Stellar Detection Counts Are Invariant Across Geomagnetic Storm Intensity in POSS-I Plates: Ruling Out the Plate Sensitivity Artifact and Confirming Source-Specific Transient Suppression

Abstract: The VASCO project has identified over 100,000 optical transients on photographic plates from the First Palomar Observatory Sky Survey (POSS-I, 1949-1957). Cann (2026a) demonstrated a dose-dependent suppression of transient detection rates across five geomagnetic storm intensity (Kp) bins (Cochran-Armitage: Z = -3.391, p = 0.0007, 3.4 sigma). A principal objection to this finding is that geomagnetic storms enhance atmospheric airglow, reducing overall plate sensitivity and thus suppressing detection of all sources, not just transients. We test this artifact hypothesis directly using the Minnesota Automated Plate Scanner (MAPS) Catalog of the POSS-I archive, which records stellar detection counts (NSTARS) for each of 638 fields with precise observation dates. Cross-referencing NSTARS against the GFZ Potsdam Kp archive reveals no significant trend across five Kp intensity bins (Spearman rho = 0.017, p = 0.673, 0.4 sigma), in sharp contrast to the transient suppression established in Cann (2026a). Geomagnetic storms suppress transient detections dose-dependently while leaving stellar detection counts unchanged. The plate sensitivity artifact hypothesis is ruled out. Combined with four independent lines of evidence, the overall significance of the transient phenomenon reaches 4.9-5.5 sigma (Fisher's method).