HEAVY-ELEMENT ABUNDANCES IN PECULIAR A-STARS

On the theory that peculiar A stars were once secondaries in binary systems in which the primaries exploded as type II supernovae, the nucleosynthesis during the final stages of evolution of massive stars is investigated. For heavy elements (Z>30) the observed abundances in peculiar. A stars reflect the composition of material ejected by the exploding primaries. Peculiar A stars are divided into two groups, the main group and the Mn group, and abundances in each group are summarised. During the explosions of the primaries, rapid (n, γ) or (γ, n) reactions operate on the abundance peaks previously formed by the s-process during the giant phase. In the main group primaries (n, γ) reactions predominate, and rare-earths are formed from the Ba peak. In the Mn group primaries (γ, n) reactions operate on the Sr, Ba and Pb peaks to form Kr, Xe and Hg. © 1969 D. Reidel Publishing Company.