Observational constraints on the origin of the elements

A J Gallagher,M Bergemann,B Plez,S A Yakovleva,J Leenaarts,A K Belyaev,R Collet,M Carlsson

doi:10.1051/0004-6361/201936104

Abstract

Context. The pursuit of more realistic spectroscopic modelling and consistent abundances has led us to begin a new series of papers designed to improve current solar and stellar abundances of various atomic species. To achieve this, we have begun updating the three-dimensional (3D) non-local thermodynamic equilibrium (non-LTE) radiative transfer code, MULTI3D, and the equivalent one-dimensional (1D) non-LTE radiative transfer code, MULTI 2.3. Aims. We examine our improvements to these codes by redetermining the solar barium abundance. Barium was chosen for this test as it is an important diagnostic element of the s-process in the context of galactic chemical evolution. New Ba II + H collisional data for excitation and charge exchange reactions computed from first principles had recently become available and were included in the model atom. The atom also includes the effects of isotopic line shifts and hyperfine splitting. Methods. A grid of 1D LTE barium lines were constructed with MULTI 2.3 and fit to the four Ba II lines available to us in the optical region of the solar spectrum. Abundance corrections were then determined in 1D non-LTE, 3D LTE, and 3D non-LTE. A new 3D non-LTE solar barium abundance was computed from these corrections. Results. We present for the first time the full 3D non-LTE barium abundance of A(Ba) = 2.27 ± 0.02 ± 0.01, which was derived from four individual fully consistent barium lines. Errors here represent the systematic and random errors, respectively.

Highlights

Barium is a key element that is used in heavy element studies in stars
Given how important barium is to galactic chemical evolution studies because it traces the effect of neutron-capture nucleosynthesis, we present a thorough analysis of the solar barium abundance using a handful of Ba II optical lines that are computed using the two statistical equilibrium codes and the same barium model atom
We examine the effect that dynamical gas flows have on Ba II by utilising a 3D radiative hydrodynamical model to compute full 3D non-local thermodynamic equilibrium (non-LTE) radiative transfer, as well as 3D LTE, 1D LTE, and 1D non-LTE

Summary

Introduction

Barium is a key element that is used in heavy element studies in stars. Its abundance patterns in the halo, in field stars, and in clusters have been carefully measured over the past several decades. Like most other heavy elements, mostly forms through a series of neutron captures through either the rapid (r-) process or slow (s-) process channels. These two neutron capture channels have very different sites. The barium isotope ratio, fodd, of a star is a useful quantity as it provides precise information on the s- and r-process contribution, but it is exceedingly difficult to measure. This information is only measured in some 1 fodd ≡ N(135Ba) + N(137Ba) /N(Ba)

Objectives

Results

Conclusion