A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283

Abstract

Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron capture processes: the s- and r-process. Metal-poor stars should contain fewer isotopes that form via the s-process, according to currently accepted theory. It has been shown in several investigations that theory and observation do not agree well, raising questions on the validity of either the methodology or the theory. We analyse the metal-poor star HD140283, for which we have a high quality spectrum. We test whether a 3D LTE stellar atmosphere and spectrum synthesis code permits a more reliable analysis of the iron abundance and barium isotope ratio than a 1D LTE analysis. Using 3D model atmospheres, we examine 91 iron lines of varying strength and formation depth. This provides us with the star's rotational speed. With this, we model the barium isotope ratio by exploiting the hyperfine structure of the singly ionised 4554 resonance line, and study the impact of the uncertainties in the stellar parameters. HD140283's vsini = 1.65 +/- 0.05 km/s. Barium isotopes under the 3D paradigm show a dominant r-process signature as 77 +/- 6 +/- 17% of barium isotopes form via the r-process, where errors represent the assigned random and systematic errors, respectively. We find that 3D LTE fits reproduce iron line profiles better than those in 1D, but do not provide a unique abundance (within the uncertainties). However, we demonstrate that the isotopic ratio is robust against this shortcoming. Our barium isotope result agrees well with currently accepted theory regarding the formation of the heavy-elements during the early Galaxy. The improved fit to the asymmetric iron line profiles suggests that the current state of 3D LTE modelling provides excellent simulations of fluid flows. However, the abundances they provide are not yet self-consistent. This may improve with NLTE considerations and higher resolution models.

16 pages, 10 figures, 5 tables. Accepted for publication in A&A

References in corpus (8)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• First Stars VIII -- Enrichment of the neutron-capture elements in the early Galaxy
• HE 1327-2326, an unevolved star with [Fe/H]<-5.0. II. New 3D-1D corrected abundances from a VLT/UVES spectrum
• Line shift, line asymmetry, and the 6Li/7Li isotopic ratio determination
• 3D hydrodynamical CO5BOLD model atmospheres of red giant stars: I. Atmospheric structure of a giant located near the RGB tip
• 6Li/7Li estimates for metal-poor stars
• Origin of the heavy elements in HD 140283. Measurement of europium abundance
• 3D spectral synthesis and rotational line broadening

Cited by in corpus (10)

• The evolution of CNO isotopes: a new window on cosmic star-formation history and the stellar IMF in the age of ALMA
• The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams
• Observational constraints on the origin of the elements II. 3D non-LTE formation of Ba ii lines in the solar atmosphere
• Element abundance patterns in stars indicate fission of nuclei heavier than uranium
• An extended and refined grid of 3D STAGGER model atmospheres. Processed snapshots for stellar spectroscopy
• Chemical Evolution of R-process Elements in Stars (CERES): IV. An observational run-up of the third r-process peak with Hf, Os, Ir, and Pt
• An investigation of the formation and line properties of MgH in 3D hydrodynamical model stellar atmospheres
• The odd-isotope fractions of Barium in CEMP-r/s star HE 0338-3945 and r-II star CS 31082-001
• Unlocking the mystery of Sr synthesis in the early Galaxy through analysis of barium isotopes in very metal-poor stars
• Barium lines in high-quality spectra of two metal-poor giants in the Galactic halo