7. celldetect Parameters & Data Products Reference

This chapter lists all the celldetect parameters in alphabetical order for quick reference. In addition, a guide to the data products output by celldetect is provided.

7.1 Default Parameter File

unix% plist celldetect

Parameters for /soft/ciao/param/celldetect.par

#   celldetect parameter file
#   input  
        infile =                  Input file
#   output
       outfile =                  Output source list
       (expstk = )                list of exposure map files
      (regfile = none)            ASCII regions file
#   output options
       (kernel = default)         Output file format
      (clobber = no)              Overwrite exiting outputs?
#   output content/format options
       (thresh = 3)               Source threshold
    (findpeaks = yes)             Find local peaks?
     (centroid = yes)             Compute source centroids?
     (ellsigma = 3)               Size of output source ellipses (in sigmas)
     (expratio = 0)               cutoff ratio for source cell exposure variation
#   detect cell size parameters
    (fixedcell = 0)               Fixed cell size to use (0 for variable cell)
      (xoffset = INDEF)           Offset of x axis from data center
      (yoffset = INDEF)           Offset of y axis from data center
        (eband = 1.4967)          Energy band
      (eenergy = 0.8)             Encircled energy of PSF
     (psftable = ${ASCDS_CALIB}/psfsize20010416.fits -> /soft/ciao/data/psfsize20010416.fits) Table of PSF size data
     (cellfile = )                Output cell size image stack name
#   background parameters
      (bkgfile = )                Background file name
     (bkgvalue = 0)               Background count/pixel
  (bkgerrvalue = 0)               Background error
#   using defaults is recommended here
     (convolve = no)              Use convolution?
      (snrfile = )                SNR output file name (for convolution only)
#   run log verbosity and content
      (verbose = 0)               Log verbosity level
          (log = no)              Make a celldetect.log file?
#   mode
         (mode = ql)

7.2 Parameter Descriptions

In the following parameter descriptions, "required=yes" indicates that the user must provide a value for the indicated parameter (e.g. infile) before the program will run. Also, the empty string (" ") is equivalent to the string none for filenames.

7.3 Data Product Descriptions

Source List File (outfile )

The primary output of celldetect is the FITS file of source detections. If the signal-to-noise (S/N) ratio in a detect cell exceeds the threshold set by the user (thresh ), then the cell location is considered a source candidate and the following properties are recorded in the output file: 7.1

Data item Unit Description
RA deg Source right ascension
DEC deg Source declination
RA_ERR deg Source right ascension error
DEC_ERR deg Source declination error
POS(X,Y) pixel Physical coordinates
X_ERR pixel Source X position error
Y_ERR pixel Source Y position error
CELLPOS(CELL_X,CELL_Y) pixel Physical coordinates
DETSIZE pixel Source cell size
BKGSIZE pixel Background cell size
NPIXSOU pixel Pixels in source cell
NPIXBKG pixel Pixels in background cell
NET_COUNTS count Net source counts
NET_COUNTS_ERR count Error in net source counts
BKG_COUNTS count Background counts (scaled to source cell)
BKG_COUNTS_ERR count Error in background counts
NET_RATE$ ^\dagger$ count/s Source count rate
NET_RATE_ERR$ ^\dagger$ count/s Source count rate error
BKG_RATE$ ^\dagger$ count/s Background count rate
BKG_RATE_ERR$ ^\dagger$ count/s/pixel Background count rate error
EXPTIME$ ^\dagger$ s Effective exposure time
SNR   Signal-to-noise ratio
SHAPE   Shape of source region
R[2]   Radii of source region
ROTANG deg Rotation angle of source region
PSFRATIO   Ratio of source ellipse size to PSF size
BLOCK   Blocking factor
COMPONENT   Source number
EXPO_RATIO   Ratio of average background and detect cell exp
DOUBLE   Double detection flag
DOUBLE_ID   Double source component

ASCII Source Region File (regfile )

In addition to the source list file (outfile ), the user may also select to have a source region file (regfile ) output.

This region file is useful for subsequent input into ds9, particularly to overlay region markers over each detection; see Chapter 1, Section 1.4 for details.

The source region file from the example in Chapter 4, Section 4.2.2:

unix% more example2_out.reg 

Log File (logfile )

If log is set to yes, then the log information will be written to the file celldetect.log.

The log file from the example in Chapter 4, Section 4.2.2:

unix% more celldetect.log
input file: data/datasetA.fits[123:630,109:614]
output file: example2_out.fits
ASCII source regions file: example2_out.reg
creating cell size table
reading data image
creating candidate source list
cell size 3
cell size 6
cell size 9
cell size 12
Writing out cell file: datasetA_cell_1.fits

Cell Size Image (cellfile )

If a filename is provided for the cellfile parameter, then one or more images are created which contain the detect cell size at each pixel location (see Example 4.2.2). Pixels in the cell size image have values equal to the cell size used to search for sources at those pixel locations.

Signal-to-noise Ratio Map (snrfile )

The convolve option produces a pixel-by-pixel map of the S/N, which is written to the file specified by snrfile . A S/N value is computed for every pixel in the input dataset, not just for source locations. The file snrfile is then an image of these values.