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

Bordiu, C., Rizzo, J. R., Ritacco, A. 2019. A slowly expanding torus associated with the candidate LBV MGE 042.0787+00.5084. Monthly Notices of the Royal Astronomical Society 482, 2, 1651-1663 DOI: 10.1093/mnras/sty2726

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 1300 in a field of 1.5 x 1.5 arcmin around the recently identified candidate LBV MGE 042.0787+00.5084, using the Institut de Radioastronomie Millimetrique 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 H-2 of the order of 10(3) 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-circle dot and a dynamical age of 6 x 10(4) yr, leading to an average mass-loss rate of 0.8-1.2 x 10(-5) M-circle dot yr(-1).

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