| photman | Version-3.0 | photman |
VI. Photometry
1. Introduction
2. Options and data
3. Reading the data from tape
4. Photometry with SPHOT
4.1 Obtaining the object coordinates
4.1.1 Centers using DAOFIND
4.1.2 Centers using Imtool
4.1.3 Centers using rimcursor
4.1.4 Using SPHOT in batch mode
4.2 Using SPHOT interactively
5. Photometry with APPHOT
5.1 APPHOT With the Imtool Window
5.2 APPHOT With Graphics : Making the image plots
5.3 Setting the parameters
5.4 Running the task phot
Lisa Wells
August 31, 1992
This document is intended as a guideline for using aperture photometry reduction packages available at CTIO. The transformation of instrumental magnitudes to standard magnitudes is handled by the package PHOTCAL, see section VIII of this manual. If you do not have experience with the software there are staff members who can assist you. If you do not have experience using IRAF then we suggest you start by reading through, "An Introduction to IRAF" which will give you a general idea of IRAF structure as well as a few fundamental tools. If you are a first time user of the CTIO computers, there is a document available called "Using the Computers at CTIO". There is a copy near every console terminal and it can also be found in the last appendix of the IRAF Reduction Manuals found in the red binder in each console room. If you have never used DAOPHOT, it is strongly suggested that you read through the manual. DAOPHOT manuals can be found in the computer rooms in La Serena and in the computer rooms at the 1 and 4 meter telescopes.
The examples shown here are just that, examples. The user must decide upon the reduction procedure, naming, convention, etc., appropriate for his own data and use the cookbook and examples as guidelines only. The IRAF examples are shown with prompts for the package containing the tasks (do not type the prompts, of course). It is strongly recommended that you perform an lpar on every task immediately before using it, unless you are familiar with all of its parameters. This is not always shown in the examples, but is normal practice even among seasoned IRAF users.
IRAF uses two conventions that you should always keep in mind. First, images consist of lines and columns (not rows and columns). Second, the "order" of a function is the number of independent coefficients for a polynomial, or the number of intervals for a spline curve. For example, a cubic (third-degree) polynomial is described as "order=4" (four coefficients).
If you require personal assistance in using IRAF for your reductions please contact either Mauricio Navarrete or Nelson Saavedra on Tololo, or Mario Hamuy in La Serena (ex 210). If you have trouble with DAOPHOT, contact Alistair Walker, Doug Geisler, or Mario Hamuy.
There are many photometry software packages now available at CTIO. We do not directly support this phase of data reduction however we felt it necessary to inform the users of the options. DAOPHOT has been incorporated into IRAF with minor changes in the parameters files. However, it still runs the same. There is also the APPHOT package in IRAF. There is another program in IRAF which was taken from the mountain photometry program used in FORTH on the LSI11s. This is called sphot, it was written for use at the telescope to do quick look photometry but it can be used for the final product as well. A note of warning however, the output format for sphot is not standard and therefore does not have a preprocessor for use in the photometric transformation package. If you plan to use PHOTCAL to transform your magnitudes, do not use sphot. However, both DAOPHOT and APPHOT have output which may be handled by the PHOTCAL package. The possible photometry options are:
1. If your images are not crowded fields of stars, a quick method is available. This is also used on the mountain at the telescope for quick look photometry. It is a two step process of first making a list of the object positions on the image and then doing the aperture photometry in batch mode using SPHOT. This method doesn't work well in crowded fields, and in this case you should probably be using DAOPHOT. There are two ways to make a list of your objects and this is all described in section 3. This may also be run interactively with the imtool display window.
2. APPHOT is a package in IRAF which works with the imtool display window or graphics window on the SUN console. This is a very versatile and complicated method of doing photometry. This manual is an attempt to clarify its operation and use. There are many algorithms incorporated for the experienced photometrist with special needs.
3. DAOPHOT is used to find objects, calculate the aperture photometry, calculate the point spread function, calculate the coordinates and magnitudes, and subtract stars from the image. It is quite useful for crowded fields. A typical run of DAOPHOT is described in the standard DAOPHOT manual, though the IRAF convention is very different.
The PHOTCAL package can be used to transform photometry done using DAOPHOT or APPHOT. The PHOTCAL package is relatively new and has some naming conventions that you must be made aware of, for example the filter header keyword is very important. The preprocessor which formats the instrumental magnitudes for use in the package pulls out the filter parameter called IFILTER in the output files from APPHOT and DAOPHOT but reads only the first number in the field. If your images headers tabulate several filter bolts, then the first number may not correspond to the main filter being used as is the case at CTIO. Direct imaging on the 0.9 meter telescope records two filter bolt positions in the fits image header, which for the V filter looks like this "0 3". The preprocessor takes the 0 for the filter type not the 3. Editing the image headers or editing the photometry output files so that the filter type is set to "3 3" will take care of this. In making the instrumental magnitude tables the objects in an image are sorted in the y-coordinate. It is easiest then, to mark your objects in increasing y order to ensure proper tracking of the object names. You must keep track of the object coordinates so that you can name them properly.
