The Hamburg/ESO R-process Enhanced Star survey (HERES) VI. The Galactic Chemical Evolution of Silicon

Abstract

We determined the silicon abundances of 253 metal-poor stars in the metallicity range $-4<[Fe/H]<-1.5$, based on non-local thermodynamic equilibrium (NLTE) line formation calculations of neutral silicon and high-resolution spectra obtained with VLT-UT2/UVES. The $T_{\mathrm{eff}}$ dependence of [Si/Fe] noticed in previous investigation is diminished in our abundance analysis due to the inclusion of NLTE effects. An increasing slope of [Si/Fe] towards decreasing metallicity is present in our results, in agreement with Galactic chemical evolution models. The small intrinsic scatter of [Si/Fe] in our sample may imply that these stars formed in a region where the yields of type II supernovae were mixed into a large volume, or that the formation of these stars was strongly clustered, even if the ISM was enriched by single SNa II in a small mixing volume. We identified two dwarfs with $[Si/Fe]\sim +1.0$: HE 0131$-$3953, and HE 1430$-$1123. These main-sequence turnoff stars are also carbon-enhanced. They might have been pre-enriched by sub-luminous supernovae.

12 pages, 9 figures, 1 electronical table. Accepted by A & A

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• Normal and Outlying Populations of the Milky Way Stellar Halo at [Fe/H] < -2
• Pre-galactic metal enrichment - The chemical signatures of the first stars
• The Chemical Imprint of Silicate Dust on the Most Metal-Poor Stars
• The chemistry of the most metal-rich damped Lyman $\alpha$ systems at z$\sim 2$ II. Context with the Local Group
• G64-12 and G64-37 are Carbon-Enhanced Metal-Poor Stars
• Star Formation Timescales of the Halo Populations from Asteroseismology and Chemical Abundances
• The Hamburg/ESO R-process Enhanced Star survey (HERES)VII. Thorium abundances in metal-poor stars
• Gaia-Sausage-Enceladus star formation history as revealed by detailed elemental abundances
• Inferring the velocity of early massive stars from the abundances of extremely metal-poor stars
• Carbon Abundances of Metal-Poor Star Determined from the C I 1.068-1.069 micron Lines
• The metal-poor end of the Spite plateau. II. Detailed chemical investigation