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.
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/
