Chemical Evolution of R-process Elements in Stars (CERES). III. Chemical abundances of neutron capture elements from Ba to Eu

Abstract

The chemical abundances of elements such as barium and the lanthanides are essential to understand the nucleosynthesis of heavy elements in the early Universe as well as the contribution of different neutron capture processes (for example slow versus rapid) at different epochs. The Chemical Evolution of R-process Elements in Stars (CERES) project aims to provide a homogeneous analysis of a sample of metal-poor stars ( [Fe/H]\<-1.5) to improve our understanding of the nucleosynthesis of neutron capture elements, in particular the r-process elements, in the early Galaxy. Our data consist of a sample of high resolution and high signal-to-noise ratio UVES spectra. The chemical abundances were derived through spectrum synthesis, using the same model atmospheres and stellar parameters as derived in the first paper of the CERES series. We measured chemical abundances or upper limits of seven heavy neutron capture elements (Ba, La, Ce, Pr, Nd, Sm, and Eu) for a sample of 52 metal-poor giant stars. We estimated through the mean shift clustering algorithm that at Ba/H =-2.4 and Fe/H =-2.4 a variation in the trend of X/Ba with X=La,Nd,Sm,Eu, versus Ba/H occurs. This result suggests that, for Ba/H $\<$$-2.4$, Ba nucleosynthesis in the Milky Way halo is primarily due to the $r$-process, while for Ba/H \<-2.4 the effect of the s-process contribution begins to be visible. In our sample, stars with Ba/Eu compatible with a Solar System pure r-process value (hereafter, r-pure) do not show any particular trend compared to other stars, suggesting r-pure stars may form in similar environments to stars with less pure r-process enrichments. Homogeneous investigations of high resolution and signal-to-noise ratio spectra are crucial for studying the heavy elements formation, as they provide abundances that can be used to test nucleosynthesis models as well as Galactic chemical evolution models.

Astronomy & Astrophysics - A&A, In press

References in corpus (38)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• The Gaia mission
• The GALAH Survey: Scientific Motivation
• 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?
• A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars
• Identification of strontium in the merger of two neutron stars
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• Galactic Chemical Evolution and solar s-process abundances: dependence on the 13C-pocket structure
• Neutron-capture elements in the very metal-poor star HD122563
• Production of Light Element Primary Process nuclei in neutrino-driven winds
• The s process in massive stars at low metallicity. Effect of primary N14 from fast rotating stars
• The rp-Process in Neutrino-driven Winds
• The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability
• Complete element abundances of nine stars in the r-process galaxy Reticulum II
• Nucleosynthesis in the Early Galaxy
• Silver and palladium help unveil the nature of a second r-process
• Neutron-capture elements in the very metal-poor star HD88609: another st ar with excesses of light neutron-capture elements
• Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
• The role of neutron star mergers in the chemical evolution of the Galactic halo
• Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy
• An inhomogeneous model for the Galactic halo: a possible explanation for the spread observed in s- and r-process elements
• Modelling the spectra of the kilonova AT2017gfo -- I: The photospheric epochs
• Explaining the Ba, Y, Sr, and Eu abundance scatter in metal-poor halo stars: constraints to the r-process
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• How many nucleosynthesis processes exist at low metallicity?
• The Hamburg/ESO R-process Enhanced Star survey (HERES) X. HE 2252-4225, one more r-process enhanced and actinide-boost halo star
• High-resolution abundance analysis of very metal-poor r-I stars
• The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis. II. Early chemical enrichment
• Observational constraints on the origin of the elements II. 3D non-LTE formation of Ba ii lines in the solar atmosphere
• Abundances and kinematics of carbon-enhanced metal-poor stars in the Galactic halo*; A new classification scheme based on Sr and Ba
• Evidence for $\gtrsim 4$ Gyr timescales of neutron star mergers from Galactic archaeology
• A Minimum Dilution Scenario for Supernovae and Consequences for Extremely Metal-Poor Stars
• The Hamburg/ESO R-process Enhanced Star survey (HERES) IX. Constraining pure r-process Ba/Eu abundance ratio from observations of r-II stars
• Constraints on stellar rotation from the evolution of Sr and Ba in the Galactic halo
• The low Sr/Ba ratio on some extremely metal-poor stars
• Chemical Evolution of R-process Elements in Stars (CERES). I. Stellar parameters and chemical abundances from Na to Zr
• The formation of the Milky Way halo and its dwarf satellites: a NLTE-1D abundance analysis. IV. Segue 1, Triangulum II, and Coma Berenices UFDs