Origin of wavelength-dependent iron-abundance systematics

Determine the origin of the wavelength-dependent systematic that produces lower recovered [Fe/H] values from narrow Fe lines between approximately 1150 and 1300 nm in K2-18, TOI-1201, and Barnard's Star.

Background

The authors find that Fe lines between approximately 1150 and 1300 nm yield systematically lower iron abundances than Fe lines elsewhere in the spectra of K2-18, TOI-1201, and Barnard's Star. Statistical tests indicate that the effect cannot be attributed solely to the line-weighting prescription. Possible causes include inaccurate oscillator strengths or damping constants, continuum placement, and inadequate pressure-broadening treatments, but the paper does not resolve which mechanism is responsible.

References

The origin of any wavelength dependence remains unclear, but possible contributors include inaccurate oscillator strengths or damping constants, continuum placement, and deficiencies in the treatment of pressure broadening.

— Elemental Abundances of Cool Stars: A Spectroscopic Framework Applied to Five Planet-Host Stars  (2609.24970 - Gromek et al., 21 Sep 2026) in Section 5.1, Elemental Trends