HELP NEEDED

From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Sat Apr 03 2004 - 16:17:12 PST

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    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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