The O-Na and Mg-Al anticorrelations in turn-off and early subgiants in globular clusters

By R. Gratton, P. Bonifacio, A. Bragaglia, E. Carretta, V. Castellani, M. Centurión, A. Chieffi, R. Claudi, Gisella Clementini, F. D’Antona and 9 more. 2000

448 citations recorded by the source corpus.

High dispersion spectra (R > 40 000) for a quite large number of stars at the main sequence turn-o and at the base of the giant branch in NGC 6397 and NGC 6752 were obtained with the UVES on Kueyen (VLT UT2). The (Fe/H) values we found are 2:03 0:02 0:04 and 1:42 0:02 0:04 for NGC 6397 and NGC 6752 respectively, where the rst error bars refer to internal and the second ones to systematic errors (within the abundance scale dened by our analysis of 25 subdwarfs with good Hipparcos parallaxes). In both clusters the (Fe/H)'s obtained for TO-stars agree perfectly (within a few percent) with that obtained for stars at the base of the RGB. The (O=Fe) = 0:21 0:05 value we obtain for NGC 6397 is quite low, but it agrees with previous results obtained for giants in this cluster. Moreover, the star-to-star scatter in both O and Fe is very small, indicating that this small mass cluster is chemically very homogenous. On the other hand, our results show clearly and for the rst time that the O-Na anticorrelation (up to now seen only for stars on the red giant branches of globular clusters) is present among unevolved stars in the globular cluster NGC 6752, a more massive cluster than NGC 6397. A similar anticorrelation is present also for Mg and Al, and C and N. It is very dicult to explain the observed Na-O, and Mg-Al anticorrelation in NGC 6752 stars by a deep mixing scenario; we think it requires some non internal mechanism.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b72c044eafd30f1c86087b0ee00be6166a8711ff

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In Astronomy and Astrophysics

