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On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei

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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.

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Notes

  1. Image Reduction and Analysis Facility (http://iraf.noao.edu/)

  2. Munich Image and Data Analysis System (http://www.eso.org/sci/data-processing/software/esomidas/)

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Acknowledgements

One of the authors (AG) would like to thank Dr. Santosh Joshi (ARIES) for carrying out optical observations on a few occasions.

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Authors and Affiliations

  1. National Centre for Radio Astrophysics (NCRA), TIFR, Pune, 411 007, India

    Arti Goyal &  Gopal-Krishna

  2. Inter University Centre for Astronomy and Astrophyics (IUCAA), Post Bag 4 Ganeshkhind, Pune University Campus, Pune, 411 007, India

    Arti Goyal &  Gopal-Krishna

  3. Department of Physics, Pune University, Pune, 411 007, India

    Mukul Mhaskey

  4. Department of Physics, The College of New Jersey, PO Box 7718, Ewing, NJ, 08628-0718, USA

    Paul J. Wiita

  5. Indian Institute of Astrophysics (IIA), Bangalore, 560 034, India

    C. S. Stalin

  6. Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital, 263 129, India

    Ram Sagar

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  1. Arti Goyal
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Correspondence to Arti Goyal.

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Goyal, A., Mhaskey, M., Gopal-Krishna et al. On the Photometric Error Calibration for the Differential Light Curves of Point-like Active Galactic Nuclei. J Astrophys Astron 34, 273–296 (2013). https://doi.org/10.1007/s12036-013-9183-7

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