A warm molecular ring in AG Car: composing the mass-loss puzzle

Abstract

We present APEX observations of CO J=3-2 and ALMA observations of CO J=2-1, 13CO J=2-1 and continuum toward 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$\pm$0.9 solar masses. 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 date of $1.55\pm 0.21\times 10^{-5}$ solar masses / yr. 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 ionised 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$\%$ 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.

16 pages, 13 figures. Accepted for publication in MNRAS

References in corpus (16)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Luminous Blue Variables are Antisocial: Their Isolation Implies that they are Kicked Mass Gainers in Binary Evolution
• Luminous Blue Variables and superluminous supernovae from binary mergers
• The Triple-Ring Nebula around SN1987A: Fingerprint of a binary merger
• And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae
• Neutral material around the B[e] supergiant star LHA 115-S 65: An outflowing disk or a detached Keplerian rotating disk?
• $\eta$ Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
• The isolation of Luminous Blue Variables: On subdividing the sample
• Discovery of warm and dense molecular gas surrounding the ring nebula G79.29+0.46
• A disrupted molecular torus around Eta Carinae as seen in 12CO with ALMA
• The Herschel view of the nebula around the luminous blue variable star AG Carinae
• Ionization structure in the winds of B[e] supergiants II. Influence of rotation on the formation of equatorial hydrogen neutral zones
• Exploring the multifaceted circumstellar environment of the Luminous Blue Variable HR Carinae
• The LBV HR Car has a partner: Discovery of a companion with the VLTI
• The canonical Luminous Blue Variable AG Car and its neighbor Hen 3-519 are much closer than previously assumed
• Very Large Array Observations of Winds from Massive Stars

Cited by in corpus (2)

• MeerKAT reveals a ghostly thermal radio ring towards the Galactic Centre
• The rich molecular environment of the luminous blue variable star AFGL 2298