Re: HELP NEEDED

From: Vitaliy Fadeyev (VAFadeyev@lbl.gov)
Date: Sat Apr 03 2004 - 22:11:34 PST

  • Next message: Greg Aldering: "Re: HELP NEEDED"

    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

    --
    -------------------------------------------------
     Vitaliy Fadeyev
     SCP group at LBNL
     phone:  510-486-4169
     web:    http://www-physics.lbl.gov/~fadeyev/
    -------------------------------------------------
    


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