On the need of the Light Elements Primary Process (LEPP)

Abstract

Extant chemical evolution models underestimate the Galactic production of Sr, Y and Zr as well as the Solar System abundances of s-only isotopes with 90<A<130. To solve this problem, an additional (unknown) process has been invoked, the so-called LEPP (Light Element Primary Process). In this paper we investigate possible alternative solutions. Basing on Full Network Stellar evolutionary calculations, we investigate the effects on the Solar System s-only distribution induced by the inclusion of some commonly ignored physical processes (e.g. rotation) or by the variation of the treatment of convective overshoot, mass-loss and the efficiency of nuclear processes. Our main findings are: 1) at the epoch of the formation of the Solar System, our reference model produces super-solar abundances for the whole s-only distribution, even in the range 90<A<130; 2) within errors, the s-only distribution relative to 150Sm is flat; 3) the s-process contribution of the less massive AGB stars (M<1.5 M_SUN) as well as of the more massive ones (M>4.0 M_SUN) are negligible; 4) the inclusion of rotation implies a downward shift of the whole distribution with an higher efficiency for the heavy s-only isotopes, leading to a flatter s-only distribution; 5) different prescriptions on convection or mass-loss produce nearly rigid shifts of the whole distribution. In summary, a variation of the standard paradigm of AGB nucleosynthesis would allow to reconcile models predictions with Solar System s-only abundances. Nonetheless, the LEPP cannot be definitely ruled out, because of the uncertainties still affecting stellar and Galactic chemical evolution models.

Accepted for publication on ApJ

References in corpus (33)

• Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood
• Neutron capture in low mass Asymptotic Giant Branch stars: cross sections and abundance signatures
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The s Process: Nuclear Physics, Stellar Models, Observations
• Chemical evolution with radial mixing
• Galactic Evolution of Sr, Y, Zr: A Multiplicity of Nucleosynthetic Processes
• Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program.Galactic stellar populations and planets
• Nearby Supernova Rates from the Lick Observatory Supernova Search. III. The Rate-Size Relation, and the Rates as a Function of Galaxy Hubble Type and Colour
• Spin down of the core rotation in red giants
• Evolution, nucleosynthesis and yields of low mass AGB stars
• Evolution, nucleosynthesis and yields of low mass AGB stars at different metallicities (II): the FRUITY database
• Beyond Inside-Out Growth: Formation and Evolution of Disk Outskirts
• Explosive yields of massive stars from Z=0 to Z=Zsun
• Chemo-spectrophotometric evolution of spiral galaxies: I. The model and the Milky Way
• Galactic Chemical Evolution and solar s-process abundances: dependence on the 13C-pocket structure
• s Process in low-mass Asymptotic Giant Branch Stars
• Galactic chemical evolution of heavy elements: from Barium to Europium
• Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo
• R-Process Abundances and Chronometers in Metal-Poor Stars
• Nucleosynthesis in the Early Galaxy
• The History of the Comic Supernova Rate Derived from the Evolution of the Host Galaxies
• The chemical composition of White Dwarfs as a test of convective efficiency during core He-burning
• Carbon and oxygen abundances in stellar populations
• The effects of rotation on the s-process nucleosynthesys in Asymptotic Giant Branch stars
• Lead: Asymptotic Giant Branch production and Galactic Chemical Evolution
• News on the s process from young open clusters
• Molecular opacities for low-mass metal-poor AGB stars undergoing the Third Dredge Up
• Heavy elements in Globular Clusters: the role of AGB stars
• s-Processing in AGB Stars Revisited. I. Does the Main Component Constrain the Neutron Source in the 13C-Pocket?
• The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains
• The Chemical Evolution of the Milky Way: the Three Infall Model
• A Method to Derive the Absolute Composition of the Sun, the Solar System and the Stars
• Dust mass-loss rates from AGB stars in the Fornax and Sagittarius dwarf Spheroidal galaxies

Cited by in corpus (43)

• Chemical evolution with rotating massive star yields: I. The solar neighbourhood and the s-process elements
• Evolution, nucleosynthesis and yields of AGB stars at different metallicities (III): intermediate mass models, revised low mass models and the ph-FRUITY interface
• The 12C(a,g)16O reaction and its implications for stellar helium burning
• Neutron Star Mergers Might not be the Only Source of r-Process Elements in the Milky Way
• $s$-process production in rotating massive stars at solar and low metallicities
• Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program II: Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu
• $s$-Processing in AGB Stars Revisited. II. Enhanced ${}^{13}$C Production Through MHD-Induced Mixing
• The origin of s-process isotope heterogeneity in the solar protoplanetary disk
• The Origin of Fluorine: Abundances in AGB Carbon Stars Revisited
• The s Process and Beyond
• Ages and heavy element abundances from very metal-poor stars in the Sagittarius dwarf galaxy
• Galactic Chemical Evolution: the Impact of the 13C-pocket Structure on the s-process Distribution
• Abundances of carbon-enhanced metal-poor stars as constraints on their formation
• The s process in AGB stars as constrained by a large sample of Barium stars
• Constraints of the physics of low-mass AGB stars from CH and CEMP stars
• i-Process Contribution of Rapidly Accreting White Dwarfs to the Solar Composition of First-Peak Neutron-Capture Elements
• s-Processing in AGB Stars Revisited. III. Neutron captures from MHD mixing at different metallicities and observational constraints
• The Gaia -ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc
• Abundances of disk and bulge giants from high-resolution optical spectra -- IV. Zr, La, Ce, Eu
• Presolar grain isotopic ratios as constraints to nuclear and stellar parameters of AGB nucleosynthesis
• Abundances of neutron-capture elements in thin- and thick-disc stars in the solar neighbourhood
• Magnetic-buoyancy-induced mixing in AGB Stars: fluorine nucleosynthesis at different metallicities
• On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios
• On the neutron-capture elements across the Galactic thin disk using Cepheids
• Barium stars as tracers of s-process nucleosynthesis in AGB stars I. 28 stars with independently derived AGB mass
• Observing the metal-poor solar neighbourhood: a comparison of galactic chemical evolution predictions
• Partial mixing and the formation of 13C pockets in AGB stars: effects on the s-process elements
• Mono-enriched stars and Galactic chemical evolution -- Possible biases in observations and theory
• Nuclear processes in Astrophysics: Recent progress
• First direct limit on the 334 keV resonance strength in the ${}^{22}$Ne(α,γ)${}^{26}$Mg reaction
• Extreme r-process enhanced stars at high metallicity in Fornax
• Galactic Chemical Evolution of Radioactive Isotopes with an s-process Contribution
• Enrichment of the Galactic disc with neutron capture elements: Sr
• Measurement of the ${}^{154}$Gd(n,$\gamma$) cross section and its astrophysical implications
• NGC 1261: an $r$-process enhanced globular cluster from the Gaia-Enceladus event
• Nucleosynthesis signatures of neutrino-driven winds from proto-neutron stars: a perspective from chemical evolution models
• Neutron-capture elements in dwarf galaxies III: A homogenized analysis of 13 dwarf spheroidal and ultra-faint galaxies
• A comparative study of two 47 Tuc giant stars with different s-process enrichment
• Signature of a massive rotating metal-poor star imprinted in the Phoenix stellar stream
• The NuGrid AGB Evolution and Nucleosynthesis Data Set
• Representation of s-process abundances for comparison to data from bulk meteorites
• Dependence of the Sr-to-Ba and Sr-to-Eu Ratio on the Nuclear Equation of State in Metal Poor Halo Stars
• Neutron-capture elements record the ordered chemical evolution of the disc over time