A warm molecular ring in AG Car: composing the mass-loss puzzle. Issue 4 (20th November 2020)

• Record Type: Journal Article
• Authors: Bordiu, C; Bufano, F; Cerrigone, L; Umana, G; Rizzo, J R; Buemi, C S; Leto, P; Cavallaro, F; Ingallinera, A; Loru, S; Trigilio, C; Riggi, S
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 500:Issue 4(2021)
• Page Start: 5500
• Page End: 5514
• Publication Date: 2020-11-20
• Subjects: stars: evolution -- stars: individual: AG Carina -- stars: massive -- stars: mass-loss -- ISM: abundances -- ISM: molecules; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3606
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present APEX observations of CO J = 3 → 2 and ALMA observations of CO J = 2 → 1, 13 CO J = 2 → 1, and continuum towards the Galactic luminous blue variable AG Car. These new observations reveal the presence of a ring-like molecular structure surrounding the star. Morphology and kinematics of the gas are consistent with a slowly expanding torus located near the equatorial plane of AG Car. Using non-LTE line modelling, we derived the physical parameters of the gas, which is warm (∼50 K) and moderately dense (∼10 3 cm −3 ). The total mass of molecular gas in the ring is 2.7 ± 0.9 M⊙ . We analysed the radio continuum map, which depicts a point-like source surrounded by a shallow nebula. From the flux of the point-like source, we derived a current mass-loss rate of $\dot{M} = (1.55\pm 0.21)\times 10^{-5}\, \mathrm{M}_{\odot}$ yr −1 . Finally, to better understand the complex circumstellar environment of AG Car, we put the newly detected ring in relation to the main nebula of dust and ionized gas. We discuss possible formation scenarios for the ring, namely, the accumulation of interstellar material due to the action of the stellar wind, the remnant of a close binary interaction or merger, and an equatorially enhanced mass-loss episode. If molecular gas formed in situ as a result of a mass eruption, it would account for at least a $30{{\ \rm per\ cent}}$ of the total mass ejected by AG Car. This detection adds a new piece to the puzzle of the complex mass-loss history of AG Car, providing new clues about the interplay between LBV stars and their surroundings.