Explain the missing intermediate-wavelength ERE emission

Determine why the proposed Extended Red Emission interpretation of the VY Canis Majoris shell does not produce detectable emission in the SPHEREx frame centered near 7645 Å, despite the shell being detected in the neighboring frames centered near 7451 Å and 7827 Å.

Background

The paper tentatively proposes that the shell may arise from Extended Red Emission, a photoluminescence process in which dust grains absorb higher-energy ultraviolet or visible photons and re-emit red light. The authors note that published photoluminescence yields for silicates and silica peak near 7000 Å and decline toward longer wavelengths, which could account for detections near 7451 Å and 7827 Å and weaker emission near 8014 Å.

However, the proposed interpretation encounters an unresolved observational inconsistency: the shell is not detected in the intervening SPHEREx frame near 7645 Å. The authors identify this absence as a serious difficulty for the ERE hypothesis.

References

However, it is difficult to explain why ERE is not seen in the SPHEREx frame centered at $\sim7645$~\AA\ (which is not shown here but which can be seen at the SPHEREx site), between the frames at 7451~\AA\ and 7827~\AA.

— A large shell around the hypergiant VY Canis Majoris  (2609.18895 - Banerjee et al., 16 Sep 2026) in Section 4, subsection “What it might be”