Observations of Cassiopeia A at 20 and 25 MHz with the uran-1 interferometer

The variation in elemental depletions seen in diffuse clouds in the interstellar medium is shown to be consistent with the exposure of grains to weak shocks. Shocks remove a weakly bound layer of amorphous oxide material from refractory cores. Depletions are shown to be the result of the incorporation of elements in refractory cores formed during equilibrium condensation in high temperature sources together with accretion under low (T1000K) temperature conditions. Evidence is presented for the high temperature condensation of CaAlTi grains. In addition to refractory CaAlTi particels, a refractory condensate containing 20% of available Mg, 60% of Si and 90% of Fe is inferred from data on depletions. An amorphous layer with a composition (2MgO) (SiO) condenses on these cores.     

Spectral characteristics of components of a model radio-brightness distribution for the radio galaxy 3C 234

Physical processes that can, under cosmic conditions, give rise to emission whose spectrum peaks at some frequency are discussed in the context of the spectrum of the central extended component of a model brightness distribution for the radio galaxy 3C 234. This component is not detected at decameter wavelengths, probably due to the absorption of the radiation in the plasma in the source itself.     

Decametric survey of discrete sources in the northern sky

Spectra of 197 discrete sources have been obtained in a frequency range 10–1400 MHz. The sources lie at declinations between 0° and +10° and right ascensions from 0–24 h. The spectra have been constructed on the basis of a decametric survey carried out at Grakovo with the UTR-2 radio-telescope, as well as a number of higher frequency surveys performed at Culgoora, Cambridge, Parkes and Ohio. Analysis of the spectrum plots shows that 84% of the spectra are linear (in the logarithmic scale), 11% are characterized by positive and 5% by negative curvature.     

The magnetic fields and angular sizes of radio sources displaying synchrotron self-absorption

A method for estimating the magnetic-field strengths and angular sizes of radio sources displaying synchrotron self-absorption based on their observed radio spectra is considered. The method is used to derive the angular sizes of compact radio sources (components) and the magnetic fields in these regions, as well as the energy and number of relativistic electrons and the radiative power of a number of quasars and radio galaxies.     

Structure investigations of 3C 196 and 3C 280 in the decameter waveband

Observational results are presented concerning the structure of the quasar 3C 196 and the radio galaxy 3C 280 at 20 and 25 MHz, obtained by the scintillation method with the URAN-1 interferometer. Angular dimensions of the scintillating components and extended regions of the sources have been evaluated. In the case of the quasar 3C 196, the effective angular size of the scintillating component equals 2±1 _. 5 and that of the extended region 18×25.The contribution of the compact component into the total radiation flux is 0.46±0.20. Spectra of the structural formations in 3C 196 have been obtained in the range 20–5000 MHz.For the radio galaxy 3C 280 the effective angular size of the scintillating component equals 1 _. 5±1 _. 2. and that of the extended region exceeds 10 _. The contribution into the total flux due to the scintillating part is 0.35±0.20.The data obtained are analyzed together with the results measured at higher frequencies. It is pointed out that in a wide frequency range, the effect of wave scattering in the interstellar medium does not exceed measurement errors,hence bringing about no increase in the compact component sizes of the sources observed.     

The structure of the radio galaxy 3C388 at decameter wavelengths

Observations of the structure of the radio galaxy 3C338 at decameter wavelengths obtained using the URAN-1 and URAN-2 radio interferometers are presented. The structure of this object at these wavelengths differs appreciably from images obtained at higher frequencies. The most probable simple models for the radio brightness distributions at 25 and 20 MHz are determined: two extended components with sizes from 40″ to 50″ whose centers are separated by 90″–100″ in position angle about 100°, and a single compact component 9″×4″ in size, whose flux density does not exceed 10% of the total flux density of the radio galaxy.     

An investigation of the Cassiopeia A radio-image in the decameter range

The observation results of the supernova remnant Cassiopeia A, obtained with the aid of two decameter radio interferometers at 20 and 25 MHz, are presented. The so obtained dependences of the visibility function modulus on the hour angle are compared with calculations based on the brightness distribution measurements of this source using the VLA at 1381 MHz. Discrepancies between the experimental data and the calculations considerably increase with the decrease in the frequency. It is suggested that interstellar medium absorption, causing a distortion in the source spectrum over the decameter range, may be responsible for changes in the Cas A brightness distribution at these frequencies as well.     

The beginnings of decameter radio astronomy: pioneering works of Semen Ya. Braude and his followers in Ukraine

S.Ya. Braude (1911–2003) was the well‐known radio astronomer, one of the founders of low‐frequency astronomical research in the world, in particular in the former Soviet Union. He began to work in this field of science in 1957, in Kharkiv city (Ukraine), from the design and manufacturing small decameter interferometer ID‐1 and ID‐2. Since that time Braude and his team have developed more sophisticated radio decameter telescopes as UTR‐1 and UTR‐2 (the largest in the world till now) as well as the first decameter VLBI network URAN. They have obtained some important pioneering results about low‐frequency radio emission of objects in our Solar system, Galaxy and Metagalaxy by means of these telescopes. In this paper the key events of early history of decameter radio astronomy research in the former USSR are mentioned with emphasizing the role of S. Braude. For the period of 1957–1962, the quotations of Braude's Personal Diary (2003) are first laying open to the public. The most important results obtained by S.Ya. Braude and his followers as well as perspectives of decameter radio astronomy in Ukraine and in the world are highlighted briefly. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Physics of Spectral Maxima in the Radiation from Non-Thermal Cosmic Radio Sources

Universal expressions are presented for spectral characteristics of non-thermal cosmic radio sources which show maxima of the spectral density of radiation at specific frequencies (negative slopes spectra). For a number of quasars, radio galaxies and their individual details the most probable physical processes in space leading to spectra of the kind are determined, and some parameters of the space medium, magnetic field and angular sizes of compact radio sources are estimated.     

Decametric survey of discrete sources in the Northern sky

A new method was developed for comparing absolute flux scales of the decametric surveys. The absolute scales of the new survey performed with the UTR-2 in the 10 to 25 MHz frequency range are compared with UTR-1 data and surveys at 10.03, 22.25, 26.3 and 38 MHz operating frequencies.