The intermediate neutron-capture process and carbon-enhanced metal-poor stars

Abstract

Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP-s/r stars, which show both Ba and Eu enrichment, are particularly puzzling since the s and the r processes require neutron densities that are more than ten orders of magnitude apart, and hence are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patterns of CEMP-s/r stars can arise from the nucleosynthesis of the intermediate neutron-capture process (the i process), which is characterised by neutron densities between those of the s and the r processes. Using nuclear network calculations, we study neutron capture nucleosynthesis at different constant neutron densities n ranging from $10^7$ to $10^{15}$ cm${}^{-3}$. With respect to the classical s process resulting from neutron densities on the lowest side of this range, neutron densities on the highest side result in abundance patterns that show an increased production of heavy s-process and r-process elements but similar abundances of the light s-process elements. Such high values of n may occur in the thermal pulses of asymptotic giant branch (AGB) stars due to proton ingestion episodes. Comparison to the surface abundances of 20 CEMP-s/r stars show that our modelled i-process abundances successfully reproduce observed abundance patterns that could not be previously explained by s-process nucleosynthesis. Because the i-process models fit the abundances of CEMP-s/r stars so well, we propose that this class should be renamed as CEMP-i.

16 pages, 28 figures. Accepted for publication in ApJ

References in corpus (19)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances
• Super and massive AGB stars - IV. Final fates - Initial to final mass relation
• The Frequency of Carbon-Enhanced Metal-Poor Stars in the Galaxy from the HERES sample
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• Binarity in Carbon-Enhanced Metal-Poor stars
• The Hamburg/ESO R-process Enhanced Star survey (HERES) III. HE 0338-3945 and the formation of the r+s stars
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample
• Carbon Stars in the Hamburg/ESO Survey: Abundances
• New analysis of the two carbon-rich stars CS 22948-27 and CS 29497-34 : binarity and neutron-capture elements
• Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages
• Elemental abundances and classification of CEMP stars
• New insights on Ba over-abundance in open clusters. Evidence for the intermediate neutron-capture process at play?
• A high-resolution spectral analysis of three carbon-enhanced metal-poor stars
• Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. I. Detailed analysis of 15 binary stars with known orbital periods
• Carbon and Strontium Abundances of Metal-Poor Stars
• Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study

Cited by in corpus (61)

