S. N. TANDON
Articles written in Journal of Astrophysics and Astronomy
Volume 22 Issue 2-3 June 2001 pp 173-185
Three Galactic star forming regions associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS far infrared (FIR) bands centered at ≈140 and 200μm using the TIFR 100 cm balloon borne FIR telescope. These maps show extended FIR emission with structures. The HIRES processed IRAS maps of these regions at 12, 25, 60 & 100 ìm have also been presented for comparison. Point-like sources have been extracted from the longest waveband TIFR maps and searched for associations in the other five bands. The diffuse emission from these regions have been quantified, which turns out to be a significant fraction of the total emission. The spatial distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209), has been determined reliably from the maps in TIFR bands. The dust temperature and optical depth maps show complex morphology. In general the dust around S209 has been found to be warmer than that in W3(OH) region.
Volume 38 Issue 2 June 2017 Article ID 0028 Review Article
S. N. Tandon J. B. Hutchings S. K. Ghosh A. Subramaniam G. Koshy V. Girish P. U. Kamath S. Kathiravan A. Kumar J. P. Lancelot P. K. Mahesh R. Mohan J. Murthy S. Nagabhushana A. K. Pati J. Postma N. Kameswara Rao K. Sankarasubramanian P. Sreekumar S. Sriram C. S. Stalin F. Sutaria Y. H. Sreedhar I. V. Barve C. Mondal S. Sahu
The performance of the ultraviolet telescope (UVIT) on-board AstroSat is reported. The performance in orbit is also compared with estimates made from the calibrations done on the ground. The sensitivity is found to be within ∼15% of the estimates, and the spatial resolution in the NUV is found to exceed significantly the design value of 1.8′′ and it is marginally better in the FUV. Images obtained from UVIT are presented to illustrate the details revealed by the high spatial resolution. The potential of multi-band observations in the ultraviolet with high spatial resolution is illustrated by some results.
Volume 42 All articles Published: 26 May 2021 Article ID 0020 PAYLOAD REVIEW
S. K. GHOSH P. JOSEPH A. KUMAR J. POSTMA C. S. STALIN A. SUBRAMANIAM S. N. TANDON I. V. BARVE A. DEVARAJ K. GEORGE V. GIRISH J. B. HUTCHINGS P. U. KAMATH S. KATHIRAVAN J. P. LANCELOT D. LEAHY P. K. MAHESH R. MOHAN S. NAGABHUSHANA A. K. PATI N. KAMESWARA RAO K. SANKARASUBRAMANIAN P. SREEKUMAR S. SRIRAM
Over the last 5 years, UVIT has completed observations of more than 500 proposals with $\sim$800 unique pointings. In addition, regular planned monitoring observations have been made and from their analysis various key parameters related to in orbit performance of UVIT have been quantified. The sensitivities of the UV channels have remained steady indicating no effect of potential molecular contamination confirming the adequacy of all the protocols implemented for avoiding contamination. The quality of the PSF through the years confirms adequacy of thermal control measures. The early calibrations obtained during the Performance Verification (PV) phase have been further revised for more subtle effects. These include flat fields and detector distortions with greater precision. The operations of UVIT have also evolved through inorbit experience, e.g. tweaking of operational sequencing, protocol for recovery from bright object detection (BOD) shutdowns, parameters for BOD thresholds, etc. Finally, some effects of charged particle hits on electronics led to optimised strategy for regular resetting. The Near-UV channel was lost in one of suchoperations. All the above in-orbit experiences are presented here.
Volume 42 All articles Published: 29 May 2021 Article ID 0025 DATA PIPELINE
Volume 42 All articles Published: 2 June 2021 Article ID 0029 DATA PIPELINE
Performance of the Level-2 pipeline, which translates the UVIT data created by the ISRO’s ground segment processing systems (Level-1) into astronomer ready scientific data products, is described. This pipeline has evolved significantly from experiences during the in orbit mission. With time, the detectormodules of UVIT developed certain defects which led to occasional corruption of imaging and timing data. This article will describe the improvements and mitigation plans incorporated in the pipeline and report its efficacy and quantify the performance.
Volume 42 All articles Published: 11 June 2021 Article ID 0041 MISSION
Ultra Violet Imaging Telescope (UVIT) is one of the 5 instruments on AstroSat satellite, which was launched on September 28, 2015. UVIT was designed to make images with a resolution of <1:8$''$, simultaneously in two ultraviolet channels: Far Ultraviolet (130–180 nm) and Near Ultraviolet (200–300 nm). Images are also made in visible region (320–550 nm) for tracking drifts in pointing. The shortest wavelengths to be observed with UVIT can be heavily absorbed by mono-molecular deposits/contamination on the optical surfaces.Keeping contamination under control in UVIT was a major challenge and it required a variety of actions: (i) strict control of the payload materials and process, (ii) mechanical configuration, (iii) baking of all the parts to release all the adsorbed molecules etc., (iv) assembly in ultra cleanrooms, (v) pre-inspection and auditing of all the areas, in which UVIT was placed, for any potential for contamination, (vi) continuous purging, with ultrapure nitrogen gas, till a few days before the launch, etc. In order to minimise any possible cross contaminationsfrom the other payloads/satellite, the doors of UVIT were opened 2 months after the launch. The high performance in the orbit and high stability of the sensitivity over 4 years in the orbit shows that the contamination was negligible. This paper presents the processes and protocols followed during the integration and testingphase to minimise the contamination in order to prevent any performance degradation.
Volume 43, 2022
Continuous Article Publishing mode
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.
Click here for Editorial Note on CAP Mode