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The apphot and daophot package aperture photometry tasks have been modified
to compute the aperture sums and areas in double precision instead of real
precision. This change minimizes machine precision errors that can become
significant for large apertures and very low noise or synthetic data.
These tasks have also been modified to output negative values of the total
flux should they occur. Formerly these values were being artificially set to
0.0. This change makes it easier to see the effects of any sky value and machine
errors.
The modified apertures photometry tasks are available as part of the
external addon package digiphotx. To retrieve and install digiphotx, ftp
to 140.252.1.1, login as anonymous, cd to iraf/extern, retrieve the file
digiphotx.readme, and follow the installation instructions.
Lindsey Davis
davis@noao.edu
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