Lucky Imaging and Adaptive Optics Hybrid Systems
In 2007 astronomers at Caltech and the University of Cambridge announced the first results from a new hybrid Lucky Imaging and Adaptive Optics (AO) system. The new camera gave the first diffraction-limited resolutions on 5m-class telescopes in visible light. The research was performed on the 200 inch (5.08 meter) diameter aperture Palomar Hale telescope.
The 200-inch Hale telescope with Lucky cam and adaptive optics pushed the telescope near to its theoretical resolution, achieving up to 0.025 arc seconds for certain types of viewing. Compared to Space Telescopes like the 2.4 m Hubble, the system still has some drawbacks including narrow field of view for crisp images (typically 10" to 20"), airglow, and electromagnetic frequencies blocked by the atmosphere (see Extinction (astronomy)).
| Lucky Imaging + AO image of the core of the M13 globular cluster. The best 10% of the frames taken were aligned and summed to make this final very-high-resolution (40 milli-arcsecond) image. Approximately 1-arcsecond diameter field. | |
| Hubble Space Telescope ACS-camera image of the same field in a filter passing 660 nm light. The stars in the Lucky Imaging + AO image are much better separated, although the Hubble image is longer-exposure and so shows some fainter stars. |
When combined with an AO system Lucky Imaging selects the periods when the turbulence that the adaptive optics system must correct is reduced. In these periods, lasting a small fraction of a second, the correction given by the AO system is sufficient to give excellent resolution with visible light. The Lucky Imaging system sums the images taken during the excellent periods to produce a final image with much higher resolution than is possible with a conventional long-exposure AO camera.
This technique is applicable to getting very high resolution images of only relatively small astronomical objects, up to 10 arcseconds in diameter, as it is limited by the precision of the atmospheric turbulence correction. It also requires a relatively bright 14th-magnitude star in the field of view on which to guide. Being above the atmosphere, the Hubble Space Telescope is not limited by these concerns and so is capable of much wider-field high-resolution imaging.
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