Evidence of Multiple r-Process Sites in the Early Galaxy: New Observations of CS 22892-052.
First results are reported of a new abundance study of neutron-capture elements in the ultra-metal-poor (&sqbl0;Fe&solm0;H&sqbr0;=-3.1) halo field giant star CS 22892-052. Using new high-resolution, high signal-to-noise ratio spectra, abundances of more than 30 neutron-capture elements (Z>30) have been determined. Six elements in the 40<Z<56 domain (Nb, Ru, Rh, Pd, Ag, and Cd) have been detected for the first time in an ultra-metal-poor star. Abundances are also derived for three of the heaviest stable elements (Os, Ir, and Pb). A second transition of thorium, Th ii lambda4086, confirms the abundance deduced from the standard Th ii lambda4019 line, and an upper limit to the abundance of uranium is established from the absence of the U ii lambda3859 line. As found in previous studies, the abundances of the heavier (Z>/=56) stable neutron-capture elements in CS 22892-052 match well the scaled solar system r-process abundance distribution. From the observed Th abundance, an average age of approximately 16+/-4 Gyr is derived for CS 22892-052, consistent with the lower age limit of approximately 11 Gyr derived from the upper limit on the U abundance. The concordance of scaled solar r-process and CS 22892-052 abundances breaks down for the lighter neutron-capture elements, supporting previous suggestions that different r-process production sites are responsible for lighter and heavier neutron-capture elements.
Sneden
C
Cowan
JJ
Ivans
II
Fuller
GM
Burles
S
Beers
TC
Lawler
JE