The point spread function in Lucky Imaging and variations in seeing on short timescales
Cavendish Laboratory, Madingley Rd, Cambridge CB3 0HE, UK e-mail: [jeb;pjw]@mrao.cam.ac.uk
2 Institute of Astronomy, Madingley Rd, Cambridge CB3 0HE, UK e-mail: email@example.com
Accepted: 22 December 2007
Aims.We investigate the properties of astronomical images made by combining the best images selected from a sequence of short-exposure frames (Lucky Imaging); we assess the match between modelling and observation and discover what variations in seeing occur on very short timescales.
Methods.Numerical simulations of a random phase-changing screen passing across a telescope aperture with ideal optics are used to determine the expected point spread function and isoplanatic properties for a range of seeing conditions for comparison with observations.
Results.All the model images comprise a diffraction-limited core with Strehl ratios from 0.05–0.5 and an underlying broad disk. The isoplanatic patch sizes are large and coherence times long. The observations are a close match to the models in most respects. Large variations in seeing occur on temporal scales as short as 0.2 s and spatial scales as small as 1 m.
Key words: atmospheric effects / techniques: high angular resolution
© ESO, 2008