http://www.noao.edu/staff/mighell/qdphot

QDPHOT: Quick & Dirty CCD Stellar PHOTometry 2001JUL03

QDPHOT is a fast CCD stellar photometry task which quickly produces good CCD stellar photometry from two CCD images of a star field. QDPHOT was designed to be a data mining tool for finding high-quality stellar observations in the data archives of the National Virtual Observatory. QDPHOT typically takes just a few seconds to analyze two Hubble Space Telescope WFPC2 observations of Local Group star clusters. QDPHOT is also suitable for real-time data-quality analysis of CCD observations; on-the-fly instrumental color-magnitude diagrams can be produced at the telescope console during the few seconds between CCD readouts.

Source: QDPHOT is part of the MXTOOLS package for the IRAF image processing system. The C source code for QDPHOT can be viewed online.


This work is supported by a grant from the National Aeronautics and Space Administration (NASA),
Order No. S-67046-F, which was awarded by the Long-Term Space Astrophysics (LTSA) program (NRA 95-OSS-16).



The Hubble Space Telescope WFPC2 instrument was used to obtain snapshot observations of 25 star clusters in the Magellanic Clouds with only 2 exposures per star cluster: one exposure with the F555W (~V) filter (typically 300 seconds) and one exposure with the F450W (broad-band B) filter (typically for 600 seconds). The color-magnitude diagrams show the results of a QDPHOT analysis of the HST archival images. The name of the star cluster is given in green in the top left corner of each CMD. The number of stars found by QDPHOT in both images with a signal-to-noise ratio of at least 10 is given in magenta on the right side of each CMD. The estimated cpu execution time (for a 4 year old 200 MHz Ultra1 Sun workstation) required for the QDPHOT analysis of both observations is given in orange in top right corner of each CMD. Note that all reductions took considerably less than 10 seconds on a 4-year old 200-MHz Sun workstation. The instrumental magnitudes produced by QDPHOT were transformed to Johnson B and V using the new wfpc2color task in the MXTOOLS package.


The Annotated QDPHOT IRAF Help Pages:

    
QDPHOT (2001JUL03)             mxtools                   QDPHOT (2001JUL03)



NAME  
    qdphot -- Quick and Dirty CCD stellar PHOTometry (QDPHOT)
    
    
USAGE
    qdphot image1 image2
    
    
REQUIRED INPUT PARAMETERS *****************************************************
    
    image1
        Filename of the 1st image.
    
    image2
        Filename of the 2nd image.
    
        
OPTIONAL INPUT PARAMETERS *****************************************************
    
    out1 = STDOUT
        Filename of the output associated with the 1st image.
    
    out2 = STDOUT
        Filename of the output associated with the 2nd image.

    coords = ""
        Filename of input coordinate list [QDPHOT finds stars <- ""].

    gain1 = 1.0
        Gain of the 1st image [electrons/analog-digital-units].
    
    gain2 = [value of gain1]
        Gain of the 2nd image [electrons/analog-digital-units].
    
    ron1 = 1.0
        Readout noise of the 1st image [electrons].
    
    ron2 = [value of ron1]
        Readout noise of the 2nd image [electrons].
    
    dx1 = 0.0
        Delta offset in X of the 1st image [pixels].
    
    dy1 = 0.0
        Delta offset in Y of the 1st image [pixels].
    
    dx2 = 0.0
        Delta offset in X of the 2nd image [pixels].
    
    dy2 = 0.0
        Delta offset in Y of the 2nd image [pixels].

    idint1 = 1
        Integer identifier for the 1st image (e.g. CCD number).
    
    idint2 = [value of idint1]
        Integer identifier for the 2nd image (e.g. CCD number).
    
    bias1 = 0.0
        Bias to be subtracted from the 1st image [ADU].
    
    bias2 = [value of bias1]
        Bias to be subtracted from the 2nd image [ADU].
    
    search2 = 0.0
        Search radius for the 2nd image [pixels] (0 <= no search).
    
    mnsnr = 8.0
        Minimum signal-to-noise ratio for *both* images.
    
    mxstars = 0
        Maximum number of stars (0 <= no limit).
    
    mnpeak1 = [minimum pixel value of image1]
        Minimum peak for the 1st image [central pixel value in ADU].
    
    mnpeak2 = [minimum pixel value of image2]
        Minimum peak for the 2nd image [central pixel value in ADU].
    
    mxpeak1 = [maximum pixel value of image1]
        Maximum peak for the 1st image [central pixel value in ADU].
    
    mxpeak2 = [maximum pixel value of image2]
        Maximum peak for the 2nd image [central pixel value in ADU].
    
    mnround = 0.0
        Minimum ROUND for *both* images (eccentricity: 0<=ROUND<=1).
    
    mxround = 1.0
        Maximum ROUND for *both* images (eccentricity: 0<=ROUND<=1).
    
    mnangle = -90.0
        Minimum ANGLE for *both* images (-90 <= ANGLE degrees <= 90).
    
    mxangle = 90.0
        Maximum ANGLE for *both* images (-90 <= ANGLE degrees <= 90).
    
    mnsharp = 0.0
        Minimum SHARP for *both* images (0 <= SHARP <= 1).
    
    mxsharp = 1.0
        Maximum SHARP for *both* images (0 <= SHARP <= 1).
    
    mnkappa = -9.999
        Minimum KAPPA for *both* images.
    
    mxkappa = +9.999
        Maximum KAPPA for *both* images.
    
    rejects = no
        Show rejects? (boolean: yes or no).
        
