The Cepheid distance to the Local Group galaxy NGC 6822

Authors

  • Michael W. Feast,

    1. Astronomy, Cosmology and Gravity Centre, Department of Astronomy, University of Cape Town, 7701 Rondebosch, South Africa
    2. South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa
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  • Patricia A. Whitelock,

    1. Astronomy, Cosmology and Gravity Centre, Department of Astronomy, University of Cape Town, 7701 Rondebosch, South Africa
    2. South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa
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  • John W. Menzies,

    Corresponding author
    1. South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa
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  • Noriyuki Matsunaga

    1. Kiso Observatory, Institute of Astronomy, The University of Tokyo, 10762-30 Mitake, Kiso, Nagano 397-0101, Japan
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E-mail: jwm@saao.ac.za

ABSTRACT

Recent estimates of the Cepheid distance modulus of NGC 6822 differ by 0.18 mag. To investigate this we present new multi-epoch JHKS photometry of classical Cepheids in the central region of NGC 6822 and show that there is a zero-point difference from earlier work. These data together with optical and mid-infrared observations from the literature are used to derive estimates of the distance modulus of NGC 6822. A best value of 23.40 mag is adopted, based on a Large Magellanic Cloud (LMC) distance modulus of 18.50 mag. The standard error of this quantity is ∼0.05 mag. We show that to derive consistent moduli from Cepheid observations at different wavelengths, it is necessary that the fiducial LMC period–luminosity relations at these wavelengths should refer to the same subsample of stars. Such a set is provided. A distance modulus based on RR Lyrae variables agrees with the Cepheid result.

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