Sky coverage and PSF shape with LGS AO on 8-m telescopes

摘要

Abstract: We have analytically modeled the performances of a natural guide star and laser guide star adaptive optics system. The performance in terms of Strehl radio in J, H and K bands are presented for two atmospheric models. We use this model to derive values of sky coverage for both systems following two methods. The first one is statistical and uses a model of our Galaxy to give the stellar densities and the AO model to compute the off-axis performances. The second model uses a cross correlation of catalogues of astrophysical objects and reference stars. This gives the number of objects of a given kind that can be observed with a given Strehl. We have also modeled the PSF of a laser guide star system using the modal decomposition of the cone effect and the effect of tilt isoplanatism. It can be seen that the PSF from an LGS system differs significantly from that of a conventional AO system. !14