EXTRASOLAR PLANET EXERCISE

Dr. Richard L. Bowman
Harrisonburg, Virginia 22802
( richard.bowman@edtechbybowman.net )

Introduction

The actual discovery of extrasolar planets (or exoplanets) is relatively new with the first such observation occurring in 1994. since then this branch of research in astronomy has grown dramatically. This exercise will introduce students to this area of study--the techniques that may be used to find exoplanets, a brief overview of what is now known, a simulation to acquaint students with how the transit method works, and some plans for future research projects.

Explorations

A. Getting Ready

1. Print out a copy of these worksheets for each member of the lab group, unless your instructor has already made copies for your use.

2. At the top-right corner of the first page, write your name and the names of the persons in your lab group. Place an asterisk by your name for identification purposes.

B. General Exoplanet Information

3. Go to http://www.edtechbybowman.net/PhysAstroSims/exoplanets/ExoplanetEx.html and read the introductory information. Click on the link for "more info" and also check out the Kepler mission site.

• What does David Koch, deputy principal investigator for the Kepler Mission, say is special about the year 1996 with regard to finding exoplanets?

• List the three techniques used to find exoplanets. Identify which technique will be used by the Kepler mission.

• How many stars will the Kepler mission monitor at any one time?

• The Kepler mission scheduled for launch in what year and will last for how many years?

• ( True or False ) Exoplanets discovered to date are on the order of the mass and size of Jupiter or larger.
  [Circle the correct response.]

4. Next go to http://www.exoplanet.eu/ , "The Extrasolar Planets Encyclopedia" site.

• Read one of the latest news articles and write a two- or three-sentence summary of this news.

• Explore the actual exoplanet catalog (the listing of the currently known extrasolar planets). In the table below, record the appropriate information for two different stars and their exoplanets.

• Are there any stars with more than one exoplanet? If so, list one star's name and state how many planets are currently known to orbit it.

C. Transit Method Simulation

5. At http://www.edtechbybowman.net/PhysAstroSims/exoplanets/Transit-1.html begin the "Finding Exoplanet" simulation. First time through, do the default star (#1). Print out enough copies of the last page of the simulation for each member of your lab group. Then go back and run the simulation again for two more stars printing out the last page, if possible, in each case.. (Only one of these stars may be one of those for which an exoplanet cannot be "observed." If this is the case simply record its number here along with its spectral type.) Locate and copy the appropriate information in the chart below.

D. More Exploration of the Transit Method

6. A triumph of the transit method occurred in 1999 when the light curve of the star HD 209458 was shown to indicate the presence of a large exoplanet in transit across its surface from the perspective of Earth.(We still await results from the Kepler Mission or other projects for evidence that Earth-size planets exist around stars other than the Sun.) In addition to providing a measure of the orbital period of the exoplanet about its parent star, the light curve also provided data useful for finding other information about the exoplanet such as its radius. Subsequent spectroscopic studies with the Hubble Space Telescope have even indicated that the exoplanet's atmosphere must have sodium vapor in it.

Star Data Apparent Mag.: 7.65 Spectral Type: G0 Radius: 1.146 Rsolar Mass: 1.148 Msolar	Exoplanet Data Period: 3.52475 days Semi-major Axis: 0.04747 AU Radius: 1.38 RJupiter Mass: 0.714 MJupiter
Source: Data summarized at "The Extra-solar Planets Encyclopedia," http://exoplanet.eu/star.php?st=HD+209458 .		Source: Brown T., et al. The Astrophysical Journal, 552, 699 (2000); available through the "The Extrasolar Planets Encyclopedia," http://exoplanet.eu/papers/HST-HD209458.pdf .

7. Above are some facts about the star and its exoplanet and a refined light curve as recorded by the Hubble Space Telescope. The upper-left corner at the beginning of the drop in the light intensity curve occurred just as the leading edge of the exoplanet began to move across the star and the upper-right corner is just as the last edge of the exoplanet leaves from being in front of the star.

• Assume that the orbit of the exoplanet moves directly across the center of the star (this is not exactly true but is a reasonable first approximation), on last page of this worksheet, calculate the orbital speed of the exoplanet at this point in its orbit in m/s. (Hint: Remember that speed = distance/time.)

[Useful Data: R_solar = 6.9599 X 10⁸ m; M_solar = 1.9889 X 10³⁰ kg; R_Jupiter = 7.15 X 10⁷ m; M_Jupiter = 1.8966 X 10²⁷ kg]

Conclusion

8. Turn in your worksheet and the printouts of the results of your simulation calculations. Staple them together with the worksheet on top.

Bibliography

• Any good introductory college astronomy textbook such as:

  John D. Fix. Astronomy: Journey to the Cosmic Frontier, 6^th ed. McGraw-Hill, 2011.

• More advanced topics are covered in introductory astrophysics textbooks such as:.

  William Zeilik and Stephen A. Gregory. Introductory Astronomy and Astrophysics, 4^th ed. Fort Worth, Texas: Saunders, 1998.

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Created and maintained by: Richard L. Bowman (2004-12) (last updated: 23-Apr-12)