[vsnet-chat 2109] Re: Required CCD temperature stability

[aah@nofs.navy.mil]

Kato-san wrote:
>...I have been considering a back-illuminated SITe chip, cooled
>at around -100 deg.  I have been wondering what degree of temparature
>stability is required, in order to obtain a high degree of photometric
>stability frequently discussed in this forum. My chief concern is the
>effect of possible fringes, variabile according to temparature, in red
>pathbands.  Could someone suggest?
   Why would you expect the fringing to be different depending on
temperature?  The fringes are caused by night-sky emission lines,
not by a temperature effect.  It is true that you lose some red QE
as you cool, but these lines are well before the red cutoff of a CCD.
  We keep our systems constant to around 0.1C, but I think 1.0C is
probably adequate.  At -100C you have essentially no dark current, so
the major reason for temperature stability is that the bias level is
temperature-dependent.  I assume you will be running non-MPP since you
are going so cold?  The SITe in MPP mode doesn't need to be taken
below TEC temperatures. There are some other effects with cooling.
Hot pixels/columns will often improve.  If you go much below -100C,
you may start running into CTE problems.  Many non-scientific chips,
such as the Kodak series, are not rated for low temperature and
often cannot be taken below -50C.
Arne

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