        
OUTPUT PARAMETERS *************************************************************
    
    ostars
        Number of stars found.
    
    odx2
        Delta offset in X for the 2nd image with respect to 1st image.
    
    ody2
        Delta offset in Y for the 2nd image with respect to 1st image.
    
    ocpusec
        Estimated elapsed processing time [seconds].
    
    ostart
        Date/Time QDPHOT started.
    
    ostop
        Date/Time QDPHOT stopped.
    
    
        
DESCRIPTION
    

    QDPHOT  is a fast CCD stellar photometry task which quickly produces
    good CCD stellar photometry from two CCD images  of  a  star  field.
    QDPHOT   was   designed  to  be  a  data  mining  tool  for  finding 
    high-quality stellar  observations  in  the  data  archives  of  the
    National  Virtual  Observatory.   QDPHOT  typically takes just a few
    seconds to analyze two Hubble Space Telescope WFPC2 observations  of
    Local  Group  star  clusters.  QDPHOT is also suitable for real-time
    data-quality analysis of CCD observations;  on-the-fly  instrumental
    color-magnitude  diagrams  can  be produced at the telescope console
    during the few seconds between CCD readouts. More information  about
    QDPHOT is available at the official QDPHOT website:
    
       http://www.noao.edu/staff/mighell/qdphot/

        
EXAMPLES
    
    Let  us do a QDPHOT analysis of a Hubble Space Telescope observation
    of the Galactic globular cluster NGC 362.
    
    The WF3 camera images of these WFPC2 observations
        
      ngc362b3.fits
      ngc362v3.fits
    
    are found in the in the QDPHOT demo directory:
            
      mxtools$data
    
    To start, let us reset the QDPHOT task with the command

      unlearn qdphot
    
    This command resets  the  QDPHOT  task  to  its  standard  (default)
    values.
    
    The QDPHOT command
    
    qdphot\
      image1="mxtools$data/ngc362b3.fits[60:790,60:790]"\
      image2="mxtools$data/ngc362v3.fits[60:790,60:790]"
    
    does  the  QDPHOT  analysis  of  the  [60:790,60:790] portion of the
    images in a few  seconds  and  sends  all  of  the  results  to  the
    standard output device (STDOUT).
    
    The above command is equivalent to the following QDPHOT command
        
    qdphot\
      image1="mxtools$data/ngc362b3.fits[60:790,60:790]"\
      image2="mxtools$data/ngc362v3.fits[60:790,60:790]"\
      out1="STDOUT"\
      out2="STDOUT"
    
    The QDPHOT command

    qdphot\
      image1="mxtools$data/ngc362b3.fits[60:790,60:790]"\
      image2="mxtools$data/ngc362v3.fits[60:790,60:790]"\
      out1="ngc362b3.imag"\
      out2="ngc362v3.imag"    
    
    sends the QDPHOT results to the files
    
      ngc362b3.imag
      ngc362v3.imag
    
    in the current working directory.
    
    Let us now load the IMAGES and TV packages with the commands
    
      images
      tv
    
    We  can display the [60:790,60:790] sections of the WF3 image of the
    F439W observation of NGC 362 in frame 1 of the  image  display  with
    the following command
        
    display\
      image="mxtools$data/ngc362b3.fits[60:790,60:790]"\
      frame=1\
      fill=yes\
      erase=yes
    
    We  can show the measured stars in the F439W image with green points
    with the following command
            
    tvmark\
       frame=1\
       coords="ngc362b3.imag"\
       color=205\
       mark=point
    
    Likewise, we can display the [60:790,60:790]  sections  of  the  WF3
    image  of  the  F555W observation of NGC 362 in frame 2 of the image
    display with the following command
                
    display\
      image="mxtools$data/ngc362v3.fits[60:790,60:790]"\
      frame=2\
      fill=yes\
      erase=yes
    
    We can show the measured stars in the F555W image  with  red  points
    with the following command
    
    tvmark\
       frame=1\
       coords="ngc362b3.imag"\
       color=204\
       mark=point
        
    Let  us  now load the STSDAS, GRAPHICS, and the STPLOT packages with
    the commands

      stsdas
      graphics
      stplot
    
    The  following  command  uses  the  IGI  task  to  plot  the  QDPHOT 
    instrumental  color-magnitude  diagram  (CMD)  using  an  IGI script
    located in the QDPHOT demo directory
    
      igi < mxtools$src/qdphot/demo/demoqdphot.igi



    We see the main-sequence turnoff of NGC 362 at  the  bottom  of  the
    CMD, the red giant branch, and a stubby red horizontal branch.
    
