A new Luminous Variable in M33

TL;DR

This paper reports the discovery and analysis of a new luminous variable star in M33, highlighting its spectral features, variability, and properties that are intermediate between LBVs and hypergiants, suggesting temporary dust activity linked to eruptions.

Contribution

The study introduces a newly identified luminous variable star in M33 with detailed spectral and photometric analysis, expanding understanding of stellar variability and dust phenomena in massive stars.

Findings

Star shows strong FeII and hydrogen emission lines.

Star's luminosity and temperature are intermediate between LBVs and hypergiants.

Dust activity appears to be temporary and linked to eruptions.

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 ~ -30km/s relative to emission lines. The star is variable over seven years with 0.5 mag variations over a year. We studied its spectral energy distribution together with five confirmed Luminous Blue Variables and Var A in M33 using homogeneous data and methods. We found the star's bolometric luminosity to be log(L/Lsun)~6.27, a surface temperature of T~16000K and black body temperatures of two dust components of T~900 and 420K. The new star has properties intermediate between the LBVs and VarA (probable cool hypergiant). In 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 componets is 2.0 dex. We conclude that the dust phenomenon in the luminous variables is temporary and variable, and that dust activity may follow strong eruptions.