FWHM characteristics of plate artifacts versus stars on POSS1 plates

Determine whether specific categories of photographic plate artifacts on Palomar Observatory Sky Survey first-epoch (POSS1) plates exhibit smaller full width at half maximum (FWHM) than stars on average, to clarify the diagnostic value of FWHM in artifact rejection.

Background

The distinction between true optical flashes and artifacts has been partly based on morphological and intensity profile metrics such as FWHM.

The authors point out that it remains unresolved whether certain categories of plate artifacts systematically yield smaller FWHM than stars, which would confound the use of FWHM as a discriminant.

References

The following questions remain unanswered after N. Hambly & A. Blair (2024): (i) whether optical flashes exhibit smaller FWHM on POSS1 plates; (ii) whether any of the 8,000 features selected on plate E0070 by N. Hambly & A. Blair (2024) represent an optical flash; and (iii) whether some categories of plate artifacts exhibit a smaller FWHM when compared to stars, on average.

— Critical Evaluation of Studies Alleging Evidence for Technosignatures in the POSS1-E Photographic Plates  (2601.21946 - Watters et al., 29 Jan 2026) in Section 2