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Oops sorry , I see they are in the log sheet pf 14/15 june, day 9, sorry bothering you all ...
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Gijs: when did you observe the rotator TWILIGHTS in r?
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GS
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On Thu, 16 Jun 2011 13:30:36 +0200, Gert Sikkema wrote:
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dear all,
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I made a list of all 32 CCD pointings observerd so far:
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B,V, u, g(2x), i, z(2x)
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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.
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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.
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, I can think of several causes:
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-) it may be due to bad observing conditions (zeropoints of chips fluctuating),
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-) the flat field used is not OK (only twilights, remember that the dome flats are useless)
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-) 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.
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-) 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 )
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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
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---------------------------------
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<p>
ROTATOR ANGLE
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another point I would like to verify with you concerns the rotator angle:
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the illumation variations of the astronomical objects in a reduced science frame are mainly caused by the (twilight) flat fields used.
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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
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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.
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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...
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Gert S.
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<br />
On Thu, 16 Jun 2011 13:08:48 +0200, Gijs Verdoes Kleijn wrote:
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Dear all,
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Main points of what we have observed:
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-domeflats r at 4 rotator angles to accompany their twilight counterparts of yesterday.
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-photometry with ADC in+out
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-AO/guiding test observation, which includes pointings on Hercules.
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-daily calibrations
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Last afternoon we said goodbye to John.
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Best wishes, Gijs
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<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
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