Real-time PSF estimation with GIRMOS

GIRMOS is a multi-object adaptive optics spectrograph in the near-infrared currently being designed for the Gemini North telescope. It will allow to observe with high-quality adaptive optics correction multiple targets selected from a large field. To increase the efficiency of the nightly observations, it is important to provide a feedback in real time to operators and observers on the quality of the point-spread function, using intuitive metrics such as the full width at half maximum, the Strehl ratio and the encircled energy. We present a set of simple analytical expressions derived from other works that use the measurement of the wavefront residuals. We then compare the results to an end-to-end AO simulation of GIRMOS. We show that this approach works well with the estimation of the full width at half maximum and the Strehl ratio, while it is less successful with the encircled energy.