16 research outputs found
Sulphur in the Sculptor dwarf spheroidal galaxy - Including NLTE corrections
In Galactic halo stars, sulphur has been shown to behave like other
-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 . The abundances are derived from the S~I triplet at
9213, 9228, and 9238~\AA. 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 -elements in that galaxy (such as Mg, Si, and
Ca). At lower metallicities () the abundances are
consistent with a plateau at , similar to what is
observed in the Galactic halo, . With increasing
[Fe/H], the [S/Fe] ratio declines, reaching negative values at
. The sample also shows an increase in [S/Mg] with
[Fe/H], most probably because of enrichment from Type Ia supernovae.Comment: 9 pages, 11 figures, 2 tables + 3 online tables, accepted in A&
First stars signatures in high-z absorbers
International audienceThe first stars were likely more massive than those forming today and thus rapidly evolved, exploding as supernovae and enriching the surrounding gas with their chemical products. In the Local Group, the chemical signature of the first stars has been identified in the so-called Carbon-Enhanced Metal-Poor stars (CEMP-no). On the contrary, a similar C-excess was not found in dense neutral gas traced by high-redshift absorption systems. Here we discuss the recent discovery of three C-enhanced very metal-poor ([Fe/H] 50% of the metals in these absorber