Eclipsing Binaries Lab

We will perform differential photometry on three binary stars in order to obtain a lightcurve and determine the time of minimum. The sets of images for each star can be found on H:/Labimages/Proj-28-EclBin/ on the lab computers.

Finding Charts
Create finding charts for ab_and, bu_vul and xz_and using the Megastar program by following the instructions given by your TA.
Lightcurve of AB Andromeda
Follow the instructions given in the Image Analysis section beginning on page 194 of your lab manual.
Lightcurves of BU Vulpeca and XZ Andromeda
For this section we will use the program Photom, which is a linux program, to perform photometry on the variable star images. We will then plot a lightcurve for each star using either Excel or Gnuplot.
1. Log into the linux server using the XWin32 program on your computer. If you do not see a small X in the task tray in the lower right hand corner of your screen, you can start the program by going to the Programs->XWin32 folder in the Start menu. Click on the blue X to bring up a list of servers you can log into. Choose 'Phobos'. A dialog will appear asking you for a username and password. Get these from your TA.
2. It may help, at this point, to become familiar with several linux commands:
  - ls - lists the contents of the directory you are in
  - cd [folder] - changes your current folder to [folder]. Typing 'cd ..' will take you up one folder in the directory tree.
3. You must now create a configuration file containing instructions that tell Photom what images and what stars upon which to perform photometry. The file will have the following format:
```
10 0
FILES:
[list of files]
FIXED:
[RA&Dec coordinates for stars in the images]
```
  The first line is just some configuration parameters Photom needs; you don't need to change them. You will create a list of files in the next step. The coordinates in the fixed section should be taken from the finding charts you made earlier.
  Move into the folder containing the images of bu_vul by typing
  cd bu_vul
  Now make a file containing a list of the images in this directory by typing
  ls *.fts > [something].cfg
  where the [something] is any name you want.
4. Now you want to edit this file so that it has the format described above. Type
  nedit [something].cfg &
  The Nedit program will appear, which is very much like windows notepad. Add the lines
```
10 0
FILES:
```
  to the top of this file, and the line FIXED:, followed by a list of the coordinates of your variable star and reference stars, to the bottom of the file. Enter the coordinates in the form
  [RA hours]:[minutes]:[seconds] [DEC degrees]:[minutes]:[seconds]
  Enter coordinates for one star per line. Save the changes to this file and exit.
5. Now run Photom by typing
  photom [something].cfg
  You should see columns of information appear. Save this data to a file by typing
  photom [something].cfg > [something].out
6. You can now plot this data by copying and pasting it into Excel, or you can use Gnuplot:
  type gnuplot to start the program.
  type the following line to plot your data:
  plot '[something].out' using 7:10, '[something].out' using 7:12, '[something].out' using 7:14
  You will see a plot appear. You can now save this plot for your TA by entering the lines
```
set term postscript
set out '[something].out'
replot
```
7. Perform photometry on the remaining star by typing
```
cd ..
cd xz_and
```
  and repeating the above procedure.