Reading images from a tape is shown first but if your objects are already on the computer, skip this section and go on to the next one. Each option has a brief introduction which should help you in deciding which method is the best for you.
If your data is currently on a computer disk then skip this section. Load the dataio package, allocate the appropriate tape drive, and mount your tape:
cl> dataio
da> epar rfits
da> alloc mta
Read the data using the routine rfits. You must specify the tape-drive name, the list of files you wish to read in and the "root" file name. In choosing the root file name, it's usually a good idea to include a digit in the name to indicate the tape number (e.g., "tape2" for the second tape; files would be called "tape2001, tape2002, tape2003..."); alternatively, an offset may be added (eg, offset=89 means the first files would be called "tape2090, tape2091, tape2092..." (1+89, 2+89...)).
da> rfits mta 1-999 tape1
or
da> rfits mta 1-999 tape1 off=43
In the above examples, the file list "1-999" should more than cover the number of files on tape; the task will end gracefully at the end of tape. When finished, rewind the tape and deallocate the drive,
da> rew mta
da> dealloc mta
and remove your tape from the drive.
\fIrfits\fR
fits_file = "mta" FITS data source
file_list = "1-999" File list
iraf_file = "tape1" IRAF filename
(make_image = yes) Create an IRAF image?
(long_header = no) Print FITS header cards?
(short_header = yes) Print short header?
(datatype = "") IRAF data type
(blank = 0.) Blank value
(scale = yes) Scale the data?
(oldirafname = no) Use old IRAF name in place of iraf_file?
(offset = 0) Tape file offset
(mode = "ql")
There are two possible modes of using SPHOT, interactively with the imtool window or in batch by supplying a coordinate list of objects in your image. As stated previously, your images should already be processed, i.e. trimmed, bias subtracted,...etc, unless you are at the telescope and just need a quick magnitude. If you have not processed the images, see section II, "CCD Reductions" or load the ctio package and type help ccdman.
There are several ways of making your list of object coordinates and the method you use depends upon the number of objects in the image. If there are a large number of objects it is best to use "daofind" in the apphot package in IRAF. If there are only a few objects then it is easiest to use the current interactive capabilities of the imtool display window. There are two possibilities to be used here and both are described. This is very simple and quick so you may wish to use this method for frames with many objects also. The options are given in section 4.1. For interactive use of SPHOT, see section 4.2.
SPHOT will give you the counts or instrumental magnitudes. It is left to the observer to do the final processing from instrumental to standard magnitudes however, this is possible in IRAF using the PHOTCAL package. A good reference for this is the article by Harris et al., PASP, 93 , 507 (1981). If you require assistance, see Alistair Walker, Doug Geisler, or Mario Hamuy.
4.1 Obtaining coordinate lists for your objects
It is best to use daofind for cluttered images with a large number of objects in the field. This task convolves the data with a truncated, lowered elliptical Gaussian function to find the objects. There are other parameters which are used to locate the stars and eliminate galaxies and cosmic rays. These are the shape characteristics given by "roundlo", "roundhi", "sharplo", and "sharphi". You may wish to play with these parameters. Later you may delete other objects which you do not want. First you must load the apphot package,
cl> ctio
ct> apphot
ap>
The ap> prompt means that the apphot package has been loaded. Now edit the parameters of daofind using an epar. You must have calculated the full width half maximum and have an idea what the pixel level is to set the parameter threshold. This is usually set to a few times the error in one pixel. These parameters are in a subset listing. If you move to the "datapars" parameter in the daofind setup, and type :e you will go into another setup which must be modified. The header parameters for the exposure time, airmass and filter. Also it is a good idea to set the CCD readout noise and gain parameters so the magnitude errors are calculated properly. When these parameters are set, type '^z" and you will go back to the daofind parameters. Type ^z again to exit this. Now run it:
ap> epar daofind
ap> daofind
The file specified by the parameter output now contains the object coordinates obtained by daofind. You may repeat these steps specifying different output files for each image. Once you have all your coordinates, you may proceed to the next section.
\fIdaofind\fR
Image = "tape1003" Input image
output = "out1003" Results file (default: image.coo.?)
