Directly Characterizing Dome Seeing: Differential Image Motion Sensor Using Multisources (DIMSUM)

Abstract: Image degradation impedes our ability to extract information from astronomical observations. One factor contributing to this degradation is dome seeing", the reduction in image quality due to variations in the index of refraction within the observatory dome. Addressing this challenge, we introduce a novel setup-DIMSUM (Differential Image Motion Sensor Using Multisources)-which offers a simple installation and provides direct characterization of local index of refraction variations. This is achieved by measuring differential image motion using strobed imaging that effectivelyfreezes" the atmosphere, aligning our captured images with the timescale of thermal fluctuations, thereby giving a more accurate representation of dome seeing effects. Our apparatus has been situated within the Auxiliary Telescope of the Vera C. Rubin Observatory. Early results from our setup are encouraging. Not only do we observe a correlation between the characteristic differential image motion (DIM) values and local temperature fluctuations (a leading cause of variations in index of refraction), but also hint at the potential of DIM measures to characterize dome seeing with greater precision in subsequent tests. Our preliminary findings underscore the potential of DIMSUM as a powerful tool for enhancing image quality in ground-based astronomical observations. Further refinement and data collection will likely solidify its place as a useful component for managing dome seeing in major observatories like the Vera C. Rubin Observatory.