M. A. Sharaf
Articles written in Journal of Astrophysics and Astronomy
Volume 25 Issue 3-4 September 2004 pp 213-220
M. A. Sharaf M. I. Nouh A. S. Saad
In this paper, relation was developed for Hyades stars between a function of the right ascensions and the angular distances from the vertex. The precision criteria of this relation are very satisfactory and a correlation coefficient value of ≃ 1 was found which proves that the attributes are completely related linearly. The importance of this relation was illustrated through its usages as:
•a criterion for membership of the cluster,
•a generating function for evaluating some parameters of the cluster,
•a generating function for the initial values of the vertex equatorial coordinates which could then be improved iteratively using the procedure of differential corrections.
Volume 28 Issue 1 March 2007 pp 9-16
M. A. Sharaf M. A. Banajh A. A. Alshaary
In this paper, an efficient iterative method of arbitrary integer order of convergence ≥ 2 has been established for solving the hyperbolic form of Kepler’s equation. The method is of a dynamic nature in the sense that, moving from one iterative scheme to the subsequent one, only additional instruction is needed. Most importantly, the method does not need any prior knowledge of the initial guess. A property which avoids the critical situations between divergent and very slow convergent solutions that may exist in other numerical methods which depend on initial guess. Computational Package for digital implementation of the method is given and is applied to many case studies.
Volume 31 Issue 1 March 2010 pp 3-16
Computational Developments for Distance Determination of Stellar Groups
In this paper, we consider a statistical method for distance determination of stellar groups. The method depends on the assumption that the members of the group scatter around a mean absolute magnitude in Gaussian distribution. The mean apparent magnitude of the members is then expressed by frequency function, so as to correct for observational incompleteness at the faint end. The problem reduces to the solution of a highly transcendental equation for a given magnitude parameter 𝛼. For the computational developments of the problem, continued fraction by the Top–Down algorithm was developed and applied for the evaluation of the error function erf(𝑧). The distance equation 𝛬(𝑦) = 0 was solved by an iterative method of second order of convergence using homotopy continuation technique. This technique does not need any prior knowledge of the initial guess, a property which avoids the critical situations between divergent and very slow convergent solutions, that may exist in the applications of other iterative methods depending on initial guess.
Finally, we apply the method for the nearby main sequence late type stars assuming that the stars of each group of the same spectral type scatter around a mean absolute magnitude in a Gaussian distribution. The accuracies of the numerical results are satisfactory, in that, the percentage errors between 𝑟 and the mean values are respectively: (2.4%, 1.6%, 0.72%, 0.66%, 3.5%, 2.4%, 2%, 2.5%, 0.9%) for the stars of spectral types: (F5V, F6V, F7V, F8V, F9V, G0V, G2V, G5V, G8V).
Volume 32 Issue 3 September 2011 pp 371-376
Analytical Solution for Stellar Density in Globular Clusters
In this paper, four parameters analytical solution will be established for the stellar density function in globular clusters. The solution could be used for any arbitrary order of outward decrease of the cluster’s density.
Volume 33 Issue 4 December 2012 pp 375-386
On the Maximum Separation of Visual Binaries
In this paper, an efficient algorithm is established for computing the maximum (minimum) angular separation ρ_{max}(ρ_{min}), 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 (ρ_{max}, 𝜃 |_{ρmax}) and (ρ_{min}, 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
there is no dependence between ρ_{max} and the spectral type and
a minor modification of Giannuzzi’s (1989) formula for the upper limits of ρ_{max} functions of spectral type of the primary.
Current Issue
Volume 40 | Issue 3
June 2019
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.
© 2017-2019 Indian Academy of Sciences, Bengaluru.