Daily Image

10-02-2009
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Scanning the sky with Digestif

Submitter: George Heald for the Apertif team
Description: In a recent AJDI (4/2/2009) we showed the first synthesis image created using a telescope equipped with a Focal Plane Array (FPA). That image was made with correlations involving a single element close to the optical axis of the Digestif telescope. But the power of FPAs derives from their large number of receiving elements! Today's image shows a sequence of six synthesis images, created using elements distributed throughout the center of the Digestif FPA.

In the bottom right is an image of the 3C343 field, created using data from MFFE-equipped WSRT telescopes alone, which were processed with the Digestif backend. In the upper right is a sequence of images, each created using correlations of those same MFFE-equipped WSRT telescopes with six different elements of the Digestif FPA. The data used to form all of the images were collected simultaneously. The color range in each image is identical. The Digestif elements which were used are indicated with green circles in the upper left.

The effective primary beam of the system is the combination of the MFFE primary beam, which peaks on the optical axis, and the response pattern of each Digestif element, each of which looks at a different part of the sky (see AJDI 27/3/2008). As we scan the telescope's field of view by using different elements, the system's peak response moves across the sky, causing the relative brightness of the two sources to appear to vary (intrinsically, they have approximately the same brightness). We are still only using six elements - a huge field of view can be sampled with all of the elements of the FPA. And when all WSRT antennas are equipped with FPAs, the varying element response illustrated here will allow mapping of a huge field of view, with just a single pointing of the array.
Copyright: ASTRON
 
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