described by Barklem & O’Mara (1998), along with the solar abundances of Asplund et al. (2005). The sources of atomic lines used by [Turbospectrum]{} come from VALD (Kupka et al. 1999), Hill et al. (2002), and Masseron (2006). Line-lists for the molecular species are provided for CH (T. Masseron et al., in preparation), and CN and C$_{2}$ (B. Plez, private communication); the lines of MgH molecules are adopted from the Kurucz linelists.

When synthesizing the spectra, we increase (by the same amount) the abundances for the [$\alpha$]{}-elements (O, Mg, Si, Ca, and Ti). We assume that the $\alpha$-enhancement ratio, relative to Fe, is $+$0.4 for \[Fe/H\] $\leq -1.0$, $+$0.2 for \[Fe/H\] = $-0.5$, and 0.0 for \[Fe/H\] $\geq 0.0$. As it is often found that N is enhanced in CEMP stars (Masseron et al. 2010), we assume the same level of N enhancement as for carbon (i.e., \[N/Fe\] = \[C/Fe\]). We also assumed a carbon isotopic composition of $^{12}$C/$^{13}$C = 10. We do not consider any neutron-capture element enhancements (which in any case would have a small effect on spectra at the resolution of SDSS/SEGUE). In order to assign an appropriate microturbulence velocity ($\xi_{t}$) for each spectrum, we make use 