What process(es) produced barium in the Early Universe?

In the last years our group has found that many chemical anomalies
observed in very metal-poor halo stars in the light elements suggest
that the first stellar generations were fast rotators
(spinstars). Recently, theoretical computations have found that
spinstars can also play a role in the chemical enrichment of neutron
capture elements providing a early contribution of s-process. By means
of a stochastic chemical evolution model, it is possible to identify
the spinstars s-process contribution as the missing component
responsible for the spread in the ratio between light (Sr) to heavy
(Ba) neutron capture elements. A specific distribution is predicted
for the isotopic ratio of Ba in halo stars and this imprint could be
the smoking gun of the role played by spinstars in the spread of
[Sr/Ba] ratio. In this context, regarding the still unknown origin of
the complementary r-process component, I present new constraints on
the rate and time scales of r-process events, based on the recent
discovery of the r-process rich stars in the ultra faint galaxy
Reticulum 2.