Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

Griffith, Emily; Johnson, Jennifer A.; Weinberg, David H.; Ilyin, I.; Johnson, James W.; Martínez, Romy Rodríguez; Strassmeier, K. G.

doi:10.3847/1538-4357/aca659

Cited by 4 publications

(1 citation statement)

References 115 publications

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“…The studies mainly focus on the abundance trends of [X/Fe] versus [Fe/H] for particular chemical element X, because these trends provide observational constraints on current models of nucleosynthesis and the chemical evolution of the Galaxy (e.g., Spite & Spite 1978;McWilliam et al 1995;Cayrel et al 2004;Kobayashi et al 2006;Bensby et al 2014;Zhao et al 2016). Despite the large number of studies that have been conducted on the chemical abundances of stars, the problem of star-to-star scatter and systematic abundance shifts remains an active area of research in this field (Griffith et al 2023).…”

Section: Introductionmentioning

confidence: 99%

Sodium Abundances in Very Metal-poor Stars

Shen

Alexeeva

Zhao

et al. 2023

Res. Astron. Astrophys.

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Chemical composition of very metal-poor (VMP) stars can provide observational constraints on current models of nucleosynthesis and the chemical evolution of the Galaxy. It had been found that the scatter of [Na/Fe] versus [Fe/H] in VMP stars was very large in contrast with most of the other elements. Moreover, it was found negative slope [Na/Fe] vs. [Fe/H] for giants, which is very unlikely according to theory of nucleosynthesis. For the sample of 93 VMP stars in metallicity range -4.25 < [Fe/H] < -1.64 we obtained NLTE sodium abundances using line profile fitting method by employing accurate atmospheric parameters determined with taking into account NLTE line formation for both Fe\ione\ and Fe\ii. Originally selected from LAMOST low-resolution spectra database, the spectra of stars were obtained with the High Dispersion Spectrograph of the Subaru Telescope. For 57 turn-off stars in metallicity domain -3.04 < [Fe/H] < -1.64, we obtained mean [Na/Fe]=-0.29$\pm$0.14 and positive slope 0.09$\pm$0.06. For 21 giants distributed over metallicity -3.59 < [Fe/H] < -2.19, we obtained mean [Na/Fe]=-0.35$\pm$0.1 and positive slope 0.07$\pm$0.07. Our [Na/Fe] trend are lower by $\sim$0.2~dex, compared to modern GCE model. We believe the GCE model should be adjusted, including considering the scatter. Twelve stars in our sample are found to be outliers, with too low or too high Na abundances.

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Section: Introductionmentioning

confidence: 99%

Sodium Abundances in Very Metal-poor Stars

Shen

Alexeeva

Zhao

et al. 2023

Res. Astron. Astrophys.

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Strong outflows and inefficient star formation in the reionization-era ultrafaint dwarf galaxy Eridanus ii

Sandford,

Weinberg,

Weisz

et al. 2024

Monthly Notices of the Royal Astronomical Society

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We present novel constraints on the underlying galaxy formation physics (e.g., mass loading factor, star formation history, metal retention) at z ≳ 7 for the low-mass (M* ∼ 105 M⊙) Local Group ultra-faint dwarf galaxy (UFD) Eridanus ii (Eri ii). Using a hierarchical Bayesian framework, we apply a one-zone chemical evolution model to Eri ii’s CaHK-based photometric metallicity distribution function (MDF; [Fe/H]) and find that the evolution of Eri ii is well-characterized by a short, exponentially declining star-formation history ($\tau _\text{SFH}=0.39\pm _{0.13}^{0.18}$ Gyr), a low star-formation efficiency ($\tau _\text{SFE}=27.56\pm _{12.92}^{25.14}$ Gyr), and a large mass-loading factor ($\eta =194.53\pm _{42.67}^{33.37}$). Our results are consistent with Eri ii forming the majority of its stars before the end of reionization. The large mass-loading factor implies strong outflows in the early history of Eri ii and is in good agreement with theoretical predictions for the mass-scaling of galactic winds. It also results in the ejection of >90% of the metals produced in Eri ii. We make predictions for the distribution of [Mg/Fe]-[Fe/H] in Eri ii as well as the prevalence of ultra metal-poor stars, both of which can be tested by future chemical abundance measurements. Spectroscopic follow-up of the highest metallicity stars in Eri ii ([Fe/H] > −2) will greatly improve model constraints. Our new framework can readily be applied to all UFDs throughout the Local Group, providing new insights into the underlying physics governing the evolution of the faintest galaxies in the reionization era.

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KPM: A Flexible and Data-driven K-process Model for Nucleosynthesis

Griffith,

Hogg,

Dalcanton

et al. 2024

Self Cite

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The element abundance pattern found in Milky Way disk stars is close to two-dimensional, dominated by production from one prompt process and one delayed process. This simplicity is remarkable, since the elements are produced by a multitude of nucleosynthesis mechanisms operating in stars with a wide range of progenitor masses. We fit the abundances of 14 elements for 48,659 red-giant stars from APOGEE Data Release 17 using a flexible, data-driven K-process model—dubbed KPM. In our fiducial model, with K = 2, each abundance in each star is described as the sum of a prompt and a delayed process contribution. We find that KPM with K = 2 is able to explain the abundances well, recover the observed abundance bimodality, and detect the bimodality over a greater range in metallicity than has previously been possible. We compare to prior work by Weinberg et al., finding that KPM produces similar results, but that KPM better predicts stellar abundances, especially for the elements C+N and Mn and for stars at supersolar metallicities. The model fixes the relative contribution of the prompt and delayed processes to two elements to break degeneracies and improve interpretability; we find that some of the nucleosynthetic implications are dependent upon these detailed choices. We find that moving to four processes adds flexibility and improves the model’s ability to predict the stellar abundances, but does not qualitatively change the story. The results of KPM will help us to interpret and constrain the formation of the Galaxy disk, the relationship between abundances and ages, and the physics of nucleosynthesis.

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Untangling the Sources of Abundance Dispersion in Low-metallicity Stars

Cited by 4 publications

References 115 publications

Sodium Abundances in Very Metal-poor Stars

Sodium Abundances in Very Metal-poor Stars

Strong outflows and inefficient star formation in the reionization-era ultrafaint dwarf galaxy Eridanus ii

KPM: A Flexible and Data-driven K-process Model for Nucleosynthesis

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