• J. POSTMA

      Articles written in Journal of Astrophysics and Astronomy

    • In-orbit Performance of UVIT and First Results

      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

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      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.

    • In-orbit performance of UVIT over the past 5 years

      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

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      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.

    • Dorado and its member galaxies II: A UVIT picture of the NGC 1533 substructure

      R. RAMPAZZO P. MAZZEI A. MARINO L. BIANCHI S. CIROI E. V. HELD E. IODICE J. POSTMA E. RYAN-WEBER M. SPAVONE M. USLENGHI

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      Dorado is a nearby (17.69 Mpc) strongly evolving galaxy group in the Southern Hemisphere. We are investigating the star formation in this group. This paper provides a FUV imaging of NGC 1533, IC 2038 and IC 2039, which form a substructure, south west of the Dorado group barycentre. FUV CaF2-1UVIT-Astrosat images enrich our knowledge of the system provided by GALEX. In conjunction with deep optical wide-field, narrow-band Ha and 21-cm radio images we search for signatures of the interaction mechanisms looking in the FUV morphologies and derive the star formation rate. The shape of the FUVluminosity profile suggests the presence of a disk in all three galaxies. FUV emission is detected out to the optical size for IC 2038, and in compact structures corresponding to Ha and H ii bright features in NGC 1533. A faint FUV emission, without an optical counterpart, reminiscent of the H i structure that surrounds the outskirts of NGC 1533 and extends up to IC 2038/2039, is revealed above the local background noise.

    • A pair of UV nuclei or a compact star-forming region near the active nucleus in Mrk 766?

      P. P. DEKA G. C. DEWANGAN K. P. SINGH J. POSTMA

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      We report the discovery of a bright, compact ultraviolet source at a projected separation of 1.1 kpc from the known active galactic nucleus (AGN) in Mrk 766 based on AstroSat/UVIT observations. We perform radial profile analysis and derive the UV flux almost free from the nearby contaminating sources. The new source is about 2.5 and 5.6 times fainter than the AGN in the far and near UV bands. The two sources appear as a pair of nuclei in Mrk 766. We investigate the nature of the new source based on the UV flux ratio, X-ray and optical emission. The new source is highly unlikely to be another accreting supermassive black hole in Mrk 766 as it lacks X-ray emission. We find that the UV/optical flux of the new source measured at four different bands closely follow the shape of the template spectrum of starburst galaxies. This strongly suggests that the new source is a compact star-forming region.

    • New results from the UVIT survey of the Andromeda galaxy

      D. A. LEAHY J. POSTMA M. BUICK C. MORGAN L. BIANCHI J. HUTCHINGS

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      The Andromeda galaxy (M31) has been observed with the UltraViolet Imaging Telescope (UVIT) instrument onboard the AstroSat Observatory. The M31 sky area was covered with 19 fields, in multiple UV filters per field, over the period of 2017 to 2019. The entire galaxy was observed in the FUV F148W filter, and more than half observed in the NUV filters. A new calibration and data processing isdescribed which improves the astrometry and photometry of the UVIT data. The high spatial resolution of UVIT ($\sim$1 arcsec) and new astrometry calibration ($\sim$0.2 arcsec) allow identification of UVIT sources with stars, star clusters, X-ray sources, and other source types within M31 to a much better level than previously possible. We present new results from matching UVIT sources with stars measured as part of the Panchromatic Hubble Andromeda Treasury project in M31.

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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.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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