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Using numerical modeling and a grid of synthetic spectra, we examine theeffects that unresolved binaries have on the determination of various stellaratmospheric parameters for SEGUE targets measured using the SEGUE StellarParameter Pipeline (SSPP). To model undetected binaries that may be in theSEGUE sample, we use a variety of mass distributions for the primary andsecondary stars in conjunction with empirically determined relationships fororbital parameters to determine the fraction of G-K dwarf stars, as defined bySDSS color cuts, that will be blended with a secondary companion. We focus onthe G-K dwarf sample in SEGUE as it records the history of chemical enrichmentin our galaxy. To determine the effect of the secondary on the spectroscopicparameters, we synthesize a grid of model spectra from 3275 to 7850 K (~0.1 to1.0 \msun) and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres usingTurboSpectrum. We analyze both "infinite" signal-to-noise ratio (S/N) modelsand degraded versions, at median S/N of 50, 25 and 10. By running individualand combined spectra (representing the binaries) through the SSPP, we determinethat ~10% of the blended G-K dwarf pairs with S/N>=25 will have theiratmospheric parameter determinations, in particular temperature andmetallicity, noticeably affected by the presence of an undetected secondary. Toaccount for the additional uncertainty from binary contamination at a S/N~10,uncertainties of ~140 K and ~0.17 dex in [Fe/H] must be added in quadrature tothe published uncertainties of the SSPP. (Abridged)

Binary Contamination in the SEGUE sample: Effects on SSPP Determinations of Stellar Atmospheric Parameters