For a long time it has been thought that the lightest s-process elements (between 60<A<90) in the universe are predominantly created by massive stars. Earlier integrated nucleosynthesis calculations from the evolution and explosion of massive stars were rather successful in re-creating solar abundances by assuming most or all stars above approximately 10 Msun explode as supernovae. However, recent survey calculations that employ more realistic explosion modelling demonstrate that these species are significantly underproduced, not due to less synthesis in massive stars, but because many stars that were previously assumed to explode instead collapse to black holes. We investigate possible solutions to this underproduction by considering the uncertainty in the explosion landscape and also contributions from other sources, namely He-shell flashes on accreting white dwarfs.
