In-flight Star Calibration and Simulation Methodology for the Metis Coronagraph on board Solar Orbiter

Stellar in-flight calibration plays a pivotal role in improving the reliability of scientific data acquired by space optical instruments. Changes in sensitivity and performance of the image quality, caused by factors such as optical component degradation or misalignment, can be discovered and tracked by employing in-flight star images and comparing them with on-ground measurements. In this work, we introduce two simulation processes useful for this purpose and apply them to the Metis coronagraph aboard the ESA/NASA Solar Orbiter spacecraft. The first simulation process is a methodology for predicting star visibility in the Field of View (FoV) of the instrument. The second one improves the former code, integrating characteristics on the source, such as star magnitude, and the instrumental features, including reflectivity/transmission of the optical elements, and detector characteristics, e.g. bias, dark current,... The ultimate aim of the simulation is to generate an estimation of the intensity, in Digital Numbers, expected for each pixel of the detector, thus offering valuable insights into the instrument’s response to varying input flux conditions. This innovative approach will provide a comprehensive tool to anticipate and understand the coronagraph’s behavior in response to different celestial scenarios (e.g. from minimum to solar maximum conditions), contributing to more effective in-flight calibrations. Indeed, Metis operates in proximity to the Sun, in a challenging environment marked by high temperatures and significant temperature variations. Although the current results are preliminary, further work is needed to refine and fully understand the simulation outcomes.