Astronomy Lab 10
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University of Nebraska, Omaha *
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Course
1354
Subject
Astronomy
Date
Feb 20, 2024
Type
docx
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8
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NAME______________________
CLASS_________
Instructions:
Go to web site http://astro.unl.edu
. Click on the Nebraska astronomy applet project and then go to NAAP Modules(at top of screen) and pick HR Diagram. Read the materials and complete the guide below and complete the exercises and complete the document below—the background materials will help you answer the questions—the flash demonstration will help you complete the rest.
ON LINE LAB 10
Nebraska Astronomy Applet Project
Student Guide to the
HR DIAGRAM
_____________________________
NAAP – HR Diagram Explorer 1/8
HR Diagram – Student Guide
Pretest Score: Background Information
Work through the background sections on Spectral Classification, Luminosity, and the
Hertzsprung-Russell Diagram. Then complete the following questions related to the background
information.
Question 1: The table below summarizes the relationship between spectral type, temperature, and
color for stars. Note that the surface temperature of the stars in the table increases. Question 2: Complete the following table related to stellar luminosities in solar units using the
equation . NAAP – HR Diagram Explorer 2/8
Star
Surface
Temperature K
Spectral Type
Color
Betelguese
3,500
M2
Red
Arcturus
4,300
K5
Orange
Alpha Centrui A
5,800
G2
Yellow
Procyon A
6,500
F5
Yellow-White
Sirius A
9,100
A1
White
Rigel A
11,000
B8
Light Blue
Delta Orionis
33,000
O9
Blue
Radius (R
⊙
)
Temperature (T
⊙
)
Luminosity (L
⊙
)
1
1
1
1
2
16
3
1
9
1
1/2
1/16
Question 3: The mass luminosity relation describes the mathematical relationship
between luminosity and mass for main sequence stars. It describes how a star with a luminosity
of 2 M
⊙
would have a luminosity of ____11.31_________ L
⊙
while a star with luminosity of
3,160 L
⊙ would have an approximate mass of _______10_________ M
⊙. HR Diagram Explorer Open the HR Diagram Explorer
. Begin by familiarizing yourself with the capabilities of the
Hertzsprung-Russell Diagram Explorer through experimentation.
An actual HR Diagram
is provided in the upper right panel with an active location
indicated by a red x. This active location can be dragged around the diagram. The
options panel
allows you control the variables plotted on the x-axis: (temperature, B-V,
or spectral type) and those plotted on the y-axis (luminosity or absolute magnitude). One
can also show the main sequence, luminosity classes, isoradius lines, or the instability
strip. The Plotted Stars
panel allows you to add various groups of stars to the diagram.
The Cursor Properties
panel has sliders for the temperature and luminosity of the active
location on the HR Diagram. These can control the values of the active location or move
in response to the active location begin dragged. The temperature and luminosity (in solar
units) are used to solve for the radius of a star at the active location.
The Size Comparison
panel in the upper left illustrates the star corresponding to the
active location on the HR Diagram. Note that the size of the sun remains constant. NAAP – HR Diagram Explorer 3/8
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Exercises
Drag the active location around on the HR Diagram. Note the resulting changes in the
temperature and luminosity sliders. Now manipulate the temperature and luminosity
sliders and note the corresponding change in the active location. Question 4: Check the appropriate region of the HR diagram corresponding to each description
below.
Drag the active location around on the HR Diagram once again. This time focus on the
Size Comparison panel. Question 5: Check the appropriate region of the HR diagram corresponding to each description
below.
Check show isoradius lines. Note that at each point on a green line, stars have the same
value of radius. Use these isoradius lines to check your answers in the table above.
NAAP – HR Diagram Explorer 4/8
Description
Top
Right
Bottom
Left
Hot stars are found at the:
X
X
Faint stars are found at the:
X
X
Luminous stars are found at the: X
X
X
Cool stars are found at the:
X
X
Description
Upper
Left
Upper
Right
Lower
Right
Lower
Left
Large Blue stars are found at the:
X
Small Red stars are found at the:
X
Small Blue stars would be found at the: X
Really Large Red stars are found at the:
X
Question 6: The equation below describes the luminosity of a star in terms of its radius and
temperature. Use this equation to explain the results you found in the table of the previous
question. The size and temperature effect the luminosity of the star exponentially and that the temp has a
greater effect on the luminosity over the size.
