From: Vitaliy Fadeyev (VAFadeyev@lbl.gov)
Date: Sat Apr 03 2004 - 22:56:20 PST
Hi Greg,
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.
vitaliy
Greg Aldering wrote:
> Hi Vitaliy,
>
> Do you see this same scatter between the news and refs in a given filter?
>
> In z-band the response for ACS z' and Subaru z' could be different since
> z' is a longpass filter and Subaru CCDs are more red sensitive.
>
> - Greg
>
> On Sat, 3 Apr 2004, Vitaliy Fadeyev wrote:
>
> >
> >
> > Rob,
> >
> > Lifan and I see quite a bit of scatter while relating these
> > images and GOODs tiles, up to a factor of 2. There may be
> > some position dependence on a chip. So, there are two questions:
> > - Do you think that 0.3 mag error is "good enough" in this case?
> > - Do you have an idea for such a scatter? Perhaps a not so great
> > flatfield used?
> >
> > vitaliy
> >
> >
> > "Robert A. Knop Jr." wrote:
> >
> > > At some point (probably not until late late tonight) Subaru I-band
> > > subtractions will start showing up.
> > >
> > > These are the zeropoints that will be used for them:
> > >
> > > sub04mar/mar172004suprimea28956sum.fts | 38.1048017998
> > > sub04mar/mar172004suprimeb28956sum.fts | 38.1206147516
> > > sub04mar/mar172004suprimec28956sum.fts | 37.131587848
> > > sub04mar/mar172004suprimed28956sum.fts | 36.8684151492
> > > sub04mar/mar172004suprimef28956sum.fts | 37.7517776011
> > > sub04mar/mar172004suprimee28956sum.fts | 37.5677277862
> > > sub04mar/mar172004suprimeg28956sum.fts | 37.3110273633
> > > sub04mar/mar172004suprimeh28956sum.fts | 37.2026060372
> > > sub04mar/mar172004suprimei28956sum.fts | 37.5857562505
> > > sub04mar/mar172004suprimej28956sum.fts | 36.4820993053
> > > ^
> > > |
> > >
> > > The indicated letter is the chip of the subtraction.
> > >
> > > These zeropoints are completely bogus. (They are based on the R
> > > magnitudes from the USNO catalog and should not be trusted to better
> > > than a magnitude or two.) I need somebody to figure out a reasonable
> > > zeropoint for these images. At that point, we will need to adjust any
> > > magnitudes that come off of the Subaru subtractions by the *difference*
> > > between this zeropoint and the real zeropoint determined for these
> > > images.
> > >
> > > These are I-band images. You can get at them with
> > >
> > > finddbfile -g <filename>
> > >
> > > or
> > >
> > > imview -scp <filename>
> > >
> > > Note that the night was decidedly not photometric, so just taking a
> > > published Suprime-Cam zeropoint won't work. (Plus, I'm not sure about
> > > the units of this sum.) We have to do something empirical to get a
> > > vega-based zeropoint for these imgaes. Perhaps match and compare to
> > > GODOS images (whose zeropoints *should* be good), or perhaps match and
> > > compare to pre-existing calibrated data.
> > >
> > > This will be a painful hand-work task, and I don't have time to do it.
> > >
> > > The same may eventually need to be done for the subaru z-band images.
> > >
> > > -Rob
> > >
> > > --
> > > --Prof. Robert Knop
> > > Department of Physics & Astronomy, Vanderbilt University
> > > robert.a.knop@vanderbilt.edu
> >
> > --
> >
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