2010/09/22 by I. U. Roederer, Ian U. Roederer, John J. Cowan +13 · 1 citation
Physics and Astronomy · #Abundance (ecology) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Asymptotic giant branch #Giant star #Metallicity #Nucleosynthesis #Spectral line #Spectrograph #Stars #Stellar, planetary, and galactic studies #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/724/2/975
Accepted for publication in the Astrophysical Journal. 25 pages, 13 figures
arxiv created 2010/09/22 · openalex publication_date 2010/11/10 · arxiv updated 2015/05/20 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
ABSTRACT To better characterize the abundance patterns produced by the r -process, we have derived new abundances or upper limits for the heavy elements zinc (Zn, Z = 30), yttrium (Y, Z = 39), lanthanum (La, Z = 57), europium (Eu, Z = 63), and lead (Pb, Z = 82). Our sample of 161 metal-poor stars includes new measurements from 88 high-resolution and high signal-to-noise spectra obtained with the Tull Spectrograph on the 2.7 m Smith Telescope at the McDonald Observatory, and other abundances are adopted from the literature. We use models of the s -process in asymptotic giant branch stars to characterize the high Pb/Eu ratios produced in the s -process at low metallicity, and our new observations then allow us to identify a sample of stars with no detectable s -process material. In these stars, we find no significant increase in the Pb/Eu ratios with increasing metallicity. This suggests that s -process material was not widely dispersed until the overall Galactic metallicity grew considerably, perhaps even as high as [Fe/H] =−1.4, in contrast with earlier studies that suggested a much lower mean metallicity. We identify a dispersion of at least 0.5 dex in [La/Eu] in metal-poor stars with [Eu/Fe] <+0.6 attributable to the r -process, suggesting that there is no unique “pure” r -process elemental ratio among pairs of rare earth elements. We confirm earlier detections of an anti-correlation between Y/Eu and Eu/Fe bookended by stars strongly enriched in the r -process (e.g., CS 22892–052) and those with deficiencies of the heavy elements (e.g., HD 122563). We can reproduce the range of Y/Eu ratios using simulations of high-entropy neutrino winds of core-collapse supernovae that include charged-particle and neutron-capture components of r -process nucleosynthesis. The heavy element abundance patterns in most metal-poor stars do not resemble that of CS 22892–052, but the presence of heavy elements such as Ba in nearly all metal-poor stars without s -process enrichment suggests that the r -process is a common phenomenon.