PLATO: PSF modelling using a microscanning technique

Abstract. The PLATO space mission is designed to detect telluric planets in the hab-itable zone of solar type stars, and simultaneously characterise the host star using ultra high precision photometry. The photometry will be performed on board using weighted masks. However, to reach the required precision, corrections will have to be performed by the ground segment and will rely on precise knowledge of the instrument PSF (Point Spread Function). We here propose to model the PSF using a microscanning method. 1 The Microscanning Method 1.1 Super-resolved problem PLATO will be equipped with 34 12cm aperture telescopes, each one of which composed of 4 CCDs of 4510×4510 pixels (15 arcsec), to cover about 50 % of the sky. The telescopes were designed to be almost focused, except for a slight misalignment of the CCD plane with respect of the focal plane. Therefore, 90 % of the light flux from a star would be collected in a 2×2 pixels square surface. This resolution is insufficient when very precise measurements are desired, which require fine corrections of the jitter (1/3000 CCD pixels) for instance. In this case, the PSF must be modeled with subpixel accuracy. Building a super-resolved PSF from pixel-resolved ones is possible, in practice, through th