We present a method for the determination of [α/Fe] ratios from low-resolution (R = 2000) SDSS/SEGUE stellar spectra. By means of a star-by-star comparison with degraded spectra from the ELODIE spectral library and with a set of moderately high-resolution (R = 15, 000) and medium-resolution (R = 6000) spectra of SDSS/SEGUE stars, we demonstrate that we are able to measure [α/Fe] from SDSS/SEGUE spectra (with S/N20/1) to a precision of better than 0.1 dex, for stars with atmospheric parameters in the range T eff = [4500, 7000] K, log g = [1.5, 5.0], and [Fe/H] = [–1.4, +0.3], over the range [α/Fe] = [–0.1, +0.6]. For stars with [Fe/H] –1.4, our method requires spectra with slightly higher signal-to-noise to achieve this precision (S/N25/1). Over the full temperature range considered, the lowest metallicity star for which a confident estimate of [α/Fe] can be obtained from our approach is [Fe/H] ~–2.5; preliminary tests indicate that a metallicity limit as low as [Fe/H] ~–3.0 may apply to cooler stars. As a further validation of this approach, weighted averages of [α/Fe] obtained for SEGUE spectra of likely member stars of Galactic globular clusters (M15, M13, and M71) and open clusters (NGC?2420, M67, and NGC?6791) exhibit good agreement with the values of [α/Fe] from previous studies. The results of the comparison with NGC?6791 imply that the metallicity range for the method may extend to ~+0.5.
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