Cannot clean sources outside the primary beam...

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Cannot clean sources outside the primary beam...

Postby taianmoon » Wed Nov 09, 2016 4:13 am

Hi,

I'm producing a 5500MHz image which has an image size of four times the primary beam. But it seems that I cannot clean a source that are outside the primary beam (the bright source near the right edge of the image, as in the attachment), so its dirty beam pattern is contaminating the whole image . This source seems not to be cleaned after "mfclean" was used, and when "cgcurs" was then used to specify its region, Miriad just complained that the region selected is too big, no matter how small I selected the region.

I'm not sure yet what caused this and is still struggling cleaning that source.

Thanks a lot!

Tai-An
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Re: Cannot clean sources outside the primary beam...

Postby Mark.Wieringa » Wed Nov 09, 2016 8:44 am

Hi Tai-An,

The first thing to do is use options=double in invert, to create a beam twice the size of the image. This means you can clean all of the image with clean and 2/3 of the image with mfclean. Then you need to make sure the image is big enough so that the source you want to clean falls within the inner 2/3 of the image. In mfclean you then specify region=perc(66) to clean the inner 66% of the image, which is the maximum mfclean can do.

If after doing that you still find the source doesn't clean away completely (it should improve it significantly compared to the dirty image), then you may need to use selfcal to improve the calibration. This should get you another order of magnitude improvement. If you're still having problems after that, you may need 'peeling', see section 3.2 in http://adsabs.harvard.edu/abs/2007MNRAS.382..543H for details on how to do that.

Cheers,

Mark
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