IRAF Newsletter -- Number 14 -- April 1998

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DIGIPHOT Package Update

The default magnitude zero point of the apphot package has been changed from 26.0 to the default daophot package value of 25.0 in order to minimize confusion for users who switch back and forth between the two packages. For greater cross package consistency the magnitude zero point of the imexamine task has also been changed from 30.0 to 25.0.

The apphot and daophot package aperture photometry tasks have been modified to compute the aperture sums and aperture areas in double precision rather than in real precision. This change was made to minimize machine precision errors for sums computed over large, e.g., galaxy sized, apertures and for low noise or synthetic image data. The same tasks have been modified to output any negative total flux values should they occur, in order to make it easier to examine the effects of sky value and machine precision errors. In former versions of the apphot and daophot packages negative flux values were regarded as non-physical and were set to 0.0.

Lindsey Davis

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IRAF Group, National Optical Astronomy Observatories, P.O. Box 26732, Tucson, AZ 85726, Phone: (520) 318-8160, FAX: (520) 318-8360, Email

Posted: 07May1998