MN112: a new Galactic candidate Luminous Blue Variable

We report the discovery of a new Galactic candidate Luminous Blue Variable (cLBV) via detection of an infrared circular nebula and follow-up spectroscopy of its central star. The nebula, MN112, is one of many dozens of circular nebulae detected at 24µm in the Spitzer Space Telescope archival data, whose morphology is similar to that of nebulae associated with known (c)LBVs and related evolved massive stars. Specifically, the core-halo morphology of MN112 bears a striking resemblance to the circumstellar nebula associated with the Galactic cLBV GAL079.29+00.46, which suggests that both nebulae might have a similar origin and that the central star of MN112 is a LBV. The spectroscopy of the central star showed that its spectrum is almost identical to that of the bona fide LBV PCygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude (& 1 mag) photometric variability of the central star using archival and newly obtained photometric data covering a 45 year period. We found that the B magnitude of the star was constant (' 17.1� 0.3 mag) over this period, while in the I band the star brightened by ' 0.4 mag during the last 17 years. Although the non-detection of large photometric variability leads us to use the prefix ‘candidate’ in the classification of MN112, we remind that the long-term photometric stability is not unusual for genuine LBVs and that the brightness of PCygni remains relatively stable during the last three centuries.