Abundances in the Uranium-Rich Star CS 31082-001

Abstract

The recent discovery by Cayrel et al. of U in CS 31082-001 along with Os and Ir at greatly enhanced abundances but with [Fe/H]=-2.9 strongly reinforces the argument that there are at least two kinds of SNII sources for r-nuclei. One source is the high-frequency H events responsible for heavy r-nuclei (A>135) but not Fe. The H-yields calculated from data on other ultra-metal-poor stars and the sun provide a template for quantitatively predicting the abundances of all other r-elements. In CS 31082-001 these should show a significant deficiency at A<135 relative to the solar r-pattern. It is proposed that CS 31082-001 should have had a companion that exploded as an SNII H event. If the binary survived the explosion, this star should now have a compact companion, most likely a stellar-mass black hole. Comparison of abundance data with predicted values and a search for a compact companion should provide a stringent test of the proposed r-process model. The U-Th age determined by Cayrel et al. for CS 31082-001 is, to within substantial uncertainties, in accord with the r-process age determined from solar system data. The time gap between Big Bang and onset of normal star formation only allows r-process chronometers to provide a lower limit on the age of the universe.