A slowly expanding torus associated with the candidate LBV MGE 042.0787+00.5084

The luminous blue variable (LBV) phase is a poorly understood stage in the evolution of high-mass stars, characterized by its brevity and instability. The surroundings of LBV stars are excellent test beds to study their dense stellar winds and eruptive mass-loss events. Aiming to improve our knowledge of the LBV phase, we observed the J = 1 → 0 and J = 2 → 1 lines of CO and ¹³CO in a field of 1.5 × 1.5 arcmin around the recently identified candidate LBV MGE 042.0787+00.5084, using the Institut de Radioastronomie Millimétrique 30-m radio telescope. We report the first detection of molecular emission associated with this source, tracing a structure with an evident circumstellar distribution. The morphology and kinematics of the gas can be explained by an expanding torus, a structure that may have originated from stellar ejecta, or the action of stellar winds on to the parent molecular cloud. We derive the physical properties of the gas by means of local thermodynamic equilibrium (LTE) and non-LTE line modelling, obtaining densities of H₂ of the order of 10³ cm^-3 and kinetic temperatures below 100 K. In addition, we build a kinematic model to reproduce the structure and velocity field of the gas, which are in good agreement with the observations. We estimate a total molecular gas mass of 0.6 ± 0.1 M_⊙ and a dynamical age of 6 × 10⁴ yr, leading to an average mass-loss rate of 0.8-1.2 × 10^-5 M_⊙ yr^-1.