MN112: a new Galactic candidate Luminous Blue Variable

TL;DR

The paper reports the discovery of a new Galactic candidate Luminous Blue Variable (cLBV) identified through infrared nebula detection and spectroscopic analysis, with long-term photometry showing stability consistent with LBV characteristics.

Contribution

This study introduces MN112 as a new Galactic cLBV candidate based on nebula morphology and spectral similarity to known LBVs, expanding the catalog of such objects.

Findings

MN112 exhibits a nebula similar to known LBV-associated nebulae.

Spectroscopy shows the central star's spectrum matches that of P Cygni.

Long-term photometry indicates stability typical of LBVs.

Abstract

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 $24 \mu$m in the {\it 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 GAL 079.29+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 P Cygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude ($\ga 1$ 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 ($\simeq$ 17.1$\pm$0.3 mag) over this period, while in the I band the star brightened by $\simeq 0.4$ 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 P Cygni remains relatively stable during the last three centuries.