<p>
hi all,
</p>
<p>
I constructed the 4 images r band rotation.
</p>
<p>
These are: fixed rawdome at angle = 0 degrees divided by rawtwilights @ different rotation angles: -166,-76,13,103 degrees respectively.
</p>
<p>
see top 4 plots of:
</p>
<p>
http://wiki.astro-wise.org/projects:omegacam:commissioning:flatfields
</p>
<p>
the fits files can be found at:
</p>
<p>
/net/thomson/data/users/sikkema/DOWNLOAD/WD2/june/z/*deg*fits
</p>
<p>
cheers,
</p>
<p>
Gert S
</p>
<p>
On Thu, 16 Jun 2011 13:51:00 +0200, "Edwin A. Valentyn" wrote:
</p>
<blockquote style="padding-left: 5px; border-left: 2px solid #1010ff; margin-left: 5px; width: 100%">
Thanks Gert,<br />
<br />
few comments<br />
<br />
On 16-6-2011 1:30, Gert Sikkema wrote:
<blockquote>
<p>
dear all,
</p>
<p>
I made a list of all 32 CCD pointings observerd so far:
</p>
<p>
B,V, u, g(2x), i, z(2x)
</p>
<p>
g and z were observed two times, but the first of each of these
bands was done with cirrus in the sky, this can at least be seen
in my analysis of g.
</p>
<p>
I also analyzed the u band data of SA113, but the resulst of
this do not make any sense ( I included both gain and/or QE
corrections), I do not see a smooth picture, but many discrete
off-sets of magnitudes between chips.
</p>
<p>
, I can think of several causes:
</p>
<p>
-) it may be due to bad observing conditions (zeropoints of
chips fluctuating),
</p>
<p>
-) the flat field used is not OK (only twilights, remember that
the dome flats are useless)
</p>
<p>
-) the QE has a large gradient as a function of wavelength at
low wavelengths, my correction based the 360 nm part of table
2.A.1 of Fabrice his thesis may not be a good estimate of the
QE.
</p>
<p>
-) another possibility is that the standard star catalog is not
really good here (however the scatter was only ~0.05 mags for
each chip using ~30 standard stars )
</p>
<p>
So...if you have some time left it may be a good idea to
re-observe in the u band in good conditions at
SA107
</p>
</blockquote>
True.<br />
Indeed we are faced with large colour terms in u, and it will take
some effort to work these out.<br />
on<br />
<a href="http://www.astro-wise.org/~omegacam/preparing_obs/throughput.jpg" class="moz-txt-link-freetext">http://www.astro-wise.org/~omegacam/preparing_obs/throughput.jpg</a><br />
you can see why this term are so large<br />
<blockquote>
<p>
---------------------------------
</p>
<p>
ROTATOR ANGLE
</p>
<p>
another point I would like to verify with you concerns the
rotator angle:
</p>
<p>
the illumation variations of the astronomical objects in a
reduced science frame are mainly caused by the (twilight) flat
fields used.
</p>
<p>
This means that the illumination correction is only dependend on
the rotator angle of the twilight flat field and not on the
rotator angles of the science frames
</p>
<p>
Not that a varying illumination will also occur in the sky
background --> this DOES depend on the rotator angle of the
science frames. Deviding this with an (twilight) flatfield with
another rotation angle will cause some strange effects on the
sky background.
</p>
<p>
So if we want to use a default illumination correction frame in
the future, this should mean that the twilight frames in
observing mode should always have a similar rotation angle as
the ones used for the twilight flatframes that were used to
calculate the default illumination correction frame...
</p>
</blockquote>
I'm afraid you are right, in case we make nightsky flats, but not if
we simply apply twilight flats and let the sky- substraction in
Sextractor do the rest for cataloguing.<br />
For making nice images with flat sky you point is also valid of
course- but this is more cosmetic.<br />
<br />
regards<br />
Edwin<br />
<blockquote>
<p>
Gert S.
</p>
<p>
<br />
On Thu, 16 Jun 2011 13:08:48 +0200, Gijs Verdoes Kleijn wrote:
</p>
<blockquote style="padding-left: 5px; border-left: 2px solid #1010ff; margin-left: 5px; width: 100%">
<p>
Dear all,
</p>
<p>
</p>
<p>
Main points of what we have observed:
</p>
<p>
-domeflats r at 4 rotator angles to accompany their twilight
counterparts of yesterday.
</p>
<p>
-photometry with ADC in+out
</p>
<p>
-AO/guiding test observation, which includes pointings on
Hercules.
</p>
<p>
-daily calibrations
</p>
<p>
</p>
<p>
Last afternoon we said goodbye to John.
</p>
<p>
</p>
<p>
Best wishes, Gijs
</p>
<p>
</p>
</blockquote>
<span id="_rc_sig">
<pre>
dr. Gert Sikkema
Kapteyn Institute Zernike Building, room 133,
P.O. Box 800 9700 AV Groningen
sikkema@astro.rug.nl
homepage: http://www.astro.rug.nl/~sikkema
31-50-3634548
Popular lectures on:
- Einstein's theory of Relativity
- Globular Clusters
- Active Galactic Nuclei
</pre>
</span>
<p>
</p>
<pre>
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<pre class="moz-signature">
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Coordinator Target www : <a href="http://www.rug.nl/target" class="moz-txt-link-abbreviated">www.rug.nl/target</a>
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</pre>
</blockquote>
<p>
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