Volume 4, Issue 4
December 1983, pages 225-306
pp 225-233 December 1983
We propose a test for the existence of prolate elliptical galaxies based on the properties of the photometric parameters introduced in the Córdoba surface photometry.
pp 235-252 December 1983
Low-dispersion spectra of the order of 1000 Å mm-1 have been obtained for stars in several faint galactic clusters with a transmission grating placed in front of the photographic plate at the Cassegrain focus of the Kavalur 102-cm telescope. The intensity distribution in the shorter wavelengths has been taken as the principal criterion for the spectral classification of the individual stars in the area covered by the photographic plate. The uncertainty in this procedure has been found to be about two spectral subclasses. A combination of these spectral classes with the visual magnitudes derived from the image diameters on the POSS charts provide the HR diagrams for each cluster area. These diagrams are adequate to establish the cluster membership of any star to a first approximation. This technique has been tested on six galactic open clusters, four of which are well-studied. We find good agreement both in terms of the ages of the clusters and individual stellar membership.
pp 253-260 December 1983
High resolution (3 arcsec-4 arcsec) maps of three compact sources in CTB 80, observed with the Very Large Array at 6 and 20 cm wavelengths are presented. The central core consists of a limb-brightened shell (of diameter 30 arcsec) superimposed on a diffuse emission of size 75 arcsec x 45 arcsec. The compact sources 1949 + 324 and 1952 + 332 located near the tips of the southwest and northeast ridges are rather remarkable and possibilities for these to be fragments ejected by the SN are examined. 1949 + 324 is fully resolved by the 4 arcsec beam and shows structure with multiple components oriented perpendicular to the ridge. 1950 + 326 is a background radio source.
pp 261-269 December 1983
Choosing an appropriate neutral-density model of martian atmosphere, the photoionization processes have been studied. Using relevant charge transfer and recombination reactions, the equilibrium electron-ion production rates have been computed for all species. The resultant electron-density profiles are compared with the ones measured experimentally by Viking 1 and 2. The theoretical electron-density profile compares well with the measured profiles at low altitudes, but shows rather large values at higher altitudes. The observed oscillation in the electrondensity profile at high altitudes is attributed to the variable nature of impact ionization produced by suprathermal charged particles of solar wind origin.
pp 271-288 December 1983
Convolution methods for modelling of astronomical seeing effects have been investigated. The advantages and disadvantages of several techniques are discussed, and particular attention is given to the fast Fourier transform (FFT) method. This method is then applied to two classes of problems, the structure of cores of elliptical galaxies, appearance of distant galaxies and the consequences of seeing effects in some cosmological tests. Estimates are presented for dimming of the central surface brightness and changes in the apparent core radius for elliptical galaxies, as well as seeing-induced changes in ellipticity. Modelling of galaxies with stellar nuclei has also been performed. Some consequences of these effects in investigations of dynamics of elliptical galaxies are addressed briefly. The influence of seeing in observational cosmology is discussed in the context of Hubble diagram (m-z) tests. It is shown that inadequate compensation for seeing effects can seriously distort the conclusions in such tests. Some suggestions for future work in this direction are offered.
pp 289-293 December 1983
Changes in solar radio-brightness temperature were derived at 2.8,19.3 and 22.2 GHz from the observations of radio flux during the total eclipse of 1980 February 16. High-resolution MEM spectra of the brightness temperature fluctuations at the three frequencies showed periodicities ranging from 3.5 min to 128 min. Between 3.5 min and 14.6 min there are several periodicities of comparable significance common to the three operating frequencies. If the corresponding variations in brightness temperature are assumed to result from spatial variations in the solar radio emission, the observed periodicities imply scale sizes in the range 76000 km to 320000 km.
pp 295-300 December 1983
The Bianchi type I cosmological models have been extensively studied in the past especially as examples of the homogeneous shearing universe. This paper presents a tilted universe solution admitting this group of motion where the velocity field is shear-free but there is an energy flux term.
pp 301-306 December 1983
Recent observations indicate that the primordial abundance of4He could be smaller than 0.24. It may then be necessary to invoke neutrino degeneracy in the early universe to explain the primordial abundances of helium and deuterium. It is shown here that the necessary degeneracy, though small, gives rise to a large asymmetry between the present number densities of neutrinos and antineutrinos. The effect of degeneracy on the upper limit to the neutrino masses is also considered.
Volume 40 | Issue 2
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