AST1120-lab6
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Astronomy
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Apr 3, 2024
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AST 1120: Stellar Astronomy
Name:
Lab 6 (40 points) Stellar Evolution
Learning Goals
Describe key differences between open star clusters and globular star clusters
Determine the age of a star cluster from its main sequence turnoff point
Describe the HR diagram of a globular star cluster
Explain how stars evolve after leaving the main sequence
Part 1 – Star Clusters
Read about star clusters in Chapter 22.2
and use that information to answer the following questions. Figure 1 – Pleiades open cluster
1.
The star cluster pictured at top left is the Pleiades, in the constellation Taurus. Describe some of the evidence that this is a young, open cluster. Figure 2 - 47 Tucanae globular cluster
2.
The star cluster at bottom left is 47 Tucanae, in the southern constellation of Tucana. Describe
some of the evidence that this is an old, globular cluster
You can read more about the Main Sequence Turnoff in Chapter 22.3
.
107 below is really 10
7
, 108 is 10
8
, etc. where 10
7
years is 10 million years. 10
10
years is
10 billion years
Figure 3 - Star Clusters Plotted on an H-R Diagram
3.
Which cluster on the chart above is youngest? Explain how you know this. 4.
Which cluster on the chart above is oldest? Explain how you know this. Check out this site about the goals of the Gaia mission
. It may take a minute to load. You will need to scroll down to advance the site. 2
5.
How many stars are shown in the Gaia image? 6.
What causes the dark patches in the Milky Way? 7.
What properties are used to sort the star cluster stars? 8.
Click on the box for NGC0869 (h Persei). What color star is highlighted?
9.
Click on the box for NGC0104 (47 Tucanae). What color star is highlighted? 10.Click on All 47 clusters. As you continue to scroll down, what happens to the blue
stars? Part 2 – Stellar Evolution
Open your Star in A Box
. Select Advanced before you open the lid. M
ʘ =
M
sun In Star In a Box, you can select the Mass in the bottom left (this is the Mass on the Main
Sequence). Click the clock icon in the bottom right to see the clickable stages of the 3
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star’s life. Click the weight icon to see the star’s mass at any stage. Press play to run through all stages of a star’s life.
11.Fill in the Table 1 below.
Mass on Main
Sequence (M
ʘ
)
0.2 M
sun
1 M
sun
10 M
sun
40 M
sun
Mass at Hertzsprung Gap (M
sun
)
Mass at Core Helium Burning (M
sun
)
n/a Mass at End of
Life (M
sun
)
Age at Hertzsprung Gap (Myr)
Age at last clickable stage
(Myr)
Name of Final Stage (top right corner)
Supernova (yes/no)
12.Which stars in Table 1 lose less than half of their mass over their lifetimes?
13.Refer to Table 1. How does the Mass on the Main Sequence effect the overall lifetime of a star? 4
14.If a star cluster contained all of the stars in Table 1, which star evolves off the main sequence first and which star stays on the main sequence longest?
Figure 4 - Stages for a Sun-like star after it leaves the Main Sequence.
15.Why does a star move up and to the right on the HR diagram (as seen in Figure 4) during stages when the core is inert? 16.During the planetary nebula stage, the outer atmosphere of a star is pushed completely away, exposing the core which will become a white dwarf. What is the
white dwarf composed of? Figure 5 is from Chandra X-ray observatory
. You can use this image as reference for the next several questions.
5
Figure 5 - Stellar Evolution for stars of different masses. Most massive at the top, down to least massive at the bottom
17.What objects can be left behind after a Type II supernova? 18.What is the only stage that all stars go through, regardless of their initial mass? 19.What is the end of the line for a star that had spectral type O on the Main Sequence? 6
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20.What is the end of the line for a star that had spectral type M on the Main Sequence? Conclusion
21.Explain why star clusters are so important for understanding stellar evolution.
7