Počet nalezených dokumentů: 231
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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. 2017 - anglický 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. Klíčová slova: Sun; chromosphere; photosphere Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Flows along arch filaments observed in the GRIS `very fast spectroscopic mode'

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 ...

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.
Astronomický ústav, 2017

Analytical solution for charged fluid pressure profiles - circulation in combined electromagnetic field Kovář, J.; Slaný, P.; Stuchlík, Z.; Karas, Vladimír; Trova, A. 2017 - anglický We introduce a general transformation leading to an integral form of pressure equations characterizing equilibrium configurations of charged perfect fluid circling in strong gravitational and combined electromagnetic fields. The transformation generalizes our recent analytical treatment applicable to electric or magnetic fields treated separately along with the gravitational one. As an example, we present a particular solution for a fluid circling close to a charged rotating black hole immersed in an asymptotically uniform magnetic field. Klíčová slova: charged perfect fluid; toroidal structures; compact object Dokument je dostupný na externích webových stránkách. Analytical solution for charged fluid pressure profiles - circulation in combined electromagnetic field

We introduce a general transformation leading to an integral form of pressure equations characterizing equilibrium configurations of charged perfect fluid circling in strong gravitational and combined ...

Kovář, J.; Slaný, P.; Stuchlík, Z.; Karas, Vladimír; Trova, A.
Astronomický ústav, 2017

Hysteresis behavior of shocks in low angular momentum flows Suková, Petra 2017 - anglický 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. Klíčová slova: black hole; microquasars; accretion flows Dokument je dostupný na externích webových stránkách. Hysteresis behavior of shocks in low angular momentum flows

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 ...

Suková, Petra
Astronomický ústav, 2017

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 ...

Astronomický ústav, 2017

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 ...

Horák, Jiří
Astronomický ústav, 2017

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 ...

Horák, Jiří; Straub, O.; Šrámková, E.; Goluchová, K.; Török, G.
Astronomický ústav, 2017

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 ...

Török, G.; Goluchová, K.; Šrámková, J.; Horák, Jiří; Bakala, P.; Urbanec, M.
Astronomický ústav, 2017

Chaotic motion in the Johannsen-Psaltis spacetime Zelenka, O.; 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 ...

Zelenka, O.; Lukes-Gerakopoulos, Georgios
Astronomický ústav, 2017

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 ...

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 - 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 ...

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

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