No (136)
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Feature extraction using wavelet power spectrum for stellar spectra clustering
Škoda, Petr; Bromová, P.; Zendulka, J.
2012 - English
This paper analyses the capabilities of using wavelet power spectrum for clustering of Be-type stars spectra. We propose a method using discrete wavelet transform for feature extraction and the wavelet power spectrum as a feature vector.
Keywords:
Be star; stellar spectrum; feature extraction
Available at various institutes of the ASCR
Feature extraction using wavelet power spectrum for stellar spectra clustering
This paper analyses the capabilities of using wavelet power spectrum for clustering of Be-type stars spectra. We propose a method using discrete wavelet transform for feature extraction and the ...
Analysis and Suppression of Noise in Astronomical Video
Švihlík, J.; Fliegel, K.; Koten, Pavel; Jerhotova, E.; Vítek, S.; Páta, P.
2011 - English
This paper is devoted to noise suppression in systems for double station observation of meteors, nowadays known as MAIA (Meteor Automatic Imager and Analyzer). The noise analysis based on acquisition of testing video sequences at different lighting conditions and their statistical evaluation were described in our previous paper The measurement showed that the type of noise generated by the system is signal-independent in a certain illumination range. The noise and image models in the wavelet domain are based on the Generalized Laplacian Model (GLM) and it is the most convenient to estimate the model parameters using the moment method. Furthermore, the noise component may be modeled by the GLM also in the space domain. Overall, we verified that the GLM allows for modeling various types of probability density functions. In the final section of this paper, the performance of the proposed advanced de noising algorithm is verified on the real data, which were acquired in the Astronomical Institute.
Keywords:
MAIA; meteor; noise analysis
Available at various institutes of the ASCR
Analysis and Suppression of Noise in Astronomical Video
This paper is devoted to noise suppression in systems for double station observation of meteors, nowadays known as MAIA (Meteor Automatic Imager and Analyzer). The noise analysis based on acquisition ...
Extremal energy shifts of radiation from a ring near a rotating black hole
Sochora, Vjačeslav; Karas, Vladimír
2010 - English
We present a semi-analytical solution to the problem of finding minimal and maximal energy shifts of radiation originating from an accretion ring near a black hole. The solution is given implicitly in terms of a set of two coupled equations for two unknowns – the constants of photon motion.
Keywords:
black holes; accretion
Available at various institutes of the ASCR
Extremal energy shifts of radiation from a ring near a rotating black hole
We present a semi-analytical solution to the problem of finding minimal and maximal energy shifts of radiation originating from an accretion ring near a black hole. The solution is given implicitly in ...
The study of magnetic clouds: expansion and discontinuities
Lynnyk, A.; Vandas, Marek
2009 - English
Magnetic clouds observed during the 1995-2003 years are fitted using force-free cylindrical flux rope models. The cloud parameters yielded by a static model are compared with those obtained from a modified model that includes magnetic cloud expansion.
Keywords:
magnetic field; magnetic cloud; solar wind
Available at various institutes of the ASCR
The study of magnetic clouds: expansion and discontinuities
Magnetic clouds observed during the 1995-2003 years are fitted using force-free cylindrical flux rope models. The cloud parameters yielded by a static model are compared with those obtained from a ...
Shell-Like Structures in the ISM: Observation Versus Simulations
Sidorin, Vojtěch; Palouš, Jan
2009 - English
The interstellar medium in galaxies is a turbulent environment with a plethora of holes, bubbles and shells. All these shell-like structures are thought to be closely related to the formation, evolution and death of stars. In most cases, they are likely created by the winds of OB stars and supernovae. The material collected along the borders of shells may fragment, become unstable under its own gravity, and create a new generation of stars. This is a variant of triggered star formation referred to as the collect-and-collapse scenario. The aim of our research is to compare numerical simulations of shell-like structures to observations and to search for and investigate regions of triggered star formation in the Milky Way.
Keywords:
shells; ism; triggered star formation
Available at various institutes of the ASCR
Shell-Like Structures in the ISM: Observation Versus Simulations
The interstellar medium in galaxies is a turbulent environment with a plethora of holes, bubbles and shells. All these shell-like structures are thought to be closely related to the formation, ...
