Origin of the heavy elements in HD 140283

Mello, C. Siqueira; Barbuy, B.; Spite, M.; Spite, F.

doi:10.1051/0004-6361/201220100

Cited by 16 publications

(7 citation statements)

References 25 publications

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“…The average difference in the present sample is +0.23 dex. The same discrepancy was also found by Siqueira-Mello et al (2012) for HD 140283, and by Johnson (2002), who analyzed the V abundance in 23 metal-poor stars. Johnson suggested that the cause of this discrepancy might be that hyperfine splitting and NLTE effects had been neglected in the computations.…”

Section: Odd-z Elements: Al K and Scsupporting

confidence: 78%

High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars

Siqueira-Mello

Hill²,

Barbuy

et al. 2015

Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII)

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Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are at least four times as common as those that are greatly enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. Aims. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with −3.4 ≤ [Fe/H] ≤ −2.4 classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is(are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. Methods. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph, using spectra in the wavelength ranges 3400 -4500 Å, 6800 -8200 Å, and 8700 -10,000 Å, with resolving power R ∼ 40 000 (blue arm) and R ∼ 55 000 (red arm). The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. Results. We have derived abundances of the light elements Li, C, and N, the α-elements Mg, Si, S, Ca, and Ti, the odd-Z elements Al, K, and Sc, the iron-peak elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the actinides (Th) regions. The results are compared with values for these elements for r-II and "normal" very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections were presented. Although the abundance ratios of the second r-process peak elements (usually associated with the main r-process) are nearly identical for r-I and r-II stars, the first r-process peak abundance ratios (probably associated with the weak r-process) are more enhanced in r-I stars than in r-II stars, suggesting that differing nucleosynthesis pathways were followed by stars belonging to these two different classifications.

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Section: Odd-z Elements: Al K and Scsupporting

confidence: 78%

High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars

Siqueira-Mello

Hill²,

Barbuy

et al. 2015

Proceedings of XIII Nuclei in the Cosmos — PoS(NIC XIII)

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“…Using the Arlandini et al (1999) nuclear network, the s-processonly [Ba/Eu] 1 ratio is [Ba/Eu] = +1.13, while the r-process-only ratio is [Ba/Eu] = −0.69. In general, the europium and barium ratios indicate that HD 140283 has a higher fraction of r-process elements than s-process elements (Lambert & Allende Prieto 2002;Siqueira Mello et al 2012). In Gallagher et al (2010) we set a lower limit for the [Ba/Eu] ratio, [Ba/Eu] > −0.66, as limited quality in the spectrum around the europium 4129 Å line and uncertainties concerning blends around the europium 4205 Å line did not allow us to make a definitive measurement.…”

Section: Introductionmentioning

confidence: 97%

“…Peterson 2011;Roederer 2012;Siqueira Mello et al 2012). By measuring the ratio of a heavy element whose origin is primarily of the rapid (r-) neutron-capture process with another synthesised primarily through the slow (s-) process, it is possible to determine the ratio of r-to s-process in a star.…”

Section: Introductionmentioning

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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“…HD 140283 has been the subject of numerous studies, especially in more recent years where more sophisticated stellar atmosphere models have been used to determine accurate metallicities and α abundances (e.g. Charbonnel & Primas 2005) and to study neutron-capture elements to understand better heavy element nucleosynthesis (Siqueira Mello et al 2012;Gallagher et al 2010;Collet et al 2009). Concerning the fundamental properties of this star, Bond et al (2013) published a refined parallax π = 17.15 + −0.14 mas, an uncertainty one fifth of that determined by the Hipparcos satellite (van Leeuwen 2007, 17.16 ± 0.68 mas), and assuming zero reddening determined an age of 14.5 Gyr.…”

Section: Introductionmentioning

confidence: 99%

Benchmark stars forGaiaFundamental properties of the Population II star HD 140283 from interferometric, spectroscopic, and photometric data

Creevey

Thévenin

Berio

et al. 2015

A&A

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Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental properties of the stars must first be determined. HD 140283 is the closest and brightest metal-poor Population II halo star (distance = 58 pc and V = 7.21), an ideal target that allows us to approach these questions, and one of a list of 34 benchmark stars defined for Gaia astrophysical parameter calibration. In the framework of characterizing these benchmark stars, we determined the fundamental properties of HD 140283 (radius, mass, age, and effective temperature) by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer VEGA on the CHARA array and we determined a 1D limb-darkened angular diameter of θ 1D = 0.353 ± 0.013 milliarcsec. Using photometry from the literature we derived the bolometric flux in two ways: a zero reddening solution (A V = 0.0 mag) of F bol of 3.890 ± 0.066 × 10 −8 erg s −1 cm −2 , and a maximum of A V = 0.1 mag solution of 4.220 ± 0.067 × 10 −8 erg s −1 cm −2 . The interferometric T eff is thus between 5534 ± 103 K and 5647 ± 105 K and its radius is R = 2.21 ± 0.08 R . Spectroscopic measurements of HD 140283 were obtained using HARPS, NARVAL, and UVES and a 1D LTE analysis of Hα line wings yielded T eff spec = 5626 ± 75 K. Using fine-tuned stellar models including diffusion of elements we then determined the mass M and age t of HD 140283. Once the metallicity has been fixed, the age of the star depends on M, initial helium abundance Y i , and mixing-length parameter α, only two of which are independent. We derive simple equations to estimate one from the other two. We need to adjust α to much lower values than the solar one (∼2) in order to fit the observations, and if A V = 0.0 mag then 0.5 ≤ α ≤ 1. We give an equation to estimate t from M, Y i (α), and A V . Establishing a reference α = 1.00 and adopting Y i = 0.245 we derive a mass and age of HD 140283: M = 0.780 ± 0.010 M and t = 13.7 ± 0.7 Gyr (A V = 0.0 mag), or M = 0.805 ± 0.010 M and t = 12.2 ± 0.6 Gyr (A V = 0.1 mag). Our stellar models yield an initial (interior) metal-hydrogen mass fraction of [Z/X] i = −1.70 and log g = 3.65 ± 0.03. Theoretical advances allowing us to impose the mixing-length parameter would greatly improve the redundancy between M, Y i , and age, while from an observational point of view, accurate determinations of extinction along with asteroseismic observations would provide critical information allowing us to overcome the current limitations in our results.

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Origin of the heavy elements in HD 140283

Cited by 16 publications

References 25 publications

High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars

High-Resolution Abundance Analysis of Very Metal-Poor R-I Stars

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

Benchmark stars forGaiaFundamental properties of the Population II star HD 140283 from interferometric, spectroscopic, and photometric data

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