  We have carried out a detailed abundance analysis for a sample of 16 carbon
stars found among candidate extremely metal-poor (EMP) stars from the
Hamburg/ESO Survey. We find that the Fe-metallicities for the cooler C-stars
(Teff ~ 5100K) have been underestimated by a factor of ~10 by the standard HES
survey tools. The results presented here provided crucial supporting data used
by Cohen et al (2006) to derive the frequency of C-stars among EMP stars.
  C-enhancement in these EMP C-stars appears to be independent of
Fe-metallicity and approximately constant at ~1/5 the solar C/H. The mostly low
C12/C13 ratios (~4) and the high N abundances in many of these stars suggest
that material which has been through proton burning via the CN cycle comprises
most of the stellar envelope. C-enhancement is associated with strong
enrichment of heavy nuclei beyond the Fe-peak for 12 of the 16 stars. The
remaining C-stars from the HES, which tend to be the most Fe-metal poor, show
no evidence for enhancement of the heavy elements. Very high enhancements of
lead are detected in some of the C-stars with highly enhanced Ba. (We show
that) the s-process is responsible for the enhancement of the heavy elements
for the majority of the C-stars in our sample.
  We suggest that both the s-process rich and Ba-normal C-stars result from
phenomena associated with mass transfer in binary systems. This leads directly
to the progression from C-stars to CH stars and then to Ba stars as the
Fe-metallicity increases. (abridged and slightly edited to shorten)
