We determined the silicon abundances of 253 metal-poor stars in the metallicity range -4 < \mathrm { [ 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 \mathrm { [ 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 .