Identifying Type IIn supernova progenitors in our Galaxy: the circumstellar environment of the Galactic luminous blue variable candidate Gal 026.47+0.02

Abstract

New data from the Herschel Infrared Galactic Plane Survey (Hi-GAL) and the Expanded Very Large Array, together with ancillary multifrequency data from different archives, have provided a comprehensive picture of the circumstellar envelope (CSE) surrounding the Galactic luminous blue variable (LBV) candidate Gal 026.47+0.02. The high angular resolution of both the 70-μm and 6-cm maps has allowed us to appreciate finest details of the nebula, whose morphology is consistent with a series of nested tori. The inner torus, which is close to the central object, is fully ionized, indicating events of aspherical mass loss. We have derived the physical properties of the CSE, including, in particular, one of the highest current-day mass losses from the central object and a very massive nebula, which consists of, at least, 17 M_⊙ of ionized gas, with 1.2–3.2 × 10^(−2)  M_⊙ in the form of dust. Altogether, the physical properties of Gal 026.47+0.02, including a very high stellar luminosity, point towards a very massive progenitor on the main sequence. According to the current models for Type IIn supernovae, the CSEs associated with possible progenitors have well constrained properties in both content and morphology. The derived physical characteristics of the nebula associated with Gal 026.47+0.02 actually satisfy all such requirements, providing some observational evidence of a direct link between a LBV and a possible Type IIn supernova.