[Aavso-photometry] Linearity test puzzle

[Michael Newberry]

Michael,

Be sure to read the paper that Wolfgang Renz referenced. I think it shows 
what you are seeing. Thanks for the link, Wolfgang.

This subject is interesting in that cold traps, which are dark, are also a 
function of temperature---the lower the temperature the worse they get---  
and they result from point defects in the substrate. It seems like the ghost 
effect described in the paper is simply a manifestation of the same 
phenomenon as cold traps.

In my personal experience, I've dealt with cold traps often, but I've not 
really seen ghosting caused by residual charge. Over the last umpteen years 
I've used mostly thinned chips, which seem to have cold traps but not much 
of the ghosting effect.

Michael Newberry

----- Original Message ----- 
From: "Michael Koppelman" <lolife at bitstream.net>


>I do get ghosting on bright stars. Usually I sit on the same field  for 
>hours and if there are bright stars in the field (bright being  relative to 
>exposure length) I see them on my darks for 5 minutes or  so. I've wondered 
>whether this indicates a problem with my CCD. I am  currently testing an 
>ST-7XME (I own a ST-7XE) and they both do it.
>
> Michael
>
> On Jan 26, 2006, at 6:54 PM, M Newberry wrote:
>
>> It also takes electronics working properly to transfer charge 
>> efficiently so, a modern CCD showing ghost images is either likely  to be 
>> on the verge of death or the electronics are not clocking the  array in 
>> the optimal way.
>
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