Approximately 20 % of very metal-poor stars ( [ Fe/H ] < –2.0 ) are strongly enhanced in carbon ( [ C/Fe ] > +1.0 ) .
Such stars are referred to as carbon-enhanced metal-poor ( CEMP ) stars .
A variety of abundance patterns are found among CEMP stars .
Strong overabundances of nitrogen are common , and overabundances of neutron capture elements are often , however not always , present .
The variety of abundance patterns among CEMP stars strongly suggests that this population of stars comprises several astrophysical origins .

We are conducting a high-resolution follow-up of candidate EMP stars extracted from the Sloan Digital Sky Survey ( SDSS ; York et al .
2000 ) using UVES at the VLT .
Three of the programme stars , SDSS J0912+0216 , SDSS J1036+1212 and SDSS J1349-0229 , where deliberately targetted as CEMP stars since a strong G band was evident from the SDSS spectra and the weakness of the Ca ii K line testified their very low metallicity .
The UVES high resolution follow-up confirmed the original findings ( [ Fe/H ] < -2.50 ) and allowed a more detailed investigation of their chemical composition .

We determined the carbon abundance from molecular lines which form in the outer layers of the stellar atmosphere .
It is known that convection in metal-poor stars induces very low temperatures which are not predicted by classical 1D stellar atmospheres .
To obtain the correct temperature structure , one needs full 3D hydrodynamical models .
3D carbon abundances were determined for all three stars , using CO ^ { 5 } BOLD 3D hydrodynamical model atmospheres .
3D effects on the carbon abundance are found to be quite significant for these stars , with 3D corrections of up to –0.7 dex .

Two of the stars , SDSS J0912+0216 and SDSS J1349-0229 exhibit an overabundance of neutron capture elements which classifies them as CEMP-s. Star SDSS J1036+1212 , instead belongs to the elusive class of CEMP-no/s stars , with enhanced Ba , but deficient Sr , of which it is the third member discovered to date .