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We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six redgiant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 starobserved by Norris et al. (2010), high-resolution spectra have now beenobtained for every red giant in Segue 1. Remarkably, three of these seven starshave metallicities below [Fe/H] = -3.5, suggesting that Segue 1 is the leastchemically evolved galaxy known. We confirm previous medium-resolution analysesdemonstrating that Segue 1 stars span a metallicity range of more than 2 dex,from [Fe/H] = -1.4 to [Fe/H] = -3.8. All of the Segue 1 stars arealpha-enhanced, with [alpha/Fe] ~ 0.5. High alpha-element abundances aretypical for metal-poor stars, but in every previously studied galaxy [alpha/Fe]declines for more metal-rich stars, which is typically interpreted as ironenrichment from supernova Ia. The absence of this signature in Segue 1indicates that it was enriched exclusively by massive stars. Other lightelement abundance ratios in Segue 1, including carbon-enhancement in the threemost metal-poor stars, closely resemble those of metal-poor halo stars.Finally, we classify the most metal-rich star as a CH star given its largeoverabundances of carbon and s-process elements. The other six stars showremarkably low neutron-capture element abundances of [Sr/H] < -4.9 and [Ba/H] <-4.2, which are comparable to the lowest levels ever detected in halo stars.This suggests minimal neutron-capture enrichment, perhaps limited to a singler-process or weak s-process synthesizing event. Altogether, the chemicalabundances of Segue 1 indicate no substantial chemical evolution, supportingthe idea that it may be a surviving first galaxy that experienced only oneburst of star formation.

Segue 1: An Unevolved Fossil Galaxy from the Early Universe