Sulphur and zinc abundances in Galactic stars and damped Ly<i>α</i>systems

Nissen, P. E.; Chen, Yong J; Asplund, Martin; Pettini, Max

doi:10.1051/0004-6361:20034063

Cited by 144 publications

(227 citation statements)

References 71 publications

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“…Relative abundances of metals do not show strong variations in DLAs, despite significant changes of the absolute metallicity Z. The Fe/Zn ratio is very close to solar in metal-poor stars with metallicities typical of DLA systems (Mishenina et al 2002;Gratton et al 2003;Nissen et al 2004;see discussion in Vladilo 2004). Deviations from the solar ratio are measured in stars with extremely low metallicities.…”

Section: Extinction Versus N Zn In Dla Systemsmentioning

confidence: 85%

The dust obscuration bias in damped Lyman αsystems

Vladilo

Péroux

2005

A&A

141

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We present a new study of the effects of quasar obscuration on the statistics of Damped Ly α (DLA) systems. We show that the extinction of any Galactic or extragalactic H i region, A λ , increases linearly with the column density of zinc, with a turning point ∂A λ /∂(log N Zn ) = 1, above which background sources are suddenly obscured. We derive a relation A λ = A λ (N H , Z, z) between the extinction of a DLA system and its H i column density, N H , metallicity, Z, fraction of iron in dust, f Fe (Z), and redshift, z. From this relation we estimate the fraction of DLA systems missed as a consequence of their own extinction in magnitude-limited surveys. We derive a method for recovering the true frequency distributions of N H and Z in DLAs, f N H and f Z , using the biased distributions measured in the redshift range where the observations have sufficient statistics (1.8 ≤ z ≤ 3). By applying our method we find that the well-known empirical thresholds of DLA column densities, N Zn < ∼ 10 13.1 atoms cm −2 and N H i < ∼ 10 22 atoms cm −2 , can be successfully explained in terms of the obscuration effect without tuning of the local dust parameters. The obscuration has a modest effect on the distribution of quasar apparent magnitudes, but plays an important role in shaping the statistical distributions of DLAs. The exact estimate of the bias is still limited by the paucity of the data ( 40 zinc measurements at 1.8 ≤ z ≤ 3). We find that the fraction of DLAs missed as a consequence of obscuration is ∼30% to 50%, consistent with the results of surveys of radio-selected quasars. By modelling the metallicity distribution with a Schechter function we find that the mean metallicity can be ∼5 to 6 times higher than the value commonly reported for DLAs at z ∼ 2.3.

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Section: Extinction Versus N Zn In Dla Systemsmentioning

confidence: 85%

The dust obscuration bias in damped Lyman αsystems

Vladilo

Péroux

2005

A&A

141

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“…This is due to positive values of both [S/Fe] (Fig. 4) and [Zn/Fe] at very low metallicity (Cayrel et al 2004; see also Primas et al 2000;and Nissen et al 2004). We will discuss the evolution of the [S/Zn] ratio in the Galaxy in more detail when we have completed a new precise analysis of S abundances in less metal-poor stars.…”

Section: [S/mentioning

confidence: 89%

“…Zn] in metal-poor stars and damped Lyα systems Nissen et al (2004) suggested that the [S/Zn] ratio is higher in stars than in damped Lyα systems. Neither S nor Zn shows much affinity for dust, although MgS has been recently proposed as a possible grain constituent by Zhang et al (2009).…”

Section: [S/mentioning

confidence: 99%

“…François 1987François , 1988. However, the trend of [S/Fe] versus [Fe/H] in the early Galaxy is still debated: Israelian & Rebolo (2001) and Takada-Hidai et al (2002) found [S/Fe] to rise with decreasing [Fe/H], while Ryde & Lambert (2004) and Nissen et al (2004Nissen et al ( , 2007 found [S/Fe] to remain flat. Finally, Caffau et al (2005Caffau et al ( , 2010a, combining their own data with a large sample from the literature covering the multiplets 1, 3, 6, and 8 of S I (see Table 1), suggest a bimodal distribution of [S/Fe] Nakamura et al 2001), or even that they may be responsible for a delayed deposition of the supernova-synthesized products into the interstellar medium (Ramaty et al 2000).…”

