21-element infrared adaptive optics system at 2.16-m telescope

A 21-element adaptive optics system installed at the 2.16m telescope of Beijing Astronomical Observatory has been in operation. It is made up of a pair of shearing interferometer (SI), a 21-element deformable mirror, a fast steering mirror, a digital wavefront processor, a precise tracking subsystem and a PtSi IR CCD camera. In this paper the performance of the system will be briefly introduced. Its observation results in IR K band and in visible band are reported. For the system, 0.25 arcsec resolution has been achieved in IR K band, which approaches the diffraction limit of the 2.16m aperture. In visible band, 0.13arcsec resolution has been also achieved. For the star of magnitude 9.m2, the compensation of the system is still effective. The error rejection bandwidth of the system can be adjusted in the range from 5Hz to 40Hz according to the beacon magnitude and the strength of the atmospheric turbulence.