Sulfur in the globular clusters 47 Tucanae and NGC 6752

Sbordone, L.; Limongi, Marco; Chieffi, A.; Caffau, E.; Ludwig, H.‐G.; Bonifacio, P.

doi:10.1051/0004-6361/200811513

Cited by 16 publications

(38 citation statements)

References 52 publications

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“…Caffau et al (2005b) determined mean S abundance in Ter 7 to be slightly lower (by ∼0.1 dex) than in Galactic stars at similar metallicity. Sbordone et al (2009) analysed nine stars in the GC 47 Tuc ([Fe/H] = −0.72 dex) and four stars in NGC 6752 ([Fe/H] = −1.54 dex), deriving [S/Fe] = 0.18±0.14 and [S/Fe] = 0.49 ± 0.15 dex for the two GCs, respectively, which is consistent with the results of field stars. Curiously, Sbordone et al (2009) reported a star-to-star variation in the observed [S/Fe] ratio in 47 Tuc, which, although not significant with respect to the large measurement uncertainties, showed a strikingly clear correlation with the Na abundance.…”

Section: Introductionsupporting

confidence: 80%

“…Sbordone et al (2009) analysed nine stars in the GC 47 Tuc ([Fe/H] = −0.72 dex) and four stars in NGC 6752 ([Fe/H] = −1.54 dex), deriving [S/Fe] = 0.18±0.14 and [S/Fe] = 0.49 ± 0.15 dex for the two GCs, respectively, which is consistent with the results of field stars. Curiously, Sbordone et al (2009) reported a star-to-star variation in the observed [S/Fe] ratio in 47 Tuc, which, although not significant with respect to the large measurement uncertainties, showed a strikingly clear correlation with the Na abundance. The authors considered different possibilities for the occurrence of this correlation, including that S may be involved in the self-enrichment processes of GCs through the 31 P(p, γ) 32 S proton capture reaction.…”

Section: Introductionsupporting

confidence: 80%

“…At the same time, these brighter stars are often the only accessible tracers in remote and faint GCs. To date, the strong multiplet 1 (920 nm) has been used to obtain sulphur abundances in GCs (Caffau et al 2005b(Caffau et al , 2014Sbordone et al 2009;Koch & Caffau 2011), but these lines are often blended with telluric absorption lines, and one of them is positioned in the blue wing of the Paschen ζ line and thus cannot always be reliably measured. This makes the Mult.…”

Section: Introductionmentioning

confidence: 99%

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Galactic evolution of sulphur as traced by globular clusters

Kacharov

Koch

Caffau³

et al. 2015

A&A

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Context. Sulphur is an important volatile α element, but its role in the Galactic chemical evolution is still uncertain, and more observations constraining the sulphur abundance in stellar photospheres are required. Aims. We derive the sulphur abundances in red giant branch (RGB) stars in three Galactic halo globular clusters (GC) that cover a wide metallicity range (−2. However, some light and α elements show star-to-star variations within individual GCs, and it is as yet unclear whether the α element sulphur also varies between GC stars. Methods. We used the infrared spectrograph CRIRES to obtain high-resolution (R ∼ 50 000), high signal-to-noise (S /N ∼ 200 per px) spectra in the region of the S I multiplet 3 at 1045 nm for 15 GC stars selected from the literature (six stars in M 4, six stars in M 22, and three stars in M 30). Multiplet 3 is better suited for S abundance derivation than the more commonly used lines of multiplet 1 at 920 nm, since its lines are not blended by telluric absorption or other stellar features at low metallicity. Results. We used spectral synthesis to derive the [S/Fe] ratio of the stars assuming local thermodynamic equilibrium (LTE). We find mean [S/Fe] LTE = 0.58 ± 0.01 ± 0.20 dex (statistical and systematic error) for M 4, [S/Fe] LTE = 0.57 ± 0.01 ± 0.19 dex for M 22, and [S/Fe] LTE = 0.55 ± 0.02 ± 0.16 dex for M 30. The negative NLTE corrections are estimated to be in the order of the systematic uncertainties. We do not detect star-to-star variations of the S abundance in any of the observed GCs, with the possible exception of two individual stars, one in M 22 and one in M 30, which appear to be highly enriched in S. Conclusions. With the tentative exception of two stars with measured high S abundances, we conclude that sulphur behaves like a typical α element in the studied Galactic GCs, showing enhanced abundances with respect to the solar value at metallicities below [Fe/H] − 1.0 dex without a considerable spread.

