The first spectroscopically confirmed Mira star in M33

Abstract

We present photometry and moderate-resolution spectroscopy of the luminous red variable [HBS2006]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 665d and an amplitude exceeding 7mag in the R band. [HBS2006]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 isMK=-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 -475kms-1. There is a large negative excess (-210kms-1) in the radial velocity of [HBS2006]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. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.