Re: ACS noise(/depth?) variations

From: Robert A. Knop Jr. (robert.a.knop@vanderbilt.edu)
Date: Sun Apr 04 2004 - 14:50:44 PDT

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    On Sun, Apr 04, 2004 at 02:46:11PM -0700, Greg Aldering wrote:
    > candidates and for those from Adam's search. For the new search you
    > can see very tight loci in this parameter, however, there are multiple
    > loci with a large spread between them. If each locus is interpreted as
    > being from an image (something that could be found by probing the
    > candidates database outside SNtrak), then this suggests a rather large
    > variation in either the typical PSF or typical noise amongst images.

    Another possibility -- a variation in what the software *thought* the
    PSF was.

    The software does *not* have an aperture size hard-coded into it, even
    though that would be appropriate for this search with ACS; it still does
    the same thing it always has done, try to identify the stars and figure
    out an aperture to use based on that.

    As such, even though ideally it should be using the same aperture every
    time, it's not, and will sometimes have higher signal to noise than
    other times. (This can also lead to systematics in the *magnitudes*, if
    the aperture corrections aren't great, but I *think* that those will
    tend to be smaller than the systematics in the signal to noises.)

    It would be interesting to see how well locus membership correlates with
    the subtraction the candidate was on, which is something you can find
    from SNTrak or from the Wiki page for each candidate.

    -Rob

    -- 
    --Prof. Robert Knop
      Department of Physics & Astronomy, Vanderbilt University
      robert.a.knop@vanderbilt.edu
    


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