We report the analysis of high-resolution , high- S / N spectra of an extremely metal-poor , extremely C-rich red giant , Seg 1–7 , in the Segue 1 system – described in the literature alternatively as an unusually extended globular cluster or an ultra-faint dwarf galaxy .
The radial velocity of Seg 1–7 coincides precisely with the systemic velocity of Segue 1 , and its chemical abundance signature of [ Fe/H ] = –3.52 , [ C/Fe ] = +2.3 , [ N/Fe ] = +0.8 , [ Na/Fe ] = +0.53 , [ Mg/Fe ] = +0.94 , [ Al/Fe ] = +0.23 and [ Ba/Fe ] < –1.0 is similar to that of the rare and enigmatic class of Galactic halo objects designated CEMP-no ( Carbon-rich , Extremely Metal-Poor and with no enhancement ( over solar ratios ) of heavy neutron-capture elements ) .
This is the first star in a Milky Way “ satellite ” that unambiguously lies on the metal-poor , C-rich branch of the Aoki et al .
( 2007 ) bimodal distribution defined by field halo stars in the ( [ C/Fe ] , [ Fe/H ] ) –plane .
Available data permit us only to identify Seg 1–7 as a member of an ultra-faint dwarf galaxy or as debris from the Sgr dwarf spheroidal galaxy .
In either case , this demonstrates that at extremely low abundance , [ Fe/H ] < -3.0 , star formation and associated chemical evolution proceeded similarly in the progenitors of both the field halo and satellite systems .
By extension , this is consistent with other recent suggestions the most metal-poor dwarf spheroidal and ultra-faint dwarf satellites were the building blocks of the Milky Way ’ s outer halo .