High resolution study of the abundance pattern of the heavy elements in
  very metal-poor field stars
  The abundances of heavy elements in EMP stars are not well explained by the
simple view of an initial basic "rapid" process. In a careful and homogeneous
analysis of the "First stars" sample (eighty per cent of the stars have a
metallicity [Fe/H]=-3.1$\pm$0.4), it has been shown that at this metallicity
[Eu/Ba] is constant, and therefore the Eu-rich stars (generally called
"r-rich") are also Ba-rich. The very large variation of [Ba/Fe] (existence of
"r-poor" and "r-rich" stars) induces that the early matter was not perfectly
mixed. On the other hand, the distribution of the values of [Sr/Ba] vs. [Ba/Fe]
appears with well defined upper and lower envelopes. No star was found with
[Sr/Ba]<-0.5 and the scatter of [Sr/Ba] increases regularly when [Ba/Fe]
decreases. To explain this behavior, we suggest that an early "additional"
process forming mainly first peak elements would affect the initial composition
of the matter. For a same quantity of accreted matter, this additional Sr
production would barely affect the r-rich matter (which already contains an
important quantity of Sr) but would change significantly the composition of the
r-poor matter. The abundances found in the CEMP-rs stars reflect the transfer
of heavy elements from a defunct AGB companion. But the abundances of the heavy
elements in CEMP-no stars present the same characteristics as the the
abundances in the EMP stars.
