[Comm2011] Fwd: crosstalk

[Konrad Kuijken]

Dear all,
Dietrich's notes on crosstalk between ccds 93-96.
Koen

Begin forwarded message:

> From: Dietrich Baade <dbaade at eso.org>
> Date: May 5, 2011 8:59:27 GMT+02:00
> To: Konrad Kuijken <kuijken at strw.leidenuniv.nl>
> Cc: Olaf Iwert <oiwert at eso.org>, Steffen Mieske <smieske at eso.org>,  
> Dietrich Baade <dbaade at eso.org>
> Subject: crosstalk
>
> Dear Konrad,
>
> Appended below is a description of the crosstalk issue.  It aims to  
> be the nucleus of some sub-section in the users manual.
>
> Best regards,
>
> Dietrich.
>
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> Electronic crosstalk between CCDs
>
> CCDs ## 93-95 are known to suffer some electronic crosstalk.  Since  
> crosstalk has not been found down to very low levels in any of the  
> other CCDs, the explanation lies either in the CCDs concerned  
> themselves or some manufacturing problem of the detector-head  
> electronics.  Because the overall behaviour seems to be stable,  
> remedial action was not attempted as any intervention in the  
> detector head entails a high risk.
>
> The crosstalk has its origin in bright objects.  The threshold for  
> triggering crosstalk depends on the CCD and time.  Typically, the  
> exposure level is above 25,000 ADUs and often requires sources  
> saturating the A/D converter (65535 ADUs).
>
> The crosstalk can be both positive (bright) and negative (dark) with  
> a range of up to 0.4 %; it is the weaker the larger the distance  
> between source and target CCD is.  The ghost images always occur at  
> the same relative pixel coordinates in the target CCD, at which the  
> star in the source CCD is located.
>
> The crosstalk pattern present in any image consists of several sub- 
> patterns.  The most common ones are:
>
> (i)  Negative crosstalk from #96 to #95.  This is always present.
> (ii)  Positive crosstalk from #94 to #95 and on to #96.  It seems  
> that #95 may sometimes be skipped over.
> (iii)  Positive crosstalk from #96 to #95 to #94 and, very rarely,  
> to #93.
>
> In images with large-scale illumination, such as flat fields, the  
> threshold for the triggering of crosstalk can be as low as a few  
> 1000 ADUs.  ADD HERE IMPLICATIONS FOR DATA REDUCTION/CALIBRATION.   
> ADD PICTURE??
>
> -- 
> Dietrich Baade
> ESO - European Organisation for Astronomical Research in the  
> Southern Hemisphere
> Karl-Schwarzschild-Strasse 2,  85748 Garching bei Muenchen,  Germany
> Email: dbaade at eso.org    Tel: +49 89 3200-6388    Fax: +49 89 3202362
>