How long can LBVs sleep? A long-term photometric vaiability and spectral study of the Galactic candidate luminous blue variable MN112

TL;DR

This study investigates the long-term photometric and spectral variability of the LBV candidate MN112, revealing it as a dormant LBV that has remained inactive for at least a century, using multi-decade data and Gaia DR3 distance estimates.

Contribution

It provides a detailed long-term analysis of MN112, combining spectral modeling and Gaia data to identify it as a dormant LBV with no recent activity, expanding understanding of LBV variability.

Findings

MN112 is a dormant LBV inactive for over a century.

Gaia DR3 data increased the estimated distance, affecting the star's placement.

MN112's properties align with a 70 solar mass evolutionary track near the Humphreys--Davidson limit.

Abstract

Luminous Blue Variables (LBVs) are massive stars that show strong spectral and photometric variability. The question of what evolutionary stages they represent and what exactly drives their instability is still open, and thus is it important to understand whether LBVs without significant ongoing activity exist, and for how long such dormant LBVs may ``sleep''. In this article we investigate the long-term variability properties of the LBV candidate MN112, by combining its optical and infrared spectral data covering 12 years with photometric data covering nearly a century acquired by both modern time-domain sky surveys and historical photographic plates. We analyze the spectra, derive physical properties of the star by modelling its atmosphere and use a new distance estimate from Gaia data release 3 (DR3) to determine the position of MN112 both inside the Galaxy and in the Hertzsprung--Russell diagram. Distance estimation increased in almost two times in comparison with Gaia DR2. Due to that MN112 moved in upper part of the diagram and according to our modeling it lies on evolutionary track for star with initial mass $M_*=70 M_\odot$ near Humphreys--Davidson limit. Given the absence of any significant variability we conclude that the star is a dormant LBV that has been inactive for at least a century now.