• Saleh Mohammed Alladin

      Articles written in Journal of Astrophysics and Astronomy

    • Changes in sizes and shapes of spherical galaxies in head-on collisions

      Farooq Ahmed Saleh Mohammed Alladin

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      Head-on collisions of two identical spherical galaxies are studied for two initial velocities (1) nearly equal to and (2) greater than the capture velocity. Orbits of about 500 representative stars are computed taking into account the effects of dynamical friction in the motion of the galaxies. From the computer studies the changes in the structure of the galaxies are deduced. The galaxies contract at closest approach and expand as they recede from each other. When the initial velocity is nearly equal to the capture velocity, the mean radius expands to almost double its size and the galaxies have a prolate structure until the closest approach with the longer axis in the direction of motion. The prolate structure is destroyed as the galaxies recede. For larger collision velocity (V ∼ 1.5 Vcap), the mean radius expands by 50 per cent and the galaxies are prolate until the closest approach and distinctly oblate after the collision. The fractional increase in the binding energy is 0.46 in the first case and 0.30 in the second case.

    • N-body simulations of tidal encounters between stellar systems

      P. Devadas Rao N. Ramamani Saleh Mohammed Alladin

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      N-Body simulations have been performed to study the tidal effects of a primary stellar system on a secondary stellar system of density close to the Roche density. Two hyperbolic, one parabolic and one elliptic encounters have been simulated. The changes in energy, angular momentum, mass distribution, and shape of the secondary system have been determined in each case. The inner region containing about 40 per cent of the mass was found to be practically unchanged and the mass exterior to the tidal radius was found to escape. The intermediate region showed tidal distension. The thickness of this region decreased as we went from hyperbolic encounters to the elliptic encounter keeping the distance of closest approach constant. The numerical results for the fractional change in energy have been compared with the predictions of the available analytic formulae and the usefulness and limitations of the formulae have been discussed.

    • Gravitational potential energy of interpenetrating spherical galaxies in Hernquist’s model

      K. S. V. S. Narasimhan K. S. Sastry Saleh Mohammed Alladin

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      Hernquist’s (1990) mass model for spherical galaxies and bulges described by the deVaucouleur’s profile gives analytical expressions for the density profile and the potential. These have been used to derive a simple and exact analytical expression for the gravitational potential energy of a pair of interpene-trating spherical galaxies represented by this model. The results are compared with those for polytropic and Plummer models of galaxis.

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    • 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.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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