a wide range of parameter space, in order to match with the SDSS/SEGUE stellar spectra around the CH $G$-band region to derive the carbon-to-iron ratios. They applied their technique to the calibration stars (used for spectrophotometric corrections and tests of interstellar reddening) from SDSS/SEGUE, ending up with about 31,000 stars with derived carbon abundances (or upper limits), the largest previous effort to measure \[C/Fe\] for halo stars to date.

The SDSS/SEGUE surveys have produced an unprecedented sample of stellar spectra for more detailed analysis. SEGUE-1 was one of three sub-surveys comprising SDSS-II (Legacy, Supernova Survey, and SEGUE-1). The SEGUE-1 program obtained $ugriz$ imaging of some 3500 deg$^{2}$ of sky outside of the original SDSS footprint, and roughly 240,000 low-resolution ($R=2000$) stellar spectra covering the wavelength range 3820–9100 Å. SEGUE-2, executed during an early stage of the ongoing SDSS-III effort, observed stars fainter than the SEGUE-1 survey, and added an additional $\sim$140,000 stars. Stellar spectra obtained as calibration objects or ancillary projects during regular SDSS-I and SDSS-II operations account for roughly another 200,000 stars, yielding a total of about 600,000 stars potentially suitable for further analysis. For simplicity, we refer to all of the SDSS, SEGUE-1, and SEGUE-2 stellar spectra to 