Subaru Telescope's Adaptive Optics (AO) has seen first light. We have confirmed that the AO system provides image quality close to Subaru's theoretical limit.

Images from the ground are affected by atmospheric turbulence which causes the light to be smeared out, even at an excellent site such as the summit of Mauna Kea. The AO system has a curvature sensor to monitor the atmospheric turbulence and a bimorph deformable mirror to compensate for this turbulence, resulting in much sharper images. After attaching the AO system to the Cassegrain focus of Subaru Telescope in November, test observations were made with IRCS (InfraRed Camera and Spectrograph) from December 1 to 3, 2000.

The left figure shows a stellar image taken using the imaging mode of IRCS without AO. The star's appearance is extended due to the atmospheric turbulence. The right figure is the same star after switching on the adaptive optics. The image is much brighter and clearer, with the image quality improving from 0.33 arcsec in the left figure to 0.07 arcsec in the right figure. The fringe which can be seen around the star in the right figure indicates that we are very close to the maximum theoretical (diffraction-limited) performance of Subaru, which is limited by the size of the primary mirror and the wavelength of the observation.

AO First Light Image with IRCS

Telescope: Subaru Telescope, Cassegrain Focus
Instruments: AO + IRCS
Date: Dec 03, 2000
Left: AO-OFF, FWHM 0.33 arcsec, Right: AO-ON, FWHM 0.073 arcsec.
Wavelength: K-band (2.2 micron)
Guide star: alfa-And, mv=2.1 (with ND filter)
Exposure time: 9 sec
Image size: 1.5 x 1.5 arcsecs
Pixel scale: 0.023 arcsec/pix