| Abstract
| - In this letter we evaluate the limiting magnitude for a Pyramid Sensor operating in a closed loop astronomical Adaptive Optics system. A first heuristic analysis has shown that, when a point-like reference source is used a pyramid sensor exhibits a significant gain in terms of limiting magnitude over the widely used Shack-Hartmann sensor. This when diffraction limited conditions are reached. However, in current astronomical Adaptive Optics, diffraction limited regime at the sensing wavelength is difficult to achieve. Our simulations quantify the pyramid sensor limiting magnitude considering an Adaptive Optics system working in a partial correction regime. The simulations show that the considered gain is retained even in partial correction. An average gain of two magnitude is found in the considered case. This feature of a pyramid sensor can be very important in reducing the fundamental limit of today's Astronomical Adaptive Optics systems using natural reference sources, i.e. the limited sky-coverage.
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