Learning about the intermediate neutron-capture process from lead abundances

Abstract

Lead (Pb) is predominantly produced by the slow neutron-capture process (s process) in asymptotic giant branch (AGB) stars. In contrast to significantly enhanced Pb abundances predicted by low-mass, low-metallicity AGB-models, observations of Magellanic post-AGB stars show incompatibly low Pb abundances. Observations of carbon-enhanced metal-poor (CEMP) stars whose s-process enrichments are accompanied by heavy elements traditionally associated with the rapid neutron-capture process (r process) have raised the need for a neutron-capture process operating at neutron densities intermediate to the s and r process: the so-called i process. We study i-process nucleosynthesis with single-zone nuclear-network calculations. Our i-process models can explain the heavy-element abundance patterns measured in Magellanic post-AGB stars including their puzzlingly low Pb abundances. Furthermore, the heavy-element enhancements in the post-AGB and CEMP-i stars, particularly their Pb abundance, allow us to characterise the neutron densities and exposures of the i process that produced the observed abundance patterns. We find that the lower-metallicity CEMP-i stars ($\left[\mathrm{Fe}/\mathrm{H}\right]\approx -2.5$) have heavy-element abundances best matched by models with higher neutron densities and exposures ($\tau >2.0{\mathrm{mbarn}}^{-1}$) compared to the higher-metallicity post-AGB stars ($\left[\mathrm{Fe}/\mathrm{H}\right]\approx -1.3$, $\tau <1.3{\mathrm{mbarn}}^{-1}$). This offers new constraints and insights regarding the properties of i-process sites and demonstrates that the responsible process operates on time scales of the order of a few years or less.

accepted for publication in ApJ

References in corpus (28)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Magnetorotationally driven Supernovae as the origin of early galaxy $r$-process elements?
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Neutron Star Mergers and Nucleosynthesis of Heavy Elements
• Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger
• Super and massive AGB stars - IV. Final fates - Initial to final mass relation
• The intermediate neutron-capture process and carbon-enhanced metal-poor stars
• The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability
• Binarity in Carbon-Enhanced Metal-Poor stars
• The impact of companions on stellar evolution
• Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity
• 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
• s-Process Nucleosynthesis in Advanced Burning Phases of Massive 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
• i-process nucleosynthesis and mass retention efficiency in He-shell flash evolution of rapidly accreting white dwarfs
• New analysis of the two carbon-rich stars CS 22948-27 and CS 29497-34 : binarity and neutron-capture elements
• Elemental abundances and classification of CEMP stars
• Pop III $\text{i}$-process Nucleosynthesis and the Elemental Abundances of SMSS J0313-6708 and the Most Iron-Poor Stars
• A high-resolution spectral analysis of three carbon-enhanced metal-poor stars
• Lithium abundances in CEMP stars
• Carbon and Strontium Abundances of Metal-Poor Stars
• Constraints of the physics of low-mass AGB stars from CH and CEMP stars
• Are some CEMP-s stars the daughters of spinstars?
• Explosive Nucleosynthesis in Magnetohydrodynamical Jets from Collapsars II. Heavy-Element Nucleosynthesis of s, r, p-Processes
• Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study

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