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Počet nalezených dokumentů:
248
Publikováno od
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Truncation of AGN jets by their interaction with a passing star cluster
Araudo, Anabella; Karas, Vladimír
2017 - anglický
We study the interaction of a cluster of massive stars with AGN jets as a continuous process that must occur repetitively in galactic nuclei and a promising mechanism that can trigger production of high–energy particles.
Klíčová slova:
active galaxies; jets; clusters
Dokument je dostupný na externích webových stránkách.
Truncation of AGN jets by their interaction with a passing star cluster
We study the interaction of a cluster of massive stars with AGN jets as a continuous process that must occur repetitively in galactic nuclei and a promising mechanism that can trigger production of ...
Wave excitation at Lindblad resonances using the method of multiple scales
Horák, Jiří
2017 - anglický
In this note, the method of multiple scales is adopted to the problem of excitation of non–axisymmetric acoustic waves in vertically integrated disk by tidal gravitational fields. We derive a formula describing a waveform of exited wave that is uniformly valid in a whole disk as long as only a single Lindblad resonance is present. Our formalism is subsequently applied to two classical problems: trapped p–mode oscillations in relativistic accretion disks and the excitation of waves in infinite disk.
Klíčová slova:
perturbation methods; disk dynamics; Lindblad resonances
Dokument je dostupný na externích webových stránkách.
Wave excitation at Lindblad resonances using the method of multiple scales
In this note, the method of multiple scales is adopted to the problem of excitation of non–axisymmetric acoustic waves in vertically integrated disk by tidal gravitational fields. We derive a formula ...
Epicyclic oscillations of thick relativistic disks
Horák, Jiří; Straub, O.; Šrámková, E.; Goluchová, K.; Török, G.
2017 - anglický
We study epicyclic oscillations of thick relativistic tori with constant specific angular momentum distribution using the finite element numerical method. We have compared frequencies of the axisymmetric and non-axisymmetric modes with the analytic formulae obtained by Straub and Šrámková (2009) and Fragile et al. (2016). We have found excellent agreement in the case of axisymmetric radial epicyclic modes. In the case of the axisymmetric vertical epicyclic modes and non-axisymmetric modes in general, the analytic approximation agrees with numerical results only for tori of moderate thicknesses. Our analysis also revealed an instability of the thick constant angular momentum tori with respect to the radial epicyclic oscillation.
Klíčová slova:
black hole physics; accretion disks; oscillation
Dokument je dostupný na externích webových stránkách.
Epicyclic oscillations of thick relativistic disks
We study epicyclic oscillations of thick relativistic tori with constant specific angular momentum distribution using the finite element numerical method. We have compared frequencies of the ...
A one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations
Török, G.; Goluchová, K.; Šrámková, J.; Horák, Jiří; Bakala, P.; Urbanec, M.
2017 - anglický
Timing analysis of X-ray flux in more than a dozen low-mass X-ray binary systems containing a neutron star reveals remarkable correlations between frequencies of two characteristic peaks present in the power-density spectra. We find a simple analytic relation that well reproduces all these individual correlations. We link this relation to a physical model which involves accretion rate modulation caused by an oscillating torus.
Klíčová slova:
X-rays binaries; accretion Disks; neutron stars
Dokument je dostupný na externích webových stránkách.
A one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations
Timing analysis of X-ray flux in more than a dozen low-mass X-ray binary systems containing a neutron star reveals remarkable correlations between frequencies of two characteristic peaks present in ...
Chaotic motion in the Johannsen-Psaltis spacetime
Zelenka, Ondřej; Lukes-Gerakopoulos, Georgios
2017 - anglický
The Johannsen-Psaltis spacetime is a perturbation of the Kerr spacetime designed to avoid pathologies like naked singularities and closed timelike curves. This spacetime depends not only on the mass and the spin of the compact object, but also on extra parameters, making the spacetime deviate from Kerr. In this work we consider only the lowest order physically meaningful extra parameter. We use numerical examples to show that geodesic motion in this spacetime can exhibit chaotic behavior. We study the corresponding phase space by using Poincaré sections and rotation numbers to show chaotic behavior, and we use Lyapunov exponents to directly estimate the sensitivity to initial conditions for chaotic orbits.
Klíčová slova:
chaos; geodesic motion; black holes
Dokument je dostupný na externích webových stránkách.
Chaotic motion in the Johannsen-Psaltis spacetime
The Johannsen-Psaltis spacetime is a perturbation of the Kerr spacetime designed to avoid pathologies like naked singularities and closed timelike curves. This spacetime depends not only on the mass ...
Cristannus de Prachaticz’s Treatises on the Astrolabe
Hadrava, Petr; Hadravová, Alena
2017 - anglický
The authors' computer methods of collation and statistical treatment of variant readings are summarized and illustrated on the example of the critical edition of the treatises on Composition and Use of the Astrolabe written by the 15th-century Czech scholar Cristannus de Prachaticz.\n
Klíčová slova:
history of astronomy; computer-asisted critical editions; digital stematology
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Cristannus de Prachaticz’s Treatises on the Astrolabe
The authors' computer methods of collation and statistical treatment of variant readings are summarized and illustrated on the example of the critical edition of the treatises on Composition and Use ...
