Daily Image

12-09-2007
PreviousNext
Click here or on the picture for a full size image.

Shapelets to the rescue

Submitter: Sarod Yatawatta
Description: The LOFAR CS1 high band (HBA) observations have just high enough resolution such that CasA appears as an extended source, instead of a point source (for the long baselines). Thus, in order to have a better subtraction of CasA from our images, we need to move beyond point-source models.

This is our first result of using a shapelet model for CasA. The top-left panel shows the artefacts remaining after subtracting a point-source model for CasA. The bottom-left panel shows the residuals after using a shapelet model. It is obvious that the latter is an improvement. The top-right panel shows the cross sections of the residuals around CasA for both models, which again shows the improvement.

The bottom-righ panel shows our shapelet model coefficients, which are derived from a higher resolution VLA 74MHz image (Kassim et al.). Note that, since Cas A has a ring-like structure, the highest coefficients (red) are not in the lowest-order modes (bottom-left corner), as they would be for a source with most of its flux in the centre.
Copyright: ASTRON
 
  Follow us on Twitter
Please feel free to submit an image using the Submit page.