From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Mon Apr 05 2004 - 17:49:59 PDT
On Mon, Apr 05, 2004 at 05:19:13PM -0700, Saul Perlmutter wrote:
> We figure that you will probably be able to do this faster than us, but
> while you are re-checking candidates it might make sense for somebody
> here to start going through new images (and maybe subtraction images) by
> hand to try to calibrate them against the master GOODS fields. We're
> trying to figure out a method to do this right now -- mostly because of
> course we can't make any of the decisions about ranking the candidates
> based on magnitudes vs z, or color vs z until we know the zeropoints.
> Any extra obvious methods that you see to do this?
I *think* that the subtractions are calibrated to the new frames.
For a given image, look at
<subtractionname>.new0.fts
from the database to get the new image. I think that the reference gets
scaled to this, so the photometric system of this new image is the
photometric system of our subtractions. (I'm pretty sure.) (This is
how we have always done it.)
For instance, if a candidate is on subtraction acsapr/tiles08z, look at
image:
acsapr/tiles08z.new0.fts
(Find it with "imview" or with "finddbfile -g".)
Get somebody who knows how to use imview or ds9 to put down apertures
and do this comparison. Calculate a zeropoint (infinite-aperture) for a
few sample images, and tell me what it is. I can tell you how that
compares to the subtraction's zeropoint.
Do this on multiple subtractions in case we have scatter instead of just
a single systematic offset.
Forward this E-mail to those who can do this.
-Rob
-- --Prof. Robert Knop Department of Physics & Astronomy, Vanderbilt University robert.a.knop@vanderbilt.edu
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