Open AccessLow‐mass supernovae in the early Galactic halo: source of the double r/s‐process enriched halo stars?
Author(s) -
Zijlstra Albert A.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07552.x
Subject(s) - physics , astrophysics , supernova , metallicity , galactic halo , globular cluster , halo , stars , asymptotic giant branch , chandrasekhar limit , astronomy , white dwarf , nucleosynthesis , stellar mass , horizontal branch , star formation , galaxy
Several stars at the low‐metallicity extreme of the Galactic halo ([Fe/H]=−2.5) show strong enhancements of both s‐process and r‐process elements. The presence of s‐process elements in main‐sequence stars is explained via mass transfer from an asymptotic giant branch (AGB) companion star in a binary system. r‐process elements originate in Type II supernovae and also require mass transfer. It is, however, unclear how pollution by both an AGB star and a supernova could have occurred. Here I show that the initial–final mass relation steepens at low metallicity, due to low mass‐loss efficiency. This may cause the degenerate cores of low‐ Z , high‐mass AGB stars to reach the Chandrasekhar mass, leading to an Iben & Renzini Type 1.5 supernova. Such supernovae can explain both the enhancement patterns and the metallicity dependence of the double‐enhanced halo stars. Reduced mass‐loss efficiency predicts more massive remnants in metal‐poor globular clusters. The evidence for a high M/L population in the cores of globular clusters is briefly discussed.