(convolution = "conv") Output convolved image
(datapars = "") Data dependent parameters (fwhmpsf, threshold,
(\fIratio\fR = 1.) Ratio of sigmay to sigmax of Gaussian kernel
(theta = 0.) Position angle of major axis of Gaussian kernel
(\fInsigma\fR = 1.5) Width of convolution kernel in sigma
(sharplo = 0.2) Lower bound on sharpness for feature detection
(sharphi = 1.) Upper bound on sharpness for feature detection
(roundlo = -1.) Lower bound on roundness for feature detection
(roundhi = 1.) Upper bound on roundness for feature detection
(\fIboundary\fR = "nearest") Boundary extension (constant, nearest, reflect,
(constant = 0.) Constant for boundary extension
(graphics = "stdgraph") Graphics device
(display = "stdimage") Display device
(commands = "") Image cursor: [x y wcs] key [cmd]
(cursor = "") Graphics cursor: [x y wcs] key [cmd]
(mkdetections = no) Mark detected stars on the display
(\fIinteractive\fR = no) Interactive mode
(verify = yes) Verify critical parameters in non interactive m
(update = no) Update critical parameters in non interactive m
(verbose = no) Print messages in non interactive mode
(mode = "ql")
\fIdatapars\fR
(scale = 1.) Image scale in units per pixel
(\fIfwhmpsf\fR = 1.) FWHM of the PSF in scale units
(emission = yes) Features are positive ?
(sigma = INDEF) Standard deviation of background in counts
(datamin = INDEF) Minimum good data value
(datamax = INDEF) Maximum good data value
(threshold = 0.) Detection threshold in counts above background
(cthreshold = 0.) Centering threshold in counts above background
(noise = "poisson") Noise model
(ccdread = "") CCD readout noise image header keyword
(gain = "") CCD gain image header keyword
(\fIreadnoise\fR = 5.7) CCD readout noise in electrons
(\fIepadu\fR = 2.7) Gain in electrons per count
(\fIexposure\fR = "exptime") Exposure time image header keyword
(\fIairmass\fR = "airmass") Airmass image header keyword
(\fIfilter\fR = "filters") Filter image header keyword
(\fIobstime\fR = "exptime") Time of observation image header keyword
(itime = INDEF) Exposure time
(xairmass = INDEF) Airmass
(ifilter = "INDEF") Filter
(otime = "INDEF") Time of observation
(mode = "ql")
You may wish to look at this output, just type type out1003 and you will see:
#K IRAF = NOAO/IRAF V2.6 version %-15s
#K USER = v10 name %-15s
#K HOST = ctios3 name %-15s
#K DATE = 08-18-88 mm-dd-yr %-15s
#K TIME = 15:52:11 hh:mm:ss %-15s
#K PACKAGE = apphot name %-15s
#K TASK = daofind word %-15s
#K IMAGE = tape1003 imagename %-15s
#K FWHMPSF = 4. pixels %-15.7g
#K NSIGMA = 1.5 number %-15.7g
#K RATIO = 1. number %-15.7g
#K THETA = 0. degrees %-15.7g
#K THRESHOLD = 350. counts %-15.7g
#K SHARPLO = 0.2 number %-15.7g
#K SHARPHI = 1. number %-15.7g
#K ROUNDLO = -1. number %-15.7g
#K ROUNDHI = 1. number %-15.7g
#
#N XCENTER YCENTER MAG SHARP ROUND ID \
#U pixels pixels # # # # \
#F %-12.2f %-9.2f %-9.3f %-8.3f %-8.3f %-6d \
#
179.10 45.25 -1.869 0.606 0.295 54
195.74 91.04 -5.414 0.382 0.067 106
304.99 145.91 -5.338 0.345 0.080 167
273.96 168.81 -5.219 0.559 0.252 195
282.97 181.74 -4.221 0.763 0.297 217
290.92 184.94 -5.127 0.647 0.206 222
286.06 286.21 -1.472 0.682 0.227 363
288.68 305.03 -0.073 0.604 -0.093 387
298.23 335.88 -1.373 0.568 0.022 419
284.96 343.81 -3.996 0.771 0.202 433
327.05 431.84 -4.287 0.752 0.212 543
149.69 468.57 -5.143 0.277 0.036 583
119.95 492.87 -4.296 0.609 -0.000 609
205.22 495.12 -5.402 0.323 -0.027 613
Now that you have your data read in, we begin by displaying an image using the imtool window, you must be logged in at a SUN console to do this. This first method is best used when you have a few objects in the image or you have a few in a cluttered field for which you need magnitudes. This can be used quickly for crowded images with many program objects but a better method for these is explained in section 3.3.2. First load the tv package by typing:
cl> noao
no> tv
tv>
The tv> prompt means that the tv package has been loaded. Now display one of your images using display:
tv> display tape1003 1
The "1" at the end of the command is the frame number in which you would like your image to be displayed. There are 4 frames that can be used. If you would like more information about the console windows, type 'help console' while logged into IRAF or read the manual "Using the Computers at CTIO" located in the computer room near each console. The image specified is now visible in the imtool window. Next press the F6 key. You will see coordinates appear at the lower right of the screen. Now when you move the cursor, the coordinates keep track of where you are. It is a good idea to check the coordinates by moving the cursor to the lower left corner of the image to look for the origin (1,1). If one of the corners doesn't give the origin coordinates then the imtool is not set up properly and you should ask Mario Hamuy, Mauricio Navarrete, or Nelson Saavedra for assistance. The frame number at the top of the screen is important here since now you will begin writing the coordinates of your objects to a file by that title.
