• Jagdev Singh

      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.

    • Analysis of Ca+ K plage area for short period variation

      Jagdev Singh S. K. Jain

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      We have analysed the observations of Solar Ca+K daily plage area for the period 1951-1977 to find evidence for the existence of short period (around 12–13 days) variation in the data. We divided the data in three groups—two corresponding to 10–20‡N and 10–20‡S latitude belts, and one corresponding to the total plage area—and used the power spectrum and autocorrelation techniques for the analysis. Both the techniques clearly show the 27-day periodicity due to solar rotation modulation in all the sets. A 12–13 day periodicity is seen in only 3, out of a total of 57 data sets when autocorrelation technique is used. A generally weak peak around 12–13 days is, however, seen in the power spectrum of all the data sets. The relative power in the 12–13 day peak is found to be significantly higher in those three data sets where the autocorrelation also shows this periodicity. On these two epochs the sunspot area distribution showed the existence of two distinct active longitudes separated by about 140–170 degrees. This seems to be the cause for the existence of a periodicity around 12–13 days in the autocorrelation and enhancement in the relative power of the 12–13 days peak in the power spectrum of these two epochs

    • Tessellation of SoHO magnetograms

      R. Srikant Jagdev Singh

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      A gradient based algorithm which divides arbitrary images into non-overlapping surface filling tiles of opposite polarity is used to study the flux and size distributions of large scale magnetic flux concentrations in solar and heliospheric observatory (SoHO) magnetograms. The mean absolute flux and size of the concentrations at the considered scale is found to be about 1.7 × 1018Mx and 5.2Mm for both polarities. The form of the flux distribution is characterized by a skewness of α3 = 4.9 and a kurtosis of α4 = 42.8. The fall in the distribution in the range 6.5 × 1017 Mx to 5×1018 Mx is described by an exponential fit, in agreement with a model for the sustenance of quiet region flux.

    • Spectroscopic studies of solar corona VI: Trend in line-width variation of coronal emission lines with height independent of the structure of coronal loops

      Jagdev Singh Takashi Sakurai Kiyoshi Ichimoto S. Muneer

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      We have obtained spectroscopic observations in coronal emission lines by choosing two lines simultaneously, one [Fe x] 6374 Å and the other [Fe xi] 7892 Å or [Fe xiii] 10747 Å or [Fe xiv] 5303 Å. We found that in 95 per cent of the coronal loops observed in 6374 Å, the FWHM of the emission line increases with height above the limb irrespective of the size, shape and orientation of the loop and that in case of 5303 Å line decreases with height in about 89 per cent of the coronal loops. The FWHM of 7892 Å and 10747 Å emission lines show intermediate behavior. The increase in the FWHM of 6374 Å line with height is the steepest among these four lines. We have also studied the intensity ratio and ratio of FWHM of these lines with respect to those of 6374 Å as a function height above the limb. We found that the intensity ratio of 7892 Å and 10747 Å lines with respect to 6374 Å line increases with height and that of 5303 Å to 6374 Å decreases with height above the limb. This implies that temperature in coronal loops will appear to increase with height in the intensity ratio plots of 7892 Å and 6374 Å; and 10747 Å and 6374 Å whereas it will appear to decrease with height in intensity ratio of 5303 Å to 6374 Å lineversus height plot. These findings are up to a height of about 200 arcsec above the limb. The varying ratios with height indicate that relatively hotter and colder plasma in coronal loops interact with each other. Therefore, the observed increase in FWHM with height above the limb of coronal emission lines associated with plasma at about 1 MK may not be due to increase in non-thermal motions caused by coronal waves but due to interaction with the relatively hotter plasma. These findings also do not support the existing coronal loop models, which predict an increase in temperature of the loop with height above the limb.

    • Proposed National Large Solar Telescope

      Jagdev Singh

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      Sun’s atmosphere is an ideal place to study and test many magnetohydrodynamic (MHD) processes controlling turbulent plasma. We wish to resolve some of the finest solar features (which remain unresolved presently) and study their dynamics. Indian Institute of Astrophysics has proposed to design, fabricate and install a 2-meter class solar telescope at a suitable site in India to resolve features on the Sun of the size of about 0.1 arcsec. The focal plane instruments will include a high resolution polarimeteric package to measure polarization with an accuracy of 0.01 per cent; a high spectral resolution spectrograph to obtain spectra in 5 widely separated absorption lines simultaneously and high spatial resolution narrow band imagers in various lines. The Himalayan region appears to be a good choice keeping in view the prevailing dry and clear weather conditions. We have started detailed analysis of the weather conditions in the area and at some other locations in India. The site characterization will be done using the Sun-photometer, S-DIMM and SHABAR techniques to determine the seeing conditions.

    • Temporal Variation of Ca–K Line Profile of the Sun during the Solar Cycle 22 and 23

      G. Sindhuja Jagdev Singh

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      We obtained the Ca–K line profile of the Sun as a star since 1969 at the Kodaikanal Observatory (KO) and analysis of the data showed the need to delineate the role of different chromospheric features to the variations of solar irradiance. We, therefore, initiated a new methodology to make observations of Ca–K line profiles of the Sun as a function of latitude and integrated over the longitude on a daily basis since 1986. We have collected the data for about thousand days, spread over two solar cycles. Earlier data (before 1997) were recorded on the photographic film and later data using the CCD detector. The photographic film data were digitized and analysed along with the data obtained from CCD camera. From these data, we computed K1 and K2 widths for the Sun as a star, using all the observed line profiles as a function of latitude. In addition, we have analyzed the spectra of the whole Sun as a star obtained on some days and compared it with the results obtained from latitude spectra of the same day. The K1 and K2 widths of the Sun as a star derived from the KO data are compared with values determined from the observations made at other observatories to compare results from the new methodology of observations adopted by us and the earlier techniques. The average values of K1 width during the minimum period. of solar cycle 23 are smaller than those during the minimum period of cycle 22. Day-to-day variations in the K1 and K2 widths and plage areas may imply that irradiance variations occur not only due to large-scale solar activity, but also because of variations in some of the three types of network in quiet regions of the Sun. The variation in intensity of the plages can also cause day-to-day variations in widths.

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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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