We present an AAOmega spectroscopic study of red giant stars in Boötes I , which is an ultra-faint dwarf galaxy , and Segue 1 , suggested to be either an extremely low-luminosity dwarf galaxy or a star cluster .
Our focus is quantifying the mean abundance and abundance dispersion in iron and carbon , and searching for distant radial-velocity members , in these systems .

The primary conclusion of our investigation is that the spread of carbon abundance in both Boötes I and Segue 1 is large .
For Boötes I , four of our 16 velocity members have [ C/H ] \lesssim –3.1 , while two have [ C/H ] \gtrsim –2.3 , suggesting a range of \Delta [ C/H ] \sim 0.8 .
For Segue 1 there exists a range \Delta [ C/H ] \sim 1.0 , including our discovery of a star with [ Fe/H ] = –3.5 and [ C/Fe ] = +2.3 , which is a radial velocity member at a distance of 4 half-light radii from the system center .
The accompanying ranges in iron abundance are \Delta [ Fe/H ] \sim 1.6 for both Boötes I and Segue 1 .
For [ Fe/H ] < –3.0 , the Galaxy ’ s dwarf galaxy satellites exhibit a dependence of [ C/Fe ] on [ Fe/H ] which is very similar to that observed in its halo populations .
We find [ C/Fe ] \sim 0.3 for stars in the dwarf systems that we believe are the counterpart of the Spite et al .
( 2005 ) “ unmixed ” giants of the Galactic halo and for which they report [ C/Fe ] \sim 0.2 , and which presumably represents the natal relative abundance of carbon for material with [ Fe/H ] = –3.0 to –4.0 .

Our second conclusion is confirmation of the correlation between ( decreasing ) luminosity and both ( decreasing ) mean metallicity and ( increasing ) abundance dispersion in the Galaxy ’ s dwarf satellites .
This correlation extends to at least as faint as M _ { V } = –5 , and may continue to even lower luminosities .
The very low mean metallicity of Segue 1 , and the high carbon dispersion in Boötes I , consistent with inhomogeneous chemical evolution in near zero-abundance gas , suggest these ultra-faint systems could be surviving examples of the very first bound systems .