The following scheme is proposed to check the validity of the self-calibration solution:
From our experience, the number of loops blueSELF_NLOOP does not impact
much the quality of the solution, and 2 to 3 iterations are usually
sufficient.
Warning: the comparison with theoretical noise relies on a proper
scaling of the weights of the UV data. This is fine for the IRAM array,
but data exported from CASA is not always correct in this respect.
magentaUV_PREVIEW can warn you about potential issues in this respect.
magentaUV_REWEIGHT can also evaluate the scaling factor that should be
applied to the weights to recover the apparent noise level. magentaUV_PREVIEW
requires a sufficient number of spectral channels for this purpose.
By default, magentaUV_REWEIGHT suffers from a similar restriction,
and both commands may fail if the bandwidth is clobbered with spectral lines or has
strong continuum. However, magentaUV_REWEIGHT as a magentaTIME mode where
the noise is estimated from consecutive visibilities, and thus is not
affected by this limitation.
The appropriate scaling factor can be specified in magentaSELFCAL by
variable blueSELF_SNOISE.
Both options may be explored, and it is recommended to check afterwards the final angular
resolution with and without flagging.
Yes : will result in no contamination by bad data, but
may lead to lower angular resolution since long baselines may be flagged.
No: will avoid loosing all long baselines (where the SNR is lower)
s, and for NOEMA in the range
s. Alternatively, you
can also try to decrease blueSELF_SNR to lower values, but never
less than 3.
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Gildas manager
2023-06-01