The Binary Frequency of r-Process-Element Enhanced Metal-Poor Stars and its Implications: Chemical Tagging in the Primitive Halo of the Milky Way

Abstract

A few rare halo giants in the range [Fe/H] $\simeq -2.9\pm 0.3$ exhibit {\it r}-process element abundances that vary as a group by factors up to [$r$/Fe] $\sim 80$, relative to those of the iron peak and below. Yet, the astrophysical production site of these {\it r}-process elements remains unclear. We report initial results from four years of monitoring the radial velocities of 17 {\it r}-process-enhanced metal-poor giants to detect and characterise 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 AGB 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 {\it s}-process elements. We conclude that the {\it 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 tracers of the inhomogeneous nature of the early Galactic halo system.

References in corpus (20)

• First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy
• R-Process Nucleosynthesis in Dynamically Ejected Matter of Neutron Star Mergers
• The Hamburg/ESO R-process Enhanced Star survey (HERES) II. Spectroscopic analysis of the survey sample
• The early star generations: the dominant effect of rotation on the CNO yields
• The Rise of the s-Process in the Galaxy
• Neutron star mergers versus core-collapse supernovae as dominant r-process sites in the early Galaxy
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• The r-Process Enriched Low Metallicity Giant HD 115444
• Neutron-capture elements in the very metal-poor star HD122563
• The Ubiquity of the Rapid Neutron-Capture Process
• Nucleosynthesis in the Early Galaxy
• The Hamburg/ESO R-process Enhanced Star survey (HERES). I. Project description, and discovery of two stars with strong enhancements of neutron-capture elements
• Are C-rich ultra iron poor stars also He-rich?
• The Hamburg/ESO R-process Enhanced Star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312
• Mg abundances in metal-poor halo stars as a tracer of early Galactic mixing
• The Hamburg/ESO R-process Enhanced Star survey (HERES). V. Detailed abundance analysis of the r-process enhanced star HE 2327-5642
• RR Lyrae Stars, Metal-Poor Stars, and the Galaxy
• Extreme Enhancements of r-process Elements in the Cool Metal-Poor Main-Sequence Star SDSS J2357-0052
• First Stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876--032
• Abundances in the Uranium-Rich Star CS 31082-001

Cited by in corpus (26)

• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Binarity in Carbon-Enhanced Metal-Poor stars
• The $R$-Process Alliance: First Release from the Southern Search for $r$-Process-Enhanced Stars in the Galactic Halo
• The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars -- CEMP-s stars
• Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars
• An R-process enhanced star in the dwarf galaxy Tucana III
• The role of binaries in the enrichment of the early Galactic halo. II. Carbon-Enhanced Metal-Poor Stars - CEMP-no stars
• First stars XVI. STIS/HST abundances of heavy-elements in the uranium-rich star CS 31082-001
• Exploring the Origin of Lithium, Carbon, Strontium and Barium with four new Ultra Metal-Poor Stars
• Elemental abundances and classification of CEMP stars
• Carbon-Enhanced Metal-Poor Stars: CEMP-s and CEMP-no Sub-Classes in the Halo System of the Milky Way
• Nine New Metal-Poor Stars on the Subgiant and Red Horizontal Branches with High Levels of r-process Enhancement
• The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars
• The R-Process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510
• A Near-infrared RR Lyrae census along the southern Galactic plane: the Milky Way's stellar fossil brought to light
• A spectroscopic binary in the Hercules dwarf spheroidal galaxy
• Seven New Carbon-Enhanced Metal-Poor RR Lyrae Stars
• HE 0017+0055 : A probable pulsating CEMP-rs star and long-period binary
• Chemical analysis of two extremely metal-poor stars HE 2148-2039 and HE 2155-2043
• Observational nuclear astrophysics: neutron-capture element abundances in old, metal-poor stars
• Probing the nucleosynthetic contribution of low-metallicity, low-mass star companions of CEMP stars
• "In-System" Fission-Events: An Insight into Puzzles of Exoplanets and Stars?
• Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097
• CEMP-s and CEMP-s/r stars: last update