• S. Muneer

      Articles written in Journal of Astrophysics and Astronomy

    • 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.

    • A 10-m class national large optical-IR telescope

      G. C. ANUPAMA G. MAHESWAR S. SRIRAM T. SIVARANI P. S. PARIHAR S. NAGABHUSHAN DORJE ANGCHUK S. BARWAY B. C. BHATT R. BANYAL ALIKHAN BASHEER PRASANNA DESHMUKH DEVIKA DIVAKAR TSEWANG DORJAI ARUNA GOSWAMI K. V. GOVINDA SONAM JORPHAIL U. S. KAMATH MADAN MOHAN KEMKAR TASHI TSERING MAHAY S. MUNEER C. MUTHUMARIAPPAN SHANTIKUMAR SINGH NINGOMBAM G. PANDEY B. E. REDDY D. K. SAHU D. S. SANDEEP RAMYA SETHURAM C. S. STALIN S. SUBRAMANIAN STANZIN TSEWANG A. SUBRAMANIAM

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      An observatory class national large optical-IR telescope (NLOT), is proposed to be built and located in the country. The telescope consists of a 10–12 m segmented primary. In order to cater to a diversity of observational programs, the telescope is designed with high throughput in both the optical and IRregions (0.3–5 $\mu$m). It should perform reasonably well up to 30 $\mu$m. The telescope and instruments should have remote operations capability, allowing for the queue as well as classical scheduling and high reliability and robustness. This article provides a brief description of the science cases that drive the telescope requirements, activities related to optics design and some thoughts on the instruments.

    • Intra-night optical variability monitoring of $\gamma$-ray emitting blazars

      K. SUBBU ULAGANATHA PANDIAN A. NATARAJAN C. S. STALIN ASHWANI PANDEY S. MUNEER B. NATARAJAN

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      We present the results obtained from our campaign to characterize the intra-night optical variability properties of blazars detected by the Fermi large area telescope. This involves R-band monitoring observations of a sample of 18 blazars, which includes five flat spectrum radio quasars (FSRQs) and thirteen BL Lac objects (BL Lacs) covering the redshift range $z=0.085$-1.184. Our observations carried out using the 1.3m J. C. Bhattacharya telescope cover a total of 40 nights ($\sim$200 h) between the period December 2016 and March 2020. We characterized variability using the power enhanced $F$-test. We found duty cycle (DC) variability of about 11% for FSRQs and 12% for BL Lacs. Dividing the sample into different sub-classes based on the position of the synchrotron peak in their broadband spectral energy distribution (SED), we found DC of $\sim$16%, $\sim$10% and $\sim$7% for lowsynchrotron peaked (LSP), intermediate synchrotron peaked (ISP) and high synchrotron peaked (HSP) blazars. Such high DC of variability in LSP blazars could be understood in the context of the R-band tracing the falling part (contributed by high energy electrons) of the synchrotron component of thebroadband SED. Also, the R-band tracing the rising synchrotron part (produced by low energy electrons) in the case of ISP and HSP blazars, could cause lesser variability in them. Thus, the observed high DC of variability in LSP blazars relative to ISP and HSP blazars is in accordance with the leptonic model ofemission from blazar jets.

  • 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.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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