    Not bad, at all.  However, we can do significantly better!
    
    The  gain  and  readout noise values for these observations are 14.0
    electrons/analog-digital-units and 6.58 electrons, respectively.
    
    Let us delete the existing QDPHOT files with the following commands
    
      delete "ngc362b3.imag" verify- 
      delete "ngc362v3.imag" verify- 
    
    and try the following commands
        
    unlearn qdphot
    qdphot\
      image1="mxtools$data/ngc362b3.fits[60:790,60:790]"\
      image2="mxtools$data/ngc362v3.fits[60:790,60:790]"\
      out1="ngc362b3.imag"\
      out2="ngc362v3.imag"\
      gain1=14.0\
      ron1=5.2
    igi < mxtools$src/qdphot/demo/demoqdphot.igi
    



    The default gain value for QDPHOT is 1 electron/analog-digital-unit.
    Using  the  true  gain  value  of  14.0  caused  all the stars to be
    measured  by  a  factor  of  2.67  mag  [=2.5*log_10(14.0)].    More 
    importantly,  however,  is  that  fact  that  many  more  stars were
    detected below the main-sequence turnoff.
    
    The default readout noise value for QDPHOT  is  1  electron.   Using
    the   true   readout   noise  value  gives  better  (more  accurate) 
    photometric error estimates.
    
    After deleting the existing QDPHOT files, let us try  the  following
    commands
            
    unlearn qdphot
    qdphot\
      image1="mxtools$data/ngc362b3.fits[60:790,60:790]"\
      image2="mxtools$data/ngc362v3.fits[60:790,60:790]"\
      out1="ngc362b3.imag"\
      out2="ngc362v3.imag"\
      gain1=14.0\
      ron1=5.2\
      mnpeak1=10\
      mxpeak1=3500
    igi < mxtools$src/qdphot/demo/demoqdphot.igi




    QDPHOT  found  2336  stars  instead  of  2449  ---  but  the program
    execution was over 4 times faster because we used reasonable maximum
    and  minimum peak values for stellar candidates in the observations.
    WFPC2 observations become nonlinear above approximately 3500 ADU  --
    a   reasonable   value   for  mxpeak1  and  mxpeak2  for  all  WFPC2 
    observations.  A mnpeak1 value of 10 ADU  is  a  reasonable  minimum
    peak  value  for a star in these observations --- based on the pixel
    histogram of the analyzed image sections.

    A faster QDPHOT demonstration can be done with the MXTOOLS task
                
      demoqdphot
    
    which will produce a CMD identical to the one just produced.
    
    The  data  format  of the QDPHOT output files is described in detail
    at the end of each file along  with  the  QDPHOT  command  parameter
    values  which  produced  that  result.   The X and Y location of the
    stars  are  found,  respectively,  in  columns  (1)  and  (2).   The 
    instrumental  stellar magnitudes (0 mag = 1 electron) and associated
    photometric errors are found in columns (4) and (5), respectively.
    
    
    
REFERENCES
    
    
CREDITS
    
    This research is supported by a grant from the National  Aeronautics
    and  Space  Administration  (NASA),  Order  No. S-67046-F, which was
    awarded by the Long-Term  Space  Astrophysics  (LTSA)  program  (NRA
    95-OSS-16).
    

BUGS
    
    Please send bug reports to the author:
    
    Kenneth Mighell  (mighell@noao.edu)
    Kitt Peak National Observatory           
    National Optical Astronomy Observatory
    950 North Cherry Avenue
    Tucson, AZ  85719
    

SEE ALSO
    
    Check out the official QDPHOT website:
    
       http://www.noao.edu/staff/mighell/qdphot/
    


This work is supported by a grant from the
National Aeronautics and Space Administration (NASA),
Order No. S-67046-F, which was awarded by the
Long-Term Space Astrophysics (LTSA) program (NRA 95-OSS-16).
Kenneth Mighell
Associate Scientist  
Kitt Peak National Observatory
National Optical Astronomy Observatories

EMAIL: mighell@noao.edu
 MAIL: P.O. Box 26732, Tucson, AZ  85726-6732
FEDEX: 950 N. Cherry Ave., Tucson, AZ  85719
PHONE: (520) 318-8391
  FAX: (520) 318-8360
  URL: http://www.noao.edu/staff/mighell/

Last updated: 2001 August 02