[Comm2011] archival OmegaCAM detector data?

[E. Helmich]

Hi John,

I'd rather see the images with the pinhole filter from 2005, and where that
dot saturates.

Regards,
Ewout

On Mon, 28 Mar 2011 13:26:32 +0200 (CEST), "John P. McFarland"
<mcfarland at astro.rug.nl> wrote:
> Hi Dietrich,
> 
> Here is a histogram of the maximum pixel values of ESO_CCD_#66, the one
> the
> was replaced that had two hot columns.  All maximum values are above
60000
> ADU and 25 of them are at the maximum possible of the data: 65535 ADU.
> These are taken from 1345 ILT images of all types.  I can look at all the
> other CCDs to see if they are similar.  Hopefully sometime this afternoon
> we
> will have a large amount of the commissioning data thus far ingested into
> our system and be able to do a similar investigation on that data from
> here.
> 
> Cheers,
> 
> 
> -=John
> 
> 
> On Mon, 28 Mar 2011, Dietrich Baade wrote:
> 
>> Hi Gijs, John,
>>
>> we have run into some apparent problem with the OmegaCAM science mosaic,
> and
>> Konrad amd Ewout suggested that I contact you.
>>
>> What we see
>> Bright stars saturate well below 2^16-1 ADU.  Often, this happens at
> 57,000
>> ADUs; only the brightest stars reach 62,500 ADU.  The cores of such
> images
>> have a flat plateau.  This is true for all CCDs (quite a few) in the
> mosaic
>> that I've checked. 
>>
>> What else we know
>> The CCD test reports from e2v show full-well capacities of between
> 220,000
>> and 340,000 e-/pixel.  You have previously determined gains of 2.2-2.4
>> e-/ADU.  A quick on-line estimate here suggests ~2, which I consider
>> consistent.  A gain of 2.3 e- would imply 150,000 e- @ 65,535 ADUs,
> well
>> below physical full well.  FORS2 CCDs from the same batch have a gain
> of 2.4
>> and don't run into physical saturation before the limit of the A/D
> converter
>> is reached.
>>
>> What we suspect
>> The numbers for OmegaCAM do not match.  Since the entire science mosaic
>> seems affected, the problem must be basic.  It could be a wrong gain
> setting
>> by S/W or H/W or similar.  Olaf had no time yet to look into this. 
>>
>> What could help us
>> It would be great if you could search your archive for images containing
>> saturated pixels with a value of 65535 (=2^16-1).  Don't send us such
>> images.  It will be sufficient if you could provide a brief
> description. 
>> Ideal would it be if you found a CCD with a (partial) hot column.  In
> that
>> case, give as us the location or name of the chip and the column
> number. 
>> The faulty CCD that was replaced in 2009 might also have shown such
>> saturated columns. 
>>
>> If you do not find anything quickly, suspend your work and let us know
> how
>> you've proceeded.  We would, then, tell you whether it makes sense to
>> continue.  
>>
>> Many thanks in advance for your help. 
>>
>> Best regards,
>>
>> Dietrich. 
>>
>> --
>> Dietrich Baade
>> ESO - European Organisation for Astronomical Research in the Southern
> Hemisp
>> here
>> Karl-Schwarzschild-Strasse 2,  85748 Garching bei Muenchen,  Germany
>> Email: dbaade at eso.org    Tel: +49 89 3200-6388    Fax: +49 89 3202362
>>
>>

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