• Volume 1, Issue 1

      September 1980,   pages  1-95

    • Preface

      M. K. V. Bappu

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    • Comoving frame calculations of spectral lines formed in rapidly expanding media with the partial frequency redistribution function for zero natural line width

      A. Peraiah

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      Comoving frame calculations have been used to compute the spectral lines formed in rapidly expanding spherical media. We have employed the angle-averaged partial frequency redistribution functionRI with a two-level atom model in non-LTE atom approximation. A linear velocity law increasing with radius has been employed with maximum velocity at Τ=0 being set equal to 30 mean thermal units. It is found that one obtains almost symmetric emission line profiles at large velocities similar to those found in quasars.

    • Lines formed in rotating and expanding atmospheres

      A. Peraiah

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      Spectral lines formed in a rotating and expanding atmosphere have been computed in the frame of the observer at infinity. Two kinds of velocity laws are employed: (i) a uniform radial velocity of the gas and (ii) velocity increasing with radius (i.e. velocity gradients). The atmosphere has been assumed to be rotating with constant velocity. We have considered maximum radial and rotational velocities to be 10 and 3 mean thermal units respectively in an atmosphere whose geometrical thickness is 10 times the stellar radius. The total radial optical depth at line centre is taken to be about 100. In all cases, Doppler profile and a source function which is varying as 1/r2 have been used.

      Generally, the lines are broadened when rotation is introduced. However, when radial motion is also present, broadening becomes asymmetric and the red emission and blue absorption are enhanced.

    • Pulsar activity and the morphology of supernova remnants

      V. Radhakrishnan G. Srinivasan

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      We use the recently introduced concept of a ‘window’ of magnetic field strengths in which pulsars can be active to explain the variation in morphology of supernova remnants. The striking difference between shell-type and filled-type remnants is attributed to differences in he magnetic field strengths of the neutron stars left by the respective Supernovae. Field strengths of a value permitting pulsar activity result in particle production and Crab-like centrally concentrated remnants. Other field values lead to strong magnetic dipole radiation and consequent shell formation (e.g. Cas A). Several apparent inconsistencies concerning pulsar-supernova associations appear to find a logical explanation on the basis of this hypothesis.

    • The role of general relativity in astronomy: Retrospect and prospect

      S. Chandrasekhar

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    • Evidence for a large population of shocked interstellar clouds

      V. Radhakrishnan G. Srinivasan

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      A 21 cm absorption measurement over a long path length free of the effects of differential galactic rotation indicates the existence of two distinct cloud populations in the plane. One of them consisting of cold, dense clouds has been well studied before. The newly found hot clouds appear to be at least five times more numerous. They have a spin temperature of ~ 300 K, an rms velocity of ~ 35 km s-1, twice the total mass, and hundred times the kinetic energy of the cold clouds. Over long path lengths, the hot clouds haveNH/kpc ~ 2 X 1021 cm-2 Kpc-1, and are estimated to have individual column densities ≤ 1020 cm-2. We propose that they are shocked clouds found only within supernova bubbles and that the cold clouds are found in the regions in-between old remnants, immersed in an intercloud medium. We conclude that the solar neighbourhood must be located between old supernova remnants rather than within one.

    • A search for OB stars in supernova remnants

      Sidney Van den Bergh

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      A massive binary, in which the primary becomes a supernova, should leave a luminous secondary near the centre of its remnant. Contrary to expectation no statistically significant excess of OB stars is, however, found near the centres of optically visible galactic supernova remnants.

    • XX Cam—The Inactive R CrB star

      I. Kameswara Rao N. M. Ashok P. V. Kulkarni

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      Infrared observations obtained six years apart of the R CrB type star XX Cam do not show any infrared excess, unlike all the other members of the class. The observed colours match a 7000 K black body energy distribution quite well. From the year 1898 till todate, apparently XX Cam has undergone only one visual light minimum in 1940. The lack of infrared excess, the abundance peculiarities and further lack of small amplitude light variations with periods of few tens of days, which are characteristic of R CrB type stars, are discussed in terms of theoretical pulsation models of helium stars.

    • A dispersion relation for open spiral galaxies

      G. Contopoulos

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      The Lin-Shu dispersion relation is applicable in the (asymptotic) case of tight spirals (large wave numberkR). Here we reconsider the various steps leading to the Lin-Shu dispersion relation in higher approximation, under the assumption that the wave numberkR is not large [(kRr) =O(1)], and derive a new dispersion relation. This is valid for open spiral waves and bars. We prove that this dispersion relation is the appropriate limit of the nonlinear self-consistency condition in the case where the linear theory is applicable.

  • 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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