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Title: THE BINARY FREQUENCY OF r-PROCESS-ELEMENT-ENHANCED METAL-POOR STARS AND ITS IMPLICATIONS: CHEMICAL TAGGING IN THE PRIMITIVE HALO OF THE MILKY WAY

A few rare halo giants in the range [Fe/H] {approx_equal} -2.9 {+-} 0.3 exhibit r-process element abundances that vary as a group by factors up to [r/Fe] {approx}80, relative to those of the iron peak and below. Yet, the astrophysical production site of these r-process elements remains unclear. We report initial results from four years of monitoring the radial velocities of 17 r-process-enhanced metal-poor giants to detect and characterize binaries in this sample. We find three (possibly four) spectroscopic binaries with orbital periods and eccentricities that are indistinguishable from those of Population I binaries with giant primaries, and which exhibit no signs that the secondary components have passed through the asymptotic giant branch stage of evolution or exploded as supernovae. The other 14 stars in our sample appear to be single-including the prototypical r-process-element-enhanced star CS 22892-052, which is also enhanced in carbon, but not in s-process elements. We conclude that the r-process (and potentially carbon) enhancement of these stars was not a local event due to mass transfer or winds from a binary companion, but was imprinted on the natal molecular clouds of these (single and binary) stars by an external source. These stars are thus spectacular chemical tracersmore » of the inhomogeneous nature of the early Galactic halo system.« less
Authors:
; ; ;  [1] ;  [2]
  1. Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)
  2. Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)
Publication Date:
OSTI Identifier:
22047316
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 743; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; ASYMPTOTIC SOLUTIONS; BINARY STARS; CARBON; ELEMENT ABUNDANCE; GIANT STARS; IRON; MASS TRANSFER; MILKY WAY; MONITORING; R PROCESS; RADIAL VELOCITY; S PROCESS; STAR EVOLUTION; SUPERNOVAE