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.