Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. II. Elemental Abundances

Li, Haining; Aoki, Wako; Matsuno, Tadafumi; Xing, Qianfan; Suda, Takuma; Tominaga, Nozomu; Chen, Yuqin; Honda, Satoshi; Ishigaki, Miho N.; Shi, Jianrong; Zhao, Jingkun; Zhao, Gang

doi:10.3847/1538-4357/ac6514

Cited by 40 publications

(69 citation statements)

References 207 publications

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“…1. Extending our data set to the newly available samples of metal-poor and very metal-poor stars (Li et al 2022;Lucey et al 2022;Xu et al 2022) 2. Assessing the origin of these stars through the detailed analysis of their kinematics and chemical composition.…”

Section: Discussionmentioning

confidence: 99%

Very Metal-poor Stars in the Solar Vicinity: Age Determination

Plotnikova

Carraro

Villanova

et al. 2022

ApJ

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The ages of the oldest and most metal-poor stars in the Milky Way bear important information on the age of the universe and its standard model. We analyze a sample of 28 extremely metal-poor field stars in the solar vicinity culled from the literature and carefully determine their ages. To this aim, we critically make use of Gaia data to derive their distances and associated uncertainties. Particular attention has been paid to the estimate of the reddening and its effect on the derivation of stellar ages. We employed different reddenings and superimpose isochrones from different sources on the stars' color–magnitude diagram built up with different photometric systems. We highlight subtle metallicity effects when using the Johnson photometry for low-metallicity stars and finally adopt Gaia photometry. An automatic fitting method is devised to assign ages to each individual star taking into account the uncertainties in the input parameters. The mean age of the sample turns out to be 13.9 ± 0.5 Gyr using Padova isochrones, and 13.7 ± 0.4 Gyr using BASTI isochrones. We found also a group of very metal-poor stars ([Fe/H] = −2.7 to −2.0 dex) with relatively young ages, in the range 8–10 Gyr.

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Section: Discussionmentioning

confidence: 99%

Very Metal-poor Stars in the Solar Vicinity: Age Determination

Plotnikova

Carraro

Villanova

et al. 2022

ApJ

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“…Despite the extensive searches for EMP stars in the last few decades, thus far only several hundred such stars have been confirmed by high-resolution spectroscopic analysis from which their detailed elemental abundances have been derived (e.g., Ryan et al 1996;Norris et al 2001;Aoki et al 2005Aoki et al , 2013Cayrel et al 2004;Yong et al 2013;Matsuno et al 2017;Aguado et al 2019;Yong et al 2021;Li et al 2022). This is mainly because of their rarity and the difficulty of obtaining high-quality, high-resolution spectra.…”

Section: Introductionmentioning

confidence: 99%

Search for Extremely Metal-Poor Stars with GEMINI-N/GRACES I. Chemical-Abundance Analysis

Jeong¹,

Placco²,

Kim³

et al. 2023

Preprint

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We present stellar parameters and abundances of 13 elements for 18 very metal-poor (VMP; [Fe/H] < -2.0) stars, selected as extremely metal-poor (EMP; [Fe/H] < -3.0) candidates from SDSS and LAMOST survey. High-resolution spectroscopic observations were performed using GEMINI-N/GRACES. We find ten EMP stars among our candidates, and we newly identify three carbon-enhanced metal-poor (CEMP) stars with [Ba/Fe] < 0. Although chemical abundances of our VMP/EMP stars generally follow the overall trend of other Galactic halo stars, there are a few exceptions. One Na-rich star ([Na/Fe] = +1.14) with low [Mg/Fe] suggests a possible chemical connection with second-generation stars in a globular cluster. The progenitor of an extremely Napoor star ([Na/Fe] = -1.02) with an enhancement of K-and Ni-abundance ratios may have undergone a distinct nucleosynthesis episode, associated with core-collapse supernovae (CCSNe) having a high explosion energy. We have also found a Mg-rich star ([Mg/Fe] = +0.73) with slightly enhanced Na and extremely low [Ba/Fe], indicating that its origin is not associated with neutron-capture events. On the other hand, the origin of the lowest Mg abundance ([Mg/Fe] = -0.61) star could be explained by accretion from a dwarf galaxy, or formation in a gas cloud largely polluted by SNe Ia. We have also explored the progenitor masses of our EMP stars by comparing their chemical-abundance patterns with those predicted by Population III SNe models, and find a mass range of 10 -26 M ⊙ , suggesting that such stars were primarily responsible for the chemical enrichment of the early Milky Way.

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“…At much lower metallicities, the intrinsic abundance scatter is clearly larger. In a study of very metal-poor stars (−4.3  [Fe/H]  −1.7), Li et al (2022) presented [X/Fe] versus [Fe/H] abundance trends and measured the dispersion about a linear fit. They report scatter of 0.05-0.1 dex in α and Fe-peak elements, and scatter near 0.2 dex for [Na/Fe].…”

Section: Introductionmentioning

confidence: 99%

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

Griffith

Johnson

Weinberg

et al. 2023

ApJ

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We measure abundances of 12 elements (Na, Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni) in a sample of 86 metal-poor (−2 ≲ [Fe/H] ≲ −1) subgiant stars in the solar neighborhood. Abundances are derived from high-resolution spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope, modeled using iSpec and MOOG. By carefully quantifying the impact of photon-noise (<0.05 dex for all elements), we robustly measure the intrinsic scatter of abundance ratios. At fixed [Fe/H], the rms intrinsic scatter in [X/Fe] ranges from 0.04 (Cr) to 0.16 dex (Na), with a median of 0.08 dex. Scatter in [X/Mg] is similar, and accounting for [α/Fe] only reduces the overall scatter moderately. We consider several possible origins of the intrinsic scatter with particular attention to fluctuations in the relative enrichment by core-collapse supernovae (CCSN) and Type Ia supernovae and stochastic sampling of the CCSN progenitor mass distribution. The stochastic sampling scenario provides a good quantitative explanation of our data if the effective number of CCSN contributing to the enrichment of a typical sample star is N ∼ 50. At the median metallicity of our sample, this interpretation implies that the CCSN ejecta are mixed over a gas mass ∼6 × 104 M ⊙ before forming stars. The scatter of elemental abundance ratios is a powerful diagnostic test for simulations of star formation, feedback, and gas mixing in the early phases of the Galaxy.

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Four-hundred Very Metal-poor Stars Studied with LAMOST and Subaru. II. Elemental Abundances

Cited by 40 publications

References 207 publications

Very Metal-poor Stars in the Solar Vicinity: Age Determination

Very Metal-poor Stars in the Solar Vicinity: Age Determination

Search for Extremely Metal-Poor Stars with GEMINI-N/GRACES I. Chemical-Abundance Analysis

Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

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