BINARY STARS

The Applet Used In This Exercise Was Kindly Provided By Terry Herter At Cornell University.  The Accompanying Text/Exercises Were Written By Randy Phelps.  Any Further Use Of The Applet Should Be Undertaken With Permission.

Purpose:  The purpose of this web exercise is to learn about the properties of spectroscopic binary stars.

Procedure:

  • Open the Applet by clicking here.  A new window will appear, with a description of the applet you will be using.  Become familiar with the various activities that appear in this rather busy simulation by doing the first "Exploration" described below.  Leave this window open, as you will be using it to undertake the exercises.
  • Do each  "Exploration " outlined in the first column below.  Before you actually do each "Exploration", answer the questions posed in the "Anticipate the Result" box for that "Exploration".  After you have done this, determine if the actual result was as you expected, or somehow different.  If the actual result was different, determine why before you proceed to the next step.
  • At the end of the exercise, you should have answered the "Anticipate the Results" questions, which should help clarify material presented in the lecture note portion of this module.

Exploration

 Anticipate the Results Instructions/Sugestions to Help Answer The Questions
1. Familiarize yourself with the Applet  
  • Click on the highlighted information links on the "applet page" to learn what each area diplayed represents, and how to change parameters.
  • Adjust parameters and note what happens to the views of the binary orbits, the spectral line shifts, and the radial velocity curves.  Change only one parameter at a time, and remember to click "Enter"!
2. Explore "face-on" binary systems
  • When a binary orbit is not inclined to the observer, what spectral-line shifts are observed, if any?
  • If a binary is so far away that it cannot be seen as a visual binary, and its orbital plane is not inclined, will it ever be detected as a binary?
  • Set the applet for M1=3, M2=1, a=1, e=0.0 and i=0.   Note: i=0 degrees defines what is called a "face-on" binary system.  Does this name make sense based on the "Earth view"?
  • Notice the absoption lines in the spectrum.  Does their motion, or lack therefo, make sense given the orientation (inclination) of the system with respect to the Earth?
  • Notice the radial velocity curve.  Does the curve make sense given the orientation (inclination) of the system with respect to the Earth?
3. Explore "edge-on" binary systems
  • When a binary orbit is inclined 90 degrees to the observer, what spectral-line shifts are observed, if any?
  • Which star in a binary system, the higher-mass or lower-mass one, has the highest velocity?
  • Set the applet for M1=3, M2=1, a=1, e=0.0 and i=90.   Note: i=90 degrees defines what is called an "edge-on" binary system.  Does this name make sense based on the "Earth view"?
  • Notice the absoption lines in the spectrum.  Does their motion, or lack therefo, make sense given the orientation (inclination) of the system with respect to the Earth?
  • Notice the radial velocity curve.  Does the curve  make sense given the masses of the stars in the binary system?
4. Explore binary systems with various inclinations
  • When a binary orbit is inclined 90 degrees to the observer, how do the maximum radial velocities compare to the true velocities?
  • Change the inclination to values of  i=0, 15, 30, 45, 60, 75 and 90 degrees, running the simulation after changing the inclination each time.
  • Notice the absoption lines in the spectrum.  Does the amount of the shift, as the inclination changes, make sense? 
5. Explore other binary systems  
  • Change the masses of the binaries (M1=1, M2=1 and/or M1=10, M2=1) and/or the eccentricity (e=0.5) and see how the spectral-line shifts change and how the radial velocity curves change.