An Extremely Carbon-rich, Extremely Metal-poor Star in the Segue 1
  System
  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.
