# Iron-Peak Element Abundances in Warm Very Metal-Poor Stars

**Authors:** Christopher Sneden, Ann Merchant Boesgaard, John J. Cowan, Ian U. Roederer, Elizabeth A. Den Hartog, James E. Lawler  
**arXiv:** [2304.06899](https://arxiv.org/abs/2304.06899)  
**Date:** 2023-04-14  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.06899v1/

## Key points

- The study derived new detailed abundances of Mg, Ca, and iron-group elements Sc through Zn for 37 very metal-poor stars with [Fe/H] ≤ -2.1.
- High signal-to-noise Keck HIRES optical and near-UV spectra were used to conduct the analysis.
- About 400 Fe-group lines were used to determine accurate LTE metallicities and abundance ratios for neutral and ionized species of the 10 Fe-group elements as well as alpha elements Mg and Ca.
- Good agreement was found between neutral/ion abundance for six elements in the stars in the 3100–5800 Angstrom range.
- Reports of correlated Sc-Ti-V relative overabundances were confirmed, which appear to slowly increase with decreasing metallicity.
- Zn was added to this element trio, which also appears to be increasingly overabundant at lower metallicity regimes.
- Co appears to mimic Zn's behavior but its abundance reliability is uncertain.
- Spectra were divided into 100 Angstrom segments and subjected to detailed continuum normalization with spline functions in SPECTRE as well as smoothing with 2-pixel Gaussian functions.
- All abundance computations were performed using MOOG – a plane-parallel LTE line analysis code developed by Sneden in 1973 – since all program stars are warm, high gravity stars whose continuum opacities are dominated by H− even at near UV wavelengths; no special computations were required to account for non-LTE effects.
- This study provides new insights into the abundance patterns of very metal-poor stars and emphasizes the importance of accurate abundance measurements in understanding stellar evolution and nucleosynthesis; data from this study are publicly available on Zenodo database.

## Summary

In this study, the authors derived new detailed abundances of magnesium (Mg), calcium (Ca), and the iron-group elements scandium (Sc) through zinc (Zn) for 37 main sequence turnoff very metal-poor stars with [Fe/H] ≤ -2.1. The analysis was conducted using high signal-to-noise Keck HIRES optical and near-UV spectra that were originally gathered for a beryllium abundance survey. About 400 Fe-group lines with accurate laboratory transition probabilities were used to determine accurate LTE metallicities and abundance ratios for neutral and ionized species of the 10 Fe-group elements as well as alpha elements Mg and Ca. The study found good agreement between neutral/ion abundance for the six elements with detectable transitions in their stars in the 3100–5800 Angstrom range. Reports of correlated Sc–Ti–V relative overabundances were confirmed, which appear to slowly increase with decreasing metallicity. Zn was added to this element trio, which also appears to be increasingly overabundant at lower metallicity regimes. Co appears to mimic Zn's behavior but its abundance reliability is uncertain. The final reduction steps were done using IRAF software including linecleaning and spectral order concatenation tasks. Spectra were divided into 100 Angstrom segments and subjected to detailed continuum normalization with spline functions in SPECTRE as well as smoothing with 2-pixel Gaussian functions. All abundance computations were performed using MOOG – a plane-parallel LTE line analysis code developed by Sneden in 1973 – since all program stars are warm, high gravity stars whose continuum opacities are dominated by H− even at near UV wavelengths; no special computations were required to account for non-LTE effects. This study provides new insights into the abundance patterns of very metal-poor stars and emphasizes the importance of accurate abundance measurements in understanding stellar evolution and nucleosynthesis; data from this study are publicly available on Zenodo database.