Cause of right ascension stripe depletion in SPF datasets

Ascertain the cause of the marked depletion of Selected POSS1-E Features in the right ascension interval approximately 90° to 105° across declinations in datasets derived from E. Solano et al. (2022), including whether this depletion resulted from processing steps that led from set A to sets W and R or other sampling biases.

Background

The authors identify vertical stripes of depletion in SPF number density that cross plate boundaries and span declinations, not seen in the independent MAPS dataset of likely celestial objects.

They consider and largely discount observational or storage explanations, suggesting the least unlikely cause is processing-related filtering, but explicitly note that it is not clear why this interval would be singled out, leaving the cause unresolved.

References

This leaves the least unlikely cause: (iv) SPFs within the stripes were filtered out during the processing steps that led from set A to sets W and R in E. Solano et al. (2022). It is not clear why this interval would be singled out for suppression, intentionally or by accident.

— Critical Evaluation of Studies Alleging Evidence for Technosignatures in the POSS1-E Photographic Plates  (2601.21946 - Watters et al., 29 Jan 2026) in Section 4.4