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      Permanent link:
      https://www.ias.ac.in/article/fulltext/joaa/034/03/0273-0296

    • Keywords

       

      Photometry: optical; photometry: methods: data analysis; optical: variability; AGN.

    • Abstract

       

      It is important to quantify the underestimation of rms photometric errors returned by the commonly used APPHOT algorithm in the IRAF software, in the context of differential photometry of point-like AGN, because of the crucial role it plays in evaluating their variability properties. Published values of the underestimation factor, 𝜂, using several different telescopes, lie in the range 1.3–1.75. The present study aims to revisit this question by employing an exceptionally large data set of 262 differential light curves (DLCs) derived from 262 pairs of non-varying stars monitored under our ARIES AGN monitoring program for characterizing the intra-night optical variability (INOV) of prominent AGN classes. The bulk of these data were taken with the 1-m Sampurnanad Telescope (ST). We find 𝜂 = 1.54 ± 0.05 which is close to our recently reported value of 𝜂 = 1.5. Moreover, this consistency holds at least up to a brightness mismatch of 1.5 mag between the paired stars. From this we infer that a magnitude difference of at least up to 1.5 mag between a point-like AGN and comparison star(s) monitored simultaneously is within the same CCD chip acceptable, as it should not lead to spurious claims of INOV.

    • Author Affiliations

       

      Arti Goyal1 2 Mukul Mhaskey3 Gopal-Krishna1 2 Paul J. Wiita4 C. S. Stalin5 Ram Sagar6

      1. National Centre for Radio Astrophysics (NCRA), TIFR, Pune 411 007, India.
      2. Inter University Centre for Astronomy and Astrophyics (IUCAA), Post Bag 4 Ganeshkhind, Pune University Campus, Pune 411 007, India.
      3. Department of Physics, Pune University, Pune 411 007, India.
      4. Department of Physics, The College of New Jersey, PO Box 7718, Ewing, NJ 08628-0718, USA.
      5. Indian Institute of Astrophysics (IIA) Bangalore 560 034, India.
      6. Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital 263 129, India.

    • Dates

       
      Published
      September 2013
      Manuscript received
      4 March 2013
      Accepted
      19 June 2013

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