• Issue front cover thumbnail

      Volume 33, Issue 4

      December 2012,   pages  361-422

    • Editorial

      Chanda J. Jog

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    • On the Jeans Criterion of a Stratified Heat Conducting Gaseous Medium in the Presence of Non-Uniform Rotation and Magnetic Field

      Joginder S. Dhiman Rekha Dadwal

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      The problem of self-gravitational instability of an infinite, homogeneous stratified gaseous medium with finite thermal conductivity and infinite electrical conductivity, in the presence of non-uniform rotation and magnetic field in the Chandrasekhar’s frame of reference, is studied. It is found that the magnetic field, whether uniform or non-uniform, has no effect on the Jeans’ criterion for gravitational instability and remains essentially unaffected. However, the thermal conductivity has the usual stabilizing effect on the criterion that the adiabatic sound velocity occurring in the Jeans criterion is replaced by the isothermal sound velocity. Thus, the present analysis extends the results of Chandrasekhar for the case of heat conducting medium and for non-uniform rotation and magnetic field.

    • On the Maximum Separation of Visual Binaries

      M. I. Nouh M. A. Sharaf

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      In this paper, an efficient algorithm is established for computing the maximum (minimum) angular separation ρmaxmin), the corresponding apparent position angles (𝜃|ρmax , 𝜃|ρmin) and the individual masses of visual binary systems. The algorithm uses Reed’s formulae (1984) for the masses, and a technique of one-dimensional unconstrained minimization, together with the solution of Kepler’s equation for (ρmax, 𝜃 |ρmax) and (ρmin, 𝜃 |ρmin). Iterative schemes of quadratic coverage up to any positive integer order are developed for the solution of Kepler’s equation. A sample of 110 systems is selected from the Sixth Catalog of Orbits (Hartkopf et al. 2001). Numerical studies are included and some important results are as follows:

      1. there is no dependence between ρmax and the spectral type and

      2. a minor modification of Giannuzzi’s (1989) formula for the upper limits of ρmax functions of spectral type of the primary.

    • Phase Relationship Between Sunspot Number, Flare Index and Solar Radio Flux

      X. L. Yan L. H. Deng Z. Q. Qu C. L. Xu D. F. Kong

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      To understand better the variation of solar activity indicators originated at different layers of the solar atmosphere with respect to sunspot cycles, we carried out a study of phase relationship between sunspot number, flare index and solar radio flux at 2800 MHz from January 1966 to May 2008 by using cross-correlation analysis. The main results are as follows:

      1. The flare index and sunspot number have synchronous phase for cycles 21 and 22 in the northern hemisphere and for cycle 20 in the southern hemisphere.

      2. The flare index has a noticeable time lead with respect to sunspot number for cycles 20 and 23 in the northern hemisphere and for cycles 22 and 23 in the southern hemisphere.

      3. For the entire Sun, the flare index has a noticeable time lead for cycles 20 and 23, a time lag for cycle 21, and no time lag or time lead for cycle 22 with respect to sunspot number.

      4. The solar radio flux has a time lag for cycles 22 and 23 and no time lag or time lead for cycles 20 and 21 with respect to sunspot number.

      5. For the four cycles, the sunspot number and flare index in the northern hemisphere are all leading to the ones in the southern hemisphere.

      These results may be instructive to the physical processes of flare energy storage and dissipation.

    • Revisiting the Cosmological Principle in a Cellular Framework

      L. Zaninetti

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      The cosmological principle in its various versions states that:

      1. the galaxy does not occupy a particular position,

      2. the Universe is homogeneous and isotropic.

      This statement does not agree with the recent astronomical observations in the range 𝑧 lower than 0.05 which are in agreement with a cellular structure of the Universe. Here we present a local analysis of the inhomogeneity of the Universe. When 𝑧 is greater than 0.05 our analysis cannot be applied because the astronomical sample of galaxies here processed is not complete. The two tools of the Poisson Voronoi Tessellation (PVT) and the luminosity function for galaxies allow building a new version of the local cosmological principle.

    • Acknowledgements

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    • Author Index

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    • Subject Index

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  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      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.

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