THE UBIQUITY OF THE RAPID NEUTRON-CAPTURE PROCESS
- Department of Astronomy, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States)
- Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)
- Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
- Max-Planck-Institut fuer Chemie, Otto-Hahn-Institut, J.-J.-Becherweg 27, D-55128 Mainz (Germany)
- Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, Monash University, Clayton, VIC 3800 (Australia)
- Department of Physics and Astronomy, University of Utah, 115 S. 1400 E., Salt Lake City, UT 84112-0830 (United States)
- Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, D-69117 Heidelberg (Germany)
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.
- OSTI ID:
- 21474504
- Journal Information:
- Astrophysical Journal, Vol. 724, Issue 2; Other Information: DOI: 10.1088/0004-637X/724/2/975; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CAPTURE
CHARGED PARTICLES
COSMIC NEUTRINOS
ELEMENT ABUNDANCE
ENTROPY
EUROPIUM
LANTHANUM
LEAD
NEUTRON REACTIONS
NUCLEOSYNTHESIS
R PROCESS
S PROCESS
SIGNALS
SIMULATION
SUPERNOVAE
YTTRIUM
ZINC
ABUNDANCE
BARYON REACTIONS
BINARY STARS
COSMIC RADIATION
ELEMENTARY PARTICLES
ELEMENTS
ERUPTIVE VARIABLE STARS
EVOLUTION
FERMIONS
HADRON REACTIONS
IONIZING RADIATIONS
LEPTONS
MASSLESS PARTICLES
METALS
NEUTRINOS
NUCLEAR REACTIONS
NUCLEON REACTIONS
PHYSICAL PROPERTIES
RADIATIONS
RARE EARTHS
STAR EVOLUTION
STARS
SYNTHESIS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
VARIABLE STARS