In most sources of information on the primary beam for the ATCA, it is assumed that the primary beam has rotational symmetry.
For example, http://www.atnf.csiro.au/observers/memos/d97f7b~1.pdf .
In practice, this is not quite true. This can cause a problem with sources at the edge of the primary beam having amplitude variation with time.
This there a way to correct for this within MIRIAD or CASA? This would be quite useful, especially for bright sources at the edge of the beam.
Correction for rotation of the primary beam
Moderator: Mark.Wieringa
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- ATCA Expert
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Re: Correction for rotation of the primary beam
Hi Luke,
You are quite right, in wide fields this can be an obvious problem. The solution is to use A-projection in CASA, however that requires a 2D model of the ATCA beam and its variation with frequency, which unfortunately we don't have. An added complication is that the effect differs in the X and Y polarization. We've attempted to come up with model based on beam measurements but due to rapid variation with frequency (possibly due to standing waves) it hasn't resulted in a consistent model we can use.
The alternative solution is to use peeling, this will work if the offending sources are strong enough for selfcal.
Cheers,
Mark
You are quite right, in wide fields this can be an obvious problem. The solution is to use A-projection in CASA, however that requires a 2D model of the ATCA beam and its variation with frequency, which unfortunately we don't have. An added complication is that the effect differs in the X and Y polarization. We've attempted to come up with model based on beam measurements but due to rapid variation with frequency (possibly due to standing waves) it hasn't resulted in a consistent model we can use.
The alternative solution is to use peeling, this will work if the offending sources are strong enough for selfcal.
Cheers,
Mark