1. R. Gratton
2. E. Carretta
3. Martin Asplund
4. A. Bragaglia
5. F. D’Antona
6. A. Renzini
7. C. Conroy
8. Aaron Dotter

In Instrumentation

1. R. Gratton
2. E. Carretta
3. F. D’Antona
4. A. Bragaglia
5. G. Piotto
6. C. Conroy
7. Jay Anderson
8. Martin Asplund

Citations in the corpus

• Red Giant Branch Stars: The Theoretical Framework (2002, result): “First results have been published already by Castilho et al. (2000) and Gratton et al. (2001) about NGC 6397 and NGC 6752.”
• A double stellar generation in the globular cluster NGC 6656 (M 22): Two stellar groups with different iron and s-process element abundances (2009, background): “…et al. (1998) found a CN bimodality in MS and subgiant branch (SGB) stars in 47 Tuc, and the NaO anti-correlation was observed for the MS turn off (TO) and SGB in M 13 (Cohen & Melendez 2005), NGC 6397 and NGC 6752 (Carretta et al. 2005; Gratton et al. 2001), and NGC 6838 (Ramírez & Cohen 2002).”
• A Large Stellar Evolution Database for Population Synthesis Studies. I. Scaled Solar Models and Isochrones (2004, background): “…is basically fully efficient, spectroscopic observations of, for example, stars in Galactic globular clusters or field halo stars (see, e.g., Gratton et al. 2001; Bonifacio et al. 2002 and references therein) point to a drastically reduced efficiency of diffusion that may be due to the…”
• Asteroseismology of old open clusters with Kepler: direct estimate of the integrated red giant branch mass-loss in NGC 6791 and 6819 (2011, background): “The ubiquitous presence of multiple populations in GCs has now become evident (e.g. Gratton et al. 2001; Carretta et al. 2009; Piotto et al. 2007), and the proposal that the stellar helium content of the different populations also has a role in determining the HB morphology (D’Antona et al. 2002;…”
• Oxygen, Sodium, Magnesium and Aluminium as tracers of the Galactic Bulge Formation (2006, background): “This picture is now seriously challenged since similar anomalies, first in C and N Briley et al. (1991, 2004), and thenin O, Na and Al Gratton et al. (2001) have been found also in stars on (or just evolved off) the main-sequence, whose maximum internal temperatures are not high enough to trigger…”
• The lithium content of the globular cluster NGC 6397 (2002, methodology): “Several halo field stars have been observed at twilight in the course of the program and their atmospheric parameters, determined as done for cluster stars are reported in Gratton et al. (2001).”
• A WFC3/HST VIEW OF THE THREE STELLAR POPULATIONS IN THE GLOBULAR CLUSTER NGC 6752 (2013, background): “…fact that the same light-elements variations have also been observed in unevolved cluster stars (e.g. Briley et al. 1994, 1997, Cannon et al. 1998, Gratton et al. 2001), whose internal temperatures do not allow high-T proton captures, and in fully-convective lowmass M-dwarfs (Milone et al. 2012)…”
• The ACS Survey of Galactic Globular Clusters. II. Stellar Evolution Tracks, Isochrones, Luminosity Functions, and Synthetic Horizontal-Branch Models (2007, background): “This approach is meant to satisfy the lack of observational evidence for diffusion in metal poor stars (Gratton et al. 2001; Ramı́rez & Cohen 2003, e.g.), though recently evidence for some diffusion has been reported in NGC 6397 (Korn et al. 2006).”
• The Adequacy of Stellar Evolution Models for the Interpretation of the Color-Magnitude Diagrams of Resolved Stellar Populations (2005, background): “The controversy is whether among galactic GCs there is an age spread large enough to explain their different HB morphologies.”
• On the self-enrichment scenario of galactic globular clusters: constraints on the IMF (2006, background): “…that respect from high resolution spectrographs on very large telescopes that allowed one to determine the abundances of the concerned elements in faint subgiant and turnoff stars in a couple of GCs (Gratton et al. 2001; Grundhal et al. 2002; Carretta et al. 2003, 2004; Ramirez & Cohen 2002, 2003).”
• New Analyses of Star-to-Star Abundance Variations among Bright Giants in the Mildly Metal-poor Globular Cluster M5 (2001, background): “Evidence mounts that both scenarios are needed : a typical cluster contains main-sequence stars already imprinted with variations in these elements, as studies of main-sequence stars in 47 Tuc and NGC 6752 dramatically illustrate (Briley et al. 1996 ; Cannon et al. 1998 Gratton et al. 2001).”
• Na-O anticorrelation and HB - VIII. Proton-capture elements and metallicities in 17 globular clusters from UVES spectra (2009, background): “Interestingly enough, these are also approximately the same ranges of abundance variations as seen in unevolved cluster stars (Gratton et al. 2001), pointing to the same origin for the mechanism establishing the observed chemical pattern.”
• A Helium Spread among the Main-Sequence Stars in NGC 2808 (2005, background): “In some cases these abundance spreads are seen in stars near the turnoff and along the subgiant branch (e.g., Gratton et al. 2001), suggesting that these anomalies arise from some process of selfenrichment occurring at the first stages of cluster life.”
• Abundances of C, N, O in slightly evolved stars in the globular clusters NGC 6397, NGC 6752 and 47 Tuc (2004, methodology): “In this case, the line of thought is the same as in Gratton et al. (2001): turn-off stars do not reach the temperature regime where the ON and NeNa cycles required to produce the Na-O anticorrelation are active, and moreover these stars have convective envelopes that are too small to have…”
• Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC 6397 , (2009, background): “Gratton et al. (2001) and Carretta et al. (2005) uncovered rather large variations in both O and Na, anti-correlated with each other, in SGB and dwarf stars in NGC 6397 (see also Norris & Da Costa 1995; Castilho et al. 2000, for bright giants).”
• The fraction of second generation stars in globular clusters from the analysis of the horizontal branch (2008, background): “Notice that NGC 6397 has [Fe/H]=–2 (Gratton et al. 2001) and so is not an intermediate metallicity cluster.”
• The second and third parameters of the horizontal branch in globular clusters (2010, background): “The two innovative steps taken subsequently were: – the recognition that typical GCs host at least two generations of stars: this is required to explain the abundance anomalies observed for main sequence (MS) stars by Gratton et al. (2001) and Cohen et al. (2002).”
• First stars VII - Lithium in extremely metal poor dwarfs (2006, methodology): “In this paper we have used Hα-based effective temperatures, which are usually found to be on the same scale as IRFM temperatures (Gratton et al. 2001; Barklem et al. 2002).”
• The Chemical Composition Contrast between M3 and M13 Revisited: New Abundances for 28 Giant Stars in M3 (2003, methodology): “…elements among such relatively unevolved stars have recently come to light, e.g., the correlation of CN band strengths and Na in main-sequence stars of 47 Tuc (Briley et al. 1996) and the anticorrelation of O and Na, as well as Al and Mg, among main-sequence stars of NGC 6752 (Gratton et al. 2001).”
• Detailed abundances of a large sample of giant stars in M 54 and in the Sagittarius nucleus (2010, background): “The advantage of this scenario is to include a coherent picture of the different stellar generations in GCs (Gratton et al. 2001; Carretta et al. 2009a) within a global view of the Galaxy formation.”