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Czech Informel Graphic Art
Krtička, Jiří ; Rakušanová, Marie (advisor) ; Michálek, Ondřej (referee) ; Nešlehová, Mahulena (referee)
The Printmaking of Czech Art Informel Author: Jiří Krtička Abstract The thesis deals comprehensively with the printmaking of Czech Art Informel: explores its sources, principles and themes, evaluates contributions of individual artists and analyses the technique of "structural printmaking". The first artworks in Informel style in Czechoslovakia were created during World War II by Josef Istler who belongs to European protagonists of Art Informel movement. In post-war years Istler engaged mostly in painting and monotyping. For this reason it was Vladimír Boudník who became the leading personality of Czech Informel printmaking. In 1949 he declared in two manifestos of "explosionalism" his vision of a new art that he followed and carried out with admirable consistency till the end of his life. In the middle of 1950s Boudník started to elaborate "structural printmaking" - innovative printmaking methods that became a way to fulfil his vision. His work influenced strongly the whole generation of Czech artists and essentially helped to introduce Art Informel to Czechoslovakia against the ideologic resistance of the communist regime. Czech Informel achieved excellent qualities in Europe-wide comparison and "structural printmaking" became its original contribution to the world fine art. Keywords Art Informel,...
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Structure and evolution of stars deformed by a nearby companion
Vokrouhlický, David ; Pejcha, Ondřej (advisor) ; Krtička, Jiří (referee)
The tidal field from a nearby binary companion affects the structure and evolution of stars. We successfully applied the Kippenhahn averaging formalism to the Roche potential and used the method to formulate approximate models of tidally deformed primaries in close binary systems. We considered both the detached and the contact configurations and neglected chemical composition evolution. These tidally deformed models are thermally stable. We explored the parametric dependence of the results on three quantities: mass ratio q in the binary, surface equipotential C of the primary or the fill-out factor F(C), and mass M1 of the primary. We found that the depth of the surface convective layer of low mass primaries in- creased due to tidal deformation. All models decreased their effective temperature when compared to their spherical counterparts. Our results also predict a positive correlation between the effective temperature and the fill-out factor for contact systems. Further- more, the temperature negatively correlates with the mass ratio of the deformed system. Finally, when isolating the tidal deformation effects, a jump in temperatures was found around 1.2 M⊙ for most fill-out factors. These findings could help to explain the observa- tionally reported dichotomy of contact binary systems at the temperature...
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A study of binary stars with accretion disks
Chadima, Pavel ; Harmanec, Petr (advisor) ; Krtička, Jiří (referee) ; Mourard, Denis (referee)
This thesis contains spectroscopic analyses of two unusual binaries with circum- stellar disks - β Lyr and ǫ Aur. Several hundred optical spectra were processed and analyzed for both binaries which led to several original findings. For β Lyr, it was a discovery of a weak shell spectrum originating in a disk pseudophotosphere and a hidden satellite spectrum, present only during eclipses, which arise from additional absorption of the primary light passing through the gaseous envelope around the secondary. For ǫ Aur, it led to the discovery of the apparent multiperiodic line vari- ability occuring during the current eclipse with a dominant and common period of 66d .21 and to an explanation of complex Hα line profiles during the eclipse which is again caused by an additional absorption of a primary light in an atmosphere of a dark disk around a secondary. Also rich series of radial velocity measurements and photometric observations were collected and used to determine a new precise orbital solution for ǫ Aur. Further, a hydrodynamical and a radiative modeling of a discontinuous mass transfer in a close binary system was carried out which resulted in a formation of an elongated disk with a slow prograde revolution, demonstrated itself by double emission Hα line profiles that exhibit V/R variations.
