The first spectroscopically confirmed Mira star in M33

TL;DR

This paper reports the discovery and confirmation of the first Mira-type variable star in M33, highlighting its extreme luminosity, long pulsation period, and peculiar velocity, which are significant for stellar evolution studies.

Contribution

It provides the first spectroscopic confirmation of a Mira star in M33 and details its unique properties, expanding knowledge of variable stars in external galaxies.

Findings

First confirmed Mira star in M33

Extremely luminous with M_K = -9.5 and M_bol = -7.4

Exhibits a long period of 665 days and peculiar radial velocity

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 found that the star is a pulsating Mira-type variable with a long period of 665 days and an amplitude exceeding 7 mag 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 is M_K = -9.5, its bolometric magnitude measured in the maximum light is also extreme, M_bol = -7.4. The spectral type of the star in the maximum is M2e - M3e. The heliocentric radial velocity of the star is -475 km/s. There is a big negative excess (-210~km/s) in radial velocity of [HBS2006] 40671 relative to the average radial velocity of stars in its neighborhood pointing at an exceptional peculiar motion of the star. All the extreme properties of the new Mira star make it important for further studies.