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         title="Permalink to CASA Selfcal: Good & Awful">CASA Selfcal: Good &amp; Awful</a></h2>
 
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    <abbr class="published" title="2016-01-28T09:20:00-07:00">
      2016/01/28
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    <address class="vcard author">
      By <a class="url fn" href="https://keflavich.github.io/blog/author/adam-ginsburg-adamgginsburggmailcom.html">Adam Ginsburg (Adam.G.Ginsburg@gmail.com)</a>
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    <p>Self-calibration is necessary for some images to get a decent dynamic range or
to see anything at all in the images.  So, I did some tests using self-cal on
the central field of Sgr B2 (<a class="reference external" href="https://github.com/keflavich/SgrB2_ALMA_3mm_Mosaic/blob/master/script_12m_te/selfcal_centralfield.py">source</a>)
and it worked great:</p>
<img alt="" src="https://keflavich.github.io/blog/images/casa/sgrb2_selfcal_good.png" style="width: 600px;" />
<p>That image is actually from <a class="reference external" href="https://github.com/keflavich/SgrB2_ALMA_3mm_Mosaic/blob/master/script_12m_te/selfcal_continuum.py">self-calibrating the whole field</a>,
which also worked great.  Except, it deleted all the flux outside of the bright regions:</p>
<img alt="" src="https://keflavich.github.io/blog/images/casa/sgrb2_selfcal_bad.png" style="width: 600px;" />
<p>This is awful.  It is just deleting flux!  I had previously thought that the
<tt class="docutils literal">applyonly</tt> option would only apply solutions that it actually found, but
that appears not to bt true.  Instead, it seems that even phase solutions with
<em>no</em> signal are being applied, which effectively removes everything from the
image.  I could have understood if this was happening to amplitude
self-calibration, but I can't understand how it is happening with phase
self-cal.</p>

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