Optimized Wide-Field Survey Telescope Using Adaptive Optics

We describe a new technique for ground-based telescopic surveys that can deliver a wide field of view and nearly diffraction-limited image quality. We discuss a very low cost, yet sensitive and efficient, concept to perform science previously considered from space. For ground-based telescopes with small D/r0 (aperture over turbulence cell diameter) a significant improvement in point source sensitivity can be achieved with tip-tilt correction only. However, the solid angle over which image motion is constant is typically less than an arcminute. To achieve tip-tilt correction over a larger field we propose to use a high order adaptive optics system where one pupil sub-aperture now corresponds to one isokinetic patch. The high order deformable mirror is conjugated to an atmospheric height where the tip-tilt "beams" separate from each other while the overall tip-tilt can be taken out with a tip-tilt secondary mirror conjugated to low height. One source per square arcminute with V ≤ 18^m is required for the determination of the image motion, allowing a sky coverage of more than 50%. The improvement over seeing limited observations is maximal at D/r_0 ≈ 4 with a S/N improvement of a factor of four. An inexpensive system with 500 actuators can correct a field of view of 0.4 × 0.4 deg^2. It is thus well-suited for searches of point sources, e.g. high-z SN Ia or other transient phenomena.