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

Ezzeddine, Rana; Frebel, Anna; Plez, B.

doi:10.3847/1538-4357/aa8875

Cited by 44 publications

(56 citation statements)

References 79 publications

(168 reference statements)

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“…We also investigates the [Zn/Fe] abundance ratio using the Gaia DR2 stellar parameters which yield slightly lower 1D, LTE Zn and 1D, NLTE Fe abundances of [Zn/H] = −4.70 and [Fe/H] = −5.40, respectively. This 1D, NLTE abundance of Fe was determined following the same setup used in Ezzeddine et al (2017). Compared to our other value, the [Zn/Fe] decreases only slightly, to 0.70±0.25.…”

Section: [Zn/h] and [Zn/fe] Abundances In He 1327−2326mentioning

confidence: 78%

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

Ezzeddine

Frebel

Roederer

et al. 2019

ApJ

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We present observational evidence that an aspherical supernova explosion could have occurred in the first stars in the early universe. Our results are based on the first determination of a Zn abundance in a Hubble Space Telescope/Cosmic Origins Spectrograph high-resolution UV spectrum of a hyper metalpoor (HMP) star, HE 1327−2326, with [Fe/H](NLTE) = −5.2. We determine [Zn/Fe] = 0.80 ± 0.25 from a UV Zn i line at 2138Å, detected at 3.4 σ. Yields of a 25 M aspherical supernova model with artificially modified densities exploding with E = 5 × 10 51 ergs best match the entire abundance pattern of HE 1327−2326. Such high-entropy hypernova explosions are expected to produce bipolar outflows which could facilitate the external enrichment of small neighboring galaxies. This has already been predicted by theoretical studies of the earliest star forming minihalos. Such a scenario would have significant implications for the chemical enrichment across the early universe as HMP Carbon Enhanced Metal-Poor (CEMP) stars such as HE 1327−2326 might have formed in such externally enriched environments.

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Section: [Zn/h] and [Zn/fe] Abundances In He 1327−2326mentioning

confidence: 78%

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

Ezzeddine

Frebel

Roederer

et al. 2019

ApJ

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“…Further literature data are available that provide 1D,LTE corrections of Fe I. Results from the work of Amarsi et al (2016), Collet et al (2006Collet et al ( , 2007Collet et al ( , 2018, Ezzeddine et al (2017), andFrebel et al (2008) are presented in Columns (4) -(7) of We conclude this section with two comments. First, as the reader can confirm from inspection of the middle panel (b) of Figure 2, the (3D-1D),LTE corrections are in the opposite sense to those for the 1D,(NLTE-LTE) case.…”

Section: D and Nlte Corrections For The G-band And Fe I Linesmentioning

confidence: 89%

“…Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. Collet et al (2006Collet et al ( , 2007Collet et al ( , 2018, Ezzeddine et al (2017, Gallagher et al (2016) and Spite et al (2013) (see Table 2). The panel ( -41 -…”

Section: Appendix: the 14 Most Iron-poor Starsmentioning

confidence: 98%

The Most Metal-poor Stars. V. The CEMP-no Stars in 3D and Non-LTE

Norris

Yong

2019

ApJ

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We explore the nature of carbon-rich ([C/Fe] 1D,LTE > +0.7), metal-poor ([Fe/H 1D,LTE ] < -2.0) stars in the light of post 1D,LTE literature analyses, which provide 3D-1D and NLTE-LTE corrections for iron, and 3D-1D corrections for carbon (from the CH G-band, the only indicator at lowest [Fe/H]). Highexcitation C I lines are used to constrain 3D,NLTE corrections of G-band analyses. Corrections to the 1D,LTE compilations of Yoon et al. and Yong et al. yield 3D,LTE and 3D,NLTE Fe and C abundances. The number of CEMP-no stars in the Yoon et al. compilation (plus eight others) decreases from 130 (1D,LTE) to 68 (3D,LTE) and 35 (3D,NLTE). For stars with -4.5 < [Fe/H] < -3.0 in the compilation of Yong et al., the corresponding CEMP-no fractions change from 0.30 to 0.15 and 0.12, respectively. We present a toy model of the coalescence of pre-stellar clouds of the two populations that followed chemical enrichment by the first zero-heavy-element stars: the C-rich, hyper-metal-poor and the C-normal, very-metal-poor populations. The model provides a reasonable first-order explanation of the distribution of the 1D,LTE abundances of CEMP-no stars in the A(C) and [C/Fe] vs. [Fe/H] planes, in the range -4.0 < [Fe/H] < -2.0. The Yoon et al. CEMP Group I contains a subset of 19 CEMP-no stars (14% of the group), 4/9 of which are binary, and which have large [Sr/Ba] 1D,LTE values. The data support the conjectures of Hansen et al. (2016b, 2019) and Arentsen et al. (2018) that these stars may have experienced enrichment from AGB stars and/or "spinstars". -2 -The predicted 3D corrections for molecular lines would also alleviate the extraordinarily large C abundances found in some very metal-poor stars. ... Similarly, the fraction of strongly C-enhanced ([C/Fe] > ∼ +1.0) metal-poor stars is likely substantially less than the claimed >20% for [Fe/H] < ∼ -2.0. ... -M. Asplund (2005) 1 We note for future reference that for some of the CEMP-s stars in the Yoon et al. sample the carbon abundances are based on the C 2 molecule rather than on CH.-3highlighted in the above introductory quotation, one should be alive to the possibility that some of the apparent characteristics of the CEMP-no stars might result from the 1D,LTE assumptions made in the analysis, rather than the potentially more realistic 3D and non-LTE (hereafter 3D,NLTE) ones. More generally, while 1D,LTE is currently a more precise formalism than 3D,NLTE (which is a much more challenging endeavor) it is the latter that will result in more accurate results.The aim of the present work is to use literature-based corrections determined by adopting the assumptions of 3D,NLTE to correct carbon and iron abundances based on those of 1D,LTE. The outline of the paper is as follows. In Section 2 we address semantics of carbon richness relevant to the present work. Section 3 summarizes results from the literature for 3D-1D,LTE corrections for the analysis of both the G-band and Fe I lines and 3D-1D,NLTE corrections for Fe I lines. In order to address the problem that determination of NLTE co...

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“…Other parameters: To relate [Fe/H] and [M/H] it is assumed that, at solar metallicities, α-elements are solar-scaled and the α-element abundance linearly increases towards lower metallicities, reaching a plateau of [α/Fe] = +0.4 at [Fe/H]= −1. However, at lower metallicities, variations in C and N might further affect the opacities, and a proper atmosphere model should be adopted to avoid additional uncertainties in abundances (Ezzeddine, Frebel & Plez 2017).…”

Section: Stellar Parametersmentioning

confidence: 99%

Accuracy and Precision of Industrial Stellar Abundances

Jofré

Heiter

Soubiran

2019

Annu. Rev. Astron. Astrophys.

179

158

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

Cited by 44 publications

References 79 publications

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

The Most Metal-poor Stars. V. The CEMP-no Stars in 3D and Non-LTE

Accuracy and Precision of Industrial Stellar Abundances

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

Cited by 44 publications

References 79 publications

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326∗

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326∗

The Most Metal-poor Stars. V. The CEMP-no Stars in 3D and Non-LTE

Accuracy and Precision of Industrial Stellar Abundances

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Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗

Evidence for an Aspherical Population III Supernova Explosion Inferred from the Hyper-metal-poor Star HE 1327–2326^∗