MULTIPLE STELLAR POPULATIONS IN 47 Tucanae

By A. Milone, G. Piotto, L. Bedin, I. King, Jay Anderson, A. Marino, Andrea Bellini, R. Gratton, A. Renzini, P. Stetson and 9 more. 2011

218 citations recorded by the source corpus.

We use Hubble Space Telescope (HST) and ground-based imaging to study the multiple populations of 47 Tucanae (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 into two branches, and we find that this duality is repeated in the subgiant and red giant regions, and on the horizontal branch. We calculate theoretical stellar atmospheres for main-sequence 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 red giant and red horizontal branch stars with that pair of compositions also give colors that fit our observations. We suggest that the different strengths of molecular bands of OH, CN, CH, and NH, falling in different photometric bands, are responsible for the color splits of the two populations. Near the cluster center, in each portion of the color–magnitude diagram the population with primeval abundances makes up only ∼20% of the stars, a fraction that increases outward, approaching equality in the outskirts of the cluster, with a fraction ∼30% averaged over the whole cluster. Thus the second, He/N-enriched population is more concentrated and contributes the majority of the present-day stellar content of the cluster. We present evidence that the color–magnitude diagram of 47 Tuc consists of intertwined sequences of the two populations, whose separate identities can be followed continuously from the main sequence up to the red giant branch, and thence to the horizontal branch. A third population is visible only in the subgiant branch, where it includes ∼8% of the stars.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e6a3a3dd4d709cf194829a82bdf51431475e4088

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In Astronomy and Astrophysics

1. Jay Anderson
2. G. Piotto
3. F. D’Antona
4. L. Bedin
5. A. Milone
6. A. Renzini
7. Santi Cassisi
8. A. Karakas

Citations in the corpus

• A WFC3/HST VIEW OF THE THREE STELLAR POPULATIONS IN THE GLOBULAR CLUSTER NGC 6752 (2013, methodology): “…host multiple main sequences (MSs) including ω Centauri, NGC2808, 47 Tuc, NGC6752, and NGC6397 (Anderson 1997, Bedin et al. 2004, Piotto et al. 2007, Milone et al. 2010, 2012a,b), which have been associated with stellar populations with different helium abundances (D’Antona & Caloi 2004, Norris…”
• THE HUBBLE SPACE TELESCOPE UV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. I. OVERVIEW OF THE PROJECT AND DETECTION OF MULTIPLE STELLAR POPULATIONS (2014, methodology): “This technique has been successfully applied to a few GCs, and differences in helium among different stellar populations have been measured in 47 Tuc, NGC 6397, NGC 288 and NGC 6752 (Milone et al. 2013, and references therein).”
• The SUMO project: a SUrvey of Multiple pOpulations in globular clusters (2013, methodology): “In case of NGC 104, there are two groups of CN-rich and CN-poor red-HB stars (Norris & Freeman 1982), that define two sequences along the red HB, when observed in appropriate filters (Milone et al. 2012).”
• The Dawes Review 2: Nucleosynthesis and Stellar Yields of Low- and Intermediate-Mass Single Stars (2014, background): “Increases in He and changes to the PASA (2014) doi:10.1017/pas.2014.xxx composition of the light elements C, N, and O are the most likely cause of the multiple main sequence, subgiant, and giant branches observed in all clusters that have Hubble Space Telescope photometry (e.g., for 47 Tucanae, NGC ”
• THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED METHOD ALONG WITH COLOR–MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES (2013, methodology): “…and Lardo et al. 2012, respectively) and/or very careful and precise photometry near the cluster centers has been required to discover them; see, the studies of 47 Tuc by Anderson et al. (2009) and Milone et al. (2012b), of NGC 6752 by Milone et al. (2010), and of NGC 6397 by Milone et al. (2012a).”
• The Hubble Space Telescope UV Legacy Survey of Galactic globular clusters – IX. The Atlas of multiple stellar populations (2016, methodology): “To do this we have used the method by Milone et al. (2012b).”
• The Hubble Space TelescopeUV Legacy Survey of Galactic Globular Clusters – V. Constraints on formation scenarios (2015, background): “Instead, in some cases such as the GC 47 Tuc, a sizable depletion in oxygenb at least a factor of∼ 3 (Carretta et al. 2009) is accompanied by only a modest∆Y ≃ 0.03 increase in helium abundance (Milone et al. 2012).”