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Keywords:

  • stars: AGB and post AGB;
  • stars: variables: general;
  • galaxies: general;
  • galaxies: individual: M33

ABSTRACT

We present photometry and moderate-resolution spectroscopy of the luminous red variable [HBS 2006] 40671, originally detected as a possible nova in the galaxy M33. We find that the star is a pulsating Mira-type variable with a long period of 665 d and an amplitude exceeding 7 mag in the R band. [HBS 2006] 40671 is the first confirmed Mira-type star in M33. It is one of the most luminous Mira-type variables. In the K band its mean absolute magnitude is MK=−9.5, while its bolometric magnitude measured at maximum light is also extreme, Mbol=−7.4. The spectral type of the star at maximum is M2e–M3e. The heliocentric radial velocity of the star is −475 km s−1. There is a large negative excess (210 km s−1) in the radial velocity of [HBS 2006] 40671 relative to the average radial velocity of stars in its neighbourhood, pointing at an exceptional peculiar motion of the star. All the extreme properties of the new Mira star make it an important candidate for further studies.