Orateur
Description
Accurate modeling of precipitable water vapor (PWV) variations is essential to meet Rubin Observatory’s photometric precision requirements, particularly in the Y band. Simulations with getObsAtmo and rubin_sim show that achieving photometric errors below 1, 5, and 10 mmag corresponds respectively to statistical PWV uncertainties of ΔPWVₛₜₐₜ < 0.03, 0.1, and 0.5 mm.
PWV measurements combining the empty and OG550 filters currently reach a repeatability of σ(PWV) ≈ 0.1 mm, consistent with the 5 mmag precision goal. However, systematic effects — including diffraction order contamination, biased throughput , and bad PSF model — still dominate, keeping repeatability about an order of magnitude above the statistical limit. Restricting the analysis to the OG550 filter mitigates first- and second-order mixing, revealing statistical errors as low as 0.01 mm.
Residual differences between targets are weakly correlated with magnitude or color and may partly reflect real atmospheric fluctuations. Observations separated by more than one hour show random PWV variations of 0.1–0.2 mm, consistent with genuine temporal and spatial gradients in atmospheric transmission.
From steady-phase observations, a per-measurement precision of σ(PWV) = 0.07 mm is achieved. Considering the current level of systematics and the demonstrated statistical performance, a precision of 0.01 mm in PWV — equivalent to 1 mmag accuracy in the Y band — appears attainable after forthcoming instrumental improvements.
