Temp variations are quite rare, but when they do happen, the effect
is or can be dramatic. But I agree that they are definitely not
the main cause of the fringe pattern variations. On the other
hand this observation points to some sort of mechanical component
to fringe pattern variations, in addition to the excitation effect.
The effect is not zenith distance related - I've checked that. (Here
I'm talking about an effect over and above optical depth effects.
I do see the expected fringe amp \propto secz, but there is no obvious
change in the structure of the fringe pattern with secz.)
Two questions: (1) what is the thickness of the CCD's; and (2) How
are the CCD's mounted: is there any tension or pressure between CCDs
in the row direction or column direction?
Jean-Charles Cuillandre wrote:
> Chris,
>
> Temperature variations are rare though, and the biggest contribution
> I have found in the time of the night (distance in time from sunset,
> again a direct link to excitation effect of the atmosphere.
>
> 2 months is about my timescale also - let's work on this together
> with some full data sets!
>
> Jean-Charles.
>
>>> ... And now
>>> that flats are (presumed) final, a focus on the defringing recipe is needed
>>> as well.
>> Forgot to comment on this ... As you know, I was trying in December
>> to come up with some better procedure for defringing. There is some
>> tentative evidence that fringing is improved when you defringe with
>> fringes of about the same amplitude in DU/s (after allowing for airmass
>> effects). This is maybe not surprising: night sky level is an excita-
>> tion effect, and excitation affects the relative strengths of lines
>> in the airglow.
>>
>> However by far the biggest effect I found was that the really gross
>> defringing problems happen when the mosaic is not at the proper
>> temperature. This was quite striking.
>>
>> I'm afraid I won't have a chance to work on this further for a
>> month or two.
>>
>> -----------------------------------------------------------------
>> Chris Pritchet pritchet at uvic.ca
>> Dept of Physics & Astronomy http://www.astro.uvic.ca/~pritchet
>> University of Victoria
>> P.O. Box 3055 250-721-7744 (office)
>> Victoria, BC V8W 3P6 250-884-5047 (cell)
>> CANADA 250-721-7715 (FAX)
>> -----------------------------------------------------------------
>
--
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Chris Pritchet pritchet at uvic.ca
Dept of Physics & Astronomy http://www.astro.uvic.ca/~pritchet
University of Victoria
P.O. Box 3055 250-721-7744 (office)
Victoria, BC V8W 3P6 250-884-5047 (cell)
CANADA 250-721-7715 (FAX)
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Received on Tue Feb 19 2008 - 07:35:46 HST