkovo | Miletsky E.V.,Central Astronomical Observatory at Pulkovo
Solar Physics | Year: 2010

Based on the extended Greenwich - NOAA/USAF catalogue of sunspot groups, it is demonstrated that the parameters describing the latitudinal width of the sunspot generating zone (SGZ) are closely related to the current level of solar activity, and the growth of the activity leads to the expansion of the SGZ. The ratio of the sunspot number to the width of the SGZ shows saturation at a certain level of the sunspot number, and above this level the increase of the activity takes place mostly due to the expansion of the SGZ. It is shown that the mean latitudes of sunspots can be reconstructed from the amplitudes of solar activity. Using the obtained relations and the group sunspot numbers by Hoyt and Schatten (Solar Phys. 179, 189, 1998), the latitude distribution of sunspot groups ("the Maunder butterfly diagram") for the eighteenth and the first half of the nineteenth centuries is reconstructed and compared with historical sunspot observations. © 2010 Springer Science+Business Media B.V.

Krasnikov S.V.,Central Astronomical Observatory at Pulkovo
Gravitation and Cosmology | Year: 2013

I show that there is a significant lacuna in the proof of the theorem known as "Topological Censorship" (a theorem forbidding a solution of Einstein's equations to have some topological features, such as traversable wormholes, without violating the averaged null energy condition). To fill the lacuna one would probably have to revise the class of spacetimes for which the theorem is formulated. © 2013 Pleiades Publishing, Ltd.

Silant'ev N.A.,Central Astronomical Observatory at Pulkovo | Gnedin Y.N.,Central Astronomical Observatory at Pulkovo | Piotrovich M.Y.,Central Astronomical Observatory at Pulkovo | Natsvlishvili T.M.,Central Astronomical Observatory at Pulkovo | Buliga S.D.,Central Astronomical Observatory at Pulkovo
Monthly Notices of the Royal Astronomical Society | Year: 2016

In most type 1 Seyfert active galactic nuclei (AGNs), the optical linear continuum polarization degree is usually small (less than 1 per cent) and the polarization position angle is nearly parallel to the AGN radio axis. However, there are many type 1 AGNs with unexplained intermediate values for both positional angles and polarization degrees. Our explanation of polarization degree and positional angle of type 1 Seyfert AGNs focuses on the reflection of non-polarized radiation from sub-parsec jets in optically thick accretion discs. The presence of a magnetic field surrounding the scattering media will induce Faraday rotation of the polarization plane, which may explain the intermediate values of positional angles if there is a magnetic field component normal to the accretion disc. The Faraday rotation depolarization effect in the disc diminishes the competition between polarization of the reflected radiation with the parallel component of polarization and the perpendicular polarization from internal radiation of the disc (the Milne problem) in favour of polarization of the reflected radiation. This effect allows us to explain the observed polarization of type 1 Seyfert AGN radiation even though the jet optical luminosity is much lower than the luminosity of the disc. We present the calculation of polarization degrees for a number of type 1 Seyfert AGNs. © 2016 The Authors.

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