• G. STEWART

      Articles written in Journal of Astrophysics and Astronomy

    • Observations of bright stars with AstroSat soft X-ray telescope

      K. P. SINGH G. STEWART S. CHANDRA G. C. DEWANGAN4, S. BHATTACHARYYA N. S. KAMBLE S. VISHWAKARMA J. G. KOYANDE

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      We present observations of four bright stars observed with the AstroSat Soft X-ray Telescope (SXT). Visible light from bright stars like these can leak through the very thin filter in front of the CCD in the focal plane CCD camera of the SXT and thus making the extraction of X-ray events difficult. Here, we showhow to extract the X-ray events without contamination by the visible light. The procedure applied to four bright stars here demonstrates how reliable X-ray information can be derived in such cases. The sample of bright stars studied here consists of two A spectral types (HIP 19265, HIP 88580), one G/K giant (Capella), and a nearby M-type dwarf (HIP 23309). No X-ray emission is observed from the A-type stars, as expected. X-ray spectra of Capella and HIP 23309 are derived and modeled here, and compared with the previous X-ray observations of these stars to show the reliability of the method used. We find that optical light can start to leak in the very soft energy bands below 0.5 keV for stars with $V= 8$ mag. In the process, we present the first X-ray spectrum of HIP 23309.

    • Observations of AR Sco with Chandra and AstroSat soft X-ray telescope

      K. P. SINGH V. GIRISH J. TIWARI P. E. BARRETT D. A. H. BUCKLEY S. B. POTTER E. SCHLEGEL V. RANA G. STEWART

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      We present our AstroSat soft X-ray observations of a compact binary system, AR Sco, and analysis of its X-ray observations with Chandra that were taken only about a week before the AstroSat observations. An analysis of the soft X-ray (0.3–2.0 keV) data limits the modulation of the spin, orbital, or beat periods to less than 0.03 counts s$^{-1}$ or <10% of the average count rate. The X-ray flux obtainedfrom both observatories is found to be almost identical (within a few percent) in flux, and about 30% lower than reported from the nine months older observations with XMM-Newton. A two-temperature thermal plasma model with the same spectral parameters fit Chandra and AstroSat data very well, and requires very little absorption in the line of sight to the source. The low-temperature component has thesame temperature ($\sim$1 keV) as reported earlier, but the high-temperature component has a lower temperature of $5.0^{+0.8}_{-0.7}$ keV as compared to 8.0 keV measured earlier, however, the difference is not statistically significant.

  • 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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