On mutual relation of kHz QPOs
Török, G.; Bursa, Michal; Horák, Jiří; Stuchlík, Z.; Bakala, P.
2007 - English We further investigate the issue of kHz QPO frequency ratios in neutron star low mass X-ray binaries. In this note we report on recent analysis of occurrences and properties of kHz QPOs in the source 4U1636-53. Assuming that kHz QPOs occur in pairs whose frequencies are linearly correlated, we find a prominent frequency range that separates upper and lower QPO observations. Na základě analýzy dat QPO frekvencí zdroje 4U1636-53 a pěti dalších zdrojů ukazujeme, že páry QPO jsou detekovány zejména v okolí přechodových bodů, kde se mění některé vlastnosti QPO, zejména amplituda a koherence QPO. Keywords: X-rays; binaries stars; accretion disks Available at various institutes of the ASCR On mutual relation of kHz QPOs

We further investigate the issue of kHz QPO frequency ratios in neutron star low mass X-ray binaries. In this note we report on recent analysis of occurrences and properties of kHz QPOs in the source ...

Török, G.; Bursa, Michal; Horák, Jiří; Stuchlík, Z.; Bakala, P.
Astronomický ústav, 2007

Disk instability as an energy source for quasi-periodic oscillations
Horák, Jiří
2007 - English We discuss a scenario, in which the energy for quasi-periodic oscillations comes from instabilities of the accretion disk. We demonstrate this mechanism on the interaction among stable and unstable modes of oscillations in slender accretion tori. In our model, the unstable non-axisymmetric corotation modes are nonlinearly coupled to stable acoustic modes of torus oscillations. The increasing energy of corotation modes is advected to the acoustic modes by the means of parametric instability. The stable modes may reach substantial amplitudes even if they are damped according to the linear theory. Energie pro kvazi-periodické oscilace může pocházet z nestabilit akrečního disku. Jako příklad je diskutována interakce mezi stabilními a nestabilními mody malého akrečního torusu. V našem případě je nestabilní neaxiálně symetrický korotující mod svázán nelineární vazbou se dvěma stabilními akustickými mody. Rostoucí energie korotujícího modu je předávána akusticým modum pomocí parametrické nestability. Stabilní mody mohou dosáhnout značných amplitud i když jsou podle lineární teorie tlumeny. Keywords: black hole physics; accretin discs; instabilities Available at various institutes of the ASCR Disk instability as an energy source for quasi-periodic oscillations

We discuss a scenario, in which the energy for quasi-periodic oscillations comes from instabilities of the accretion disk. We demonstrate this mechanism on the interaction among stable and unstable ...

Horák, Jiří
Astronomický ústav, 2007

Optical spectroscopy of Cyg X-1
Hadrava, Petr
2007 - English 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). Hvězda HDE 226868, známá jako optický protějšek objektu Cyg X-1 s předpokládanou černou dírou, byla pozorována v oblasti H_alfa spektrografem ondřejovského 2-m dalekohledu. Orbitální parametry jsou určeny z čáry HeI pomocí autorovy metody fourierovského disentanglingu. V práci jsou předloženy také předběžné výsledky disentanglingu čáry H_alfa na P-Cyg profil optického primáru a na emisní profil okolohvězdné hmoty (a na telurickou složku). Keywords: Cyg X-1 Available at various institutes of the ASCR Optical spectroscopy of Cyg X-1

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 ...

Hadrava, Petr
Astronomický ústav, 2007

Modulation of high-frequency QPOs
Bursa, Michal
2007 - English We study strong-gravity effects on modulation of radiation emerging from accreting compact objects as a possible mechanism for flux modulation in QPOs. Zkoumáme vlivy silné gravitace na modulaci záření z akrečních disků jako možný zdroj mechanismus modulace kvaziperiodických oscilací. Keywords: black hole physics; gravitation; X-rays Available at various institutes of the ASCR Modulation of high-frequency QPOs

We study strong-gravity effects on modulation of radiation emerging from accreting compact objects as a possible mechanism for flux modulation in QPOs....

Bursa, Michal
Astronomický ústav, 2007

Vývoj a čísla
Rajchl, Jaroslav
2006 - Czech Keywords: evolution; numbers; dynamical systems Available at various institutes of the ASCR Vývoj a čísla

Rajchl, Jaroslav
Astronomický ústav, 2006

Asymmetries of Spectral Lines in Solar Flares
Prosecký, Tomáš
2006 - English This contribusion deals with line profile asymmetries in solar flares. Basic knowledge of asymmetries and review of possible explanations and recent works is presented. Week of doctoral students 2006. Proceedings of contributed papers. Praha : Matfyzpress, 2006. Part III - Physics, p. 27-32. Praha, 06.06.2006-9.06.2006 Keywords: solar flares; spectrum; line profile asymmetry Available at various institutes of the ASCR Asymmetries of Spectral Lines in Solar Flares

This contribusion deals with line profile asymmetries in solar flares. Basic knowledge of asymmetries and review of possible explanations and recent works is presented....

Prosecký, Tomáš
Astronomický ústav, 2006

A manifestation of the Kozai mechanism in the galactic nuclei
Šubr, L.; Karas, Vladimír
2005 - English Kozai mechanism is studied in galactic nuclei. Studujeme vliv Kozaiova mechanismu na jádra galaxií. Keywords: galaxies Available at various institutes of the ASCR A manifestation of the Kozai mechanism in the galactic nuclei

Kozai mechanism is studied in galactic nuclei.

Šubr, L.; Karas, Vladimír
Astronomický ústav, 2005

High-frequency QPOs in GRO J1655-40
Bursa, Michal
2005 - English We determine angular momentum from QPOs. Určujeme moment hybnosti pomocí studia QPO. Keywords: quasiperiodic oscillations Available at various institutes of the ASCR High-frequency QPOs in GRO J1655-40

We determine angular momentum from QPOs.

Bursa, Michal
Astronomický ústav, 2005

Center for Earth Dynamics Research (CEDR) - results of five years of activity
Kostelecký, J.; Vondrák, Jan; Zeman, A.; Kalvoda, J.; Schenk, Vladimír
2005 - English Five years of activities of the Center of Earth Dynamics Research is described. Jsou popsány aktivity Výzkumného centra dynamiky Země za posledních pět let. Keywords: geodynamics; geodesy Available at various institutes of the ASCR Center for Earth Dynamics Research (CEDR) - results of five years of activity

Five years of activities of the Center of Earth Dynamics Research is described.

Kostelecký, J.; Vondrák, Jan; Zeman, A.; Kalvoda, J.; Schenk, Vladimír
Astronomický ústav, 2005

The relativistic shift of spectral lines from black-hole accretion discs
Pecháček, T.; Dovčiak, Michal; Karas, Vladimír
2005 - English We study gravitational redshift of spectral lines. Studujeme gravitační posuv spektrálních čar. Keywords: accretion Available at various institutes of the ASCR The relativistic shift of spectral lines from black-hole accretion discs

We study gravitational redshift of spectral lines.

Pecháček, T.; Dovčiak, Michal; Karas, Vladimír
Astronomický ústav, 2005