Quantitative prevalence of emulsion holes and bubbles on POSSI copy materials

Determine the quantitative prevalence of emulsional defects, specifically emulsion holes and bubbles, on the National Geographic Society–Palomar Observatory Sky Survey (POSSI) glass copy plates and the intermediate glass positives used during contact-printing reproduction, given that existing digitised survey catalogues from the SuperCOSMOS Sky Survey and the Digitised Sky Survey ignore sub-sky-density features and therefore cannot provide this assessment.

Background

The paper argues that apparent optical transients reported on POSSI glass copy plates are likely spurious artefacts arising from photographic emulsion defects and the plate copying process. The authors suggest that bubbles and holes in the emulsion of the intermediate glass positives used to produce copy negatives could manifest as dark spots on the copies and be misidentified as transient sources.

Because the SuperCOSMOS and DSS digitisation pipelines catalogued only dark detections above the sky background, low-density features such as emulsion holes and bubbles were not measured. This prevents a direct quantitative assessment from the available catalogues of how common such defects are across POSSI copy materials, motivating the need for methods or data that can quantify their prevalence.

References

Unfortunately we cannot make any quantitative assessment of the prevalence of holes and bubbles like those illustrated in Figure~\ref{fig:blemishes} since the automated analysis in the digitised sky survey programmes considered only dark detections in an otherwise light background as potential sources and densities below that of the sky were ignored.

— On the nature of apparent transient sources on the National Geographic Society-Palomar Observatory Sky Survey glass copy plates  (2402.00497 - Hambly et al., 2024) in Section 3, Discussion