Isotope shifts and hyperfine structure of<sup>134-138</sup>Ba II by fast ion beam-laser spectroscopy

Villemoes, P.; Arnesen, A.; Heijkenskjöld, Filip; Wännström, A.

doi:10.1088/0953-4075/26/22/030

Cited by 52 publications

(40 citation statements)

References 26 publications

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“…We adopt the accurate g fvalues available from Davidson et al (1992) and Kurz et al (2008 138 Ba = 0.1:0.1:2.4:6.6:7.9:11.2:71.7 (Rosman & Taylor 1998), with only the odd-A nuclei possessing nuclear spin (I = 3 2 in both cases). We obtained isotopic separations for the 455.4 nm line from Wendt et al (1984), from van Hove et al (1982) for the 585.4 nm line, and from Villemoes et al (1993) for the 649.7 nm line. We also drew on the latter for HFS data, along with the papers of Trapp et al (2000) and van Hove et al (1985).…”

Section: Bariummentioning

confidence: 99%

The elemental composition of the Sun

Grevesse

Scott

Asplund

et al. 2014

A&A

213

252

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We re-evaluate the abundances of the elements in the Sun from copper (Z = 29) to thorium (Z = 90). Our results are mostly based on neutral and singly-ionised lines in the solar spectrum. We use the latest 3D hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in 1D. In order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. Our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. This analysis constitutes both a full exposition and a slight update of the relevant parts of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data that we have employed.

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Section: Bariummentioning

confidence: 99%

The elemental composition of the Sun

Grevesse

Scott

Asplund

et al. 2014

A&A

213

252

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“…Barium lines are synthesised using hfs information from Wendt et al (1984) and Villemoes et al (1993). For detailed information on the line list, we refer the reader to Paper I.…”

Section: Synthesising the Barium Linementioning

confidence: 99%

A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD 140283

Gallagher

Ludwig

Ryan

et al. 2015

A&A

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Context. Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron capture processes: the slow (s-) and the rapid (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. Aims. We analyse the metal-poor star HD 140283, for which we have a high quality spectrum. We test whether a three-dimensional (3D) local thermodynamic equilibrium (LTE) stellar atmosphere and spectrum synthesis code permits a more reliable analysis of the iron abundance and barium isotope ratio than a one-dimensional (1D) LTE analysis. Methods. Using 3D hydrodynamical 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 Å resonance line, and study the impact of the uncertainties in the stellar parameters. Results. The star's rotational speed was found to be 1.65 ± 0.05 km s −1 . Barium isotopes under the 3D paradigm show a dominant r-process signature as 77 ± 6 ± 17% ( f odd = 0.38 ± 0.02 ± 0.06) 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. Conclusions. 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 non-LTE considerations and higher resolution models.

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“…Line lists with all hfs components of the Ba line at 4554 Å, which is used to determine f odd , were constructed using isotopic information from Arlandini et al (1999) and hfs information from Wendt et al (1984) and Villemoes et al (1993) for pure s-and pure r-process mixtures (corresponding to f odd = 0.11 and 0.46 respectively). Hybrid line lists for −0.24 ≤ f odd ≤ 0.46 were created from these by adjusting the line strengths of the Ba isotopes.…”

Section: Barium Line Listsmentioning

confidence: 99%

The barium isotopic fractions in five metal-poor stars

Gallagher

Ryan

Hosford

et al. 2012

A&A

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Context. Theory and observations of heavy element nucleosynthesis are in conflict with one-another. Theory states that in the most metal-poor stars, the rapid (r-) neutron-capture nucleosynthetic process would be dominant over the slow (s-) process. The most recent determinations of r-and s-process yields do not support this. Aims. We provide measurements of the Ba isotopic fractions for five metal-poor stars derived with a local thermodynamic equilibrium (LTE) analysis with 1D model stellar atmospheres. This increases the comparisons with heavy element nucleosynthesis theory. Methods. We use high resolution (R ≡ λ/Δλ = 90 000−95 000), very high signal-to-noise (S /N > 500) spectra to determine the fraction of odd Ba isotopes ( f odd ) by measuring subtle asymmetries in the profile of the Ba ii line at 4554 Å. We also use two different macroturbulent broadening techniques, Gaussian and radial-tangential, to model the Fe lines of each star, and propagate each technique to model macroturbulent broadening in the Ba 4554 Å line. We conduct a 1D non-LTE (NLTE) treatment of the Fe lines in the red giant HD 122563 and the subgiant HD 140283 in an attempt to improve the fitting. We determine [Ba/Eu] ratios for the two giants in our study, HD 122563 and HD 88609, which can also be used to determine the relative contribution of the s-and r-processes to heavy-element nucleosynthesis, for comparison with f odd . Results. We find mathematical solutions of f odd for HD 122563, HD 88609 and HD 84937 of −0.12 ± 0.07, −0.02 ± 0.09, and −0.05 ± 0.11 respectively. BD+26 • 3578 yielded a value for f odd = 0.08 ± 0.08. Only BD−04 • 3208 was found to have a physical f odd ratio of 0.18 ± 0.08. This means that all stars examined here show isotopic fractions more compatible with an s-process dominated composition. The [Ba/Eu] ratios in HD 122563 and HD 88609 are found to be −0.20 ± 0.15 and −0.47 ± 0.15 respectively, which indicate instead an r-process signature. We report a better statistical fit to the majority of Fe profiles in each star when employing a radial-tangential broadening technique during our 1D LTE investigation. Conclusions. With the increase of the number of stars for which the Ba isotope fraction f odd has been measured, and the nature of their results, there is now a stronger argument to suggest that other synthesis codes that employ alternative approaches to radiative transfer (e.g. 3D hydrodynamics) have to be considered to tackle the high level of precision required for the determination of isotopic ratios. We have shown that, from a statistical point of view, one must consider using a radial-tangential broadening technique rather than a Gaussian one to model Fe line macroturbulences when working in 1D. No improvement to Fe line fitting is seen when employing a NLTE treatment of the Fe lines.

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Isotope shifts and hyperfine structure of^134-138Ba II by fast ion beam-laser spectroscopy

Cited by 52 publications

References 26 publications

The elemental composition of the Sun

The elemental composition of the Sun

A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD 140283

The barium isotopic fractions in five metal-poor stars

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Isotope shifts and hyperfine structure of134-138Ba II by fast ion beam-laser spectroscopy

Cited by 52 publications

References 26 publications

The elemental composition of the Sun

The elemental composition of the Sun

A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD 140283

The barium isotopic fractions in five metal-poor stars

Contact Info

Product

Resources

About

Isotope shifts and hyperfine structure of^134-138Ba II by fast ion beam-laser spectroscopy