Photometry with TUG data
As a last step we
will do photometry to out images. We will first make aperture
photometry and then the differenfial photometry.
Aperture photometry is being done by using
the IRAF package apphot and task qphot. But to do photometry to all of
the stars in a field we should first give IRAF the coordinates of the
stars. To do so we will use the IRAF task daofind. But most generally
to do photometry of a GRB afterglow one will only need to do photometry
of 3-5 stars and this can also be done using the interactive mode of
qphot which will statistically be more healthy.
DAOFIND
To start the daofind :
cl> noao
no> digiphot
di> apphot
ap> daofind
Daofind is a task to create a list of objects file which will be then
used as input to qphot and daophot.
PACKAGE = apphot
TASK = daofind
image = cr0001_1_al.fit
Input image(s)
(output
=
default) The output coordinates list(s) (default: image.c
(starmap=
) The output density enhancement image(s)
(skymap
=
) The output sky image(s)
(datapar=
) Data dependent parameters
(findpar=
) Object detection parameters
(boundar=
nearest) Boundary extension (constant, nearest, reflect,
(constan=
0.) Constant for constant boundary extension
(interac=
no) Interactive mode ?
(icomman=
) Image cursor: [x y wcs] key [cmd]
(gcomman=
) Graphics cursor: [x y wcs] key [cmd]
(wcsout
=
)_.wcsout) The output coordinate system (logical,tv,physica
(cache
=
)_.cache) Cache the image pixels ?
(verify
=
)_.verify) Verify critical parameters in non-interactive mo
(update
=
)_.update) Update critical parameters in non-interactive mo
(verbose=
)_.verbose) Print messages in non-interactive mode ?
(graphic=
)_.graphics) Graphics device
(display=
)_.display) Display device
(mode
=
ql)
Instead of these options the most critical options of the task will be
asked to you when you execute it.
ap> daofind
Input image(s) (cr0001_1_al.fit):
FWHM of features in scale units (2.5) (CR or value):
3.5
New FWHM of features: 3.5
scale units 3.5 pixels
Standard deviation of background in counts (INDEF) (CR or value): 25
New standard deviation of
background: 25. counts
Detection threshold in sigma (4.) (CR or value):
New detection threshold: 4.
sigma 100. counts
Minimum good data value (INDEF) (CR or value): 4500
New minimum good data value:
4500. counts
Maximum good data value (INDEF) (CR or value): 60000
New maximum good data value:
60000. counts
Here the
options Standard Deviation of background in counts is important since
it will find the sources by comparing this value and the Detection
Threshols Sigma to find a new source. If you give a small number for
the deviation then it is aiming to find two or three sources in one
bright star. Also if you play with the Minimum and Maximum good data
value you will see that the number of the sources algorithm finds will
change. The best thing is to check the image with imstat and imexamine
before giving these values in order to be accurate enough.
After running daofind it will create a
map file named *.coo.1, if you run daofind for several times for the
same file it will increase the number instead of overwriting the file.
You can check your source file by
giving this command :
tvmark 1 cr0001_1_al.fit.coo.12 mark=circle radii=10
color=205
This will overplot an image loaded in DS9 and you will be able to check
whether the sources are OK or not. After an header file you coordinates
file should look something like this.
#N XCENTER YCENTER
MAG SHARPNESS
SROUND
GROUND
ID \
#U pixels pixels
#
#
#
#
# \
#F %-13.3f %-10.3f %-9.3f
%-12.3f %-12.3f
%-12.3f
%-6d \
#
902.538 2.781
-2.915 0.472
-0.465
0.283 1
861.789 10.481
-4.665 0.404
0.141
-0.076 2
857.760 12.703
-2.587 INDEF
0.121
-0.074 3
866.244 12.714
-2.682 INDEF
0.075
-0.057 4
510.490 15.283
-4.180 0.398
0.344
-0.200 5
624.560 48.969
-4.935 0.400
0.282
-0.192 6
629.242 51.723
-2.495 INDEF
-0.228
-0.047 7
268.964 59.290
-4.121 0.396
0.108
-0.149 8
316.710 63.303
-2.225 0.465
0.516
-0.063 9
719.808 67.788
-2.282 0.409
-0.313
-0.013 10
274.825 87.849
-4.621 INDEF
-0.044
-0.013 11
295.174 91.839
-1.285 INDEF
0.737
-0.007 12
265.828 94.948
-0.481 INDEF
-0.163
0.163 13
282.792 96.047
-6.716 0.330
0.290
0.744 14
281.366 97.599
-6.682 INDEF
-0.615
0.531 15
284.584 101.061 -6.505
0.322
0.974
0.884 16
285.239 110.452 -6.334
INDEF
-0.558
0.104 17
279.431 112.906 -6.290
0.306
0.975
0.988 18
284.581 112.925 -6.508
0.311
-0.680
0.923 19
300.214 114.800 -0.123
INDEF
-0.657
0.020 20
266.789 115.788 -0.604
INDEF
0.485
-0.001 21
270.788 119.793 -0.409
INDEF
0.418
0.009 22
282.134 121.804 -6.900
INDEF
0.717
1.285 23
Apeture Photometry
After finding the stars in the field
you can start qphot to do aperture photometry. There are two ways to do
photmetry one is the automatic way and the second one is the
interactive way. Here we will first go with the automatic way, this is
OK when you know the properties of your image and if you will make
photometry of a lot of stars from a lot of images. The importantant
parameters are the source annulus, centering box, The width of the
annulus, parameters which can also be determined in the interactive
mode.