Now move the cursor to your object and press the left button on the mouse. A number will appear up and to the right of your object to indicate your choice and the coordinates are written to the file called frame.1.1 in your uparm directory. The cursor position is important since this does not use a centering algorithm. Do this for all the objects in this frame for which you need magnitudes. When you are finished repeat the process on your next image and mark the objects. The title of the image is written to the output file and is taken from the comment header parameter. Now if you wish to look at one of your coordinate files:
tv> type uparm/frame.1.1
This will show:
# Thu Aug 18 15:38:26 1988
# [1] frame.1.1: tape1003 - Cen A R
206.646 494.282
119.793 492.055
148.744 467.558
328.018 430.812
285.705 342.845
305.748 336.164
309.088 303.873
285.705 287.17
290.159 184.728
285.705 181.387
274.569 169.139
305.748 145.755
195.511 91.1937
159.879 46.6536
Now you may skip section 3.3.2 and go on to the photometry reduction in section 3.4.
This is an interactive task using the imtool window. It is first necessary to display the object in the imtool window using the tv package and run the task rimcursor. First load the lists package;
cl> tv
tv> lists
li> display tape1003 1
li> rimcursor > out1003
This will run the task rimcursor and open the file "out1003". The cursor loop has been entered and the objects in the image can be put in the file list by moving the cursor to an object and pressing the 'space bar'. There is a zoom option used by typing Z. To get the whole image back, type 0. Typing return will quit the task. An example of the format of this file is shown below. Now this file can be used as the input coordinate list in sphot.
li> type out1003
205.000 495.000 101 \040
122.000 490.000 101 \040
148.000 465.000 101 \040
329.000 346.000 101 \040
285.000 342.000 101 \040
305.000 334.000 101 \040
308.000 301.000 101 \040
282.000 286.000 101 \040
288.000 186.000 101 \040
285.000 179.000 101 \040
275.000 167.000 101 \040
302.000 147.000 101 \040
194.000 94.1000 101 \040
157.000 43.0000 101 \040
SPHOT is located in the ctio package at CTIO. This task is an IRAF adaptation of the FORTRAN program called ssphot (single star photometry or the "Harvey Butcher Mountain Photometry Code") used at KPNO. Begin by loading the ctio package and editing the sphot parameters:
cl> ctio
ct> epar sphot
You may wish to change the sky window radii or other parameters. When you are satisfied type ^z to exit. The position file is the output from imtool, uparm/frame.1.1 or the file from daofind, tape1003. The output is written directly to the terminal so you may wish to redirect the output to a file, so run the task,
lo> sphot tape1003 out1003 > phot1003
The file phot1003 now contains all the information for that image. If you would like a hardcopy of the file, send the file to the laser printer using:
lo> lpr phot1003
This will show the calculated parameters, there is a verbose boolean parameter which will give a long explanation if set to yes. It is up to you to choose the setting required. Typing out the file will result in the following:
Image = dev$pix Title = Cen A R
Exp. time = 300.00 Airmass = no data Filter = no data
Setup parameters:
radius of stellar aperture = 10.000
inner sky radius = 10.500
outer sky radius = 18.000
maximum shift from initial position = 5.000
number of iterations for centroid = 5
half width of centering box = 3
sky = mode
sigma rejection parameter = 3.000
magnitude zero point = 23.500
gain (electrons/ADU) = 10.500
Star # 1:
number of sky pixels = 672
sky mean = 794.56
sky median = 745.25
sky mode = 646.64
sigma sky = 219.55
number of pixels in star aperture = 315
total star counts = 43142.0
error in magnitude: dm(n) = 0.002
error in magnitude: dm(sky) = 0.004
error in magnitude: dm(noise) = 0.098
x position = 179.38
y position = 44.80
magnitude = 18.106
sigma magnitude = 0.098
Star # 2:
number of sky pixels = 671
sky mean = 879.25
sky median = 835.33
sky mode = 747.49
sigma sky = 270.31
number of pixels in star aperture = 316
total star counts = 326918.9
error in magnitude: dm(n) = 0.000
error in magnitude: dm(sky) = 0.000
error in magnitude: dm(noise) = 0.016
x position = 195.50
y position = 91.08
magnitude = 15.907
sigma magnitude = 0.016
Star # 3:
etc....
Now it is up to you to convert to the standard scale and write the paper.
