[en] The authors present a detailed study of the bremsstrahlung gamma-ray emissivity of the galactic disk. It is shown that there are large uncertainties in the production spectrum of photons in the medium energy range (10-100 MeV) due to our lack of knowledge of the interstellar electron spectrum below a few hundred MeV. In fact, gamma-ray observations can be of great help in determining this spectrum. At present, the spectral shape of the local gamma-ray emissivity above 30 MeV is available, thanks to the SAS-II and the COS-B satellites. Comparing it to the present calculations, the authors determine the local interstellar electron flux in the 50-500 MeV range; the corresponding integrated gamma-ray emissivity above 100 MeV is equal to 2.4x10^-25 photons s^-1 (H-atom)^-1, 60% higher than previously accepted values. (Auth.)

[en] Observations of the ionized hydrogen region NGC 1499 have been carried out with the radio telescope UTR-2 at frequencies 12.6, 14.7, 16.7, 20 and 25 MHz. The half-power resolution of the instrument to zenith is 28' X 34' at 25 MHz. The average volume density of the non-thermal radio emission between the Sun and the nebula (1.75 X 10^-40 W m^-3 Hz^-1 ster^-1 at 25 MHz), the electron temperature of the H II nebula (Tsub(e) = 4400 K), the measure of emission (ME = 1500 cm^-6 pc) and other parameters have been obtained. Maps of brightness distribution over the source are presented for each observation frequency. The results are compared with previously obtained data. (Auth.)

[en] Deep Hα + [N II] photographs of five giant shell-like nebulae in the LMC are compared to 21 cm H I maps, Schmidt photographs showing the O and B associations and the UV sources from 1200 to 1600 A. The formation of all shell-like nebulae which do not appear to be supernova remnants and which have diameters between 1 pc and 1900 pc is discussed. (Auth.)

[en] A charged particle detector array flown on a high altitude balloon has detected and measured some 3 x 10⁴ cosmic-ray nuclei with Z >= 12. The charge spectrum at the top of the atmosphere for nuclei with E > 650 MeV.n^-1 and the energy spectrum for 650 <= E < 1800 MeV.n^-1 are reported and compared with previously published results. The charge spectrum at the 'source' of cosmic rays is deduced from these data and compared with a recent compilation of 'galactic' abundances. (Auth.)

[en] An exact analysis of Stokes' problem for an infinite vertical plate, whose temperature varies linearly with time, has been presented. It is observed that the velocity near the plate increases with the time t, and the Grashof number Gr. The skin-friction has been found to vary as tsup(7/2) and the Nusselt number varies as √t or √P+1 where P is the Prandtl number. (Auth.)

[en] The structure of a slow reaction front on the surface of a dwarf, with a wake of escaping matter above it, is investigated. Simple expressions for all the important properties of such a front are given. It is found that a hydrogen or helium burning front is possible on a dwarf heavier than about one solar mass. For heavier fuels such a process seems impossible. (Auth.)

[en] Multi-aperture photometry of 262 bright southern galaxies in the Johnson UBV system is given. Most of these are south of delta = -30⁰, although some northward to delta = -10⁰ are included. A total of 169 objects have published radial velocity determinations. These provide distances, and enable construction of colour-magnitude diagrams for this subset of objects througha physical diameter of 2.0 kpc (with H₀ = 100). The two-colour diagrams for the inner regions of the galaxies differ from those of integrated galaxies due to the colour changes towards their centres. Comparison with theoretical models of Larson and Tinsley (1978) suggest that the colours of the inner portions of most ellipticals and lenticulars are consistent with their having all stars formed at nearly one epoch with little subsequent star formation, while for spirals larger amounts of star formation, either in bursts of continuously, are suggested. This simple picture is complicated by the presence of certain objects having peculiar colours indicative of large amounts of recent star formation. (Auth.)

[en] The contribution of gravitationally bound subsystems to the potential energy of systems of galaxies is investigated. A statistical correction factor to the virial mass is derived using Holmberg's observed frequency function of multiple galaxies. It is of the order of ten for groups of galaxies and negligible for rich clusters. However, it is emphasized that an individual treatment is necessary. As an illustration the contribution to the binding energy by observed binary galaxies in the de Vaucouleurs groups 48 and 49, and the Coma Cluster, is calculated. In all three cases a single double galaxy removes the virial mass paradox. It is concluded that corrections for subclustering are substantial in stability analyses of systems of galaxies, and they can remove easily mass discrepancies of the order of ten in groups and rich clusters, and that they should be made individually and not statistically. (Auth.)

[en] The authors set up diffusion equations for the nuclear component of cosmic rays and solve these to find the ratio of light to medium nuclei in the cosmic rays as well as the gamma-ray distribution in the Galaxy. From a comparison of the calculated quantities with observational data the values of various parameters appearing in the model are determined. It is found that best agreement between theory and observations is obtained if the cosmic-ray confinement region consists of a narrow disk of total height 160 pc and radius 16 kpc, where the cosmic-ray sources are located, and an extensive halo of height 20 kpc. The diffusion coefficient near the Sun must be between 10²⁶ and 10²⁷ cm² s^-1, while it equals 10²⁸ to 10²⁹ cm² s^-1 in the halo. Finally, it is found that the diffusion coefficient in the Galaxy must depend on the gas density as a power law with an index of the order of - 1. (Auth.)

[en] The author considers the problem of determination of the emergent intensity from the bounding face and the intensity at any optical depth within a plane-parallel semi-infinite atmosphere by the Laplace transform and the Wiener-Hopf technique if the incoming intensity at the boundary face of the atmosphere is known. The solution is exact. As a particular case, the solution of Das (1978) is obtained. (Auth.)