Visible and infrared wavefront sensing for astronomical adaptive optics.

The applicability of adaptive optics to astronomical standard observing critically depends on the ability to provide with sufficient sensitivity a reference measurement of the wavefronts distorted by the atmosphere. We describe successful operation of the VLT Adaptive Optics Prototype, called COME-ON, with two reference channels: a visible one, quantum noise limited, and an infrared one. We define the adaptive optics limiting magnitudes (m λ ) for closed-loop operation of a given system with a given turbulence and demonstrate on a 3.6-m telescope the lower limits (m R ) = 13 and (m K ) = 1.6