\fIsphot\fR
images = "tape1003" Image file names
(\fIcursor\fR = "out1003") Image cursor
(\fIstarlist\fR = "") Star position file
(\fIrstar\fR = 10.) Radius of stellar aperture
(\fIr1\fR = 10.5) Inner sky radius
(\fIr2\fR = 18.) Outer sky radius
(rdel = 5.) Maximum shift from initial position
(niter = 5) Number of iterations for centroid
(cside = 3) Half width of centering box
(\fIsky\fR = "mode") Sky determination
(\fIksig\fR = 3.) Sigma rejection parameter for sky determination
(\fIzpoint\fR = 23.5) Magnitude zero point
(\fIgain\fR = 10.5) Gain (electrons/ADU)
(verbose = yes) Long output format
(mode = "ql")
Now if you wish to interactively use the task sphot, first load the ctio package and edit the parameters of sphot. Since the imtool window will be used, the tv package must be loaded also.
cl> noao
no> tv
tv> ctio
ct> epar sphot (see the parameters below)
The major difference from the batch mode is that the parameter cursor must be left blank to read from the image cursor. The parameter star list must also be blank. The output is written directly to the terminal so you may wish to redirect the output to a file, so run the task,
lo> sphot tape1003 out1003 > phot1003
Now you are interactively using sphot. Just move the cursor to the stars for which you want magnitudes and press the space bar. The output will go directly into the file phot1003 and will not echo on the terminal. When all your stars have been done, just type q. The file "phot1003" now contains all the information for that image. If you would like a hardcopy of the file, send the file to the laser printer using:
lo> lpr phot1003
An example of the format of this file in shown in the previous section. Now it is up to you to convert to the standard scale and write the paper.
\fIsphot\fR
images = "tape1003" Image file names
(cursor = "") Image cursor
(starlist = "") Star position file
(\fIrstar\fR = 10.) Radius of stellar aperture
(\fIr1\fR = 10.5) Inner sky radius
(\fIr2\fR = 18.) Outer sky radius
(rdel = 5.) Maximum shift from initial position
(niter = 5) Number of iterations for centroid
(cside = 3) Half width of centering box
(\fIsky\fR = "mode") Sky determination
(\fIksig\fR = 3.) Sigma rejection parameter for sky determination
(\fIzpoint\fR = 23.5) Magnitude zero point
(\fIgain\fR = 10.5) Gain (electrons/ADU)
(verbose = yes) Long output format
(mode = "ql")
APPHOT runs a bit differently than SPHOT and there are many more options for the centering, sky evaluation, and photometry algorithms. It also has many modes of use, interactively with the imtool or graphics windows, or in batch. Only one of these methods, using the graphics window is shown below. As stated previously, your images should already be processed, i.e. trimmed, bias subtracted,...etc, unless you are at the telescope and just need a quick magnitude. If you have not processed the images, see section V, CCD Direct Imaging Reductions or load the ctio package and type help ccdman. If you have crowded fields, use DAOPHOT. It is important to know what mode is best to use for your images. This section examples only one mode but there are many ways to use apphot. If you would like to know about the other ways to use this package see the help page for the task phot which gives examples of the different modes of use.
There are a few standard things about running the photometry task in apphot, called "phot". First, the definition of the stdimcur is very important. To check its current value, type show stdimcur. Depending upon the mode you are using, this may need to be changed. Every time phot is run interactively, a help menu first appears and typing q will begin the interactive mode you are using. Also, the parameters must be set either interactively or by editing the parameters of all the relevant tasks. This can be done all in one step by editing the parameters for phot. All other relevant parameters are linked to this one. There may be some special preparation necessary before running phot like displaying images or making contour plots of images. While running phot, radial profiles of stars may be performed as an option. This is complicated since there are many levels to the program and you have different keypad mappings depending on the level. If at any time you don't know the command needed, just type ? and a help page will come up on the gterm screen. This only works if you are in the interactive mode.
The easiest way to use the task phot is with the imtool display window. This is done by first displaying the image and then running phot. Now you must set up the many parameters used by phot. This method creates a single file of output for each image and is very slow unless you only have a few images. There are 4 planes of memory in the imtool window which can be used at one time and using all of them with phot will give one output file for four images. This could also be used at the telescope for quick look photometry.
If you have many images and only a few objects in each but would like one large output file for a night's worth of data, then using the graphics window with contour plots of your images is the best method. This involves some amount of typing which is tedious, but is the most convenient for large amounts of data. Contour plots of all your images must be made and reviewed to be sure that the correct objects appear. The environment variable stdimcur must be set properly. Now phot can be run using the graphics window. This method will be described in the following sections.
To run in batch mode you must first create a file with the positions of your objects. This is done one file at a time using any of the methods described in section 4.1 of this manual. The parameters must also be specified before running the task phot. This also is meant to do images one at a time and a coordinate list must be done for each image.
Other programs in apphot that do the photometry calculations are qphot (quick photometry), and polyphot which uses polygon shaped apertures. The latter is currently being written and is not yet ready. The qphot task is just like the sphot in the ctio package used here at CTIO but has many parameters. It prompts the user for all the important parameters used in the photometry algorithms. The task sphot has a much more simplified parameter setup which hopefully won't confuse the first time users of aperture photometry methods.
