Na-O anticorrelation and HB - VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra

By E. Carretta, A. Bragaglia, R. Gratton, S. L. I. Bologna, Inaf - Padova, Excellence Cluster Universe, Garching. 2009

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We present homogeneous abundance determinations for iron and some of the elements involved in the proton-capture reactions (O, Na, Mg, Al, and Si) for 202 red giants in 17 Galactic globular clusters (GCs) from the analysis of high-resolution UVES spectra obtained with the FLAMES facility at the ESO VLT2 telescope. Our programme clusters span almost the whole range of the metallicity distribution of GCs and were selected to sample the widest range of global parameters (horizontal-branch morphology, masses, concentration, etc.). In this paper we focus on the discussion of the Na-O and Mg-Al anticorrelations and related issues. Our study finds clear Na and O star-to-star abundance variations, exceeding those expected from the error in the analysis, in all clusters. Variations in Al are present in all but a few GCs. Finally, a spread in abundances of Mg and Si are also present in a few clusters. Mg is slightly less overabundant and Si slightly more overabundant in the most Al-rich stars. The correlation between Si and Al abundances is a signature of production of 28 Si leaking from the Mg-Al cycle in a few clusters. The cross sections required for the proper reactions to take over in the cycle point to temperatures in excess of about 65 million K for the favoured site of production. We used a dilution model to infer the total range of Al abundances starting from the Na and Al abundances in the FLAMES-UVES spectra, and the Na abundance distributions found from analysis of the much larger set of stars for which FLAMES-GIRAFFE spectra were available. We found that the maximum amount of additional Al produced by first-generation polluters contributing to the composition of the second-generation stars in each cluster is closely correlated with the same combination of metallicity and cluster luminosity that reproduced the minimum O-abundances found from GIRAFFE spectra. We then suggest that the high temperatures required for the Mg-Al cycle are only reached in the most massive and most metal-poor polluters.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/5ad76733c0c0f3c6e20d9e330889a230b3076da7

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Citations in the corpus

Detailed abundances of a large sample of giant stars in M 54 and in the Sagittarius nucleus (2010, methodology): “Red filled circles are the 19 GCs previously analysed by ourselves (Carretta et al. 2009c), which can be assumed to be mono-metallic, as far as the iron abundance is concerned.”
THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. IX. HORIZONTAL BRANCH MORPHOLOGY AND THE SECOND PARAMETER PHENOMENON (2009, background): “However, the recent results from Carretta et al. (2009b, 2009c) lend some insight into the problem of deriving GC ages in the presence of light element abundance variations.”
Abundance patterns of multiple populations in globular clusters: a chemical evolution model based on yields from AGB ejecta (2010, methodology): “Carretta et al. (2009a) find that the upper limit to the scatter of iron is less than 0.05 dex in the 19 clusters they examine.”
Properties of stellar generations in globular clusters and relations with global parameters (2010, methodology): “In summary, in this paper we combine the results of our extensive survey of abundances in RGB stars in 19 GCs (Carretta et al. 2009a,b,c) with previous knowledge of a GC, in order to discuss scenarios for their formation.”
Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti (2010, unknown): “2005; Carretta et al. 2009).”
A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY (2010, background): “The lowest metallicity Segue 1 giants are also at least a factor of four more metal-poor than any known star in a globular cluster (e.g., King et al. 1998; Kraft & Ivans 2003; Preston et al. 2006; Carretta et al. 2009).”
CHEMICAL ABUNDANCES FOR 855 GIANTS IN THE GLOBULAR CLUSTER OMEGA CENTAURI (NGC 5139) (2010, methodology): “Monometallic globular clusters typically consist of ∼20–40% of stars belonging to the primordial component, ∼30–80% in the intermediate component, and .20% in the extreme component (e.g., Carretta et al. 2009a).”
Intrinsic iron spread and a new metallicity scale for globular clusters (2009, methodology): “However, the error would be larger where the two sequences are so close that cannot be distinguished, but separated enough to give a wrong temperature when the luminosity is used, as in the procedure adopted in our analysis (see Carretta et al. 2009a for further details).”
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): “For example, ages as young as 11 Gyr (di Cecco et al. 2010) or as old as 13.5 Gyr (VandenBerg, Casagrande, & Stetson 2010) have been derived for M 92, which has [Fe/H] ≈ −2.35 (Carretta et al. 2009a, hereafter CBG09).”
Target Selection for the SDSS-IV APOGEE-2 Survey (2017, background): “…Calibration A subset of stars in many of the targeted open and globular clusters have existing multi-element abundance, stellar parameter, and radial velocity derivations from high resolution optical spectroscopy, in many cases homogeneously observed and analyzed (e.g., Carretta et al. 2009b,c).”
The bifurcated age–metallicity relation of Milky Way globular clusters and its implications for the accretion history of the galaxy (2013, methodology): “Although some studies (e.g., Brown, Wallerstein & Zucker 1997, Pritzl, Venn & Irwin 2005) found [α/Fe] ' 0.0 for Ruprecht 106, they also reported [Fe/H] values that are 0.3–0.4 dex higher than the value ([Fe/H] = −1.78) given by Carretta et al. (2009a).”
MULTIPLE STELLAR POPULATIONS IN 47 Tucanae (2011, methodology): “O anticorrelation in RGB stars of 47 Tuc has recently been studied by Carretta et al. (2009b), and their data are shown in Figure 24, where we have made an arbitrary division into Na-poor/O-rich stars (green triangles) and Na-rich/O-poor stars (magenta circles).”
Multiple populations in globular clusters (2012, methodology): “…al. 2011); NGC 288, NGC 362 (Smith et al. 2009; Carretta et al. 2009a,b); 47 Tuc, NGC 1904, NGC 3201, NGC 4590, NGC 6171, NGC 6254, NGC 6809, NGC 6838, NGC 7078, NGC 7099 (Carretta et al. 2009a,b: these papers present results on the first 19 globular clusters of a survey with FLAMES@VLT, see Fig.”
The second and third parameters of the horizontal branch in globular clusters (2010, methodology): “…magnitude diagrams (CMD) and accurate ages provided by ground (Rosenberg et al. 2000a,b) and space observations (e.g., Piotto et al. 2002), and the extensive data on the Na-O anticorrelation from our FLAMES survey (Carretta et al. 2009a,b and references therein), complemented by literature data.”
Non-LTE calculations for neutral Na in late-type stars using improved atomic data (2011, background): “…process that so efficiently polluted the star-forming gas with the nucleosynthesis products of hot H-burning through the CNO-cycle and the related NeNa- and MgAl-chains (i.e. enhancement of N, Na, and Al, and depletion of C, O, and Mg, see e.g. Lind et al. 2011; and Carretta et al. 2009).”
THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS (2011, background): “…behaviors of globulars include star-to-star scatter of light element [el/Fe] ratios (for C, N, O, Na, Mg, and Al) in both main sequence and giant stars (this is in contrast to the abundance trends of halo field stars; e.g. Carretta et al. 2009a(18) and Gratton, Sneden, & Carretta 2004(36))1.”