Sulphur abundances in halo stars from multiplet 3 at 1045 nm

Caffau, E.; Sbordone, L.; Ludwig, H.‐G.; Bonifacio, P.; Spite, M.

doi:10.1002/asna.201011353

Cited by 15 publications

(33 citation statements)

References 23 publications

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“…2. In contrast to previous studies by Israelian & Rebolo (2001), Takada-Hidai et al (2002), Caffau et al (2005Caffau et al ( , 2010, no stars with extremely high sulphur abundances are observed, nor are the sulphur abundances found to increase towards lower metallicities. In fact, the opposite is observed -a linear fit for the metal-poor ( is found to decrease as the metallicity increases, which is expected of α-elements (solid line).…”

Section: Sulphur Abundancescontrasting

confidence: 99%

“…On the other hand, a number of studies (e.g, Ryde & Lambert 2004;Korn & Ryde 2005;Nissen et al 2007;Spite et al 2011) have found little to no evidence of high ([S/Fe] 0.6) sulphur abundances at any metallicity and instead argued that sulphur is a fairly typical α-element and forms a plateau of [S/Fe] ∼ 0.3 below [Fe/H] ∼ −1, which points to an origin in Type II supernovae (e.g., Kobayashi et al 2006). Finally, a combination of the two patterns, which implies a very complex history of chemical evolution of sulphur, has been found by Caffau et al (2005Caffau et al ( , 2010. It is open to debate whether there exist metal-poor stars with extremely high sulphur abundances, and the discrepant findings of previous studies could either reflect reality or differences in the employed analyses.…”

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

Galactic chemical evolution of sulphur

Matrozis¹,

Ryde²,

Dupree³

2013

A&A

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Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], which is typical for α-elements, while others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. The aim of this study is to contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-local thermodynamic equilibrium (LTE) insensitive spectral diagnostics in disk and halo stars with homogeneously determined stellar parameters. Methods. We derived effective temperatures from photometric colours, surface gravities from stellar isochrones and Bayesian estimation, and metallicities and sulphur abundances from spectrum synthesis. We derived sulphur abundances from the [S ] λ1082 nm line in 39 mostly cool and metal-poor giants using 1D LTE MARCS model atmospheres to model our high-resolution near-infrared spectra obtained with the VLT, NOT, and Gemini South telescopes. Results. We derive homogeneous stellar parameters for 29 of the 39 stars. Our results argue for a chemical evolution of sulphur that is typical for α-elements, contrary to some previous studies that have found high sulphur abundances ([S/Fe] 0.6) for stars with −2.5 < [Fe/H] < −1. Our abundances are systematically higher by about 0.1 dex than those of other studies that arrived at similar conclusions using other sulphur diagnostics. Conclusions. We find the [S ] line to be a valuable diagnostic of sulphur abundances in cool giants down to [Fe/H] −2.3. We argue that a homogeneous determination of stellar parameters is necessary, since the derived abundances are sensitive to them. Our results ([S/Fe]) agree reasonably well with predictions of contemporary models of Galactic chemical evolution. In these models sulphur is predominantly created in massive stars by oxygen burning and is ejected into the interstellar medium during Type II supernovae explosions. Systematic differences with previous studies most likely fall within modelling uncertainties.

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Section: Sulphur Abundancescontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Galactic chemical evolution of sulphur

Matrozis¹,

Ryde²,

Dupree³

2013

A&A

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“…These studies are also consistent with a plateu of enhanced [S/Fe] values at low metallicities, both in the Galactic halo (Caffau et al 2010;Jönsson et al 2011;Takeda & Takada-Hidai 2012) and also in globular clusters (Kacharov et al 2015).…”

Section: Based On Observations Made With Eso/vlt/flames At the La Silsupporting

confidence: 88%

“…The S-poor Spite et al (2011;dark grey). Sulphur abundances in halo stars determined from multiplet 3 are shown with pluses (Takeda & Takada-Hidai 2012), asterisks (Jönsson et al 2011), and exes (Caffau et al 2010). In all cases, NLTE corrections have been applied.…”

Section: Resultsmentioning

confidence: 99%

Sulphur in the Sculptor dwarf spheroidal galaxy

Skúladóttir

Andrievsky

Tolstoy

et al. 2015

A&A

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In Galactic halo stars, sulphur has been shown to behave like other α-elements, but until now, no comprehensive studies have been done on this element in stars of other galaxies. Here, we use high-resolution ESO VLT/FLAMES/GIRAFFE spectra to determine sulphur abundances for 85 stars in the Sculptor dwarf spheroidal galaxy, covering the metallicity range −2.5 ≤ [Fe/H] ≤ −0.8. The abundances are derived from the S I triplet at 9213, 9228, and 9238 Å. These lines have been shown to be sensitive to departure from local thermodynamic equilibrium, i.e. NLTE effects. Therefore, we present new NLTE corrections for a grid of stellar parameters covering those of the target stars. The NLTE-corrected sulphur abundances in Sculptor show the same behaviour as other α-elements in that galaxy (such as Mg, Si, and Ca).

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“…By extrapolating the NLTE results from the grid of Takeda et al (2005) to the stellar parameters of our stars, we found According to calculations by Jönsson et al (2011), based on the 3D model atmospheres of Collet et al (2007Collet et al ( , 2009, the 3D corrections for S abundances derived from multiplet 3 are constant and positive at all metallicities for stars with similar parameters to ours and are in the order of Δ 3D = +0.20 dex. Caffau et al ( , 2010 explored the 3D effects of multiplet 3 in dwarf stars and also found positive corrections based on the CO 5 BOLD 3D model atmospheres. Although it is inconsistent to apply their results to giant stars, there is an agreement that the 3D corrections for the lines at 1045 nm are always positive.…”

Section: Nlte and 3d Effectsmentioning

confidence: 99%

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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Sulphur abundances in halo stars from multiplet 3 at 1045 nm

Cited by 15 publications

References 23 publications

Galactic chemical evolution of sulphur

Galactic chemical evolution of sulphur

Sulphur in the Sculptor dwarf spheroidal galaxy

Galactic evolution of sulphur as traced by globular clusters

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