Properties of stellar generations in globular clusters and relations with global parameters

By E. Carretta, A. Bragaglia, R. Gratton, A. Recio-Blanco, S. Lucatello, V. D’Orazi, Santi Cassisi INAF-Oss.Astr.Bologna, INAF-Oss.Astr.Padova, Observatoire Cote d'Azur, Excellence Cluster Universe and 1 more. 2010

388 citations recorded by the source corpus.

We revise the scenario of the formation of Galactic globular clusters (GCs) by adding the observed detailed chemical composition of their different stellar generations to the set of their global parameters. We exploit the unprecedented set of homogeneous abundances of more than 1200 red giants in 19 clusters, as well as additional data from literature, to give a new definition of bona fide GCs, as the stellar aggregates showing the Na-O anticorrelation. We propose a classification of GCs according to their kinematics and location in the Galaxy in three populations: disk/bulge, inner halo, and outer halo. We find that the luminosity function of GCs is fairly independent of their population, suggesting that it is imprinted by the formation mechanism only marginally affected by the ensuing evolution. We show that a large fraction of the primordial population should have been lost by the proto-GCs. The extremely low Al abundances found for the primordial population of massive GCs indicate a very fast enrichment process before the formation of the primordial population. We suggest a scenario for the formation of GCs that includes at least three main phases: i) the formation of a precursor population (likely due to the interaction of cosmological structures similar to those that led to the formation of dwarf spheroidals, but residing at smaller Galactocentric distances, with the early Galaxy or with other structures); ii) the triggering of a long episode of star formation (the primordial population) from the precursor population; and iii) the formation of the current GC, mainly within a cooling flow formed by the slow winds of a fraction of the primordial population. The precursor population is very effective in raising the metal content in massive and/or metal-poor (mainly halo) clusters, while its role is minor in small and/or metal-rich (mainly disk) ones. Finally, we use principal component analysis and multivariate relations to study the phase of metal enrichment from first to second generation. We conclude that most of the chemical signatures of GCs may be ascribed to a few parameters, the most important being metallicity, mass, and cluster age. Location within the Galaxy (as described by the kinematics) also plays some role, while additional parameters are required to describe their dynamical status.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e203b20bd1cc6b9e45777781729d9c4b60f9e9ca

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. C. Conroy
2. Hans-Walter Rix
3. R. Gratton
4. E. Carretta
5. A. Bragaglia
6. S. Majewski
7. F. D’Antona
8. G. Piotto

Citations in the corpus

• Multiple populations in globular clusters (2012, methodology): “The resulting scenario is one where probably all globular clusters, and not only the most massive ones (see Carretta et al. 2010a; Kravtsov & Gnedin 2005; Böker 2008), formed at the centre of larger systems.”
• Improving PARSEC models for very low mass stars (2014, background): “Carretta et al. (2010) give a distance modulus of (m−M)V = 13.32, an age of 12.83 Gyr, and a reddening of E(B−V ) = 0.04 mag, while Hansen et al. (2013) determines an age of 9.7 Gyr from the white dwarf cooling sequence.”
• A stellar census in globular clusters with MUSE: multiple populations chemistry in NGC 2808 (2019, background): “D-0175(A)). halo, ∼7% in the bulge) among stars of the Galactic field (Martell & Grebel 2010; Carretta et al. 2010; Schiavon et al. 2017; Koch et al. 2019).”
• A WFC3/HST VIEW OF THE THREE STELLAR POPULATIONS IN THE GLOBULAR CLUSTER NGC 6752 (2013, background): “1 by Carretta et al. (2010) shows an almost continuous distribution of stars in the Na versus O plane, despite the fact that photometric evidence in many of the clusters included in that figure (e.g. NGC2808, NGC6397, NGC6752 as shown in the present paper) show multimodal, maybe discrete, sequences…”
• 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, background): “N and O–Na anticorrelations appear to be a universal property of all globular clusters (Carretta et al. 2010b).”
• Photometric signatures of multiple stellar populations in galactic globular clusters (2011, background): “…GCs, the range of colours spanned by our isochrones should give a rough idea – considering also that the extension of the abundance anticorrelations varies from cluster to cluster (e.g. Carretta et al. 2010b) – of the maximum colour spread to be expected in the CMD of a generic Galactic GC.”
• Detailed abundances of a large sample of giant stars in M 54 and in the Sagittarius nucleus (2010, methodology): “The presence and different extension of the Na-O anticorrelation (also supported by the Mg-Al data) for the metal-poor and moderately metal-rich cluster components suggest a simple extension of the scenario for the formation of GCs illustrated in Carretta et al. (2010a).”
• The GALAH survey: scientific motivation (2015, background): “The small fraction of such stars in the field (e.g. Carretta et al. 2010; Martell et al. 2011; Wylie-de Boer et al. 2012) are interpreted as evidence of cluster mass-loss and dissolution.”
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, methodology): “However, Carretta et al. (2010) reported that there is tentative evidence for the presence of a correlation between GC metallicity and the extension of the Na-O anticorrelation and, by association, the incidence of N-rich-like, SG stars in Galactic GCs.”