In addition to the isoradius lines, check show luminosity classes
. This green region
(dwarfs V) is known as the main sequence and contains all stars that are fusing hydrogen
into helium as their primary energy source. Over 90% of all stars fall in this region on
the HR diagram. Move the active cursor up and down the main sequence and explore the
different values of stellar radius.
Question 7: Describe the sizes of stars along the main sequence. What are stars like near the top
of the main sequence, the middle, and the bottom?
At the top of the main sequence the stars have a high temperature and a high luminosity resulting
in the stars being quite large in comparison to the Sun. The middle of the main sequence has a
lower temp and a lower luminosity resulting in a star that is smaller than the top of the main
sequence but still larger than the Sun. The bottom of the main sequence has a very low
temperature and very low luminosity which results in a star that is much smaller than the Sun.
The background pages of this module talked about the mass-luminosity relationship for
stars on the main sequence: Question 8: What can you conclude about the masses of stars along the main sequence? The higher the luminosity of the star the higher the mass is as well.
NAAP – HR Diagram Explorer 5/8
L
R
M
T
Question 9: Use the results from the previous 5 questions to construct a “conceptual” HR
Diagram. You simply want to draw arrows showing the direction in which variables are
increasing. a) Draw in an arrow on the y axis showing the direction of increasing “intrinsic luminosity” of
the stars. (This is complete for you.)
b) Draw in an arrow on the x-axis showing the direction of increasing surface temperature of the
stars.
c) Draw in an arrow showing the direction of increasing radius on the diagram. (hint: thus must
be perpendicular to the isoradius lines.)
d) Draw in an arrow showing the direction of increasing mass form main sequence stars on the
diagram. (Note that his arrow only applies to main sequence stars, but that is over 90% of stars.)
Figure 1: Conceptual HR Diagram
NAAP – HR Diagram Explorer 6/8
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Uncheck show luminosity classes and check show instability strip
. Note that his region of the HR Diagram indicates where pulsating stars are found such as RR Lyrae stars and Cepheid variable stars. These stars vary in brightest because they are pulsating – alternately growing bigger and smaller – which changes their radii and surface temperatures and resulting their luminosities. Question 10: Describe the characteristics of stars that are found in the instability strip. You
should cover their range of temperatures, colors, luminosities, and sizes. (Hint: Comparing them
to the sun is useful.) Are variable stars necessarily on the main sequence?
The stars found in the stability strip are larger, more luminous, and hotter than the sun.
Check the plotted stars option the nearest stars
. You should cover their range of
temperatures, colors, luminosities, and sizes.
Question 11: Describe the characteristics of the nearest stars. The nearest stars have a low temperature, low luminosity, and are much smaller than the Sun.
Question 12: Do you think these stars are rare or very common among all of the stars of our
galaxy? Explain your reasoning. Are any assumptions involved in your reasoning?
I I think these stars are very common among all stars in our galaxy. There are very many of them
in a dense area, whereas the bigger stars seem to be fewer and more spaced out within the
galaxy.
Uncheck the plotted stars option the nearest stars
and check the brightest stars
. Why
are these stars are the brightest in the sky? Three students debate this issue:
Student A: “I think it’s because these stars must be very close to us. That would make them
appear brighter to use in the sky.”
Student B: “I think it’s because these stars are very luminous. They are putting out a
tremendous amount of energy.”
Student C: “ I think its because these stars are very close and very luminous.” Question 13: Use the tools of the HR Diagram to support the views of one of the three students.
Why are the stars we perceive as bright in the night sky really bright?” (hint: You may find the
options labeled both the nearest and brightest stars
and the overlap
useful.)
NAAP – HR Diagram Explorer 7/8
The “brightest stars” are putting out a very large amount of energy. By putting out a large
amount of energy the stars are able to shine brightly, more so than the more common stars. Question 14: Do you think that these bright stars are very common (make up a large percentage
of all stars in general)? Explain your reasoning.
I don’t believe the “bright stars” are very common. I believe that there are many other stars in the
galaxy that far outnumber the “bright stars”.
NAAP – HR Diagram Explorer 8/8