NAME:
  nic1scan
 PURPOSE:
  Scan for best spectrum location of a weak-signal NICMOS spectrum.
 DESCRIPTION:

 CATEGORY:
  Spectroscopy
 CALLING SEQUENCE:
  nic1scan,obs,dy,nstep
 INPUTS:
  obs - anonymous structure containing the NICMOS data.  This structure
           is initially created by NICINIT.PRO
  dy  - Delta y, step size for scan.
  nstep - number of steps to go away from "center".  There will be 2*nsteps+1
            trial spectra computed for this.
 OPTIONAL INPUT PARAMETERS:

 KEYWORD INPUT PARAMETERS:
  SLOPE = slope override value to impose on spectral extraction
  YPOS  = position override value to impose on spectral extraction,
            this sets the new "zero-point" or the center of the scan.
  PSF   - PSF to use for extraction.  Can either be an array or a file name.
            Default=use last known PSF.
 OUTPUTS:
  Changes are made to some tags of the obs structure:
    .coeffn - modified by SLOPE/YPOS and result of scan
    .spec   - Best spectrum (most flux) found.
    .yc     - Y location of best spectrum
    .xp     - new spatial profile
    .yp     - new spatial profile
    .pnp

 KEYWORD OUTPUT PARAMETERS:

 COMMON BLOCKS:

 SIDE EFFECTS:

 RESTRICTIONS:
 Note, this routine does not apply the pixel response function correction.
 This means you must make sure all objects are done without the PRF
   correction to get a consistent flux value.
 PROCEDURE:

 MODIFICATION HISTORY:
  Written by Marc W. Buie, Lowell Observatory, 2001/01/30