[fitsbits] Appropriate BUNIT for ADUs vs electrons?

[Steve Allen]

On Fri 2011-03-04T13:27:10 -0300, James Turner hath writ:
> What do other observatories do?

Ponder the same question, but for reasons noted at the end it's a bit
moot for us.

As you note, one common way at the telescope and during intial
reduction is to leave the array values as DN/adu/count and to include
the GAIN keyword with a value according to the convention used in
various IRAF procedures.  If GAIN is reset to 1 when it is applied
then the conventional IRAF meaning is retained.  This is all, of
course, dependent on keyword conventions for images from CCDs which
are not registered with the IAUFWG.

Keck data acquisition systems generally do not include a GAIN keyword.
Lick data acquisition systems have GAIN with entirely different meaning.

--
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