• A. K. Saxena

      Articles written in Journal of Astrophysics and Astronomy

    • Eclipse observations of coronal emission lines. I. [Fex] 6374Å profiles at the eclipse of 16 February 1980

      Jagdev Singh M. K. V. Bappu A. K. Saxena

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      Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm-1. The observed line profiles from 1.1 to 1.7 R with a spatial resolution of 10 × 22 arcsec2, give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 106 K. If temperature of the order of 1.3 × 106 K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s-1 to -17 km s-1. Most of the locations have velocities less than ±5 km s-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down.

    • Mid-term periodicities and heliospheric modulation of coronal index and solar flare index during solar cycles 22–23


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      We applied fast Fourier transform techniques and Morlet wavelet transform on the time series data of coronal index, solar flare index, and galactic cosmic ray, for the period 1986–2008, in order to investigate the long- and mid-term periodicities including the Rieger ($\sim$130 to $\sim$190 days), quasi-period ($\sim$200 to $\sim$374 days), and quasi-biennial periodicities ($\sim$1.20 to $\sim$3.27 years) during the combined solar cycles 22–23. We emphasize the fact that a lesser number of periodicities are found in the range of low frequencies, while the higher frequencies show a greater number of periodicities. The rotation rates at the base of convection zone have periods for coronal index of $\sim$1.43 years and for solar flare index of $\sim$1.41 year, and galactic cosmic ray, $\sim$1.35 year, during combined solar cycles 22–23. In relation to these two solar parameters (coronal index and solar flare index), for the solar cycles 22–23, we found that galactic cosmic ray modulation at mid cut-offrigidity (${\rm Rc} = 2.43$GV) is anti-correlated with time-lag of few months.

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      Posted on January 27, 2016

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