R. Schoedel, S. Yelda, A. Ghez, J. H. V. Girard, L. Labadie, R. Rebolo, A. Perez-Garrido, M. Morris
We present a method for speckle holography that is optimised for crowded fields. Its two key features are an iterative improvement of the instantaneous PSFs extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise and accuracy be achieved on the PSFs for each short exposure, which results in sensitive, high-Strehlreconstructed images. W e have tested our method with different instruments, on a range of targets, and from the N- to the I-band. In terms of PSF cosmetics and stability as well as Strehl ratio, holographic imaging can be equal, or even superior, to thecapabilities of currently available AO systems. It outperforms lucky imaging because it makes use of the entire PSF and reduces the need for frame selection, thus leading to higher Strehl and improved sensitivity. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to the capabilities of a multi-conjugate adaptive optics systems. Our work opens new possibilities for sub-arcsecond resolution imaging of large crowded fields with high PSF stability, while keeping the complexity and costs of instruments small. Moreover, the presented method can be used to significantly improve the angular resolution of any existing imaging instrument that provides sufficiently fine spatial sampling and fast readout capability.
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http://arxiv.org/abs/1110.2261
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