The output file from phot, qphot or polyphot (not yet completed) is a large file containing first the parameters used in running the task. This is to ensure that the parameters can be duplicated at a later date if necessary. Following this header information is the object header format and the individual photometry for each object. Certain fields can be pulled out of this file to create a small file to be plotted for example or to be input into another task to calculate the standard magnitudes for that night. A package called photcal was written to do this calculation in IRAF. For more information about this, load the ctio package and type "help stphot".
The parameters that govern the photometry calculations are different for use of the Imtool window. First we need to edit the parameters of the task phot. An example of this setup is given below. The four parameter files, datapars, centerpars, fitskypars and photpars are all linked to other parameter sets. To get into these, move the cursor to this parameter using the arrow cursor pad and type :e. This will bring up the other parameter set. To get back to the original setup just type the usual escape command ^z. In general the defaults are used in the centerpars and fitskypars but other algorithms are available. To get more information about these tasks, just type help centerpars or help fitskypars.
It is possible to interactively set up all these parameters but it is easier to set them in the task set ups and then they won't vary. All the examples below show one possible setup, but do not be afraid to change some of the parameters. The parameters in datapars are not terribly important but the fwhmpsf should be left to "1" to ensure that the rest of the parameters are specified in pixels. You may however wish to use the scale of the CCD in this parameter to set up everything in arcseconds for example. The choice of aperture size and sky annulus are completely up to the observer. Also, the readnoise and epadu parameters are only used in the error determinations. Be sure that exposure is set to the proper header keyword for the exposure time. Using "default" as the value in the "output" parameter, the output file will be the same base name of the image with a ".mag.#" applied to the end.
\fIphot\fR
image = "obj1002" Input image
skyfile = "" Sky file
(datapars = "") Data dependent parameters
(centerpars = "") Centering parameters
(fitskypars = "") Sky fitting parameters
(photpars = "") Photometry parameters
(coords = "") Coordinate list
(\fIoutput\fR = "default") Results file
(plotfile = "") File of plot metacode
(graphics = "stdgraph") Graphics device
(display = "stdimage") Display device
(commands = "") Image cursor: [x y wcs] key [cmd]
(cursor = "") Graphics cursor: [x y wcs] key [cmd]
(radplots = no) Plot the radial profiles
(\fIinteractive\fR = yes) Mode of use
(verify = yes) Verify critical parameters in non interactive mode
(update = no) Update critical parameters in non interactive mode
(verbose = no) Print messages in non interactive mode
(mode = "ql")
\fIdatapars\fR
(scale = 1.) Image scale in units per pixel
(\fIfwhmpsf\fR = 1.0) FWHM of the PSF in scale units
(emission = yes) Features are positive
(sigma = 15.) Standard deviation of background in counts
(datamin = INDEF) Minimum good data value
(datamax = INDEF) Maximum good data value
(threshold = 0.) Detection threshold in counts above background
(cthreshold = 0.) Centering threshold in counts above background
(\fInoise\fR = "poisson") Noise model
(ccdread = "") CCD readout noise image header keyword
(gain = "") CCD gain image header keyword
(\fIreadnoise\fR = 8.) CCD readout noise in electrons
(\fIepadu\fR = 4.) Gain in electrons per count
(\fIexposure\fR = "exptime") Exposure time image header keyword
(\fIairmass\fR = "airmass") Airmass image header keyword
(\fIfilter\fR = "filters") Filter image header keyword
(\fIobstime\fR = "exptime") Time of observation image header keyword
(itime = INDEF) Integration time
(xairmass = INDEF) Airmass
(ifilter = "INDEF") Filter
(otime = "INDEF") Time of observation
(mode = "ql")
\fIcenterpars\fR
(calgorithm = "centroid") Centering algorithm
(\fIcbox\fR = 3.) Centering box width in scale units
(\fImaxshift\fR = 5.) Maximum center shift in scale units
(minsnratio = 1.) Minimum SNR ratio for centering
(cmaxiter = 20) Maximum iterations for centering algorithm
(clean = no) Symmetry clean before centering
(rclean = 1.) Cleaning radius in scale units
(rclip = 2.) Clipping radius in scale units
(kclean = 3.) K-sigma rejection criterion in skysigma
(mkcenter = no) Mark the computed center
(mode = "ql")
\fIfitskypars\fR
(salgorithm = "mode") Sky fitting algorithm
(\fIannulus\fR = 15.00000000) Inner radius of sky annulus in scale units
(\fIdannulus\fR = 10.00000000) Width of sky annulus in scale units
(skyvalue = 0.) User sky value
(smaxiter = 10) Maximum number of sky fitting iterations
(\fIsnreject\fR = 50) Maximum number of sky fitting rejection iterati
(skreject = 3.) K-sigma rejection limit in sky sigma
(khist = 3.) Half width of histogram in sky sigma
(binsize = 0.10000000149012) Binsize of histogram in sky sigma
(smooth = no) Lucy smooth the histogram
(rgrow = 0.) Region growing radius in scale units
(mksky = no) Mark sky annuli on the display
(mode = "ql")
\fIphotpars\fR
(\fIweighting\fR = "constant") Photometric weighting scheme for wphot
(\fIapertures\fR = "6.0,9.0,12.0,15.0") List of aperture radii in scale units
(zmag = 26.) Zero point of magnitude scale
(mkapert = no) Draw apertures on the display
(mode = "ql")
You must first display up to 4 images in the imtool window by using the
task display. You must be logged in at a SUN console to do this. First
load the tv package by typing:
.nf
cl> noao
no> tv
tv>
The tv> prompt means that the tv package has been loaded. Now display one of your images using display:
tv> display tape1002 1
The "1" represents the frame number in which you would like your image to be displayed. There are 4 frames that can be used. If you would like more information about the console windows, type help console while logged into IRAF with the ctio package loaded or read the manual "Using the Computers at CTIO" located in the computer room near each console or in the red binder at the end of the appendices. The image specified is now visible in the imtool window. Next press the F6 key. You will see coordinates appear at the lower right of the screen. Now when you move the cursor, the coordinates keep track of where you are. It is a good idea to check the coordinates by moving the cursor to the lower left corner of the image to look for the origin (1,1). If one of the corners doesn't give the origin coordinates then the imtool is not set up properly and you should ask Mario Hamuy, Mauricio Navarrete, or Nelson Saavedra for assistance.
