• Volume 9, Issue 1

      March 1988,   pages  1-65

    • Editorial

      J. C. Bhattacharyya

      More Details Fulltext PDF
    • Thermal-convective instability of a composite rotating plasma in a stellar atmosphere with finite larmor radius

      K. C. Sharma

      More Details Abstract Fulltext PDF

      Thermal-convective instability of a hydromagnetic, composite, rotating, inviscid and infinitely conducting plasma in a stellar atmosphere has been studied in the presence of finite Larmor radius. It is found that the criterion for monotonic instability holds good in the presence of the effects due to rotation and finite Larmor radius.

    • Constraints on the176Lu cosmochronometer

      J. R. De Laeter B. J. Allen G. C. Lowenthal J. W. Boldeman

      More Details Abstract Fulltext PDF

      In an endeavour to resolve reported discrepancies in the value of the branching ratio of176Lu at astrophysical energies, a new determineation of the175Lu ()176mLu capture cross section has been measured as 958 ± 58 mb. This gives a value of the branching ratio of 0.21 ±0.05. This result indicates that some reequilibration of the ground and isomeric states of176Lu occurs in stellar environments undergoing s-process nucleosynthesis, and confirms that176Lu is not a reliable cosmochronometer. However the very existence of176Lu in the solar system implies that the ground state of176Lu was not completely depopulated, and provides the possibility of using this nuclide as a sensitive thermometer for stellar processes.

    • CCD star images: On the determination of Moffat’s PSF shape parameters

      O. Bendinelli G. Parmeggiani F. Zavatti

      More Details Abstract Fulltext PDF

      Among the variety of empirical models of optical Point Spread Function used in the astronomical environment, only the Moffat’s (1969) one is able to describe by means of two parameters (in the circular case) both the inner and the outer star image regions. In view of this very important feature, the problem of the simultaneous estimates of Moffat’s PSF shape parameters, off-centring, and the background level in CCD star images has been investigated. The problem does not seem to be rigorously resolvable, but an approximate way to calculate all the parameters except off-centring is shown. It must be stressed that, the Moffat’s PSF model being a softened power law belonging to the family of modified King and Hubble models, the present discussion can be of aid in many other research fields. Also, the integral equation enabling us to convolve a spherical source with Moffat’s PSF is given and applied for comparison to Multi-Gaussian convolution.

    • Accretion effects on compact members of binary stars

      N. Spyrou

      More Details Abstract Fulltext PDF

      We explore the change in the period of axial rotation and in the radius of a magnetized compact star in a binary system, induced by the accretion on it of mass with angular momentum from the surface of its non-compact companion. No specific assumption is made concerning the accretion model, and the primary’s interior is described by the Fermi-Dirac statistics for degenerate matter. The rate of change with time of the period and radius is expressed in terms of the compact primary’s physical parameters and total absolute luminosity. The conditions are fully derived under which the above changes can be positive, negative or even vanish. In the case of the millisecond pulsars in binary X-ray sources the predicted values of the period time derivative, depending on the values of the accretion rate and. the absolute luminosity, can be positive or negative—if not vanishing—and they fall absolutely in the range 10−21 −10−17 ss−1, in good agreement with current observational data. The corresponding rate of change of radius, either positive or negative, fall in the range of 10−3 −10−1 cm y−1. Finally, it is proved that the well-known bursters can be explained by thermonuclear flash due to gravitational instability in the accreted matter, but their explanation as a result of direct contraction could be possible only for quite high accretion rates (>10−7M ⊙ y−1). This last result indicates that, in contrast to the accretion-induced change in period, which can be of either sign irrespective of the primary’s age, the accretion-induced non-catastrophic contraction is impossible, while according to repent results the contraction in general is possible for young compact objects.

    • Evidence for moving features in the corona from emission line profiles observed during eclipses

      A. B. Delone E. A. Makarova G. V. Yakunina

      More Details Abstract Fulltext PDF

      Using the line profiles of [Fe x] 6374 å and [Fe XIV] 5303 å emission lines observed during five total solar eclipses, we address the problem whether the solar corona is static or contains moving features. Many of the profiles of both emission lines have complicated shapes, which we interpret as an evidence for the existence of many, small, moving features in the corona. The line-of-sight velocities observed by other investigators (e.g. Desai, Chandrasekhar & Angreji 1982) also support this view. On the other hand, about 15 recent interferometric and multislit investigations of coronal emission lines have not shown evidence of moving elements. We suggest that this is due to insufficient spatial resolution.

    • Spacetime with self-gravitating thick disc

      Sandip K. Chakrabarti

      More Details Abstract Fulltext PDF

      We compute the metric coefficients and study some properties of the spacetime comprising of a Schwarzschild hole distorted by a self gravitating thick disc.

    • Occultations by possible material in Saturn’s outer magnetosphere

      R. Vasundhara

      More Details Abstract Fulltext PDF

      Results of a search for occultations of stars in the SAO catalogue by Saturn’s outer magnetosphere during 1988 are presented.

  • 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.

© 2017-2019 Indian Academy of Sciences, Bengaluru.