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Section: Introductionsupporting

confidence: 80%

Section: Introductionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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Galactic evolution of sulphur as traced by globular clusters

Kacharov

Koch

Caffau³

et al. 2015

A&A

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“…A result concerning P evolution that we find intriguing, is that of Sbordone et al (2009), who found that the sulphur A&A 532, A98 (2011) abundance in the globular cluster 47 Tuc displays a significant correlation with the Na abundance. The authors point out that S could be produced through proton capture reactions on P ( 31 P (p, γ) 32 S).…”

Section: Introductionsupporting

confidence: 55%

The Galactic evolution of phosphorus

Caffau

Bonifacio

Faraggiana

et al. 2011

A&A

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Context. As a galaxy evolves, its chemical composition changes and the abundance ratios of different elements are powerful probes of the underlying evolutionary processes. Phosphorous is an element whose evolution has remained quite elusive until now, because it is difficult to detect in cool stars. The infrared weak P i lines of the multiplet 1, at 1050−1082 nm, are the most reliable indicators of the presence of phosphorus. The availability of CRIRES at VLT has permitted access to this wavelength range in stellar spectra. Aims. We attempt to measure the phosphorus abundance of twenty cool stars in the Galactic disk. Methods. The spectra are analysed with one-dimensional model-atmospheres computed in local thermodynamic equilibrium (LTE). The line formation computations are performed assuming LTE. Results. The ratio of phosphorus to iron behaves similarly to sulphur, increasing towards lower metallicity stars. Its ratio with respect to sulphur is roughly constant and slightly larger than solar, [P/S] = 0.10 ± 0.10. Conclusions. We succeed in taking an important step towards the understanding of the chemical evolution of phosphorus in the Galaxy. However, the observed rise in the P/Fe abundance ratio is steeper than predicted by Galactic chemical evolution model developed by Kobayashi and collaborators. Phosphorus appears to evolve differently from the light odd-Z elements sodium and aluminium. The constant value of [P/S] with metallicity implies that P production is insensitive to the neutron excess, thus processes other than neutron captures operate. We suggest that proton captures on 30 Si and α captures on 27 Al are possibilities to investigate. We see no clear distinction between our results for stars with planets and stars without any detected planet.

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“…The recognition of this fact came with the increasing observational evidence for what was called "star-to-star abundance variations" or "abundance anomalies", which manifest themselves as variations of nitrogen, oxygen, and sodium, and in some clusters of magnesium and aluminum abundances. Lithium has been found to vary in a few cases (NGC 6752, NGC 6397, and 47 Tucanae, Pasquini et al 2005;Bonifacio et al 2007;Lind et al 2009;Shen et al 2010), anticorrelating with sodium, and hints exist that elements as heavy as sulfur might be affected (in 47 Tuc, Sbordone et al 2009). These abundance variations are found in stars of all evolutionary stages.…”

Section: Introductionmentioning

confidence: 99%

Photometric signatures of multiple stellar populations in Galactic globular clusters

Sbordone

Salaris

Weiß

et al. 2011

A&A

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We calculated synthetic spectra for typical chemical element mixtures (i.e., a standard α-enhanced distribution, and distributions displaying CN and ONa anticorrelations) found in the various subpopulations harboured by individual Galactic globular clusters. From the spectra we determined bolometric corrections to the standard Johnson-Cousins and Strömgren filters and finally predicted colours. These bolometric corrections and colour-transformations, coupled to our theoretical isochrones with the appropriate chemical composition, provided us with a complete and self-consistent set of theoretical predictions for the effect of abundance variations on the observed cluster colour-magnitude diagrams. CNO abundance variations affect mainly wavelengths shorter than ∼400 nm owing to the rise of molecular absorption bands in cooler atmospheres. As a consequence, colour and magnitude changes are largest in the blue filters, independently of using broad or intermediate bandpasses. Colour-magnitude diagrams involving uvy and UB filters (and their various possible colour combinations) are therefore best suited to infer photometrically the presence of multiple stellar generations in individual clusters. They are particularly sensitive to variations in the N abundance, with the largest variations affecting the red giant branch (RGB) and lower main sequence (MS). BVI diagrams are expected to display multiple sequences only if the different populations are characterized by variations of the C+N+O sum and/or helium abundance that lead to changes in luminosity and effective temperature, but leave the flux distribution above 400 nm practically unaffected. A variation of just the helium abundance up to the level we investigate here exclusively affects the interior structure of stars, and is largely irrelevant for the atmospheric structure and the resulting flux distribution in the whole wavelength range spanned by our analysis.

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Sulfur in the globular clusters 47 Tucanae and NGC 6752

Cited by 16 publications

References 52 publications

Galactic evolution of sulphur as traced by globular clusters

Galactic evolution of sulphur as traced by globular clusters

The Galactic evolution of phosphorus

Photometric signatures of multiple stellar populations in Galactic globular clusters

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