Section: Introductionmentioning

confidence: 99%

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First stars

Spite

Caffau

Andrievsky

et al. 2011

A&A

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Context. Precise S abundances are important in the study of the early chemical evolution of the Galaxy. In particular the site of the formation remains uncertain because, at low metallicity, the trend of this α-element versus [Fe/H] remains unclear. Moreover, although sulfur is not bound significantly in dust grains in the ISM, it seems to behave differently in DLAs and old metal-poor stars. Aims. We attempt a precise measurement of the S abundance in a sample of extremely metal-poor stars observed with the ESO VLT equipped with UVES, taking into account NLTE and 3D effects. Methods. The NLTE profiles of the lines of multiplet 1 of S I were computed with a version of the program MULTI, including opacity sources from ATLAS9 and based on a new model atom for S. These profiles were fitted to the observed spectra. ratio in EMP stars is solar, as also found in DLAs. We derive an upper limit to the sulfur abundance [S/Fe] < +0.5 for the ultra metal-poor star CS 22949-037. This, along with a previously reported measurement of zinc, argues against the conjecture that the light-element abundance pattern of this star (and by analogy, the hyper iron-poor stars HE 0107-5240 and HE 1327-2326) would be due to dust depletion.

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“…Caffau et al 2007a;Ryde 2006;Caffau et al 2005b;Korn & Ryde 2005;Nissen et al 2004;Ryde & Lambert 2004, among the most recent), but agreement on its behavior at low metallicities has not been reached yet. While some of the cited authors (e.g.…”

Section: Introductionmentioning

confidence: 99%

Sulfur in the globular clusters 47 Tucanae and NGC 6752

Sbordone

Limongi

Chieffi

et al. 2009

A&A

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Context. The light elements Li, O, Na, Al, and Mg are known to show star-to-star variations in the globular clusters 47 Tuc and NGC 6752. Such variations are interpreted as coming from processing in a previous generation of stars. Aims. In this paper we investigate the abundances of the α-element sulfur, for which no previous measurements exist. In fact this element has not been investigated in any Galactic globular cluster so far. The only globular cluster for which such measurements are available is Terzan 7, which belongs to the Sgr dSph.Methods. We use high-resolution spectra of the S i Mult. 1, acquired with the UVES spectrograph at the 8.2 m VLT-Kueyen telescope, for turn-off and giant stars in the two globular clusters. The spectra were analysed making use of ATLAS static plane parallel model atmospheres and SYNTHE spectrum synthesis. We also compute 3D corrections from CO 5 BOLD hydrodynamic models and apply corrections due to NLTE effects taken from the literature. Results. In the cluster NGC 6752 sulfur has been measured only in four subgiant stars. We find no significant star-to-star scatter and a mean [S/Fe] = +0.49 ± 0.15, consistent with what is observed in field stars of the same metallicity. In the cluster 47 Tuc we measured S in 4 turn-off and 5 subgiant stars with a mean [S/Fe] = +0.18 ± 0.14. While this result is compatible with no star-to-star scatter we notice a statistically significant correlation of the sulfur abundance with the sodium abundance and a tentative correlation with the silicon abundance. Conclusions. The sulfur-sodium correlation is not easily explained in terms of nucleosynthesis. An origin due to atomic diffusion can be easily dismissed. The correlation cannot be easily dismissed either, in view of its statistical significance, until better data for more stars is available.

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Sulphur and zinc abundances in Galactic stars and damped Lyαsystems

Cited by 144 publications

References 71 publications

The dust obscuration bias in damped Lyman αsystems

The dust obscuration bias in damped Lyman αsystems

First stars

Sulfur in the globular clusters 47 Tucanae and NGC 6752

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