are made in both processes (Clayton & Rassbach 1967). Th (Z=90) and U (Z=92) can only be made in the r-process.

The surveys of metal-poor stars have uncovered stars rich in C and s-process elements and stars rich in r-process elements. These have been the subject of many follow-up studies, because of the insight they can provide on the production of the heavy elements in the early Galaxy.

The very metal-poor CH stars
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Metal-poor stars with enhanced abundances of C and s-process elements are called CH stars. In an extensive survey, McClure (1984) and McClure & Woodsworth (1990) showed that all of the CH stars in their sample were members of binary systems with orbital parameters consistent with a white dwarf secondary. The explanation for the classic CH stars is that they result from the transfer of C, N, and s-process material produced in an AGB companion which is now a white dwarf. The abundance patterns in CH stars for the heavy elements are therefore a very accessible means of empirically deriving s-process yields and for inferring the structure of, and physical conditions in, AGB stars. The traditional indicators of s-process material are super-solar \[Ba/Fe\] (the Pop I version 