• Chemical evolution with rotating massive star yields II. A new assessment of the solar s- and r- process components
• The $R$-Process Alliance: Fourth Data Release from the Search for $r$-Process-Enhanced Stars in the Galactic Halo
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• Pop III $\text{i}$-process Nucleosynthesis and the Elemental Abundances of SMSS J0313-6708 and the Most Iron-Poor Stars
• Novel Techniques for Constraining Neutron-Capture Rates Relevant for r-Process Heavy-Element Nucleosynthesis
• The activation method for cross section measurements in nuclear astrophysics
• Learning about the intermediate neutron-capture process from lead abundances
• Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
• Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars
• Binary Stars in the New Millennium
• Constraints of the physics of low-mass AGB stars from CH and CEMP stars
• The R-Process Alliance: Chemo-Dynamically Tagged Groups of Halo $r$-Process-Enhanced Stars Reveal a Shared Chemical-Evolution History
• Are some CEMP-s stars the daughters of spinstars?
• Evidence for $\gtrsim 4$ Gyr timescales of neutron star mergers from Galactic archaeology
• The intermediate neutron capture process. III. The i-process in AGB stars of different masses and metallicities without overshoot
• Chemical Cartography. I. A Carbonicity Map of the Galactic Halo
• High-resolution spectroscopy of extremely metal-poor stars from SDSS/SEGUE. III. Unevolved Stars with $[Fe/H]\lesssim -3.5$
• Deep underground laboratory measurement of ${}^{13}$C($\alpha$,$n$)${}^{16}$O in the Gamow windows of the $s$- and $i$-processes
• Origin of the CEMP-no Group Morphology in the Milky Way
• The R-Process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510
• Origin of large meteoritic SiC stardust grains in metal-rich AGB stars
• J0815+4729: A chemically primitive dwarf star in the Galactic Halo observed with Gran Telescopio Canarias
• Observing the metal-poor solar neighbourhood: a comparison of galactic chemical evolution predictions
• Chemical analysis of CH stars - III: Atmospheric parameters and elemental abundances
• The R-Process Alliance: J1521-3538, a very metal-poor, extremely r-process-enhanced star with [Eu/Fe]=+2.2, and the class of r-III stars
• Heavy elements in barium stars
• Chemical Cartography. II. The Assembly History of the Galactic Stellar Halo Traced by Carbon-Enhanced Metal-Poor Stars
• Chemical Evolution of R-process Elements in Stars (CERES). I. Stellar parameters and chemical abundances from Na to Zr
• Neutron-capture elements in dwarf galaxies II: Challenges for the s- and i-processes at low metallicity
• Unusual neutron-capture nucleosynthesis in a carbon-rich Galactic bulge star
• X-shooter spectroscopy of young stellar objects in Lupus: Lithium, iron, and barium elemental abundances
• The R-Process Alliance: Fifth Data Release from the Search for R-Process-Enhanced Metal-poor Stars in the Galactic Halo with the GTC
• The stellar beta-decay rate of 134Cs and its impact on the Barium nucleosynthesis in the s process
• First determination of s-process element abundances in pre-main sequence clusters: Y, Zr, La, and Ce in IC 2391, the Argus association and IC 2602
• Enrichment of the Galactic disc with neutron capture elements: Sr
• Chemical Evolution of Fluorine in the Milky Way
• Identification of Absorption Lines of Heavy Metals in the Wavelength Range 0.97--1.32 Micron
• A chemical signature from fast-rotating low-metallicity massive stars: ROA 276 in omega Centauri
• The Pristine Inner Galaxy Survey (PIGS) VII: a discovery of the first inner Galaxy CEMP-r/s star
• A strong neutron burst in jet-like supernovae of spinstars
• Search for Extremely Metal-Poor Stars with GEMINI-N/GRACES I. Chemical-Abundance Analysis
• HCT/HESP study of two carbon stars from the LAMOST survey
• Spectroscopic study of four metal-poor carbon stars from the Hamburg/ESO Survey: On confirming the low-mass nature of their companions
• Constraining Nucleosynthesis in Two CEMP Progenitors Using Fluorine
• Li distribution, kinematics and detailed abundance analysis among very metal-poor stars in the Galactic halo from the HESP-GOMPA survey
• Cross Section Measurement of the ${}^{82}$Kr(p,$\gamma$)${}^{83}$Rb Reaction in Inverse Kinematics
• Carbon-enhanced metal-poor stars in the SDSS-APOGEE database
• Indirect measurement of the $(n,\gamma {)}^{127}$Sb cross section
• A wide angle view of the Sagittarius dwarf spheroidal galaxy -- II. A CEMP-r/s star in the Sagittarius dwarf Spheroidal Galaxy
• Abundance Analysis of New $r$-Process-Enhanced Stars from the HESP-GOMPA Survey
• High-resolution spectroscopic analysis of four new chemically peculiar stars
• Optical and NIR spectroscopy of cool CEMP stars to probe the nucleosynthesis in low mass AGB binary system
• s-process Enriched Post-AGB Star J003643.94-723722.1 in the SMC with an Extreme C/O Ratio and the First Precise Detection of Lead
• i-process nucleosynthesis: observational evidences from CEMP stars
• Fluorine abundances in CEMP stars at the lowest metallicity: Hints on the nature of the first stars
• Chemical analysis of a carbon-enhanced very metal-poor star: CD-27 14351
• An empirical metallicity tracer in CEMP and C-normal stars
• Status and future directions for direct cross-section measurements of the 13C(a,n)16O reaction for astrophysics
• Heavy Elements -- They came out of the blue
• Abundances of neutron-capture elements in CH and Carbon-Enhanced Metal-Poor (CEMP) stars
• UVES analysis of red giants in the bulge globular cluster NGC 6522