NAOS (Nasmyth Adaptive Optics System, Fig. 8.16) is the first set of adaptive optics mounted on one (Yepun) of the four 8.2-m telescopes of the European VLT on the summit of Mount Paranal in Chile. The instrument is coupled with the CONICA infrared camera (1-5 |m). The system, which has a deformable mirror with 185 actuators, a special tip/tilt wavefront correction system, and two wavefront analyzers (one in the visible region, and one in the near infrared), has been available to the scientific community since the end of 2002, and enables images to be obtained over a field that may amount to as much as 2 arcmin, with a Strehl ratio of up to 30-60 per cent, depending on seeing conditions. The instrument is used for all applications that require high angular resolution. The camera has a filter wheel which not only allows specific photometric bands to be chosen but also permits more specific modes of operation. In particular, a 4-quadrant coronagraph (cf. Chap. 2) is available and provides extinctions up to 500. It is this instrument that obtained what appears to be one of the first, if not the first, resolved image (Fig. 8.17) of a planet around its star (a brown dwarf, in fact), which in this case was 2MASS 1207, a young object, with a typical age of a few million years (and thus still hot) of about 5 Jupiter masses lying about 55 AU from the brown dwarf and where the contrast was favourable for detection (Chauvin et al., 2005).
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