Natural Guide Star Acquisition for LINC-NIRVANA’s MCAO systems

This paper describes the positioning routine for the pickup optics of LINC-NIRVANA’s wavefront sensors which is executed during the acquisition of multiple natural guide stars. The near-infrared interferometric imaging camera for the LBT, LINC-NIRVANA, incorporates layer oriented multi-conjugate adaptive optics sys- tems. They can use up to 20 natural guide stars within a 6 arcminute field of view for wavefront sensing. Each guide star is used to sense the turbulence in one of two discrete atmospheric layers. To be able to combine the wavefront information from each natural guide star, opto-mechanical pickup units have to be positioned in the physically large focal planes of the wavefront sensors. These pickup units contain the pyramids of the wavefront sensors. They will be moved in parallel and have to be accurately positioned on the targets. Collisions have to be prevented. The exploitation of large fields of view for multi-object Adaptive Optics is a challenge that will become more and more prevalent with increasing aperture sizes, especially for the upcoming generation of extremely large telescopes.