From: Isobel Hook (imh@astro.ox.ac.uk)
Date: Sat Nov 02 2002 - 02:28:12 PST
Hi Greg,
> Am I right that with nod & shuffle one does pixel-by-pixel subtraction
> of sky observed at the SN location for each nod position? Subtracting
> "sky" from "object+sky" on a pixel-by-pixel basis gives a sqrt(2) hit
> in S/N (for "object" << "sky"), unless "sky" is obtained by including
> sky observations from several additional images.
Yes you are right. I see what you mean now.
So we can still take Nod & Shuffle exposures for faint targets and reduce
them either way, provided we are careful about the nods we use (and we
should probably offset subsequent N&S exposures of the same target).
Your r=24 boundary for what we call faint sounds reasonable. Lets see how
many good ones we get as a function of magnitude and pick a couple of the
faintest for Nod & Shuffle. There wont be time to do more than a few of
these once you factor in overheads (setup & nodding etc). By the way, in
the past we did about 3x1800s on r~24.3 objects and about 2hrs on source
for fainter ones at Gemini.
Isobel.
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