NICMOSlook Setup Parameters

In the calibration subdirectory mentioned in the section above, the file calnicc.setup contains variety of parameters that can be set to modify the behavior of NICMOSlook. It is possible to modify these parameters while running NICMOSlook. Use the button to change the values. This will pop-up the parameter editor. All parameters are described in plain English and can be changed (see Figure 5.2). The changes take effect immediately after hitting the button on the editor pop-up. In addition, the values are written back to the file $NICMOSLOOK_BASE/calib/calnicc.setup. See table E.2 for the default values of the parameters described below.

 

Object Finding

• BADPIX_THRESH
  Pixel coordinates that contain object information are compared with a bad pixel map. A ratio of total pixels to the number of the bad pixels is calculated and compared to this parameter. If the ratio is higher than this value, the object is removed from the object list.
• MAXOBJS
  For computing resource purposes, this number determines how many objects on an image set are to be examined.
• REJ_THRESH
  Currently not used.
  Spectrum Extraction
  
• SZ_FACTOR
  Width of a spectrum in units of the 2nd order moment of the object on the direct image.
• WEIGHTPERC
  When computing the set of extraction weights for unweighted extraction, the extent of the array is derived from the object's profile. All the weights corresponding to regions that contribute less than WEIGHTPERC percents of the maximum flux are set to zero. The rest of the weights are all set to the same values and scaled to conserve the total extracted flux.
• NOFLATFIELD
  This parameter allows users to turn off (or on) the flatfielding of the extracted spectra.
• NODTQ
  This parameter allows users to turn off (or on) the use of the Data Quality information. When DTQ is used, pixels marked as bad are ignored.
• DTQ_MASK
  Mask for rejection of pixels based on the value of the Data Quality image. The mask is given as an integer value. Its corresponding binary number is used to reject pixel witch have flags set where the binary number of the mask is one. For example, if this parameter is set to 3 (which has a binary code of 11), all pixels are rejected with the first and second flat set.
• ASSOCFF
  This parameter allows users to turn off (or on) the use of a NICMOS ``association file'' to construct a flatfield for a particular chopping pattern.
• POS_ERR
  This field should contain an estimate of the uncertainty (in pixel) in objects' coordinates. This value is used to derive an error estimate when applying a response function to an extracted spectrum.
• PUNITSW
  The units to use for the spectral plots. Valid choices are dn, mjy, or erg. The grism response function from the file grismspec.dat will be applied if necessary.
• NOWEIGH
  This parameter has only an effect when running Calnic C. It allows a user to turn on (or off) the use of weighted extraction.
• CORRECTPRF
  This parameter allows users to turn off (or on) the use of correction for the effect of the intra-pixel response function.
• ADCGAIN
  Analog to digital gain in electrons/ADU. This value will be used as a default IF no keyword ADCGAIN is found in the image header.
  Background
  
• BG_PIXELS
  Calculate a background estimate for an object during spectral extraction, the mean value of the pixels surrounding the edge of the object is calculated. This parameter determines the width of the region used in this calculation.
• NOBACKGND
  This parameter allows users to turn off (or on) background subtraction before spectral line extraction commences.
• NOINTERPOL
  If this parameter is turned on, then the program will use interpolated values of the surrounding image background when subtracting the background. If this parameter is turned off, then the calibration background file is scaled and subtracted from the image instead.
  Line Detection
  
• CONT_FACTOR
  This factor determines the region for which the average of the continuum "longwards" of the line with the longest wavelength and "shortwards" of the line with the shortest wavelength is computed. The "long" region is the peak of the line with the longest wavelength added to the $\sigma$ of that line multiplied with this factor. The "short" region is the peak of the line with the shortest wavelength minus the $\sigma$ of that line multiplied with this factor.
• DET_THRESH
  Threshold used in the spectral line search to identify lines in units of the rms of the spectrum.
• FIT_ORDER1
  A polynomial is fitted to the continuum in each spectrum. After the first fit, deviating points are removed from the fit region and the process is iterated. This parameter is the order of the polynomial for the first N_ITERLOW iterations (see below).
• FIT_ORDER2
  Polynomials are iteratively fitted to the continuum in each spectrum. After each fit, deviating points are removed from the fit region for the next iteration. This parameter is the order of the polynomial for all but the first N_ITERLOW iterations (see below).
• MAXLINES
  This parameter determines the maximum number of lines which can be detected in any spectrum.
• MIN_NPOINTS
  This parameter is the minimum number of consecutive points which deviate from the continuum fit in the spectrum which are considered as a spectral line.
• MIN_PIX_NO
  Minimum line width for a line to be considered as real.
• BLEND_FACTOR
  In the spectral line search process, 2 lines are considered to be the same line if the separation of the peaks is smaller than the sum of the line widths multiplied with this factor. In that case, the region of the two lines are joined and a new Gaussian is fitted over the entire wavelength range of the line.
• MIN_SIGNSE
  Detected lines whose signal-to-noise ratio is less than this value are rejected.
• N_ITERATIONS
  The fit to the continuum in the spectrum is discontinued after this number of iterations.
• N_ITERLOW
  The fit of a polynomial to the continuum in the spectrum is done in two steps. For the first iterations, a low order polynomial is fitted in order to identify strong lines. After several iterations in which deviant points are rejected and a new polynomial is fit, the order of the fit is increased. This parameter determines the number of iterations before the next higher fit order is used.
  Image Registration
  
• NOWCS
  Parameter to turn off / on the use of the WCS in the image header to register the images. If WCS registration is turned off, the pixel coordinates in the images are used (i.e. the images are assumed to be perfectly registered).
• FROMWCS
  Parameter to turn off / on the use of ra and dec in input object lists. If this option is turned on, the pixel coordinates will be used instead.
  Deblending
  
• NODEBL
  This parameter has only an effect when running Calnic C. It allows a user to turn on (or off) deblending.
• O_THRESH1
  Close spectra on the grism image potentially contaminate each other. This parameter is the maximum distance of 2 spectra on the grism image for them to be considered being exactly aligned. The parameter is in units of the sum of the line widths of both spectra.
• O_THRESH2
  Close spectra on the grism image potentially contaminate each other. This parameter is the maximum distance of 2 spectra on the grism image for which a contamination is expected and Calnic C attempts to "deblend".
• O_THRESH3
  Close spectra on the grism image potentially contaminate each other. This parameter is the maximum distance of 2 spectra on the grism image for which a contamination is considered to be still possible.
• DEBLEND_ERR_MIN
  When calculating the deblending error, this value is substituted for deblending errors that are of smaller value.
  Debugging
  
• DEBUG_LEVEL
  This parameter determines the verbosity of Calnic C's output messages. The higher its value, the more information is printed to the debugging output file. This parameter allows for detailed debugging messages. Refer to section 5.2 for more information.
• MAXPIX
  For computing resource considerations, the maximum size of input images processed by Calnic C in pixels.
• MAXPIXX
  (Not Used)
• MAXPIXY
  (Not Used)

 

Figure 5.2: The NICMOSlook Parameter Editor. NICMOSlook provides an easy way to change the parameters of either NICMOSlook or Calnic C.