Number of found documents: 244
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Chaotic motion in the Johannsen-Psaltis spacetime
Zelenka, Ondřej; Lukes-Gerakopoulos, Georgios
2017 - English
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. Keywords: chaos; geodesic motion; black holes Fulltext is available at external website.
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 ...

Zelenka, Ondřej; Lukes-Gerakopoulos, Georgios
Astronomický ústav, 2017

Numerical implementation of equations for photon motion in Kerr spacetime
Bursa, Michal
2017 - English
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. Keywords: Kerr spacetime; raytracing; photon motion Fulltext is available at external website.
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 ...

Bursa, Michal
Astronomický ústav, 2017

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 - English
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. Keywords: black hole physics – Galaxy: centre –; galaxy centra; radiative transfer Fulltext is available at external website.
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 ...

Zajaček, M.; Karas, Vladimír; Hosseini, E.; Eckart, A.; Shahzamanian, B.; Valencia-S, M.; Peissker, F.; Busch, G.; Britzen, S.; Zensus, J. A.
Astronomický ústav, 2017

Cristannus de Prachaticz’s Treatises on the Astrolabe
Hadrava, Petr; Hadravová, Alena
2017 - English
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 Keywords: history of astronomy; computer-asisted critical editions; digital stematology Available at various institutes of the ASCR
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 ...

Hadrava, Petr; Hadravová, Alena
Astronomický ústav, 2017

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 - English
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. Keywords: ALMA; images regions; magnetic neutral lines Fulltext is available at external website.
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 ...

Skokić, Ivica; Brajša, R.; Sudar, D.; Kuhar, M.; Benz, A. O.
Astronomický ústav, 2017

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 - English
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 Keywords: ALMA; solar research; observing modes Fulltext is available at external website.
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 ...

Brajša, R.; Skokić, Ivica; Bárta, Miroslav; Bastian, T.S.; Shimojo, M.; White, S. M.; Iwai, K.
Astronomický ústav, 2017

Modelling the bow–shock evolution along the DSO/G2 orbit in the Galactic centre
Štofanová, L.; Zajaček, M.; Kunneriath, D.; Eckart, A.; Karas, Vladimír
2017 - English
A radially directed flow of gaseous environment from a supermassive black hole affects the evolution of a bow–shock that develops along the orbit of an object passing through the pericentre. The bow–shock exhibits asymmetry between the approaching and receding phases, as can be seen in calculations of the bow-shock size, the velocity profile along the shocked layer, and the surface density of the bow–shock,\nand by emission-measure maps. We discuss these effects in the context of the recent pericentre transit of DSO/G2 near Sagittarius A*. Keywords: galactic center; Sagittarius A*; astrophysical processes Fulltext is available at external website.
Modelling the bow–shock evolution along the DSO/G2 orbit in the Galactic centre

A radially directed flow of gaseous environment from a supermassive black hole affects the evolution of a bow–shock that develops along the orbit of an object passing through the pericentre. The ...

Štofanová, L.; Zajaček, M.; Kunneriath, D.; Eckart, A.; Karas, Vladimír
Astronomický ústav, 2017

ALMA Development Plan Study: Solar Research with ALMA. Science cases
Brajša, R.; Bárta, Miroslav; Skokić, Ivica; Wedemeyer, S.; Bastian, T.S.; Shimojo, M.; White, S. M.
2016 - English
A mid-term progress 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 results of the WP1: Solar science cases. Possible solar science cases have been identified and optimal observation, calibration and imaging strategies for individual cases suggested. The report has been reviewed by international expert panel nominated by ESO.\n\n\n Keywords: ALMA; solar research; observing modes Fulltext is available at external website.
ALMA Development Plan Study: Solar Research with ALMA. Science cases

A mid-term progress 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 ...

Brajša, R.; Bárta, Miroslav; Skokić, Ivica; Wedemeyer, S.; Bastian, T.S.; Shimojo, M.; White, S. M.
Astronomický ústav, 2016

ALMA Development Plan Study: Solar Research with ALMA. Progress Report
Brajša, R.; Bárta, Miroslav; Skokić, Ivica; Bastian, T.S.; Shimojo, M.; White, S. M.; Iwai, K.
2016 - English
A mid-term progress 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 results of the WP2: Observing modes and ALMA software requirements. Technical ALMA requirements of solar observing mode are studied and summarised. The ALMA user software was reviewed and its changes complying with the Solar Observing Mode has been proposed. The report has been reviewed by international expert panel nominated by ESO.\n\n\n Keywords: ALMA; solar research; observing modes Fulltext is available at external website.
ALMA Development Plan Study: Solar Research with ALMA. Progress Report

A mid-term progress 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. ...

Brajša, R.; Bárta, Miroslav; Skokić, Ivica; Bastian, T.S.; Shimojo, M.; White, S. M.; Iwai, K.
Astronomický ústav, 2016

Study of Cataclysmic Variables with the Satellites LOFT and Gaia
Hudec, René; Šimon, Vojtěch
2015 - English
The goal of this paper is to discuss the capabilities of ESA satellite missions Gaia (already in space) and LOFT\n(considered for the ESA M4 slot) for investigation of cataclysmic variables (CVs). Both Gaia and LOFT\ncan contribute to study of CVs and related objects. Spectrophotometry and low dispersion spectroscopy are the most important for CV analyses with the observations of Gaia. We present the possible strategies for investigation of CVs in the sampled photometric\nand spectroscopic data provided by Gaia. E.g. statistical properties of the long-term activity of various types of CVs can be determined from them. LOFTcan be a promising satellite to provide a sensitive X-ray monitor which will enable to investigate the little studied long-term activity of various types of CVs (especially the magnetic ones) in the X-ray band. Keywords: catalysmic variables; dwarf novae -; intermediate polar Available at various institutes of the ASCR
Study of Cataclysmic Variables with the Satellites LOFT and Gaia

The goal of this paper is to discuss the capabilities of ESA satellite missions Gaia (already in space) and LOFT\n(considered for the ESA M4 slot) for investigation of cataclysmic variables (CVs). ...

Hudec, René; Šimon, Vojtěch
Astronomický ústav, 2015

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