We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Boötes 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 Boötes 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 ” .