High-efficiency lucky imaging

Abstract

Lucky imaging is now an established observing procedure that delivers near-diffraction-limited images in the visible on ground-based telescopes up to 2.5 m in diameter. Combined with low-order adaptive optics it can deliver a resolution several times better than that of the Hubble Space Telescope. Many images are taken at high speed as atmospheric turbulent effects appear static on these short time-scales. The sharpest images are selected, shifted and added to give a much higher resolution than is normally possible in ground-based long exposure time observations. The method is relatively inefficient as a significant fraction of the frames are discarded because of their relatively poor quality. This paper shows that a new lucky imaging processing method involving selection in Fourier space can substantially improve the selection percentages. The results show that high-resolution images with a large isoplanatic patch size may be obtained routinely both with conventional lucky imaging and with the new lucky Fourier method. Other methods of improving the sensitivity of the method to faint reference stars are also described.