<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 <very> good conditions at SA107
</p>
<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>
<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>