Astrometry and infrared observations of the Mira variable stars AP Lyncis, V837 Herculis, and BX Camelopardalis: Implications for the period–luminosity relation of the Milky Way

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  • James O Chibueze
    Centre for Space Research, Physics Department, North-West University , Potchefstroom 2520, South Africa
  • Riku Urago
    Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
  • Toshihiro Omodaka
    Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
  • Yuto Morikawa
    Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
  • Masayuki Y Fujimoto
    Department of Physics, Hokkaido University , Sapporo, Hokkaido 060-0810, Japan
  • Akiharu Nakagawa
    Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
  • Takahiro Nagayama
    Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
  • Takumi Nagayama
    Mizusawa VLBI Observatory, National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
  • Ken Hirano
    Mizusawa VLBI Observatory, National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

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<jats:title>Abstract</jats:title> <jats:p>AP Lyn and V837 Her are long-period Mira variable stars in the Milky Way. We performed VLBI Exploration of Radio Astrometry (VERA) phase-referenced observations towards H2O masers associated with AP Lyn and V837 Her. The annual parallaxes of AP Lyn and V837 Her were obtained to be 2.008 ± 0.038 mas and 1.090 ± 0.014 mas, corresponding to distances of 498 ± 10 pc and 917 ± 12 pc, respectively. From our multi-epoch infrared observations using the Kagoshima University 1 m telescope, we derived the mean J-, H-, and K′-band magnitudes of AP Lyn, V837 Her, and an additional long-period Mira variable BX Cam, whose parallax is known. We derived their pulsation periods to be 433 ± 1 d, 520 ± 1 d, and 458 ± 1 d, respectively, using the K′-band light curves. The MK–log P relation of long-period Mira variables seem to be violated by Mira variable stars with larger-than-expected MK values (like OZ Gem) in the Milky Way because of circumstellar extinction leading to an observed dimming effect. AP Lyn, V837 Her, and BX Cam (like OZ Gem) are dimming from the trend to O-rich stars in the Large Magellanic Cloud. This implies that the high metallicity of the Milky Way galaxy increases the opacity of the Mira-type variable stars and strengthens mass loss.</jats:p>

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