LAUSR

Observations suggest that the interstellar medium (ISM) might have been highly enriched in carbon at very early times. We explore the presupernova nucleosynthesis in massive carbon-enhanced metal-poor (CEMP) stars of 12--$40M_\odot$ formed from such an ISM with [Fe/H]~$\leq-2$. We find substantial production of elements heavier than Fe, mostly up to Sr, by the weak $s$-process in stars with initial abundances of ${\rm [C/H]}\gtrsim-1.5$. Even heavier elements up to Ba can also be produced for ${\rm [C/H]}\gtrsim-0.5$. The efficiency of this $s$-process is sensitive to the initial C enhancement and mass of the star, with the yield of heavy elements increasing approximately linearly with the initial Fe abundance. The $s$-process in CEMP stars of $\gtrsim 20 M_\odot$ with initial abundances of ${\rm [C/H]}\gtrsim -1.5$ can be an important source for heavy elements in the early Galaxy.