The formation of multiple populations in the globular cluster 47 Tuc

• Published in: Monthly notices of the Royal Astronomical Society Vol. 437; no. 4; pp. 3274 - 3282
• Main Authors: Ventura, P., Criscienzo, M. Di, D'Antona, F., Vesperini, E., Tailo, M., Dell'Agli, F., D'Ercole, A.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 01-02-2014
• Subjects: Aluminum; Nitrogen; Oxygen; Sodium; Star & galaxy formation; stars: AGB and post-AGB; globular clusters: general; stars: abundances
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt2126

We use the combination of photometric and spectroscopic data of 47 Tuc stars to reconstruct the possible formation of a second generation of stars in the central regions of the cluster, from matter ejected by massive asymptotic giant branch (AGB) stars diluted with pristine gas. The yields from massive AGB stars with the appropriate metallicity (Z = 0.004, i.e. [Fe/H] = −0.75) are compatible with the observations in terms of extension and slope of the patterns observed, involving oxygen, nitrogen, sodium and aluminium. Based on the constraints on the maximum helium of 47 Tuc stars provided by photometric investigations and on the helium content of the ejecta, we estimate that the gas out of which second-generation stars formed was composed of about one-third of gas from intermediate-mass stars, with M ≥ 5 M and about two-thirds of pristine gas. We tentatively identify the few stars whose Na, Al and O abundances resemble the undiluted AGB yields with the small fraction of 47 Tuc stars populating the faint subgiant branch. From the relative fraction of first- and second-generation stars currently observed, we estimate that the initial first-generation population in 47 Tuc was about 7.5 times more massive than the cluster current total mass.