A new luminous variable in M33

Abstract

Abstract We present a new luminous star in M33 located in the nuclear region. The star shows strong Feii and [Feii] forest, hydrogen emissions in the spectrum, as well as nebular lines. Tiii and Siii lines were detected in absorption, their radial velocity shifted by ≈−30kms−1 relative to emission lines. The star is variable over 7 yr with 0.5 mag variations over a year. We studied its spectral energy distribution together with five confirmed luminous blue variables (LBVs) and VarA in M33 using homogeneous data and methods. We found the star's bolometric luminosity to be logL/L⊙≈ 6.27, a surface temperature of T∼ 16000K and blackbody temperatures of two dust components of T∼ 900 and 420K. The new star has properties intermediate between the LBVs and VarA (probable cool hypergiant). At the same time, it has a hot photosphere, LBV-like luminosity and an extensive circumstellar material (strong [Caii] lines). In these seven luminous variables in M33, we find the total range of the hot component luminosities is 1.0 dex, but that of the dust components is 2.0 dex. We conclude that the dust phenomenon in the luminous variables is temporary and variable, and that the dust activity may follow strong eruptions.