Name_________________________
STUDENT INSTRUCTION AND ANSWER
SHEET
Activity 3: Concept
Application: Discovering New Planets
In this activity, you will
examine real data gathered by astronomers in their pursuit to find planets
orbiting distant stars.
A. The tables below provide
information about the motion of two stars (51 Pegasi, and Tau Boo).* Based
on the data provided in these tables, do you believe there is a companion
planet in orbit about these stars? Explain your reasoning.
B. Describe how the motion of the star differs when it has a positive
versus a negative velocity.
C. How do we detect that the
stars are moving with a radial velocity? (Hint: Consider your answer to
question G in Activity #1.)
* This data was inferred form the actual velocity versus time graphs,
which can be found at:
http://cannon.sfsu.edu/~gmarcy/planetsearch/doppler.html
D. Use the grid below to construct
a radial velocity versus time graph for 51 Pegasi.
E. Use the grid below to construct a radial velocity versus time graph
for Tau Boo.
F. Describe the similarities and differences in your graphs.
G. Based on your graphs, would you infer that the stars 51 Pegasi and
Tau Boo are in orbit with a companion planet? Explain your reasoning.
H. How long would it take
the companion planet to complete one full orbit for each of these stars?
Explain your reasoning.
I.
Below are the velocity versus time graphs for two stars (47 Ursae Majoris
and HR 3522)* that might have a companion planets in orbit about them.
For each star state whether or not you think the star has a companion
planet and if so estimate the orbital period of the planet. If not, explain
why not.
i. 47 Ursae Majoris
ii. HR 3522
* The original versions of these graphs can be found at: http://cannon.sfsu.edu/~gmarcy/planetsearch/doppler.html
J. At what time(s) was each
star moving towards Earth with the greatest velocity?
i. 47 Ursae Majoris
ii. 55 Rho cnc
K. At what time(s) was each companion planet moving towards Earth with
the greatest velocity?
i. 47 Ursae Majoris
ii. 55 Rho cnc
L. Was the velocity of either star ever zero? If so when, and if not why
not?
i. 47 Ursae Majoris
ii. 55 Rho cnc
M. What was the maximum value of the tangential velocity of each star?
Explain your reasoning.
N. Like our Sun, both 47 Ursae Majoris, and 55 Rho cnc, are "G"
type stars. Therefore, to a good approximation, we know that each of these
stars have a mass of approximately 2 x 10^{30} kg. Scientists have estimated
that the companion planet orbiting 47 Ursae Majoris has a mass of 2.6
Jupiter masses (mass of Jupiter is 1.9 x 10^{27} kg) and is 2.11 AU's ( 1
AU = 1.5x10^{11}m) away from the star. They have also estimated that the
companion planet orbiting 55 Rho cnc has a mass of .84 Jupiter masses
(mass of Jupiter is 1.9 x 10^{27} kg) and is .11 AU's ( 1 Uu = 1.5x10^{11}m)
from the star.
i. Find the location of the
center of mass for the 47 Ursae Majoris and planet system. Draw a sketch
of the system below and label the planet, star and location of the center
of mass.
ii. Find the location of the center of mass for the 55 Rho cnc and planet
system. Draw a sketch of the system below and label the planet, star
and location of the center of mass.
