A New Luminous Blue Variable Candidate in M33

The upper H-R diagram is populated by different classes of stars that illustrate both the complexity and the importance of episodic mass loss in the final stages of massive star evolution that are not understood. Since 2012, the Barber Observatory Luminous Stars Survey has been monitoring the long-term behavior and changes in dozens of the most luminous stars in the nearby galaxy M33. We have identified a new “eruptive” variable in M33. Its light curve shows a long period of increasing brightness followed by a rapid brightening in the visual that lasted about three years. Spectra from the MMT in 2010 show a luminous hot star with strong H and He I emission. Four years later the He I emission was gone, prominent P Cyg absorption was present in the H lines, and the absorption lines suggest a transition to a cooler temperature that is supported by a corresponding shift in the visual colors. Its light curve, spectra, and position on the H-R Diagram are discussed. We suggest that this star be added to the list of LBVs.