Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.eso.org/~pmoller/FIZZWIG-FAP/Team-meetings/ActionItems Дата изменения: Wed Jul 18 16:20:32 2007 Дата индексирования: Sun Dec 23 00:02:36 2007 Кодировка: Поисковые слова: m 106

Old one: Sabine and Palle to come up with list of new fields. Ideally
8 fields separated by 3 hours.


29.06.07 Wolfram: Provide a section on the large scale filtering
algorithm and provide the filtering scale.


29.06.07 7) Wolfram to call meeting next week to discuss the issue of
Photometry and choice of parameters in more detail.
v Task completed - meeting announced for 12.07.07
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> 7) Wolfram to call meeting next week to discuss the issue of Photometry
> and choice of parameters in more detail.

I propose to have this discussion next week, say Thursday July 12 15:00.
Does this work for everybody?

The goal is to decide the best set of program/parameters to do the
photometry. I think we all agree that we want to do simple aperture
photometry, so the issues are:
- what is the optimum aperture?
- do we need aperture correction?
- do we need seeing dependence?
- do we need different apertures:
for the Landolt stars?
for relative/absolute photometry
- are there any issues with the sextractor aperture photometry?
- what are the criteria to include/exclude stars?
I will bring the parameter list I have used so far.
Wolfram
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12.07.07 Nando - Test the magnitude of aperture corrections to Landoldt
Apertures. Test scaled apertures with 4 and 5 sigma
seeing for a range of seeings.
Original text: Nando will carry out some tests to determine the
aperture correction, and compare the Stetson magnitude ZP with such
aperture compared to Landolt's ZP. He will use both Sextractor and
other programs to see whether there is any discrepancy. His tests
will be finished by mid-July, when Wolfram has time to re-run the
fitting.


12.07.07 Palle - Write up some suggestions for tests to verify which
FORS/UT combinations really have rotating features.
Original text: Sabine's flatfield versus rotators angle look
promising, but more tests should be done which do not depend on the
structure looking like a finger. These tests should also clarify
the significance of the finding. Palle will write a detailed list of
test to be carried out.
v Task completed on 16.07.07
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>Sabine's flatfield versus rotators angle look promising, but more tests
>should be done which do not depend on the structure looking like a finger.
>These tests should also clarify the significance of the finding. Palle
>will write a detailed list of test to be carried out.

Dear all,

Here the resolution of my action item.

The question is this: When we do the counter-rot of the frames, and then
co-add, how do we know that the features we see are true rotating
features, or simply remaining features seen in single frames?

In the perfect situation we have a large number of frames, evenly
distributed on rot-angles. In this situation we trust the law of large
numbers, and believe that the individual features are beaten by root(N)
where N is the number of frames. Since individual features are seen up
to 5-6%, and we are looking for features that are of order 1%, we must
require that N is much larger than 36, and that the histogram is flat.

Therefore, the first thing we need to know about the counter-rot-comb
flats is:
1) N = number of frames used for combination
2) histogram of rot-angles

I fear that in many cases there will either not be enough flats, and/or
the histogram will not be flat. For those cases we need other tests.

One test is to cut each sample into 2 halves, treat each half separately
and then check if they give the same answer or not. The halves could be
either ordered by rot-angle (e.g. 0-180 together, 180-360 together), or
totally random. The best would be to do both.

Another test is (if there is a dominating peak in the histogram) to
drop all the images of that dominating peak and only combine the rest.

I am not sure how much work all of this is, but for a start the
histograms would be good to see.

I think this is enough for now.
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I fully agree with Palle on the importance of watching the histograms. In
addition, I suggest that for any combined flat we always look at and
compare 3 versions next to each other, they should be shown with the same
scale. The three versions are:


1. The mean of all flatfields normalized by dividing by its mean

2. The flatfields divided by their mean, and counter-rotate with the
opposite of the rotator angle (as Sabine and Nando have shown before).

3. As 2., but choose the angle to rotate at random.


A feature which stays fixed on the detector should show up in 1, one which
rotates in 2.
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> 1. The mean of all flatfields normalized by dividing by its mean
>
> 2. The flatfields divided by their mean, and counter-rotate with the
> opposite of the rotator angle (as Sabine and Nando have shown before).

fine, those two are already produced.

> 3. As 2., but choose the angle to rotate at random.

What do you expect to gain by that?
best wishes, Sabine
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>> 3. As 2., but choose the angle to rotate at random.
>
> What do you expect to gain by that?

random rotations should wipe out any structure fixed to the detector or
rotating with the rotator. So in the ideal case (if we have enough
images), 1 and 2 will show us different structure, and 3 will be smooth
(or structure only a function of distance from center). Now probably we
will not have enough images to have such a clear case. But comparing the
amplitude of the other two with the one which should come out smooth
should give us some feel for the reality of any structure we might be
tempted to attribute to the detector or rotator. I think without a
comparison we will always have a hard time to decide whether what we see
is real or not. I hope it is not too much work.
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> images), 1 and 2 will show us different structure, and 3 will be smooth
> (or structure only a function of distance from center). Now probably we

ok, understood.

> comparison we will always have a hard time to decide whether what we see
> is real or not. I hope it is not too much work.

No, the hardest work for me was to figure out how to get a random angle
;-)
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