Volume 7, Issue 4
December 1986, pages 241-316
pp 241-257 December 1986
We present preliminary results of a spherical-harmonic-Fourier analysis of sunspot activity during the twenty-two years 1933–1954. The results indicate that the sunspot activity might be originating in global solar oscillations with periods of years and decades. However, except for the axisymmetric mode of degree 6, the set of other axisymmetric modes showing ∼ 11 yr periodicities are different from one sunspot cycle to another. A more detailed analysis, preferably with larger data series, will be needed to arrive at a more definite conclusion.
pp 259-273 December 1986
We present the condition of vanishing shear in a spatially homogeneous spacetime in terms of the Ricci rotation co-efficients corresponding to an orthonormal tetrad (να.Aηα) (whereνα is the unit vector along the time axis andAηα are the three independent reciprocal group vectors). Assuming that the velocity vector can be expanded in the direction ofνα and any one of theAηα’s it is shown that shear-free motion is possible only in case of some special Bianchi types, and these cases are studied assuming the velocity vector to be geodetic and that there may be a nonvanishing heat flux term.
pp 275-292 December 1986
Minimum-relative-entropy method (MREM) has been presented as a solution to the missing short-baseline problem in the synthesis observations. It is shown that a measure of distance between the prior model and the image in the plane of pixel brightness is an adequate measure of relative entropy. The method has been further extended for polarization observations and the potential of the method against the conventional MEM has been demonstrated by simulated examples.
pp 293-298 December 1986
The deep galaxy sample of MacGillivray & Dodd (1980), obtained from purely objective means, is investigated using the technique of Kuhn & Uson (1982) for the presence of structure of a filamentary nature. A variety of synthetic fields of galaxies (including both ‘filament’ and ‘non-filament’ models) generated by means of a computer simulation technique have also been studied for comparison purposes. No strong evidence for filamentary structure in the galaxy distribution is found for this deep sample.
pp 299-304 December 1986
An examination of the existing period searches for 2CG195 + 4 leads to the conclusion that the 59 second periodicity is highly significant only for the 1981 March 17–18 detection of Bignami, Caraveo & Paul (1984). The statistical significance is increased substantially if the pulsation period is half the previously reported value. The period derivative is not well determined. Here we propose that 2CG 195 + 4 is a neutron star powered by accretion from a low (≲ 1M⊙) mass main-sequence companion. A distance of a few hundred pc would imply that the neutron star is a fast rotator and is spinning down.
pp 305-316 December 1986
New spectrophotometric observations of the Wolf-Rayet system HD 50896 are presented and interpreted in terms of its binary nature. The lines of N V, N IV and C IV show moderate variations, which can be explained using a binary model with a compact companion. He n λ4686 appears to arise from a larger region compared to other lines. The distortion caused by the wind can partly explain its flux variations. The emission fluxes of He I lines are generally constant indicating their non-participation in the orbit. The results are compared with other Wolf-Rayet binaries (V444 Cyg and CQ Cep) and the evolutionary status is discussed.
Volume 40 | Issue 2
Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.