Identification of features in solar ALMA images and comparison with solar atmospheric models
Skokić, Ivica; Brajša, R.; Sudar, D.; Kuhar, M.; Benz, A. O.
2017 - anglický
Various solar features were identified in the full-disc single-dish ALMA images taken at wavelength of 1.2 and 2.8 mm and compared with H.alpha., Ca II K and EUV images and magnetograms. Assuming thermal bremsstrahlung as the dominant radiation mechanism, several models were constructed to calculate the brightness temperature of various solar features (quiet and active solar regions, filaments and coronal holes) in a wavelength range from 0.3 to 10 mm. It is found that model predictions are in a qualitative agreement with ALMA images where active regions appear brighter, while filaments and coronal holes are not discernible from the quiet Sun level. It is also found that in ALMA images regions around magnetic neutral lines appear darker than the quiet Sun. Models predict a critical frequency below which filaments should appear in absorption and above it in emission.
Klíčová slova:
ALMA; images regions; magnetic neutral lines
Dokument je dostupný na externích webových stránkách.
Identification of features in solar ALMA images and comparison with solar atmospheric models
Various solar features were identified in the full-disc single-dish ALMA images taken at wavelength of 1.2 and 2.8 mm and compared with H.alpha., Ca II K and EUV images and magnetograms. Assuming ...
Numerical implementation of equations for photon motion in Kerr spacetime
Bursa, Michal
2017 - anglický
Raytracing is one of the essential tools for accurate modeling of spectra and variability of various astrophysical objects. It has a major importance in relativisticenvironments, where light endures to a number of relativistic effects. Because the trajectories of light rays in curved spacetimes, and in Kerr spacetime in particular, are highly non-trivial, we summarize the equations governing the motion of photon\n(or any other zero rest mass particle) and give analytic solution of the equations thatcan be further used in practical computer implementations.
Klíčová slova:
Kerr spacetime; raytracing; photon motion
Dokument je dostupný na externích webových stránkách.
Numerical implementation of equations for photon motion in Kerr spacetime
Raytracing is one of the essential tools for accurate modeling of spectra and variability of various astrophysical objects. It has a major importance in relativisticenvironments, where light ...
Polarization properties of bow shock sources close to the Galactic centre
Zajaček, M.; Karas, Vladimír; Hosseini, E.; Eckart, A.; Shahzamanian, B.; Valencia-S, M.; Peissker, F.; Busch, G.; Britzen, S.; Zensus, J. A.
2017 - anglický
Several bow shock sources were detected and resolved in the innermost parsec from the supermassive black hole in the Galactic centre. They show several distinct characteristics, including an excess towards mid-infrared wavelengths and a significant linear polarization as well as a characteristic prolonged bow-shock shape. These features give hints about the presence of a non-spherical dusty envelope generated\nby the bow shock. The Dusty S-cluster Object (also denoted as G2) shows similar characteristics and it is a candidate for the closest bow shock with a detected proper motion in the vicinity of Sgr A*, with the pericentre distance of only approx. 2000 Schwarzschild radii. However, in the continuum emission it is a point-like source and hence we use Monte Carlo radiative transfer modeling to reveal its possible three-dimensional structure. Alongside the spectral energy distribution, the detection of polarized continuum emission in the near-infrared Ks-band (2.2 micrometers) puts additional constraints on the geometry of the source.
Klíčová slova:
black hole physics – Galaxy: centre –; galaxy centra; radiative transfer
Dokument je dostupný na externích webových stránkách.
Polarization properties of bow shock sources close to the Galactic centre
Several bow shock sources were detected and resolved in the innermost parsec from the supermassive black hole in the Galactic centre. They show several distinct characteristics, including an excess ...
ALMA Development Plan Study: Solar Research with ALMA. Final report
Brajša, R.; Skokić, Ivica; Bárta, Miroslav; Bastian, T.S.; Shimojo, M.; White, S. M.; Iwai, K.
2017 - anglický
The final report of the research/development project Solar Research with ALMA: Development study. The project has been demanded by ESO to the Czech node of the European ALMA Regional Center. The main goal of the project is development of the specific Solar Observing Mode for ALMA observatory. The report on demand of ESO summarizes in detail results of the WP3: Optimum strategies for project preparation, execution and post-processing. This summary of the second term of the project is precedded by a brief annoation of results described in the prevoius two mid-term reports. Main result: Based on the test (Science Verification) solar observations, which we took part in Chile in December 2014 and 2015, it has been shown that suggested procedures for solar observations with ALMA, including subsequent calibration and imaging, do work and can be used for regular ALMA science program. The report has been reviewed by international expert panel nominated by ESO.\n\n\n\n
Klíčová slova:
ALMA; solar research; observing modes
Dokument je dostupný na externích webových stránkách.
ALMA Development Plan Study: Solar Research with ALMA. Final report
The final report of the research/development project Solar Research with ALMA: Development study. The project has been demanded by ESO to the Czech node of the European ALMA Regional Center. The main ...
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