SN 2021jka , the SIMBAD biblio

We report on spurious quasi-periodic variability detected in high-cadence Zwicky Transient Facility (ZTF) Data Release 23 light curves from Field 840, observed on the night of 2024 January 9. The apparent flux variations correlate strongly with the seeing full width at half maximum. This effect can occur even in galaxies that appear point-like at ZTF resolution, making them difficult to distinguish from true astrophysical variability. This highlights the importance of careful inspection of image metadata when interpreting short-term variability in time-domain surveys.