Unidentified spectral feature near 6709 Å in giants

Identify the atomic or molecular species responsible for the prominent spectral feature near 6709 Å observed mainly in giant stars in the GALAH DR3 Li 6708 Å region, which the authors currently model as two unidentified Gaussian components.

Background

To model the Li 6708 Å region, the authors compiled a detailed line list and fitted both the Li I line (with 3D NLTE profiles) and nearby blending lines (with Gaussians). While most blends were assigned to known species (e.g., Fe I, CN, V/Ce), the authors report a prominent feature around 6709 Å in giant stars that could not be confidently identified. They therefore represented it empirically with two Gaussian lines labeled “?1” and “?2.”

This unidentified feature affects the Li region in giants and can influence abundance inferences, motivating a concrete identification of the responsible species for improved modeling and more accurate lithium abundance measurements.