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Adaptive Telescope Mirror developments in the framework of the European "ELT Design Study" project

Abstract 169

Submitted by Armando RICCARDI


A. Riccardi(1), C. Del Vecchio(1), M. Xompero(1), D. Gallieni(2), M. Mantegazza(2), R. Biasi(3), A. Merler(3), N. Hubin(4), E. Vernet(4)


(1)INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, ITALY; (2)A.D.S. International S.r.l., Via Roma 87, I-23868 Valmadrera (LC), ITALY; (3)Microgate S.r.l., Via Stradivari 4, I-39100 Bolzano, ITALY; (4)European Southern Observatory, Karl-Schwarzschild-str-2, 85748 Garching bei Muenchen, Germany


The use of Adaptive Optics (AO) in the Extremely Large Telescopes (ELT) is a key feature to accomplish most of the scientific targets addressed for this kind of telescopes. In particular the use of large-stroke Adaptive Telescope Mirrors (ATM) in place of one or more conventional ELT mirrors is a very attractive solution. The use of ATMs minimizes not only the number of surfaces in the scientific path, but also can offer, even in the case that just one ATM is used, at least Ground Layer AO capability to all the telescope focal stations or first stage compensation for other AO post-focal systems. Finally, because of the heavy effect of wind shaking on ELTs, a large stroke mirror with adaptive bandwidth might be necessary even for seeing limited operations. In the present paper we report our development of ATMs in the framework of the European "ELT Design Study" project. Two configurations for 2.5m-class mirrors have been studied: a tweeter (high order) and woofer (low order) correctors with, respectively, 25-30mm and 50mm actuator spacing. Both solutions represent the extension of the current technology of 1m-class Adaptive Secondary Mirrors for LBT and VLT towards ELTs. In particular materials and structures have been reconsidered in order to manage the larger diameter. Moreover the electro-magnetic actuators have been completely redesigned in order to provide self-containing metrology, a distributed lateral support for the deformable shell, a larger efficiency, and, for the tweeter, a larger density.