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1.
The effect of Faraday rotation is shown to lead to the appearance of linear polarization of stellar radiation scattered in an optically-thin circumstellar electron-magnetized shell, even in the case when the shell is spherical. The spectral dependence of the polarization degree is evaluated for scattering in (i) a spherically-symmetric magnetized shell with a power-law radial dependence of the electron density, and (ii) a non-spherical ellipsoidal uniform envelope. The position of maximum in the polarization spectrum permits us to determine the magnetic field magnitude on a star surface. If the rotational and magnetic axes do not coincide, the periodic variability of the polarization will be observed with the period of stellar rotation. Some Be-stars, such as Cas, 48 Lib, EW Lac, Aqr, HD 45677, X Per, are proposed as candidates to be investigated for magnetic fields, as well as some stars of the T Tau-type. This method may be also applied to supernovae shells. 相似文献
2.
M. Yu. Piotrovich N. A. Silant’ev Yu. N. Gnedin T. M. Natsvlishvili S. D. Buliga 《Astronomy Reports》2016,60(5):486-497
The magnetic-field structure in regions of stationary, planar accretion disks around active galactic nuclei where general-relativistic effects can be neglected (from 10 to 200 gravitational radii) is considered. It is assumed that the magnetic field in the outer edges of the disk, which forms in the magnetosphere of the central black hole during the creation of the relativisitic jets, corresponds to the field of a magnetic dipole perpendicular to the plane of the disk. In this case, the azimuthal field component Bφ in the disk arises due to the presence of the radial field Bρ and the azimuthal velocity component Uφ. The value of the magnetic field at the inner radius of the disk is taken to correspond to the solution of the induction equation in a diffusion approximation. Numerical solutions of the induction equation are given for a number of cases. 相似文献
3.
The spins of supermassive black holes in FR I and FR II radio galaxies are estimated using two models for the generation of the relativisitic jets, based on the Blandford–Znajek and Blandford–Payne mechanisms: the hybrid model of Meier and a flux-trapping model. The magnetic field at the event horizon is estimated assuming equipartition between the energy densities of the magnetic field and the accreting material. The magnetic field near the inner edge of the accretion disk is estimated assuming equipartition between the magnetic pressure and the radiation pressure, and also assuming proportionality between the magnetic field and the spin. In the case of FR I objects, both mechanisms for the generation of the jets (the hybrid model of Meier and a flux-trapping model) are efficient. For the FR II objects, equipartition between the energy densities of the magnetic field and the accretion flow facilitates stronger retrograde rotation of the supermassive black hole. Plots of spin versus mass suggest a predominantly chaotic character for the accretion in both types of radio galaxies. 相似文献
4.
V. L. Afanas’ev M. Yu. Piotrovich Yu. N. Gnedin S. D. Buliga T. M. Natsvlishvili 《Astronomy Reports》2018,62(2):138-143
The results of spectropolarimetric observations of a number of magnetic white dwarfs obtained on the 6-m optical telescope of the Special Astrophysical Observatory are presented. The observations were carried out using the SCORPIO focal aperture-ratio reducer in a spectropolarimetric regime. Two characteristic dependences of the degree of polarization on the wavelength are observed. For one group of objects, the degree of linear polarization grows with wavelength, suggesting that the alignment of atoms and molecules in Rydberg states in the atmosphere of the white dwarf due to the action of its magnetic field influences scattering processes. The second group of objects displays an increase in the degrees of both linear and circular polarization with wavelength, providing evidence for the presence of protoplanetary disks around these magnetic white dwarfs, in which the alignment of circumstellar grains leads to the observed behavior. 相似文献
5.
V. L. Afanasiev N. V. Borisov Yu. N. Gnedin T. M. Natsvlishvili M. Yu. Piotrovich S. D. Buliga 《Astronomy Letters》2011,37(5):302-310
We present the results of our spectropolarimetric observations for a number of active galactic nuclei (AGNs) carried out at
the 6-m telescope with the SCORPIO focal reducer. The derived wavelength dependences of the polarization have been analyzed
by taking into account the Faraday rotation of the polarization plane on the photon mean free path in a magnetized accretion
disk. As a result, based on traditional accretion disk models, we have determined the magnetic field strength and distribution
and a number of physical parameters of the accreting plasma in the region where the optical radiation is generated. 相似文献
6.
