IMAKA: imaging from Mauna KeA with an atmosphere corrected 1 square degree optical imager
Résumé
The goal of this project is to achieve exquisite image quality over the largest possible field of view, with a goal of a FWHM of not more than 0.3" over a square degree field in the optical domain. The narrow PSF will allow detection of fainter sources in reasonable exposure times. The characteristics of the turbulence of Mauna Kea, a very thin ground layer with excellent free seeing allows very wide fields to be corrected by GLAO and would make such an instrument unique. The Ground Layer AO module uses a deformable mirror conjugated to the telescope pupil. Coupled with a high order WFS, it corrects the turbulence common to the entire field. Over such large fields the probability of finding sufficiently numerous and bright natural guide sources is high, but a constellation of laser beacons could be considered to ensure homogeneous and uniform image quality. The free atmosphere seeing then limits the image quality (50% best conditions: 0.2" to 0.4"). This can be further improved by an OTCCD camera, which can correct local image motion on isokinetic scales from residual high altitude tip-tilt. The advantages of the OTCCD are not limited to improving the image quality: a Panstarrs1 clone covers one square degree with 0.1" sampling, in perfect accordance with the scientific requirements. The fast read time (6 seconds for 1.4 Gpixels) also leads to an improvement of the dynamic range of the images. Finally, the guiding capabilities of the OTCCD will provide the overall (local and global) tip-tilt signal.