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Validity of Co I NLTE correction grids for warm, metal-poor turn-off stars

Ascertain whether the Co I non-LTE correction grid of Bergemann et al. (2010) is reliable for metal-poor turn-off stars with effective temperatures around 6400 K and metallicities near [Fe/H] ≈ −2.3, such as 2MASS J00512646-1053170.

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Background

The paper finds a significant discrepancy between Co I and Co II abundances, and the NLTE corrections inferred from published grids for Co I are very large.

Because the published NLTE analysis lacks an explicit paper of stars with parameters as warm and metal-poor as J0051-1053, the applicability of the grid in this regime is uncertain.

References

We note that given the high NLTE corrections obtained and the absence of an explicit analysis of a turn-off metal-poor star in the study, it is unclear whether the grid reliably extends to temperatures as high as $6400$ K and metallicity as low as $-2.28$.

— The $R$-Process Alliance: Detailed Composition of an $R$-Process Enhanced Star with UV and Optical Spectroscopy (2401.12311 - Shah et al., 22 Jan 2024) in Section 6 (Chemical Abundances), Subsection “Fe-group Elements: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Zn”