Comparison of relativistic iron line models
Svoboda, Jiří; Dovčiak, Michal; Goosmann, René; Karas, Vladimír
2008 - English
The analysis of the broad iron line profile in the X-ray spectra of active galactic nuclei and black hole X-ray binaries allows us to constrain the spin parameter of the black hole. We compare the constraints on the spin value for two X-ray sources, MCG-6-30-15 and GX 339-4, with a broad iron line using present relativistic line models in XSPEC - LAOR and KYRLINE. Analýza profilu široké čáry železa v rentgenových spektrech aktivních galaxií a mikrokvasarů nám umožňuje určit spin černé díry. Porovnávame výsledky pro dva rentgenové zdroje, MCG-6-30-15 a GX 339-4, se širokou čárou železa pomocí současných modelů relativistické čáry v programu XSPEC - LAOR a KYRLINE.
Keywords:
accretion; accretion disks; black holes
Available at various institutes of the ASCR
Comparison of relativistic iron line models
The analysis of the broad iron line profile in the X-ray spectra of active galactic nuclei and black hole X-ray binaries allows us to constrain the spin parameter of the black hole. We compare the ...
Statistical study of the fitting of the magnetic clouds
Lynnyk, A.; Vandas, Marek
2008 - English
The paper is a statictical study on comparisons between a model of an expanding magnetic cloud and observations. Práce je statistickou studií o srovnání modelu expandujícího magnetického oblaku s pozorováními.
Keywords:
magnetic clouds; solar wind; interplanetary magnetic field
Available at various institutes of the ASCR
Statistical study of the fitting of the magnetic clouds
The paper is a statictical study on comparisons between a model of an expanding magnetic cloud and observations....
Modelling the polarization dichotomy of active galactic nuclei
Goosmann, René
2007 - English
I present polarization modelling of Active Galactic Nuclei in the optical/UV range. The modelling is conducted using the Monte-Carlo radiative transfer code Stokes, which self-consistently models the polarization signature of a complex model arrangement for an active nucleus. Prezentuji modelování polarizace záření aktivních galaktických jader v optické a UV oblasti. Při modelování je použit kód Stokes pro Monte Carlo simulace přenosu záření, který selfkonzistentně modeluje polarizaci geometricky komplexního uspořádání aktivního jádra.
Keywords:
active galaxies; radiative transfer; polarization
Available at various institutes of the ASCR
Modelling the polarization dichotomy of active galactic nuclei
I present polarization modelling of Active Galactic Nuclei in the optical/UV range. The modelling is conducted using the Monte-Carlo radiative transfer code Stokes, which self-consistently models the ...
Magnetic clouds and their expansion
Lynnyk, A.; Vandas, Marek
2007 - English
Magnetic clouds for the years 1995-1998 are analyzed using a model of a force-free cylindrical flux rope which may include cloud expansion. Clearly pronounced expansion was found in 80% cases. It was found that including the expansion makes comparison between model and experimental data better in 75% of these cases. Analyzovali jsme magnetická oblaka pro roky 1995-1998 s použitím modelu bezsilové magnetické válcové silotrubice, jež může zahrnovat expanzi. Zřetelná expanze oblaků byla zjištěna v 80%.Zahrnutí expanze zlepšuje srovnání modelu s měřeními u 75% z těchto případů.
Keywords:
magnetic clouds; solar wind; magnetic field
Available at various institutes of the ASCR
Magnetic clouds and their expansion
Magnetic clouds for the years 1995-1998 are analyzed using a model of a force-free cylindrical flux rope which may include cloud expansion. Clearly pronounced expansion was found in 80% cases. It ...
Flares from spiral waves by lensing and time-delay amplification?
Karas, Vladimír; Dovčiak, Michal; Eckart, A.; Meyer, L.
2007 - English
We examine physics of flares from spiral waves by lensing and time-delay amplification. Zabýváme se fyzikou záblesků ze spirálních vln ovlivněných efektem čočkování a časového zpoždění.
Keywords:
black holes
Available at various institutes of the ASCR
Flares from spiral waves by lensing and time-delay amplification?
We examine physics of flares from spiral waves by lensing and time-delay amplification.
Zabýváme se fyzikou záblesků ze spirálních vln ovlivněných efektem čočkování a časového zpoždění.
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