CPROF: Correct the Results of a PROFILE Calculation

CPROF enables the user to inspect the results of a PROFILE calculation in graphical form, and to modify them by replacing portions judged to be in error by the results of a second order polynomial fit to "good" regions. This often is necessary for spiral galaxies for which the outer contours can get confused.

The ellipticity, surface brightness, and semi-minor axis values stored in the PROFILE common block are first plotted on the display. Frequently one can find regions of spuriously low ellipticity and surface brightness, with a corresponding local maximum in the semi-minor axis, known as "excursions"; these represent areas in which the PROFILE iterations have converged poorly. If such a region is identified, the user is asked to specify the boundaries of regions on either side of the excursion in which the PROFILE results are judged to be acceptable; a polynomial is fit to the ellipticities, position angles, and surface brightnesses in the latter regions. The results of the fit are then used to recompute ellipticities, PA's and SB's in the excursion region. The default is to perform a second order fit, but fits of other order can be used by giving the ORDER=n keyword.

The process of plotting the profile parameters, identifying glitches, and replacing with fits continues until the user specifies that the profile is satisfactory. Another option is to fit only the surface brightnesses in a region. This is sometimes desirable when the ellipticity undergoes an abrupt, genuine increase; the surface brightness is then spuriously enhanced.

CPROF is best used when the galaxy image has been displayed, and the ellipses overplotted on the image using TVPROF. The success of a CPROF calculation is best measured by looking at this display.