Identification of an unexplained absorption line

Identify the physical species responsible for the prominent absorption line near 4980 Å in WD J204047.18−075614.88.

Background

WD J204047.18−075614.88 is presented as one of several white dwarfs with unusual spectra. Its prominent absorption feature near 4980 Å has no identified counterpart, leaving its chemical or instrumental origin unresolved.

References

WD\,J204047.18$-$075614.88 has a prominent line near 4980\,\AA, which we could not identify.

— The DESI Data Release 1 white dwarf catalogue  (2609.04314 - Swan et al., 3 Sep 2026) in Section 5.8.4, Unusual spectra