Phasing segmented mirror telescopes with adaptive optics corrected images

Abstract

Residual phasing errors from segmented mirror telescopes can significantly inhibit the performance of an adaptive optics (AO) system. One approach to quantify these errors utilizes the imaging capabilities of a telescope’s instrument suite; quantification requires images that have observed the primary, therefore these images should be on-sky and AO-corrected in the absence of a source that views the primary. An image-based phase estimation technique that can potentially make this quantification is Phase Diversity, whereby focussed/defocussed images of a bright star are compared with models to estimate phase. Traditional use of this technique with on-sky images can be difficult due to atmospheric evolution between image pairs. This is further compounded due to both NCPA and the partial AO correction of phasing errors persisting in on-sky images. Here we propose a technique that can mitigate the atmospheric effects, estimate the NCPA and assess phasing errors under partial AO correction.