by the same continuum-fitting routine used for the observed spectra.

Determination of \[C/Fe\]
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In order to determine [\[C/Fe\]]{} for the SDSS/SEGUE spectra, we first transform the vacuum wavelength scale to an air-based scale, and shift the spectrum to the rest frame using a measured radial velocity. This wavelength and redshift-corrected spectrum is linearly re-binned to 1 Å pixels over the wavelength range 4000–4650 Å, in which the CH $G$-band is included. When pre-processing the synthetic spectra, the spectrum under consideration is then normalized by dividing its reported flux by its pseudo-continuum.

The pseudo-continuum over the 4000–4650 Å range is obtained by carrying out an iterative procedure that rejects points lying more than 1$\sigma$ below and 4$\sigma$ above the fitted function, obtained from a ninth-order polynomial. Although we have a “perfect” continuum available for a given synthetic spectrum, we apply the same continuum routine to the synthetic and SDSS spectra to match with over the same wavelength range, and with the same pixel size. Application of the same continuum routine produces the same level of line-strength suppression in both spectra.

Following the above steps, we then search the grid of synthetic spectra for the best-fitting model parameters by minimizing the 