Download In this lecture tutorial we will investigate the relationship between

Motion of Extrasolar Planets
115
Center of Mass
Center of Mass
Star
Extrasolar
Planet
Extrasolar
Planet
.
Star
.
Fig 2. Extrasolar Planet and Star As
Seen Edge-On Or From The Side
Note that the extrasolar planet is
moving toward you.
(not to scale)
Fig 1. Extrasolar Planet and
Star As Seen From Above
(not to scale)
1) Figure 1 and Figure 2 show the orbits of the same extrasolar planet and star from two
different points of view. As an extrasolar planet orbits around a star, the gravitational
attraction between the two objects causes the central star to make a small orbit around
the system’s center of mass. Which object travels in the largest orbit? (circle one)?
extrasolar planet
the star
they have the same
sized orbit
you can’t determine
which has the larger
orbit
2) Which object takes a greater amount of time to complete one orbit (circle one)?
extrasolar planet
takes longer
central star takes
longer
they both take the
same amount of time
you can’t determine
which takes longer
Explain your reasoning.
3) At the instant shown in Figure 1, which direction is the extrasolar planet moving (circle
one)?
toward the bottom
of the page
toward the top
of the page
toward the
central star
4) At the instant shown in Figure 1, which direction is the central star moving (circle one)?
toward the bottom
of the page
PEARSON PRENTICE HALL
toward the top
of the page
toward the
extrasolar planet
LECTURE-TUTORIALS FOR INTRODUCTORY ASTRONOMY
SECOND EDITION, 2007
Motion of Extrasolar Planets
116
5) In general how does the direction the extrasolar planet is moving compare with the
direction the central star is moving?
6) Figure 2 shows the extrasolar planet and star from the side or as seen edge-on. At the
instant shown, which direction is the planet moving (circle one)?
coming out of the page
directly toward you
moving into the page
directly away from you
toward the
central star
7) Two students are having a discussion about the relationship between the movement of
the star and planet and Doppler shift of the light coming from the star.
Student 1: Since Figure 2 states that the extrasolar planet is moving out of the page,
directly toward us, then the light from the star we observe will be
blueshifted.
Student 2: I disagree, the light from the star will be redshifted because the star is
moving the opposite direction the planet is moving.
Do you agree or disagree with either or both of the students? Why?
8) Suppose instead that the extrasolar planet (shown in Figures 1 and 2) became much
more massive, but continued orbiting at the same distance. How would your
observations from Earth be different (circle one)?
the star’s light would be
shifted even more
the star’s light would be
shifted less than before
no change in the light
would be observed
Explain your reasoning.
9) Suppose instead that the extrasolar planet (shown in Figures 1 and 2) moved farther
away from the star, but continued to have the same mass. How would your
observations from Earth be different (circle one)?
the star’s light would be
shifted even more
the star’s light would be
shifted less than before
no change in the light
would be observed
Explain your reasoning.
LECTURE-TUTORIALS FOR INTRODUCTORY ASTRONOMY
SECOND EDITION, 2007
PEARSON PRENTICE HALL
Motion of Extrasolar Planets
117
10) Under what condition would you NOT observe a star’s light to ever undergo Doppler shift
even when there is an extrasolar planet orbiting the star? Explain your reasoning, and
include a drawing to illustrate your answer in the space below.
1
2
3
4
5
Velocity (m/s)
-20
3
20
2
4
5
8 10
Time (years)
2
20
-20
Time (years)
-20
Velocity (m/s)
1
20
Velocity (m/s)
Velocity (m/s)
11) Consider the four graphs shown below which show the radial velocity of four stars.
5
4
20
-20
10 15 20 25
Time (years)
3
9 12 15
6
Time (years)
a. From which star would you obseve the greatest Doppler Shift? Explain your
reasoning.
b. Which planet has the longest orbital period? Explain your reasoning.
PEARSON PRENTICE HALL
LECTURE-TUTORIALS FOR INTRODUCTORY ASTRONOMY
SECOND EDITION, 2007
118
Motion of Extrasolar Planets
12) Given the location marked with the dot on the star’s radial velocity curve, at what
location (1-4) would you expect the planet to be located at this time? Explain your
reasoning.
1
Radial Velocity
20 m/s
Orbit of star
Earth
10 m/s
4
2
Time
-10 m/s
- 20 m/s
Orbit of planet
LECTURE-TUTORIALS FOR INTRODUCTORY ASTRONOMY
SECOND EDITION, 2007
3
PEARSON PRENTICE HALL