Astronomický ústav

Nejnovější přírůstky:
2018-03-09
13:20
Flows along arch filaments observed in the GRIS `very fast spectroscopic mode'
Gonzalez Manrique, S. J. ; Denker, C. ; Kuckein, C. ; Pastor Yabar, A. ; Collados Vera, M. ; Verma, M. ; Balthasar, H. ; Diercke, A. ; Fischer, C.E. ; Gömöry, P. ; Bello González, N. ; Schlichenmaier, R. ; Cubas Armas, M. ; Berkefeld, T. ; Feller, A. ; Hoch, S. ; Hofmann, A. ; Lagg, A. ; Nicklas, H. ; Orozco Suárez, D. ; Schmidt, D. ; Schmid, W. ; Sigwarth, M. ; Sobotka, Michal ; Solanki, S.K. ; Soltau, D. ; Staude, J. ; Strassmeier, K.G. ; Volkmer, R. ; von der Lühe, O. ; Waldmann, T.A.
A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the "very fast spectroscopic mode" of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the "very fast spectroscopic mode" by tracking chromospheric high-velocity features in the arch filament system.

Úplný záznam
2018-03-09
13:20
Identification of features in solar ALMA images and comparison with solar atmospheric models
Skokić, Ivica ; Brajša, R. ; Sudar, D. ; Kuhar, M. ; Benz, A. O.
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.

Úplný záznam
2018-03-09
13:19
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.
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

Úplný záznam
2018-03-09
13:19
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.
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

Úplný záznam
2018-03-09
13:19
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.
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

Úplný záznam
2018-03-09
13:19
Cristannus de Prachaticz’s Treatises on the Astrolabe
Hadrava, Petr ; Hadravová, Alena
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

Úplný záznam
2018-03-07
15:28
Chaotic motion in the Johannsen-Psaltis spacetime
Zelenka, O. ; Lukes-Gerakopoulos, Georgios
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.

Úplný záznam
2018-03-07
15:28
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.
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.

Úplný záznam
2018-03-07
15:28
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.
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.

Úplný záznam
2018-03-07
15:28
Hysteresis behavior of shocks in low angular momentum flows
Suková, Petra
In this work we present the GRMHD 1D simulations of accreting matter with variable angular momentum. We focus on the existence and behaviour of the shock in the flow. We show that the location of the shock front responds to the change of the angular momentum, which also causes the accretion rate onto the black hole to vary on different time scales. We study the possible hysteresis behaviour of the shock\nfront during the time evolution of the flow. We discuss the potential observational effects of this phenomenon.

Úplný záznam