Elemental Abundances and their Implications for the Chemical Enrichment
  of the Bo\"{o}tes~I Ultra-Faint Galaxy
  We present a double-blind analysis of high-dispersion spectra of seven red
giant members of the Bo\"{o}tes I ultra-faint dwarf spheroidal galaxy,
complemented with re-analysis of a similar spectrum of an eighth member star.
The stars cover [Fe/H] from -3.7 to -1.9, and include a CEMP-no star with
[Fe/H] = -3.33. We conclude from our chemical abundance data that Bo\"{o}tes I
has evolved as a self-enriching star-forming system, from essentially
primordial initial abundances. This allows us uniquely to investigate the place
of CEMP-no stars in a chemically evolving system, in addition to limiting the
timescale of star formation. The elemental abundances are formally consistent
with a halo-like distribution, with enhanced mean [alpha/Fe] and small scatter
about the mean. This is in accord with the high-mass stellar IMF in this
low-stellar-density, low-metallicity system being indistinguishable from the
present-day solar neighborhood value. There is a non-significant hint of a
decline in [alpha/Fe] with [Fe/H]; together with the low scatter, this requires
low star formation rates, allowing time for SNe ejecta to be mixed over the
large spatial scales of interest. One star has very high [Ti/Fe], but we do not
confirm a previously published high value of [Mg/Fe] for another star. We
discuss the existence of CEMP-no stars, and the absence of any stars with lower
CEMP-no enhancements at higher [Fe/H], a situation which is consistent with
knowledge of CEMP-no stars in the Galactic field. We show that this observation
requires there be two enrichment paths at very low metallicities: CEMP-no and
"carbon-normal".
