Circumstellar CO in metal-poor stellar winds: the highly irradiated globular cluster star 47 Tucanae V3

Abstract

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.

5 pages, accepted MNRAS Letters

References in corpus (16)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• A close halo of large transparent grains around extreme red giant stars
• The wind speeds, dust content, and mass-loss rates of evolved AGB and RSG stars at varying metallicity
• Mass loss on the red giant branch: the value and metallicity dependence of Reimers' η in globular clusters
• The close circumstellar environment of Betelgeuse - V. Rotation velocity and molecular envelope properties from ALMA
• An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS), II. Discovery of Metal-poor Dusty AGB Stars
• Tracing the development of dust around evolved stars: The case of 47 Tuc
• A Spitzer Space Telescope Atlas of omega Centauri: The Stellar Population, Mass Loss, and the Intracluster Medium
• An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). IV. Discovery of High-Redshift AGB Analogs
• Ejection of globular cluster interstellar media through ionization by white dwarfs
• Spitzer Space Telescope evidence in NGC 6791: no super-mass-loss at super-solar metallicity to explain helium white dwarfs?
• An empirical mass-loss law for Population II giants from the Spitzer-IRAC survey of Galactic globular clusters
• The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
• Abundance analysis for long-period variables II. RGB and AGB stars in the globular cluster 47\,Tuc
• The mass-loss rates of red supergiants at low metallicity: Detection of rotational CO emission from two red supergiants in the Large Magellanic Cloud

Cited by in corpus (8)

• An Infrared Census Of Dust In Nearby Galaxies With Spitzer (DUSTiNGS): V. The Period-luminosity Relation For Dusty Metal-Poor AGB Stars
• The onset of the AGB wind tied to a transition between sequences in the period-luminosity diagram
• Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation
• A Census of Thermally-Pulsing AGB stars in the Andromeda Galaxy and a First Estimate of their Contribution to the Global Dust Budget
• A Census of Above-Horizontal-Branch Stars in Galactic Globular Clusters
• Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae
• The impact of third dredge-up on the mass loss of Mira variables
• The Nearby Evolved Stars Survey II: Constructing a volume-limited sample and first results from the James Clerk Maxwell Telescope