Abundances of C, N, O in slightly evolved stars in the globular clusters NGC 6397, NGC 6752 and 47 Tuc

By E. Carretta, R. Gratton, S. Lucatello, A. Bragaglia, Piercarlo Bonifacio INAF-Oss.Astr. Bologna, I. Padova, Inaf - Trieste. 2004

144 citations recorded by the source corpus.

Abundances of C and N are derived from features due to the CH G-band and to the UV CN band measured on high resolution (R > 40 000) UVES spectra of more than 40 dwarfs and subgiants in NGC 6397, NGC 6752 and 47 Tuc. Oxygen abundances (or upper limits) are available for all stars in the sample. Isotopic ratios 12 C/ 13 C were derived from the CH molecular band. This is the first determination of this ratio in unevolved dwarf stars in globular clusters. By enlarging the sample of subgiants in NGC 6397 studied in Gratton et al. (2001), we uncovered, for the first time, large variations in both Na and O in this cluster, too. The origin of the chemical inhomogeneities must be searched for outside the stars under scrutiny. Our data indicate that C abundances are low but not zero in unevolved or slightly evolved stars in these clusters, including in stars with large N-enhancements and O-depletions. The isotopic ratios 12 C/ 13 C are low, but never reach the equilibrium value of the CN-cycle. When coupled to the run of O and Na abundances, these findings may require that, in addition to CNO burning and p−captures, some triple−α process is also involved: previously evolved intermediate-mass AGB stars are then the most likely polluters.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b5981caf4de73ddf8c1404eb8b7731714fd73c75

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In Astronomy and Astrophysics

1. R. Gratton
2. E. Carretta
3. A. Bragaglia
4. F. D’Antona
5. A. Renzini
6. G. Piotto
7. A. Milone
8. Jay Anderson

In Instrumentation

1. F. D’Antona
2. R. Gratton
3. E. Carretta
4. A. Bragaglia
5. G. Piotto
6. A. Milone
7. A. Renzini
8. L. Bedin

Citations in the corpus

• Supermassive stars as a source of abundance anomalies of proton-capture elements in globular clusters (2013, methodology): “…red giant stars in the GCs ωCen, M13, M71, M4, NGC6397, NGC6752, and 47Tuc, taken from the works of Da Costa et al. (2013), Smith et al. (2005), and Carretta et al. (2005) and plotted using the original data symbols, are compared with their corresponding theoretical counterparts from our SMS…”
• Abundances in giant stars of the globular cluster NGC 6752 (2005, unknown): “…& Da Costa (1995), Minniti et al. (1996), Gratton et al. (2001), Grundahl et al. (2002), Yong et al. (2003), James et al. (2004a), Cavallo et al. (2004), James et al. (2004b), and Carretta et al. (2005) where each study focused upon a handful of abundance ratios and/or a small number of stars.”
• The fraction of second generation stars in globular clusters from the analysis of the horizontal branch (2008, background): “In the cluster NGC 6752, out of nine dwarfs and nine subgiants analyzed by Carretta et al. (2005), only one (subgiant) has a normal nitrogen content, all the others are substantially N–enriched ([N/Fe]∼ 1−1.7.”
• Formation and dynamical evolution of multiple stellar generations in globular clusters (2008, background): “Carretta et al. (2005) find that the CNO abundance is actually somewhat—although not much—larger in the SG stars.”
• The Double Subgiant Branch of NGC 1851: The Role of the CNO Abundance (2007, background): “…also of Mg and Al exist in stars within individual clusters (see, e.g., Gratton et al. 2004), and that these elements display a pattern of abundance variations that is constant along the red giant branch (RGB) and down to the turnoff (TO) (see, e.g., Gratton et al. 2001; Carretta et al. 2005).”
• A WFC3/HST VIEW OF THE THREE STELLAR POPULATIONS IN THE GLOBULAR CLUSTER NGC 6752 (2013, methodology): “Since carbon abundance was not measured by Yong et al. (2008) we adopted the [C/Fe] values from Carretta et al. (2005) and take [C/Fe]=0.15 for population a, and [C/Fe]=−0.15 for both population b, and c.”
• Origin of the abundance patterns in Galactic globular clusters: constraints on dynamical and chemical properties of globular clusters (2007, background): “PC06 find indeed 30% of normal stars in NGC 2808 while Carretta et al. (2005) infer that less than 1/3 of the stars are normal on the basis of CNO abundances in NGC 6397, NGC 6752, and 47 Tuc.”
• Abundance patterns of multiple populations in globular clusters: a chemical evolution model based on yields from AGB ejecta (2010, background): “As most of the SG stars in GCs do not show a significant increase of the total CNO (Ivans et al. 1999, 2001; Carretta et al. 2005), the matter out of which the SG forms can not come from stars in which the effect of the 3DU is relevant.”
• Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC 6397 , (2009, background): “This is in agreement with the findings by Carretta et al. (2005), which were based on six dwarfs and nine SGB stars.”
• 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).”
• Spectroscopic and photometric evidence of two stellar populations in the Galactic globular cluster NGC 6121 (M 4) (2008, background): “The Na-O anticorrelation was found at the level of the main sequence turn-off (TO) and sub giant branch (SGB) in M13 (Cohen & Meléndez 2005), NGC 6397 and NGC 6752 (Carretta et al. 2005; Gratton et al. 2001), NGC 6838 (Ramı́rez & Cohen 2002) and 47 Tuc (Carretta et al. 2004).”
• Photometric signatures of multiple stellar populations in galactic globular clusters (2011, background): “Both CNONa1 and CNONa2 mixtures are representative of extreme values of the CNONa anticorrelations observed in Galactic GCs (Carretta et al. 2005, 2010b).”
• Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters (2006, background): “Figures 10–12 display the composition of the mixed matter formed by adding 30% of pristine gas to massive star ejecta as well the observed abundance distributions in NGC 6752 (Grundahl et al. 2002; Yong et al. 2003; Carretta et al. 2005).”
• Population Synthesis in the Blue. IV. Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations (2007, background): “However, the leading scenarios attempting to explain those nitrogen abundances tend to invoke conditions that are only met in globular clusters (e.g. Cannon et al. 1998, Beasley et al. 2004, Carretta et al. 2005).”
• Multiple populations in globular clusters (2012, background): “However, when the complete set of C, N, O abundances is available (not a trivial experimental task) in globular cluster dwarfs (Carretta et al. 2005) or giants (e.g., Ivans et al. 1999; Villanova et al. 2010), the C+N+O is found to be approximatively constant (but see the results by Yong et al.…”