  Metal-poor stars were formed during the early epochs when only massive stars
had time to evolve and contribute to the chemical enrichment. Low-mass
metal-poor stars survive until the present and provide fossil records of the
nucleosynthesis of early massive stars. On the other hand, short-lived
radionuclides (SLRs) in the early solar system (ESS) reflect the
nucleosynthesis of sources that occurred close to the proto-solar cloud in both
space and time. Both the ubiquity of Sr and Ba and the diversity of
heavy-element abundance patterns observed in single metal-poor stars suggest
that some neutron-capture mechanisms other than the r-process might have
operated in early massive stars. Three such mechanisms are discussed: the weak
s-process in non-rotating models with initial carbon enhancement, a new
s-process induced by rapid rotation in models with normal initial composition,
and neutron-capture processes induced by proton ingestion in non-rotating
models. In addition, meteoritic data are discussed to constrain the
core-collapse supernova (CCSN) that might have triggered the formation of the
solar system and provided some of the SLRs in the ESS. If there was a CCSN
trigger, the data point to a low-mass CCSN as the most likely candidate. An
11.8 solar mass CCSN trigger is discussed. Its nucleosynthesis, the evolution
of its remnant, and the interaction of the remnant with the proto-solar cloud
appear to satisfy the meteoritic constraints and can account for the abundances
of the SLRs 41Ca, 53Mn, and 60Fe in the ESS.
