From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Sat Apr 03 2004 - 23:00:36 PST
On Sat, Apr 03, 2004 at 10:56:20PM -0800, Vitaliy Fadeyev wrote:
> we only looked at I-band sums, and compared them to GOODs I-band (F775W)
> tiles. Also, these are only "news", i.e. recent data. Did not look at
> the year old reference yet. The variation was found in a single chip's field
> of view, for most of the chips.
Was the variation a systematic with position, or was it just a scatter
(i.e. objects anywhere varied a lot)?
If the former, then almost certainly the flatfielding is not too good.
If the latter, then it would be interesting to try to correlate it with
the i-z colors of the objects to find out if we're just seeing the
filter differences. Also, anything near a bright star may suffer from
"oversubtraction" noise.
I haven't looked at the subtractions yet, but if they are clean across
the image, that would seem to argue against systematic
position-dependent flatfield errors of that size, for that would
definitly leave noticable residuals unless by some amazing coincidence
the giant reference we got had the same systematics.
Note that *I* did the flatfielding. Naoki et all just sent us raw data,
and I did all the preliminary reductions (very quickly). Flatfields
were combined from the night sky images.
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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