EDP Sciences
Free access
Volume 436, Number 1, June II 2005
Page(s) 373 - 378
Section Instruments, observational techniques, and data processing
DOI http://dx.doi.org/10.1051/0004-6361:20042320

A&A 436, 373-378 (2005)
DOI: 10.1051/0004-6361:20042320

On super-resolution in astronomical imaging

K. G. Puschmann and F. Kneer

Universitäts-Sternwarte, Geismarlandstr. 11, 37083 Göttingen, Germany
    e-mail: kgp@uni-sw.gwdg.de

(Received 12 October 2004 / Accepted 27 January 2005)

Our work is an attempt to fulfil one of the aims of astronomical imaging, that is, to obtain information at high angular resolution. Stars as point sources can be represented by Dirac $\delta$-functions whose Fourier transforms contain information about the position and the (integrated) intensity at all angular frequencies. Thus, we can deconvolve unresolved images of star fields even at angular distances smaller than the diffraction limit of the telescope with which the observations are performed. We give an example of reconstruction of the image of two stars with an angular separation of a factor 2.5 less than $\alpha_\mathrm{Ra}=1.22\times\lambda/D$. However, we find that super-resolution is feasible only for point sources. For extended objects the information about intensity fluctuations at angular frequencies $u>u_\mathrm{max}=D/\lambda=1/\alpha_\mathrm{min}$ is irretrievably lost. We discuss the impossibility of super-resolution for the Sun using a numerically simulated image of solar granulation. However, one can enhance the contrast of solar images, though without increasing angular resolution beyond the diffraction limit.

Key words: techniques: high angular resolution -- techniques: image processing

© ESO 2005