Detection of [TSUP]12[/TSUP]CO [ITAL]J[/ITAL] = 1 → 0 and [ITAL]J[/ITAL] = 2 → 1 Emission from the Luminous Blue Variable AG Carinae: Circumstellar Envelope or Disk?

Abstract

We present the first detection of 12 CO J =2 ! 1 and J =1 ! 0 emission from the luminous blue variable AG Carinae. We show that AG Car resides in a region that is very rich in molecular gas with complex motions. We find evidence of a slow outflow of molecular gas, expanding at ’ 7k m s � 1 . This emission appears spatially unresolved. We argue that it is spatially localized, rather than extended, and possibly associated with the immediate circumstellar region of AG Car. Both detected CO lines are characterized by a pseudoGaussian profile with FWHM ’ 15 km s � 1 , indicating a slowly expanding region of molecular gas in close proximity to the hot central star. We have explored two possible scenarios to explain the observed profile: a circumstellar envelope, similar to carbon stars, or a circumstellar disk. The option of the circumstellar disk is preferable because (1) it is consistent with additional independent indications of the existence of wind asymmetries in close proximity to the central star, found from spectropolarimetry and analysis of the UV and optical line profiles, and (2) it provides the conditions of density and shielding necessary for the survival of the CO molecules in proximity to such a hot star (Teff ’ 14,000–20,000 K). On the assumption that the CO emission originated when AG Car was in an evolved state, we derive a lower limit to the CO mass of 6.5 � 10 � 3 M� . We also estimate that the CO fraction is ’2.3 � 10 � 3 of the total mass of molecular gas, which then would amount to 2.8 M� . This is smaller, but still comparable to, the mass of ionized gas present in the circumstellar environment (4.2 M� ), with the implication that the molecular gas fraction can contribute significantly to the overall mass lost from the central star in its post–main-sequence evolution.