If your images are not on the computer, see section 3 of this document. Check the environment variable stdimcur. This should be set to stdimage.
cl> show stdimcur
If the response is other than "stdimage" then change it by typing;
cl> set stdimcur=stdimage
Now you are ready to run phot, do this by typing phot. A circular cursor will appear in the imtool window. Now move the cursor to your objects and type the space bar at each. To step through the image planes in the imtool window type "^f". You must also reset the image name for each image plane by typing ":image obj1003", for example for the image displayed in the second frame. Now do the same for this image and continue through all your images. When you are finished type q twice, in openwin you might have to type this 3 times. Now look at the output file and you will see that a large header precedes the image photometry. Currently, you must keep good notes about each object and its position so that you remember which one you did first. This will hopefully be taken care of in the future.
If you would like to make a table of the magnitudes from the largest of the apertures used, use the task "txdump". You used 4 apertures and so "txdump" should look like the setup below. Running this will pull all the fields specified out of the output file from phot and create a table with 4 columns, one for each field.
\fItxdump\fR
textfile = "obj1002.mag.1" apphot output textfile(s)
fields = "image,rapert[4],mag[4],merr[4]" fields to be extracted
expr = "yes" boolean expression
(headers = no) Print the field headers ?
(parameters = yes) Print the parameters if headers is yes ?
(mode = "ql") mode of task
First we begin by making a list of your objects, and edit this file to make a short script.
cl> plot
pl> files *.imh > proc
pl> ed proc
:1,$s/.imh//
:1,$s/.*/contour & >G plot&
:1,$s/plotobj/plot
:wq
The package containing the task contour must be loaded at the same time. Now we have a script that will make a contour plot of all the images. Next we run this by typing cl < proc. You will get a short message from the task contour for each image. Now look at all the plots to be sure that they all have the images at the right contour level to be shown. This is done using the task gkimosaic, just type gkimosaic plot*. Four plots will be shown at a time and the space bar will go on to the next four plots. If you have any plots that are missing one of you stars for example, do an implot of that image and get a value of the background and set the floor and ceiling parameters in the task contour and run it again. When all you images are visible in the image you are ready. Usually the defaults are good enough. If you find that too many objects are lost in many images, increase the number of contours to be plotted in the contour parameters, delete the plots and run the script again. About 20-30 is a good number to try.
This is being done because the tasks cannot access the display window while it is being accessed and so the best way to do a large number of images is to use the graphics window. Also, all the photometry will be output to one big file as opposed to one file per image.
Now it is time to set the parameters that will govern the photometry calculations. First we need to edit the parameters of the task phot. An example of this setup is given below. The four parameters, datapars, centerpars, fitskypars and photpars are all linked to other parameter sets. To get into these, move the cursor to this parameter using the arrow cursor pad and type :e. This will bring up the other parameter set. To get back to the original setup just type the usual escape command ^z. In general the defaults are used in the centerpars and fitskypars but other algorithms are available. To get more information about these tasks, just type 'help centerpars' or help fitskypars.
It is possible to interactively set up all these parameters but it is easier to set them in the task set ups and then they won't vary. All the examples below show one possible setup, but do ntot be afraid to change some of the parameters. The parameters in datapars are not terribly important but the fwhmpsf should be left to "1" to ensure that the rest of the parameters are specified in pixels. Also, the readnoise and epadu parameters are only used in the error determinations. Be sure that exposure is set to the proper header keyword for the exposure time.
