Analysis of the PSF moments of the Simonyi Survey Telescope

The Simonyi Survey Telescope (SST) at the Rubin Observatory, is nearing completion. Ensuring precise image quality is essential for fulfilling the observatory’s ambitious scientific goals. To this end, the Active Optics System (AOS) will correct various factors, including gravity-induced aberrations, temperature gradients, and hysteresis. During the commissioning phase, achieving precise alignment of the telescope is critical, particularly given the wide field of view. Small errors can lead to unacceptable off-axis aberrations, especially towards the field’s edge. This paper presents an analysis tool of the impact of these aberrations on the in focus PSF moments as detected in the science field. We introduce a simplified model of the optical system under generic misalignments, designed to quickly calculate the distribution of aberrated PSF across the field. By comparing the results obtained from this model with reference data simulated using accurate ray tracing software, we can assess its accuracy and employ it to infer the state of the optical system. This work will provide an additional aid for the Rubin team during the commissioning activities.