Non‐LTE iron abundances in cool stars: The role of hydrogen collisions

Ezzeddine, Rana; Merle, Thibault; Plez, B.

doi:10.1002/asna.201612384

Cited by 11 publications

(14 citation statements)

References 39 publications

(45 reference statements)

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“…The temperature and microturbulent velocity of J0937−0626 were determined by removing trends in the NLTE Fe I abundances with wavelength, reduced EW, and excitation potential (see Figure 1); the surface gravity was found by forcing agreement between NLTE Fe I and Fe II abundances. The final adopted parameters are listed in Table 1, along with the LTE parameters and the parameters derived with the 1D NLTE corrections of Ezzeddine et al (2017, also see Ezzeddine et al 2016 andSakari et al 2018b Schuster et al (2004) and Beers et al (2007) obtained photometry of J0937−0626, finding colors that are consistent with the spectroscopic parameters derived here. Schuster et al (2004) classified J0937−0626 as a "red-horizontal-branch-asymptotic-giant-branch transition" star, while Beers et al (2007) found that it was displaced from the metal-poor main sequence, potentially as a result of its lower surface gravity.…”

Section: Introductionsupporting

confidence: 76%

The R-Process Alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo

Sakari

Roederer

Placco

et al. 2019

ApJ

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Corresponding author: Charli M. Sakari sakaricm@u.washington.edu 2 Sakari et al.A new moderately r-process-enhanced metal-poor star, RAVE J093730.5−062655, has been identified in the Milky Way halo as part of an ongoing survey by the R-Process Alliance. The temperature and surface gravity indicate that J0937−0626 is likely a horizontal branch star. At [Fe/H] = −1.86, J0937−0626 is found to have subsolar [X/Fe] ratios for nearly every light, α, and Fe-peak element. The low [α/Fe] ratios can be explained by an ∼ 0.6 dex excess of Fe; J0937−0626 is therefore similar to the subclass of "iron-enhanced" metal-poor stars. A comparison with Milky Way field stars at [Fe/H] = −2.5 suggests that J0937−0626 was enriched in material from an event, possibly a Type Ia supernova, that created a significant amount of Cr, Mn, Fe, and Ni and smaller amounts of Ca, Sc, Ti, and Zn. The r-process enhancement of J0937−0626 is likely due to a separate event, which suggests that its birth environment was highly enriched in r-process elements. The kinematics of J0937−0626, based on Gaia DR2 data, indicate a retrograde orbit in the Milky Way halo; J0937−0626 was therefore likely accreted from a dwarf galaxy that had significant r-process enrichment.

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Section: Introductionsupporting

confidence: 76%

The R-Process Alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo

Sakari

Roederer

Placco

et al. 2019

ApJ

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“…However, unlike what is expected for an intrinsic atomic property, different S H were obtained by different studies which were found to be star and model atom dependent (e.g. Thévenin & Idiart 1999;Korn et al 2003;Mashonkina et al 2016;Bergemann et al 2012;Ezzeddine et al 2016a).…”

Section: Introductionmentioning

confidence: 79%

Ultra-metal-poor Stars: Spectroscopic Determination of Stellar Atmospheric Parameters Using Iron Non-LTE Line Abundances

Ezzeddine

Frebel

Plez

2017

ApJ

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We present new ultra-metal-poor (UMP) stars parameters with [Fe/H] < −4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameter and show that they can grow up to ∼ 1.00 dex in [Fe/H], ∼ 150 K in T eff and ∼ 0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely secondgeneration stars to investigate the early universe and how the chemical elements were formed.

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“…We thus also determine NLTE stellar parameters using a complete iron model atom introduced in Ezzeddine et al (2016). For inelastic hydrogen collisions, we use quantum-based rates inspired by fitting quantum rates of Na, Mg, Al, and Si and applying them to Fe (R. Ezzeddine et al 2016, in preparation).…”

Section: Observations and Abundance Analysismentioning

confidence: 99%

Chemical Diversity in the Ultra-Faint Dwarf Galaxy Tucana Ii*

Frebel

Ezzeddine

et al. 2016

ApJL

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We present the first detailed chemical abundance study of the ultra-faint dwarf galaxy TucanaII, based on highresolution Magellan/MIKE spectra of four red giant stars. =−3 is carbon-normal, and exhibits distinct light element abundance ratios from the carbon-enhanced stars. This carbonnormal star implies that at least two distinct nucleosynthesis sources, both possibly associated with PopulationIII stars, contributed to the early chemical enrichment of this galaxy. Despite its very low luminosity, TucanaII shows a diversity of chemical signatures that preclude it from being a simple "one-shot" first galaxy yet still provide a window into star and galaxy formation in the early universe.

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Non‐LTE iron abundances in cool stars: The role of hydrogen collisions

Cited by 11 publications

References 39 publications

The R-Process Alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo

The R-Process Alliance: Discovery of a Low-α, r-process-enhanced Metal-poor Star in the Galactic Halo

Ultra-metal-poor Stars: Spectroscopic Determination of Stellar Atmospheric Parameters Using Iron Non-LTE Line Abundances

Chemical Diversity in the Ultra-Faint Dwarf Galaxy Tucana Ii*

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