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      Driver procedure (for SUBSTAR) to subtract scaled PSF values


      Computes residuals of the PSF fitting program

Calling Sequence

      T_SUBSTAR, image, fitsfile, id,[ psfname, /VERBOSE, /NOPSF ]


      IMAGE - On input, IMAGE is the original image array. A scaled
              PSF will be subtracted from IMAGE at specified star positions.
              Make a copy of IMAGE before calling SUBSTAR, if you want to
              keep a copy of the unsubtracted image array


      FITSFILE - scalar string giving the name of the disk FITS ASCII
              produced as an output from T_NSTAR.

Optional Inputs

      ID - Index vector indicating which stars are to be subtracted. If
              omitted, (or set equal to -1), then stars will be subtracted
              at all positions specified by the X and Y vectors.
              (IDL convention - zero-based subscripts)
      PSFNAME - Name of the FITS file containing the PSF residuals, as
              generated by GETPSF. SUBSTAR will prompt for this parameter
              if not supplied.

Optional Input Keyword

      /VERBOSE - If this keyword is set and non-zero, then the value of each
              star number will be displayed as it is processed.
      /NOPSF - if this keyword is set and non-zero, then all stars will be
              be subtracted *except* those used to determine the PSF.
              An improved PSF can then be derived from the subtracted image.
              If NOPSF is supplied, then the ID parameter is ignored


      T_SUBSTAR does not modify the input FITS table.

Procedures Used


Revision History

      Written, R. Hill, ST Sys. Corp., 22 August 1991
      Added NOPSF keyword W. Landsman March, 1996
      Use FITS format for PSF resduals July, 1997
      Converted to IDL V5.0 W. Landsman September 1997
      Call FTINFO first to improve efficiency W. Landsman May 2000

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