Aperture Photometry Exercise using IRAF

1) On local machine, start an xgterm window and an ds9 window. To do this, type
xgterm &
ds9 &
Note: Implicitly assume that you type a  <return> after each formatted line. Explicit <return>'s are only shown where they might not be obvoious.

2) If you are running IRAF locally, skip to Step 4 .

If you are working on a remote machine, log into 'gaspra' in the xgterm window:

telnet gaspra
3) To start iraf in the xgterm window, type
setenv IMTDEV inet:5137:localmachinename
where localmachinename is the name (or IP number) of the workstation at which you are sitting (e.g., physics1).

Note: If the script 'iraf' is in your /bin directory, this can be accomplished by simply typing

iraf  machinename. (e.g., 'iraf physics1').
You are now running the computational part of iraf on the the machine gaspra and will be displaying images and results on localmachinename.

4) In the xgterm window, type

cd m67
This series of commands took you to the directory 'astro', which is your IRAF home directory. The 'ls' command lists the files and directories. Then you changed to the directory 'm67' where the photometry exercise files are located. Now you would like to display an image.

5) Convert image from FITS (standard) to IRAF format. Type

to see which images exist the current directory. Now type
and respond with
You should now see (after typing 'ls') the file 'm67v.imh' - this is the m67v image in IRAF format. Now type
and respond with
and a few <return>'s. You should see the image displayed in the ds9 window.

Check this for ds9 modifications----------------------------------
Under the Options menu, click on Control Panel. To magnify the image, click on Zoom In. Position the mouse in the lower right corner of the ximtool window, click and hold the button down, and then resize the window until the complete image fits

6) We now would like to learn a bit about the image. Position the mouse in the xgterm window and click (i.e., make the window active). Then type

A circular cursor should appear in the image window. Position this over a star (click the mouse to ensure that the window is active), and then type
on the keyboard. A radial plot of the star's intensity should appear in a new window. You may have to use the mouse to bring this image in front of the others on your screen. Experiment with imexamine a bit by positioning the circular cursor and trying out the following commands (only the letter is needed):
s  (surface plot)
e  (contour plot)
c  (plot a complete column of the image)
l  (plot a complete line of the image)
7) Now we need to get ready to do some photometry. First we need to get an idea of the width of the stellar images. To do this, use the 'r' command in imexamine. At the base of the radial plot window, look at the number in the far right. This is the full width at half-maximum (FWHM) in pixels, i.e., the width of the stars image where the intensity is one half of the central value or greater. Does this number seem to agree with the radial plot? Remember, the x-axis is the radius, not the diameter. Measure the FWHM for a couple different stars and get a rough average. (Should be somewhere between 2.1 and 2.3). When you are done, type
to quit imexamine.

8) To load the IRAF photometry packages, type

at the cl prompt. We will use the task qphot to do the photometry. However, we will also learn a new IRAF trick at this point. We have been entering responses to commands interactively until now. However, all IRAF commands have a parameter file with default responses. To modify the qphot parameter file, type
epar qphot
in the xgterm window. Enter the following parameters by using the arrow key to position the cursor, entering the value, then hitting .
image = m67v
annulus = 8.0
dannulus = 4.0
aperture = 6.0
output = m67v.mag
zmag = 22.766
The zmag entry is optional at this step. However, this value 'rigs' the zero-point of the results to be consistent with the v-magnitude of the reference star in the m67 image. When you are finished, type
to save the file. Start the photometry program by typing
and repeatedly hitting <return> to select the default values. A round cursor should appear in the image window. Center this over the reference star and type
A window should appear querying you for the redius of extraction box.
and hit
A radial plot of the reference star should appear. Note that it is contaminated by a neighboring star at about 11.5 pixels. We will now confirm that the aperture and annulus values entered previously are appropriate. Type
Successively hit
viewing the position of the inner and outer sky radii and the photometry aperture. The vertical line will position itself at the default values each time. When you reach the Mark apertures step, type
and the round cursor should reappear in the image window. Click to make the window active and then type
to save the parameters just confirmed. Now place the round cursor over each star (measure the reference star last, i.e., make it star #11) and press the
to measure each the magnitude. You should notice the results in the xgterm window. When you are finished, type
in the xgterm window, then move the cursor to the image window, click the mouse (to make window active) and type (this is quirky - the order of typing the q's is crucial)
You should now have a file 'm67v.mag' containing your results. Type
to confirm this. To view this file, type
page m67v.mag
Hit the spacebar to view the next page and hit 'q' when you are finished. This file has more info than you care about at the moment. Therefore, we will use the txdump utility to extract the info that we want. Type
epar txdump
and enter
textfile = m67v.mag
fields = id,mag,merr
to see the star id, magnitude, and the error in the mag displayed to the screen. To save these results to a file, type
txdump > results.dat
or any other filename after the '>'. Compare your results with those shown in the CCD lab handout. When you are finished, type
to exit IRAF and then
again to logout of gaspra.