The r-Process and Chronometers

Abstract

We present detailed abundance observations of the metal-poor ([Fe/H] = --2.0) Galactic halo star BD+17 3248. We have detected gold in this star, for the first time in any halo star. We also detected a weak line at 3859.60 A in the spectrum of BD+17 3248 that we tentatively identify with uranium. This would be only the second such detection of this radioactive element in any metal-poor halo stars. Similarly to the case of CS 22892--052, the heavier n-capture elements (Z >= 56) fall on the scaled solar system r-process abundance curve, while the elements with Z = 40--50 in BD+17 3248 fall below that same solar curve. Employing the newly detected Th, U and third r-process peak element (e.g., Pt, Ir) abundances, chronometric age estimates have been made for BD+17 3248. The average value of the various chronometric pairs suggests an age of 13.8 +/- 4 Gyr for this star, consistent, within error limits, with other chronometric age determinations for metal-poor Galactic halo stars.