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Radiation in stellar winds. Resonance line formation in inhomogeneous hot star winds
Šurlan, Brankica ; Kubát, Jiří (advisor) ; Krtička, Jiří (referee) ; Róžaňska, Agata (referee)
Title: Radiation in stellar winds. Resonance line formation in inhomogeneous hot star winds Author: M.Sc. Brankica Šurlan Department: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor: RNDr. Jiří Kubát, CSc., Astronomical Institute of the Academy of Sciences of the Czech Republic Abstract: To incorporate the three-dimensional (3-D) nature of stellar wind clump- ing into radiative transfer calculations, in this thesis a newly developed full 3-D Monte Carlo radiative transfer code for inhomogeneous expanding stellar winds is presented and used to investigate how different model parameters influence reso- nance line formation. Realistic 3-D models that describe the dense as well as the rarefied wind components are used to model the formation of resonance lines in a clumped stellar wind. Non-monotonic velocity fields are accounted for as well. It is shown that the 3-D density and velocity wind inhomogeneities have very strong impact on the resonance line formation. The models show that the line opacity is lower for a larger clump separation and shallower velocity gradients within the clumps. They also demonstrate that to obtain empirically correct mass-loss rates from UV resonance lines, wind clumping and its 3-D nature must be taken into account. 1
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Spectral analysis of the B[e] star V743 Mon
Jeřábková, Tereza ; Korčáková, Daniela (advisor) ; Krtička, Jiří (referee)
This thesis deals with the study of the star V743 Mon. Stellar spectrum contains forbidden emission lines of [O I], strong Balmer emission lines and also infrared excess. Due to this, V743 Mon belongs to the group of B[e] objects. Observed spectra indicate very extended and rotating circumstellar envelope composed of gas and dust. We study time variability using data obtained during 2004-2012 at the Astronomical Institue of the Academy of Sciences of the Czech Republic in Ondřejov. We reduce and rectificate these spectra. We mesure relative intensities, equivalent widths and radial velocities for lines Hα, [O I] and Fe II. Graphical description contains also lines Si II and He I. The observed spectra show time variability on both, long- and short-term scales. Spectra from SAAO observatory are used to study the short time-scale changes. The discussion of problems connected with different instruments is also presented. 1
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A new study of orbital and long-term variations of the Be star phi Persei
Jonák, Juraj ; Harmanec, Petr (advisor) ; Krtička, Jiří (referee)
The well-known spectroscopic binary ϕ Per is a peculiar compact system, composed of a Be star with an O-type subdwarf companion. A set of nearly 400 spectra in the red and blue regions from Ondřejov and Potsdam Observatories as well as spectra published in the BeSS database were examined. From the radial velocities of Hα, Hβ, and Hγ emission lines and FUV observations from the IUE and HST, a new precise ephemeris was determined. The revised values of M sin3 (i) are 11.84 and 1.48 M (with uncertainties of 0.64 and 0.09 M ), re- spectively, for the primary and secondary. In addition, the system shows cyclic variations (with a time scale of about 5 years) in the profiles of Balmer lines, manifested in their radial velocities, central intensities and V/R ratios. Understanding complex stellar systems requires combining multiple types of ob- servations and creating models of sufficient complexity. In our case, a combination of interferometric visibilities from the CHARA/VEGA array, spectral energy dis- tribution as well as individual spectral lines were used. Radiative-transfer compu- tations were performed with the program PYSHELLSPEC, and physical parameters of the ϕ Per primary and the surrounding disc were derived. They correspond to an evolved system, in which most of mass was transferred from the secondary to...
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Stability of stars undergoing rapid mass loss
Cehula, Jakub ; Pejcha, Ondřej (advisor) ; Krtička, Jiří (referee)
Binary mass transfer is a common phenomenon is stellar astrophysics. If the mass transfer proceeds on dynamical timescale, the binary can undergo a catastrophic interaction accompanied by tremendous loss of mass, angular momentum, and energy. This so-called common envelope evolution phase is a crucial step in the formation of close binaries composed of compact objects (white dwarfs, neutron stars, black holes), which includes progenitors of gravitational wave sources de- tected by LIGO. By improving existing models of binary mass transfer we can correct the predictions of common envelope evolution and constraint the rates of close binaries composed of compact objects. In this work, we introduce new model of binary mass transfer. We will treat the mass transfer as a special case of stellar wind. We will rely on the assumption that the Roche potential sets up a de Laval nozzle around the first Lagrange point. The mass is then transferred through the nozzle. Our binary mass transfer model predicts mass transfer rates in the same order of magnitude as the standard models which use the Bernoulli's law. But the advantage of our model is that it is extendable to account for radiation.
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Helium in solar flares
Frýda, Jan ; Kašparová, Jana (advisor) ; Krtička, Jiří (referee)
Solar flares are the most energetical process in the Solar system and massive amount of energy is released during such eruptions in the form of heat, radiation and accelerated particles. Propagation of electron beam in the solar atmosphere is described by the re- sults of the numerical code RADYN, whose results were used in this thesis for studying radiation losses of helium transitions and subsequent determination, if and which helium transitions are important in processes in the solar atmosphere during a solar flare. It was determined by studying height dependency of the radiation losses for various parameter combinations of the electron beam and various times of electron beam propagation in the solar atmosphere that radiation losses of helium transitions are important for modelling of solar flares. Among the most important helium transitions are the transitions 10830.29 Å, 20580.82 Å, 227.84 Å, 503.98 Å and 303.78 Å. 1
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