• J. N. Desai

      Articles written in Journal of Astrophysics and Astronomy

    • Doppler shift measurements on the green coronal line—evidence for largescale macroscopic mass motion

      J. N. Desai T. Chandrasekhar P. D. Angreji

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      Fabry-Perot interferometric observations on the green coronal line (λ 5303 å) carried out during the total solar eclipse of 1980 February 16 have yielded relative Doppler shift velocities with an accuracy of ± 7 km s-1. The values show a peak in the 30–50 km s-1 range indicating largescale macroscopic mass motion in the solar maximum corona.

    • Temperature distribution in the corona from λ 5303 Å line-width observations: Eclipse of 1980 February 16 – Tentative evidence for a temperature maximum

      J. N. Desai T. Chandrasekhar

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      Fabry-Perot interferometfic observations in the green coronal line during the total eclipse of 1980 February 16, have yielded line-width temperatures up to 1.5 over a wide range of position angles. Least square analysis of the data indicates a tentative temperature maximum near 1.2 from the centre of the Sun. The ratio of peak line intensity to square of the continuum intensity Eline/E2cont appears to be inversely correlated to the temperature. Turbulent velocities calculated using this ratio and the observed line-width temperatures show a peak at ~ 10 km s-1.

    • Optical interferometric observations of a transient event of 1986 March 13 in the coma of Comet Halley

      C. Debi Prasad T. Chandrasekhar J. N. Desai N. M. Ashok Vinod Krishan

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      During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H2 O+ emission was recorded in thecoma at ∼ 0h UT on 1986 March 13. Observations were carried out using a special IHW filter for H2 O+ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24‡39’N,72‡ 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ∼ 35km s−1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet

    • The excitation mechanism of [Fe XIV] 5303 å line in the inner regions of solar corona

      K. P .Raju J. N. Desai T. Chandrasekhar N. M. Ashok

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      The line intensity of the green coronal line and the continuum intensity are derived from the filter and white light photographs of the solar corona obtained during the 1980 total solar eclipse. Ratio of the line to continuum intensity is plotted against the radial distancer(=R/R0,R0 is the solar radius), in various position angles. A simple model assuming an electron density dependence of the line and continuum intensities suggests a dominant collisional mechanism for the excitation of the line in the innermost regions (∼ 1.4R0). The measured line to continuum ratio tends to a constant value at different radial distances in different position angles. The constancy of the measured line to continuum ratio indicates significant radiative excitation beyond 1.4 R0, in some of the position angles.

    • Porous and fluffy grains in the regions of anomalous extinction

      D. B. Vaidya B. G. Anandarao J. N. Desai R. Gupta

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      It has long been established that the ratio of total to selective extinction is anomalously large (>- 5) in certain regions of the interstellar medium. In these regions of anomalous extinction the dust grains are likely to be irregular in shape and fluffy in structure. Using discrete dipole approximation (DDA) we calculate the extinction for porous and fluffy grains. We apply DDA first to solid spheroidal particles assumed to be made of a certain (large) number of dipoles. Then we systematically reduce the number of dipoles to model the porous grains. The aggregates of these particles are suggested to form the fluffy grains. We study the extinction for these particles as a function of grain size, porosity and wavelength. We apply these calculations to interpret the observed extincttion data in the regions of star formation (e.g. the Orion complex).

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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.

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      Posted on July 25, 2019

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