Pestrá škála kosmologických testů ukazuje, že různé vlastnosti našeho vesmíru lze přesvědčivě vysvětlit, pokud je dominantní složkou jeho současného energetického obsahu rovnoměrně rozptýlená substance, jež dostala název temná energie. Jejím základním rysem je kosmická repulze způsobující zrychlené rozpínání prostoru, přičemž hustota temné energie zůstává neměnná; v Einsteinových rovnicích pole ji velmi dobře reprezentuje kosmologická konstanta Λ. Přirozeně, kosmologická konstanta se musí projevovat nejen v evoluci vesmíru, ale též v astrofyzikálních procesech. Představíme některé její astrofyzikální projevy studované opavskou relativistickou skupinou - vliv na pohyb hvězd v gravitačním poli supermasivních černých děr, na pohyb trpasličích galaxií na periferii obřích galaxií, na tvar a vlastnosti toroidálních konfigurací hmoty obíhajících supermasivní černé díry nebo sférických polytropických konfigurací modelujících hala temné hmoty., A wide range of cosmological tests indicates that various properties of the Universe can be well explained by the presence of a uniformly dispersed dominant part of the current energetic content, i.e. so-called dark energy. Its basic feature is expressed by cosmic repulsion, causing an accelerated expansion of space, whereas the density of dark energy remains unchanged; in Einstein field equations, dark energy is well described by the cosmological constant (Λ). Clearly Λ must be defined not only in Universe evolution, but also in astrophysical processes. Here we introduce some of the astrophysical phenomena of Λ studied by the relativistic group in Opava, e.g. its influence on the motion of stars in the gravitational field of supermassive black holes, on the motion of dwarf galaxies at the peripheries of giant galaxies, on the form and properties of toroidal configurations of fluid circling around supermassive black holes, or on polytrophic configurations modelling dark matter halos., Zdeněk Stuchlík, Petr Slaný, Jiří Kovář., and Obsahuje bibliografické odkazy
By taking some evolutionary models of an initially 60 M⊙-star, their radial vibrational stabilities have been investigated. These models, evolving with mass loss, are in the advanced stages of their evolution, and burn He in their cores. Calculations have been performed for the first and second harmonics as well as for the fundemental mode; and some of these models were found to be vibrationally unstable in the fundemental mode.
Part I of this review considers the outcome of different methods of observation of active regions at mm- and cm-v/aves exploring the source structures and parameters in the chromosphere and corona. Calculations of emission models invoking bremsstrahlung and gyromagnetic radiation are summarlzed applying for a great
variety of physical conditions. Diagnostic capacities of different kinds of microwave burst emission are briefly taken into account.
Part II of the review considers the dm- and m-radio spectral observations as diagnostic tool for the determination of plasma parameters in the coronal parts of solar active regions. The main attention is devoted to the radio diagnoetics of solar flares. The most important types of dm- and m-radio bursts are presented.
the latest theoretical and observational results summarized and their diagnostic aapects briefly discussed.
Fotometrie [1-3] historicky náleží k části optiky věnované zkoumání světla z hlediska jeho účinku na lidské oko. K popisu tohoto působení proto zavádíme fotometrické veličiny, mezi které řadíme např. svítivost, světelný tok nebo osvětlení. Nejdříve se podíváme na základní jednotku SI svítivost, od níž si odvodíme další fotometrické veličiny. Závěrem si ukážeme fotometrii na příkladu našeho Slunce a různé metody fotometrie v astrofyzice., Photometry historically belongs to the part of optics which examines the effects of radiation on the human eye. To describe these effects we introduce photometric quantities amongst which are luminosity, luminous flux or illumination. First, we focus on the SI base unit luminosisty from which we deduce other photometric quantities. We show how our Sun emits energy and discuss different photometric methods used in astrophysics., Jan Janík., and Obsahuje seznam literatury
The azirnuthal distribution of planes containing e^i/e pairs from
high-energy photon materialization is reminiscent, through a quadrupole anisotropy, of the degree and position angle of linear polarization of the incident photons. Data on open pairs in the COS-B spark chamber are used in a search for such an effect in
> 50 MeV photons from bright sources, such as Vela, Crab, Geminga and a reference galactic plane region in Cygnus. After a description of the method and the related simulations and tests, the analysis of the available data shows no anisotropy for the other sources, but for the Vela pulsar a low-chance-probability effect is
found apparently implying a high (~ 100%) degree of linear polarization for the Vela photons. This is discussed in light of the physics of the production mechanisms as well as of their geometry.
Despite theoretical predictions on the existence of solar gravity oscillations (g modes), their detection is still marginal. The main reasons are their frequencies, ν<0.2 mHz, and amplitudes of
less than 10 cm/s. However, because these modes are extremely sensitive to the physical conditions in the very deep sun, they can give us detailed Information on the physics of the core. Using a resontant scattering spectrophotometer we measured the radial velocity of the Sun at the KI 769.9 nm. line with very high resolution and temporal stability. The observatíons carried out at Izaňa (Tenerife) continuously for the last three years, háve been used to search for solar g modes. Analysis of the whole lot of data as one single time series provides a spectral resolution of 12 nHz, and signal with amplitude above noise level, 1 cm/s. Several techniques are used in order to find.the signature of g modes and calculate the parameters Po and vr. Individua! peaks, well above noise level, are identified and their frequencies are likely to correspond with
g modes.
V568. Cyg has been observed photometrically, spectroscopically and photographically during a campaign on 0-B runaways. These may contain either postsupernova binaries or stars dynamically ejected. from young associations. Whereas even its variability was doubtful, we have recorded photometric minima deeper from V to U as well as strong inversion of colour indexes, the star becoming redder as the minimum gets deeper:
1986 (mean value) 1987 (mean value) July 30, 86 August 2,86
B-V - 0.26 - 0.23 + 1.74 + 1.62
U-B - 0.63 - 0.59 + 1.30 + 1.05
New transient Hα emission episodes have been observed. The equivalent widths of absorption lines of hydrogen, except Hα, change in a correlated way reaching their lowest value sometimes at photometric minima. Eclipse of a hot object with a possible disk, by a late type giant in an eccentric orbit, seems the most viable explanation. The ephemeris J.D. 2446641.5 + 152.12 days may help the search for further primary minima.