Optical Design of COLIBRI: A Fast Follow-up Telescope for Transient Events

摘要

COLIBRI will be a Franco-Mexican 1.3-m telescope and imager for observing the visible and near infrared counterparts of transient events detected by the future SVOM mission. The imager is divided into two instruments: DDRAGO, with two 4k x 4k CCDs observing in gri and zy, respectively, and CAGIRE, with one 2k x 2k LYNRED or H2RG detector observing in JH. DDRAGO will directly image the telescope focal plane with a field of view (FoV) of 26 x 26 arcmin. CAGIRE will reimage the focal plane to make a pupil image available for a cold stop and adjust the plate scale to deliver a similar FoV. CAGIRE will not use a conventional collimator-camera configuration but rather an arrangement of lenses that sends the pupil image close to the focal plane after all of the reimaging optics. This allows most of the optics, including the infrared filters, to be at ambient temperature and avoids the complexity of having mechanisms and powered optics within the cryostat (CR). We present here the optical design of the system and a thorough analysis on the expected image quality of the instruments and the telescope.