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Cause of the [Fe/H]-dependent systematic difference between DD-Payne and DESI SP metallicities

Determine the underlying cause of the [Fe/H]-dependent systematic difference between the [Fe/H] values estimated by the Data-Driven Payne analysis of DESI Early Data Release spectra and the [Fe/H] values reported by the DESI Stellar Parameters (SP) pipeline, in order to reconcile the two metallicity scales.

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Background

In Section 4.1, the authors compare their [Fe/H] measurements, obtained with the Data-Driven Payne (DD-Payne), to those from the DESI SP pipeline. While there is overall good agreement and small dispersion, they observe a significant [Fe/H]-dependent systematic trend between the two scales.

They note possible contributors such as covariance with surface gravity in low-resolution spectra and complications from combining different training sets, but they explicitly state that the detailed reason for the trend is not entirely clear, leaving the origin of the systematic difference unresolved.

References

However, there is a significant [Fe/H]-dependent systematic difference. The detailed reason for such difference is not entirely clear.

— Determining Stellar Elemental Abundances from DESI Spectra with the Data-Driven Payne (2402.06242 - Zhang et al., 9 Feb 2024) in Section 4.1 (Basic stellar atmospheric parameters), discussion of Fig. 5 (right panel)