• VINITA NAVALKAR

      Articles written in Journal of Astrophysics and Astronomy

    • Thermal shaping of thin glass panels for hard X-ray telescope optics

      VINITA NAVALKAR KULINDER PAL SINGH MEHERNOSH PRESS

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      We present a process for thermal forming of thin glass panels of borosilicate glass to produce mirror segments for X-ray telescope optics. The mirror segments are required to be shaped in a parabolic and hyperbolic shape in accordance with Wolter-I type design of X-ray telescope optics. Thermal forming of glass is a low-cost method to produce light-weight mirror segments. The process makes use of a semi-cylindrical quartz mold having surface roughness of the order of 1 nm. Flat glass sheets of 0.2 mm and 0.3 mm thickness are placedon the diametric edges of the mold. With a suitable thermal cycle, the glass sheets are thermally formed as per the shape of the mold. The shape of these formed glass sheets was measured using a non-contact optical setup.The surface quality measurements of the formed glass sheets were performed using atomic force microscope and they were found to be in the range of 0.04–0.33 nm. Once tested for acceptance, these glass sheets are coatedusing sputter deposition of multi-layers of high and low atomic number materials for hard X-ray reflection. Such mirror segments do not require polishing of the surface before being coated with multi-layers.

    • Pre-flight evaluation of the soft X-ray telescope optics aboard AstroSat

      VINITA NAVALKAR KULINDER PAL SINGH HARSHIT SHAH VILAS MHATRE VISHWAS RISBUD

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      Soft X-ray telescope (SXT) built on the principle of grazing incidence optics was launched onboard AstroSat on September 28, 2015, and made operational on October 26, 2015. The telescope optics consists of two conical sections of approximate paraboloid and hyperboloid mirror segments arranged in Wolter type-I design. It comprises a total of 320 mirror segments made from aluminum foil of 0.2 mm thickness coated with gold on the front (reflective) side by the replication process that was first used in the Suzaku Observatory. The mirrors focus X-rays in the energy range of 0.3–8.0 keV on to a charged coupleddevice-based focal plane camera assembly at a distance of 2 m. We present here the pre-launch, groundbased calibration, and evaluation of SXT optics carried out at the X-ray Optics Laboratory at the Tata Institute of Fundamental Research. The SXT optics assembly was calibrated and evaluated experimentally, using scans by a collimated optical beam from a laser source, as well as using a full-aperture optical beam from an inverse telescope. A collimated beam of a red laser source was used to ensure the accuracy of mounting of individual mirror segments and the full aperture beam white light-emitting diode (LED) source was used to estimate the point spread function (PSF) of all 320 mirrors together. The approximate PSF obtained during the ground calibration was around 136.6 arcsec. These results were in accordance with theresults obtained during the in-orbit calibration post launch.

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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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