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Period–luminosity relations of type II Cepheids in the Magellanic Clouds

Authors

  • Noriyuki Matsunaga,

    Corresponding author
    1. Kiso Observatory, Institute of Astronomy, School of Science, the University of Tokyo, 10762-30, Mitake, Kiso, Kiso, Nagano 397-0101, Japan
      E-mail: matsunaga@ioa.s.u-tokyo.ac.jp
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  • Michael W. Feast,

    1. South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
    2. Astrophysics, Cosmology and Gravitation Centre and Department of Astronomy, University of Cape Town, Rondebosch 7701, South Africa
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  • Igor Soszyński

    1. Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
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E-mail: matsunaga@ioa.s.u-tokyo.ac.jp

ABSTRACT

Period–luminosity relations (PLRs) of type II Cepheids (T2Cs) in the Small Magellanic Cloud (SMC) are derived based on OGLE-III, IRSF/SIRIUS and other data, and these are compared with results for the Large Magellanic Cloud (LMC) and Galactic globular clusters. Evidence is found for a change of the PLR slopes from system to system. Treating the longer period T2Cs (W Vir stars) separately gives an SMC–LMC modulus difference of 0.39 ± 0.05 mag without any metallicity corrections being applied. This agrees well with the difference in moduli based on different distance indicators, in particular the PLRs of classical Cepheids. The shorter period T2Cs (BL Her stars) give a smaller SMC–LMC difference suggesting that their absolute magnitudes might be affected either by metallicity or by age effects. It is shown that the frequency distribution of T2C periods also changes from system to system.

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