Multiple stellar populations in 47 Tucanae
A. P. Milone, G. Piotto, L. R. Bedin, I. R. King, J. Anderson, A. F., Marino, A. Bellini, R. Gratton, A. Renzini, P. B. Stetson, S. Cassisi, A., Aparicio, A. Bragaglia, E. Carretta, F. D'Antona, M. Di Criscienzo, S., Lucatello, M. Monelli, A. Pietrinferni

TL;DR
This study uses HST and ground-based imaging to identify and characterize multiple stellar populations in 47 Tuc, revealing complex chemical compositions, spatial distributions, and evolutionary sequences within the cluster.
Contribution
It provides detailed photometric and spectroscopic analysis of multiple populations in 47 Tuc, linking chemical variations to observed color splits and spatial distributions.
Findings
Two main populations with distinct chemical compositions identified.
The second population is more centrally concentrated within the cluster.
A third, minor population is observed in the subgiant branch.
Abstract
We use Hubble Space Telescope (HST) and ground-based imaging to study the multiple populations of 47 Tuc, combining high-precision photometry with calculations of synthetic spectra. Using filters covering a wide range of wavelengths, our HST photometry splits the main sequence (MS) into two branches, and we find that this duality is repeated in the subgiant and red-giant regions (SGB, RGB), and on the horizontal branch (HB). We calculate theoretical stellar atmospheres for MS stars, assuming different chemical composition mixtures, and we compare their predicted colors through the HST filters with our observed colors. We find that we can match the complex of observed colors with a pair of populations, one with primeval abundance and another with enhanced nitrogen and a small helium enhancement, but with depleted C and O. We confirm that models of RGB and red HB stars with that pair of…
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