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Physics of X-ray binaries
Čechura, Jan ; Hadrava, Petr (advisor) ; Heyrovský, David (referee) ; Krtička, Jiří (referee)
Title: Physics of X-ray binaries Author: Jan Čechura Department: Astronomical Institute of the Academy of Sciences of the Czech Republic Supervisor: doc. RNDr. Petr Hadrava, DrSc. Abstract: We present a novel observation interpreting method for the high-mass X-ray binaries (HMXBs) based on a combination of spectroscopic data and numerical results of a radiation hydrodynamic model of stellar wind in HMXBs. By using an indirect imaging method of Doppler tomography, we calculate synthetic tomograms of a predicted emission in Low/Hard and High/Soft X-ray states and compare them with tomograms produced using phase-resolved optical spectra of Cygnus X-1, a prototype of HMXBs. The emis- sions of HMXBs are determined by the local conditions within the circumstellar medium - namely by local density, temperature, and ionization parameter. These quantities are computed by the radiation hydrodynamic code and strongly depend on the X-ray state of such systems. By increasing intensity of an X-ray emission produced by the compact companion in the HMXB-model, we achieved a complete redistribution of the circumstel- lar medium in the vicinity of the modelled system. These changes (which simulate the transitions between two major spectral states) are also apparent in the synthetic Doppler tomograms which are in a good...
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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 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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Spectroscopy of B[e] star FS CMa
Kříček, Radek ; Korčáková, Daniela (advisor) ; Krtička, Jiří (referee)
B[e] stars are a peculiar group of stars with forbidden emission lines in their spectra. This phenomenon is commonly ascribed as a result of a large shell around the star. FS Canis Majoris (FS CMa) became a prototype of one group of these stars because it was intensively studied in the past. However, in the case of this class of objects current theoretical models of the stellar evolution of a single star are not able to produce such huge amount of circumstellar matter, even if the stellar wind and rapid rotation are included into the calculations. We analysed and rectified some already reduced spectra obtained from 2005 to 2011 at the Astronomical Institute of the Academy of Sciences of the Czech Republic in Ondřejov and at SAAO observatory. Then we focused on the study of short- and long-term time variations of spectral lines in the stellar spectra, measured equivalents widths and radial velocities of the chosen spectral lines and discussed some achieved findings. Especially the short-term time variations of some spectral lines show dynamic processes of the inner star shell.
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Christologic motives in the modern Czech painting and graphic art
Krtička, Jiří ; Pech, Milan (advisor) ; Hlaváčková, Miroslava (referee)
The thesis maps the occurrence of christological motifs in the Czech painting and graphics after 1900 and compares approaches of artists of different generations to their depiction. Selected christological art works are analysed from three main aspects: 1. iconography, 2. style and form, 3. philosophical and psychological resources. A particular chapter deals with christological motifs in modern liturgical art. The conclusion of the work evaluates the significance of the christological theme in context of the modern Czech art development.
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Analýza rizik a oceňování energetických retailových kontraktů
Hron, Jiří ; Marek, Luboš (advisor) ; Málek, Jiří (referee) ; Krtička, Jiří (referee)
The presented dissertation is focused on the applications of statistical methods and ap-proaches applied in the energy business. The need for the modeling of energy risks arose only recently when the energy business was opened to competition. Therefore, the prima-ry aim of the dissertation is to clarify the main principles of the energy business which are necessary for understanding both risk principles and motivation of the proposed models. I am largely focused on retail risks, i.e., the risks associated with delivery to end-consumers. In particular, I deal with energy contracts providing volume flexibility, recalled as swing options in the literature. Therefore, the second issue on which I am focusing is a group of demand-driven swing options whose more systematic analysis in the portfolio context has not been published so far. Examining the risk, I apply the deductive (probabil-istic) analysis which reveals interesting relations between correlations. The practical ap-plications also require inductive considerations resulting in the construction of statistical estimators relying on historical data. I propose an estimator of the volumetric correlation based on a classical theory whose bias is investigated via MC simulation. To analyze a par-ticular volume-price correlation, I introduced the notion of robust dependency. Applying bootstrap procedures, robust dependency can be used both for testing purposes and for sensitivity analysis of the sample correlation. There are many works available devoted to energy price models which are different from the price models applied on financial markets. Therefore, the third target of the dis-sertation is an empirical statistical analysis of both power and natural gas Czech spot pric-es which can serve as a basis for the development of price models adapted to the Czech market environment. Finally, the fourth aim is the evaluation of power contracts which is very specific. The outputs of the model are both a synthetic market price and a hedging strategy. The model is designed to provide flexibility in practical applications.
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