PACKAGE = apphot
TASK = qphot
image =
@outim_list_1 The input image(s)
cbox
=
5. The centering box width in pixels
annulus
=
15. The inner radius of sky annulus in pixels
dannulus=
10. The width of the sky annulus in pixels
aperture=
10 The list of photometry apertures
(coords = cr0001_1_al.fit.coo.1) The input coordinate file(s) (default:
*.coo.?)
(output
=
default) The output photometry file(s) (default: *.mag.?)
(plotfil=
) The output plot metacode file
(zmag
=
25.) The zero point of the magnitude scale
(exposur=
exptime) The exposure time image header keyword
(airmass=
airmass) The airmass image header keyword
(filter
=
filter) The filter image header keyword
(obstime=
jd) The time of observation image header keyword
(epadu
=
1.5) The instrument gain in e-/ADU
(interac=
no) Interactive mode ?
(radplot=
no) Plot the radial profiles in interactive mode ?
(icomman=
) Image cursor: [x y wcs] key [cmd]
(gcomman=
) Graphics cursor: [x y wcs] key [cmd]
(wcsin
=
)_.wcsin) The input coordinate system (logical,tv,physical
(wcsout
=
)_.wcsout) The output coordinate system (logical,tv,physica
(cache
=
)_.cache) Cache input image pixels in memory ?
(verbose=
)_.verbose) Print messages in non-interactive mode ?
(graphic=
)_.graphics) Graphics device
(display=
)_.display) Display device
(mode
=
ql)
After
setting these parameters if you did not choose the interactive mode all
you need to do is to wait until it finishes. The algorithm will create
a *mag.1 file for each image with the same name. After a header part ,
the text file should look something like this.
#N
IMAGE
XINIT YINIT
ID
COORDS
LID \
#U
imagename
pixels pixels ##
filename
## \
#F
%-23s
%-10.3f %-10.3f %-6d
%-23s
%-6d
#
#N XCENTER YCENTER XSHIFT
YSHIFT XERR
YERR
CIER CERROR \
#U pixels pixels
pixels pixels pixels
pixels
## cerrors \
#F %-14.3f %-11.3f %-8.3f
%-8.3f %-8.3f
%-15.3f %-5d
%-9s
#
#N MSKY
STDEV
SSKEW
NSKY NSREJ SIER SERROR \
#U counts
counts
counts npix
npix ## serrors \
#F %-18.7g
%-15.7g
%-15.7g %-7d
%-9d %-5d
%-9s
#
#N ITIME
XAIRMASS
IFILTER
OTIME
\
#U timeunit
number
name
timeunit
\
#F %-18.7g
%-15.7g
%-23s
%-23s
#
#N RAPERT
SUM
AREA
FLUX
MAG MERR PIER PERROR \
#U scale
counts
pixels
counts mag
mag ## perrors \
#F %-12.2f %-14.7g
%-11.7g %-14.7g
%-7.3f %-6.3f %-5d %-9s
#
cr0001_1_al.fit
510.490 15.283 5
cr0001_1_al.fit.coo.12 5 \
510.491 15.393
0.001 0.110 0.003
0.003
0 NoError \
3471.444
32.51688
20.6794 955
22 0
NoError \
300.
1.212
R
2453401.4969421 \
10.00
1243015. 314.2613
152074.8 18.238 0.005 0
NoError
cr0001_1_al.fit
624.560 48.969 6
cr0001_1_al.fit.coo.12 6 \
624.533 48.925
-0.027 -0.044 0.002
0.003
0 NoError \
3473.955
31.40362
-5.067676 1250
3 0
NoError \
300.
1.212
R
2453401.4969421 \
10.00
1383630. 314.4768
291151.7 17.533 0.003 0
NoError
cr0001_1_al.fit
629.242 51.723 7
cr0001_1_al.fit.coo.12 7 \
624.533 48.925
-4.709 -2.798 0.002
0.003 107
BigShift \
3473.955
31.40362
-5.067676 1250
3 0
NoError \
300.
1.212
R
2453401.4969421 \
10.00
1383630. 314.4768
291151.7 17.533 0.003 0
NoError
cr0001_1_al.fit
268.964 59.290 8
cr0001_1_al.fit.coo.12 8 \
268.968 59.373
0.004 0.083 0.004
0.003
0 NoError \
3546.902
61.22735
50.36557 1094
161 0
NoError \
300.
1.212
R
2453401.4969421 \
10.00
1266751. 314.4289
151501.9 18.242 0.009 0
NoError
cr0001_1_al.fit
316.710 63.303 9
cr0001_1_al.fit.coo.12 9 \
317.474 63.490
0.765 0.187 0.006
0.006
0 NoError \
3533.051
50.55873
36.22818 1216
44 0
NoError \
300.
1.212
R
2453401.4969421 \
10.00
1152206. 314.0706
42578.52 19.620 0.026 0
NoError
In the
interactive mode you will have the chance to first select a star from
the DS9 window and then you will be able to select the annulus radii
interactively for that star, which will give you more confidence. And
thats all now you have found the instrumental magnitudes for the stars
in the images. After this step you will need to transform these
magnitudes to the standard system.