Re: HELP NEEDED

From: Greg Aldering (aldering@panisse.lbl.gov)
Date: Sat Apr 03 2004 - 22:44:16 PST

  • Next message: Vitaliy Fadeyev: "Re: HELP NEEDED"

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

    This archive was generated by hypermail 2.1.4 : Sat Apr 03 2004 - 22:44:36 PST