Circumstellar CO in metal-poor stellar winds: the highly irradiated
  globular cluster star 47 Tucanae V3
  We report the first detection of circumstellar CO in a globular cluster.
Observations with ALMA have detected the CO J=3-2 and SiO v=1 J=8-7 transitions
at 345 and 344 GHz, respectively, around V3 in 47 Tucanae (NGC 104; [Fe/H] =
-0.72 dex), a star on the asymptotic giant branch. The CO line is detected at 7
sigma at a rest velocity v_LSR = -40.6 km/s and expansion velocity of 3.2 +/-
~0.4 km/s. The brighter, asymmetric SiO line may indicate a circumstellar
maser. The stellar wind is slow compared to similar Galactic stars, but the
dust opacity remains similar to Galactic comparisons. We suggest that the
mass-loss rate is set by the levitation of material into the circumstellar
environment by pulsations, but that the terminal wind-expansion velocity is
determined by radiation pressure on the dust: a pulsation-enhanced dust-driven
wind. We suggest the metal-poor nature of the star decreases the grain size,
slowing the wind and increasing its density and opacity. Metallic alloys at
high altitudes above the photosphere could also provide an opacity increase.
The CO line is weaker than expected from Galactic AGB stars, but its strength
confirms a model that includes CO dissociation by the strong interstellar
radiation field present inside globular clusters.
