Open AccessNew challenges for adaptive optics: extremely large telescopes
Author(s) -
Le Louarn M.,
Hubin N.,
Sarazin M.,
Tokovinin A.
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03607.x
Subject(s) - strehl ratio , physics , adaptive optics , limiting magnitude , wavefront , telescope , sky , optics , deformable mirror , stars , laser guide star , large binocular telescope , guide star , magnitude (astronomy) , field of view , astrophysics , astronomy
The performance of an adaptive optics (AO) system on a 100‐m diameter ground‐based telescope working in the visible range of the spectrum is computed using an analytical approach. The target Strehl ratio of 60 per cent is achieved at 0.5 μm with a limiting magnitude of the AO guide source near R magnitude~10, at the cost of an extremely low sky coverage. To alleviate this problem, the concept of tomographic wavefront sensing in a wider field of view using either natural guide stars (NGS) or laser guide stars (LGS) is investigated. These methods use three or four reference sources and up to three deformable mirrors, which increase up to 8‐fold the corrected field size (up to 60 arcsec at 0.5 μm). Operation with multiple NGS is limited to the infrared (in the J band this approach yields a sky coverage of 50 per cent with a Strehl ratio of 0.2). The option of open‐loop wavefront correction in the visible using several bright NGS is discussed. The LGS approach involves the use of a faint ( R ~22) NGS for low‐order correction, which results in a sky coverage of 40 per cent at the Galactic poles in the visible.