\fIphot\fR
image = "obj201" Input image
skyfile = "" Sky file
(datapars = "") Data dependent parameters
(centerpars = "") Centering parameters
(fitskypars = "") Sky fitting parameters
(photpars = "") Photometry parameters
(coords = "") Coordinate list
(\fIoutput\fR = "magnsfeb13") Results file
(plotfile = "") File of plot metacode
(graphics = "stdgraph") Graphics device
(display = "stdgraph") Display device
(commands = "") Image cursor: [x y wcs] key [cmd]
(cursor = "") Graphics cursor: [x y wcs] key [cmd]
(radplots = no) Plot the radial profiles
(\fIinteractive\fR = yes) Mode of use
(verify = yes) Verify critical parameters in non interactive mode
(update = no) Update critical parameters in non interactive mode
(verbose = no) Print messages in non interactive mode
(mode = "ql")
\fIdatapars\fR
(scale = 1.) Image scale in units per pixel
(\fIfwhmpsf\fR = 1.0) FWHM of the PSF in scale units
(emission = yes) Features are positive
(sigma = 15.) Standard deviation of background in counts
(datamin = INDEF) Minimum good data value
(datamax = INDEF) Maximum good data value
(threshold = 0.) Detection threshold in counts above background
(cthreshold = 0.) Centering threshold in counts above background
(\fInoise\fR = "poisson") Noise model
(ccdread = "") CCD readout noise image header keyword
(gain = "") CCD gain image header keyword
(\fIreadnoise\fR = 8.) CCD readout noise in electrons
(\fIepadu\fR = 4.) Gain in electrons per count
(\fIexposure\fR = "exptime") Exposure time image header keyword
(\fIairmass\fR = "airmass") Airmass image header keyword
(\fIfilter\fR = "filters") Filter image header keyword
(\fIobstime\fR = "exptime") Time of observation image header keyword
(itime = INDEF) Integration time
(xairmass = INDEF) Airmass
(ifilter = "INDEF") Filter
(otime = "INDEF") Time of observation
(mode = "ql")
\fIcenterpars\fR
(calgorithm = "centroid") Centering algorithm
(\fIcbox\fR = 3.) Centering box width in scale units
(\fImaxshift\fR = 4.) Maximum center shift in scale units
(minsnratio = 1.) Minimum SNR ratio for centering
(cmaxiter = 20) Maximum iterations for centering algorithm
(clean = no) Symmetry clean before centering
(rclean = 1.) Cleaning radius in scale units
(rclip = 2.) Clipping radius in scale units
(kclean = 3.) K-sigma rejection criterion in skysigma
(mkcenter = no) Mark the computed center
(mode = "ql")
\fIfitskypars\fR
(salgorithm = "mode") Sky fitting algorithm
(\fIannulus\fR = 15.00000000) Inner radius of sky annulus in scale units
(\fIdannulus\fR = 10.00000000) Width of sky annulus in scale units
(skyvalue = 0.) User sky value
(smaxiter = 10) Maximum number of sky fitting iterations
(\fIsnreject\fR = 50) Maximum number of sky fitting rejection iterati
(skreject = 3.) K-sigma rejection limit in sky sigma
(khist = 3.) Half width of histogram in sky sigma
(binsize = 0.10000000149012) Binsize of histogram in sky sigma
(smooth = no) Lucy smooth the histogram
(rgrow = 0.) Region growing radius in scale units
(mksky = no) Mark sky annuli on the display
(mode = "ql")
\fIphotpars\fR
(\fIweighting\fR = "constant") Photometric weighting scheme for wphot
(\fIapertures\fR = "6.0,9.0,12.0,15.0") List of aperture radii in scale units
(zmag = 26.) Zero point of magnitude scale
(mkapert = no) Draw apertures on the display
(mode = "ql")
If your images are not on the computer, see section 3 of this document. The first step is to check the environment variable stdimcur. This should be set to stdgraph.
cl> show stdimcur
If the response is "stdgraph" then don't change it, if this is not the setting then set it by typing;
cl> set stdimcur=stdgraph
Now you are ready to run phot, do this by typing phot. Initially the help page will come up on the screen. Type q to enter the interactive mode. Now you must call up the contour plot corresponding with your first image. Do this by typing :.read plot201. Now move the cursor to your objects and type the space bar at each. To load the next image to be done, type :image obj202 followed by :.read plot202. Now do the same for this image and continue through all your images. When you are finished type q twice. Now look at the output file and you will see that a large header precedes the image photometry. Currently, you must keep good notes about each object so that you remember which one you did first. This will hopefully be taken care of in the future.
If you would like to make a table of the magnitudes from the largest of the apertures used, use the task "txdump". You used 4 apertures and so "txdump" should look like the setup below. Running this will pull all the fields specified out of the output file from phot and create a table with 4 columns, one for each field.
\fItxdump\fR
textfile = "SN89Bfeb13" apphot output textfile(s)
fields = "image,rapert[4],mag[4],merr[4]" fields to be extracted
expr = "yes" boolean expression
(headers = no) Print the field headers ?
(parameters = yes) Print the parameters if headers is yes ?
(mode = "ql") mode of task