A warm molecular ring in AG Car: composing the mass-loss puzzle
  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
$1.55\pm0.21\times10^{-5}$ 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.
