High frequency wavefront structure and its effects on the detection of faint companions using adaptive optics

This paper looks at the detection limits using the new adaptive optics system on the 3.5 m SOR telescope, reported by P. Ryan et al.(1) at this conference. We discuss recent advances in our understanding of the nature of high frequency wavefront structure. We analyze the various sources of high-frequency wavefront error, arising from residual adaptive optics errors, and other sources of scattered light. We characterize the AO system efficiency in the K band in terms of profile, noise level and noise time correlation. A sharp edge coronograph was used and it improved the performance as much as needed to detect brown dwarfs. Finally we give the exposure time required to detect such companions using the actual AO associated with the coronographic device, and we also point out what needs to be improved on the AO system as well as on the coronographic device in order to reach the level required for detecting exoplanets.