The Effect of Guide Star Variability on PLATO Pointing Stability

Abstract The main science goal of the PLAnetary Transits and Oscillations of stars (PLATO) is to detect and characterize extrasolar planets, including terrestrial planets in the habitable zone (HZ) of their host stars. Detecting rocky planets in the HZ requires high photometric stability, which depends on the spacecraft’s pointing performance. PLATO’s pointing performance is managed by the Fine Guidance System (FGS), which utilizes a catalog of guide stars to determine the spacecraft’s attitude. The FGS compares the position of these guide stars within the telescope’s CCDs to their position in the sky to determine the spacecraft’s orientation. This is critical as PLATO’s science mission requires an extremely high level of pointing accuracy. High astrophysical variability in these guide stars can cause apparent shifts in their centroids in the presence of background stellar contaminants. If this happens during science operations, the apparent movement in the guide stars’ centroids will cause the spacecraft to move in an attempt to maintain pointing direction. This movement creates systematic bias in any photometric measurements taken by the spacecraft. The goal of this project is to quantify what, if any, effect astrophysical variability in guide stars will have on PLATO’s pointing stability. By correlating the impact on performance with variability indicators (like Flicker in the Power Domain), we find that the PLATO FGS is robust against stellar variability.