Press Releases 2007

ESO PR Photo 19a/07

The MCAO Demonstrator

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The Multi-conjugated Adaptive optics Demonstrator (MAD) in operation at the Nasmyth A focus of Melipal, UT3 of ESO's Very Large Telescope.

ESO PR Photo 19b/07

The Globular Cluster Omega Centauri
(MAD/VLT)

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Mosaic of images covering the central parts of Omega Centauri, the most luminous globular cluster as seen from Earth. The images were taken with CAMCAO in Br-gamma for a total exposure time of 5 minutes (the original pixel scale is 0.028 arcsec). The stars in the 2 arcmin field of view have a FWHM between 0.08 and 0.10 arcsec.

ESO PR Photo 19c/07

The MCAO Concept

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In the Multi-Conjugate Adaptive Optics concept, several Guide Stars located in the Field of View are used simultaneously to perform a tomography of the atmospheric turbulence volume cone above the telescope by means of wavefront sensors. The measured wavefronts are combined in real-time to compute the commands applied to the deformable mirrors (two in the case of MAD) optically conjugated at different altitudes above the telescope. These deformable mirrors commands are optimized such as to homogeneously maximize the correction over the scientific field of view.

ESO PR Photo 19d/07

AO Strehl Maps

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Maps of Strehl ratio (a measure of light concentration) in the case of single conjugated adaptive optics, i.e. as used in present AO systems (SCAO; left) and multi-conjugated (MCAO; right), as measured in images of Omega Centauri. Different colours correspond to different Strehl ratios, from 0 (black) to red (35%). The SCAO map illustrates how inhomogeneous the correction is across the field of view. The peak Strehl ratio is about 30% close to the guide star, to the right, and decreases with the distance to the guide star due to atmospheric anisoplanatism. The MCAO map, however, is much more uniform across the field of view, and peaks close to the location of the three guide stars shown by crosses. A comparison between the two images clearly shows the advantage of MCAO.

ESO PR Photo 19e/07

Comparing AO Techniques

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Central parts of the globular cluster Omega Centauri, as seen using different adaptive optics techniques. The upper image is a reproduction of PR Photo 19b/07, with the guide stars used for the MCAO correction identified with a cross. A box shows a 14 arcsec area that is then observed while applying different or no AO corrections, as shown in the bottom images. From left to right: No Adaptive Optics, Single Conjugate and Multi-Conjugate Adaptive Optics corrections. SCAO has almost no effect in sharpening the star images while the improvement provided by MCAO is remarkable.