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Issue A&A
Volume 480, Number 2, March III 2008
Page(s) 589 - 597
Section Astronomical instrumentation
DOI http://dx.doi.org/10.1051/0004-6361:20079214



A&A 480, 589-597 (2008)
DOI: 10.1051/0004-6361:20079214

The point spread function in Lucky Imaging and variations in seeing on short timescales

J. E. Baldwin1, P. J. Warner1, and C. D. Mackay2

1  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: cdm@ast.cam.ac.uk

(Received 7 December 2007 / Accepted 22 December 2007)

Abstract
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

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