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Opticka spektroskopie Cyg X-1
Hadrava, Petr
The star HDE 226868 known as an optical counterpart of the black hole candidate Cyg X-1 has been observed in H_alpha region using spectrograph at Ondrejov 2-m telescope. The orbital parameters are determined from HeI-line by means of the author's method of Fourier disentangling. Preliminary results are also presented of disentangling the H_alpha-line into a P-Cyg profile of the (optical) primary and an emission profile of the circumstellar matter (and a telluric component).
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Kinetický model kvasiperiodických oscilací plynných prstenců
Hadrava, Petr
In context of 3:2 resonant quasiperiodic oscillations, a method of "1+1/2 -dimensional" non-ideal gas dynamics is used to model axisymmetric oscillations of an orbiting ring. It is shown that the characteristic frequencies of the oscillations are influenced by the degree of freedom in the inner shear of the ring and by the rate of relaxation.
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Astronomie ve středověké Praze
Hadravová, Alena ; Hadrava, Petr
Astronomy ranked among the septem artes liberales which achieved high level at the University of Prague already soon after its foundation by the Emperor Charles IV. in 1348. Master Claretus de Solentia (Bartholomaeus of Chlumec, c. 1320-1370), who composed a didactic work Astronomicus on Charles' order in about 1350, can be mentioned as an example of scholar of this early period. At the beginning of the 15th century, Masters Cristannus of Prachatice and Johannes Sindel were very influential astronomers in Prague University. The interest of both of them in astronomical instruments can be documented by their treatises.
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Formation of eccentric disks around black holes
Hadrava, Petr ; Řezáč, R. ; Oestgaard, E.
The formation and evolution of eccentric disks around black holes due to explosion of a companion on an eccetric orbit is modeled by means of exact general-relativistic N-particle treatment. It is shown that in spite of the generally accepted view that the debris must be quickly smeared out to a circular accretion disk.
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