M. Yu. Piotrovich N. A. Silant’ev Yu. N. Gnedin T. M. Natsvlishvili 《Astrophysical Bulletin》2011,66(3):320-324
Various relations are found between the key parameters of black holes and active galactic nuclei. Some have a statistical
property, others follow from the theoretical consideration of the evolution of these objects. In this paper we use a recently
discovered empirical relation between the characteristic frequency of quasi-periodic oscillations of radiation ν
br
of black holes, their masses and matter accretion rates to determine the magnetic field strength B
H
at the black hole event horizon. Since the characteristic frequency can be determined from observations, the use of a new
relation for the estimations of magnetic field B
H
can yield more definite results, since we are decreasing the number of the unknown or poorly-determined parameters of objects
(it especially concerns the accretion rate Ṁ). The typical values which we have found are B
H
≃ 108G for the stellar mass black holes, and B
H
≃ 104G for the supermassive black holes. Besides, we demonstrate that if the linear polarization of an object is caused by the
radiation of a magnetized accretion disk, then the degree of observable polarization is p ∼ ν
br
−1/2. 相似文献
7.
This article is devoted to the Pulkovo astronomer, Prof. Aleksandr Nikolaevich Deich (Deutsch) (1899-1986), on the 110-th
anniversary of his birth. Deich is known as the founder of the Pulkovo program for observing stars with invisible companions,
as well as for his research on the star 61 Cyg, which was suspected, in his time, of having invisible companions with the
masses of planets. Astrometric observations on the long focus astrograph and searches for exoplanets of nearby stars are reviewed.
Modern methods of searching for exoplanets are summarized briefly. Instrument designs proposed by astronomers at Kharkiv (Scientific
Research Institute of Astronomy at Kharkiv National University, NIIA KhNU) and Kazan (Institute of Astronomy, Kazan State
University, AO KGU) for use in the search for low-mass dark components of stars are discussed. Examples are given of confirmations
of invisible companions of stars which were first discovered by observation. A number of theoretical results on this topic
from Kharkiv National University (Scientific Research Institute of Astronomy at Kharkiv and the Dept. of Astronomy) are noted. 相似文献
8.
M. A. Kharinov A. M. Finkel’shteĭn A. V. Ipatov O. A. Tsiopa Yu. N. Gnedin M. Yu. Piotrovich 《Astronomy Reports》2010,54(9):853-860
Results of radio observations of the cosmic gamma-ray burst GRB 080319B at 8.45 GHz during the afterglow are reported. The
observations were carried out on telescopes of the Zelenchukskaya and Svetloe Observatories of the Institute of Applied Astronomy,
Russian Academy of Sciences. Two outbursts in the radio brightness were detected in the afterglow of GRB 080319B. A total
of 148 radio observations were performed at 3.5, 6.2, and 13 cm. The observations were conducted in a mode with smooth scanning
in elevation, which was also used to update the flux densities of the primary reference sources. The first powerful radio
outburst was recorded on March 28, 2008, 6.86d after the gamma-ray burst, when the maximum flux density was F
8.45 GHz = 44 ± 12 mJy. Almost two months later, a second increase in the radio brightness was observed. The flux density monotonically
increased from 19 mJy (59.55d) to 34mJy (59.79d) over 6.5 h; 1.17 d later, the flux density fell to 12mJy.At this last epoch, the radio flux demonstrated variability within
3σ on timescales of 9d−10d. The detected radio brightness increases are interpreted in terms of MHD interactions of a fast plasma outflow with a cloud
of inhomogeneous surrounding medium. This interaction is accompanied by restructuring of the relativistic plasma outflow;
the analysis of this process has been carried out. 相似文献
9.
V. L. Afanas’ev N. V. Borisov Yu. N. Gnedin S. D. Buliga T. M. Natsvlishvili M. Yu. Piotrovich 《Astronomy Reports》2014,58(10):725-732
Spectropolarimetric observations of a number of Active Galactic Nuclei obtained using the SCORPIO-2 aperture focal reducer installed on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences are used to estimate physical parameters of these objects. The measured polarization and its wavelength dependence are consistent with the expectations of a standard accretion-disk model taking into account the effect of Faraday depolarization over the mean free path of the emitted photons. Estimates of the magnetic field in the accretion disk near the innermost stable orbit and the spin of the accreting central black hole are obtained. It is concluded that supermassive black holes with standard accretion disks and equal magnetic and radiative pressures are primarily Kerr black holes. 相似文献
10.