Potential for Wide field Surveys


The Lucky Image Selection method can be applied to most kinds of imaging. For example, we can use a CIRSI type approach, with an array of L3CCDs each selecting their own Lucky images which are then mosaiced after the exposure. We use 6 pointings to cover entire field of view. In one night can survey to very faint limits and with excellent resolution using the methods outlined elsewhere.  We have already made a mosaic of 9 fields in the globular cluster M15, and compared it with an image taken with a conventional CCD camera on the same telescope at the same time.

In each of the nine fields around the core of the globular cluster we used an 80 second run with 10% selection to produce each of the nine fields. These were then merged in the computer to produce a composite Lucky image that covers just under one arc minute square. The first image was taken on the same telescope with the standard CCD camera that is use there for general-purpose imaging. It is a thinned (back illuminated) 1024 by 1024 CCD and it was used image the centre of the globular cluster with an image scale of six pixels per arc second. The seeing was approximately 0.6 arc seconds as measured on that camera, and a sequence of Lucky images were taken immediately after the standard camera image was recorded.

If you move the mouse on and off the image below you will see it change from the original standard camera image into the high-resolution Lucky mosaic image and back again.

If the "mouse-over-image" trick does not work, then click here for the image from the Standard CCD camera, and click here for the Lucky Imaging Mosaic.
CIRSI instrument. This has the sensitive areas of the detectors separated from one another by slightly less than the width of the detectors in one direction and slightly less than twice the height of the detectors in the other direction. By using six different pointings of the telescope images may be obtained over the whole sky. Each detector will have its own moments of excellent seeing and its own moments of very poor seeing. At the end of the sequence of six pointings we will have observed the entire region of the sky with the full resolution of the Lucky technique and will be able to produce images over very wide fields. For example with an array of 96 CCDs each of 1024 by 1024 pixels, in an array of 12 by 8 it would be possible to survey one quarter of the square degree in one night to limiting magnitude in the region of I ~ 24. The sort of mosaic would look rather like that shown in the following image:

This image shows the way that the frame-transfer L3CCDs might be laid out in order to allow a wide field survey to be carried out with only six telescope pointings. The area shown coloured indicates the light sensitive part of the CCD. The rest of the CCD is required for charge transfer and storage since these are all frame-transfer CCDs.

 

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Institute of Astronomy & Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, UK
Craig Mackay and the
Lucky Imaging Team  2005,2006
Site last updated on 7 April 2006.     Comments & corrections please, to: cdm@ast.cam.ac.uk