Germanium, Arsenic, and Selenium Abundances in Metal-Poor Stars*

Roederer, Ian U.

doi:10.1088/0004-637x/756/1/36

Cited by 43 publications

(55 citation statements)

References 93 publications

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“…These are a common feature in the nine metal-poor stars analyzed by Roederer (2012) and Roederer et al (2012bRoederer et al ( , 2014c. The [As/Ge] ratios range from +0.65 to +1.00 in five stars with −2.5<[Fe/H] <−0.5.…”

Section: The I-process In Other Stars In the Early Galaxymentioning

confidence: 92%

“…We adopt the model atmosphere parameters for HD 94028 derived by Roederer (2012), with effective temperature T eff =5720±71K, surface gravity logg=4.31± 0.16, microturbulence velocity v t =0.90±0.30kms -1 , and metallicity [M/H]=−1.62±0.09. The uncertainties are estimated following Section8.5 of Roederer et al (2014b).…”

Section: Model Atmospheresmentioning

confidence: 99%

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THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

Roederer

Karakas

Pignatari

et al. 2016

ApJ

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105

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We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metalpoor ( We analyze an archival near-ultraviolet spectrum of HD94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64species of 56elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s-and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99 ± 0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutroncapture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the iprocess appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the iprocess may have been common in the early Galaxy.

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Section: The I-process In Other Stars In the Early Galaxymentioning

confidence: 92%

Section: Model Atmospheresmentioning

confidence: 99%

THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

Roederer

Karakas

Pignatari

et al. 2016

ApJ

Self Cite

105

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“…Measuring the abundance of germanium is of particular interest because its nucleosynthesis resides at the transition between explosive synthesis of iron-peak elements and neutron-capture synthesis of heavier elements. In metal-poor stars, the abundance of germanium seems to follow well that of iron (Cowan et al 2005), favouring an explosive origin of this element at low metallicity, while the increase of [Ge/Fe] with metallicity (Roederer 2012) indicates the onset of s-process production of germanium at high metallicity. Here, the observed ratio is super-solar ([Ge/Fe] ∼ 0.46), similar to what is seen in other DLAs (Dessauges-Zavadsky et al 2006).…”

Section: Heavy Elementsmentioning

confidence: 96%

VLT/UVES observations of extremely strong intervening damped Lyman-αsystems

Noterdaeme

Srianand

Rahmani

et al. 2015

A&A

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We present a detailed analysis of three extremely strong, intervening damped Lyman-α systems (ESDLAs, with log N(H i) ≥ 21.7) observed towards quasars with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. We measure overall metallicities of [Zn/H] ∼ −1.2, −1.3, and −0.7 at, respectively, z abs = 2.34 towards SDSS J214043.02−032139.2 (log N(H i) = 22.4 ± 0.1), z abs = 3.35 towards SDSS J145646.48+160939.3 (log N(H i) = 21.7 ± 0.1), and z abs = 2.25 towards SDSS J015445.22+193515.8 (log N(H i) = 21.75 ± 0.15). Iron depletion of about a factor 15 compared to volatile elements is seen in the DLA towards J2140−0321, while the other two show deletion that is typical of known DLAs. We detect H 2 towards J2140−0321 (log N(H 2 ) = 20.13 ± 0.07) and J1456+1609 (log N(H 2 ) = 17.10 ± 0.09) and argue for a tentative detection towards J0154+1935. Absorption from the excited fine-structure levels of O i, C i, and Si ii are detected in the system towards J2140−0321, which has the largest H i column density detected so far in an intervening DLA. This is the first detection of O i fine-structure lines in a QSO-DLA, which also provides us with a rare possibility to study the chemical abundances of less abundant atoms like Co and Ge. Simple single-phase photo-ionisation models fail to reproduce all the observed quantities. Instead, we suggest that the cloud has a stratified structure: H 2 and C i most likely stem from a dense (log n H ∼ 2.5−3) and cold (80 K) phase and from a warm (250 K) phase. They contain a fraction of the total H i, while a warmer (T > 1000 K) phase probably contributes significantly to the high excitation of O i fine-structure levels. The observed C i/H 2 column density ratio is surprisingly low compared to model predictions, and we do not detect CO molecules: this suggests a possible underabundance of C by 0.7 dex compared to other alpha elements. The absorber could be a photo-dissociation region close to a bright star (or a star cluster) where higher temperature occurs in the illuminated region. Direct detection of on-going star formation through e.g. near-infrared emission lines in the surroundings of the gas would enable a detailed physical modelling of the system.

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“…plethora of publications (e.g. Magain & Zhao 1993;Bonifacio & Molaro 1998;Thorén & Edvardsson 2000;Asplund et al 2003;Shchukina et al 2005b;Roederer 2012;Lind et al 2012). It is one of the most well-studied metal-poor stars.…”

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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Germanium, Arsenic, and Selenium Abundances in Metal-Poor Stars*

Cited by 43 publications

References 93 publications

THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS*

VLT/UVES observations of extremely strong intervening damped Lyman-αsystems

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

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