Lab4_StellarEvolution
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Oklahoma State University *
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206
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Astronomy
Date
Apr 3, 2024
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docx
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Stellar evolution
We use the Hertzsprung-Russell diagram (H-R diagram), plotting luminosity vs. temperature to analyze stellar evolution through various parts of a star’s life. A star is formed from a fragment of a Giant Molecular Cloud, until it takes its place along the main sequence in the H-R diagram, where it then spends most of its life. When the core of a star fills with helium, hydrogen fusion in the core halts, triggering changes in the luminosity and temperature, causing the star to leave the main sequence. The evolutionary track of a star after leaving the main sequence largely depends on its mass. In this lab we will use interactive simulations to observe and analyze post-main sequence stellar evolution for low-
mass stars, sun-like stars and massive stars.
Part I.
Go to: https://starinabox.lco.global/
to access an interactive software to simulate stellar evolutionary tracks, observing changes in brightness, size, temperature and color for stars of various mass. Switch to “Advanced” and open the lid. To begin with, leave the default setting for a one solar mass star.
1. Observe and describe what happens to a 1 solar mass star after it leaves the main sequence. Choose the mass to be a 1 Solar mass star. Make sure the “Size and color” icon is selected. Click to run the simulation. Describe how the size of the star changes as it evolves after leaving the main sequence.
Notice that the evolutionary track reaches the upper right corner, then drops back down and goes up to the upper right corner again. What is happening in the star to make it go up to the upper right corner?
Why does the star suddenly drop back along its track from the upper right corner? What is happening in the star?
Why does the star go back up to the upper right corner of its track?
How do the changes in color relate to changes in temperature? What do you expect to see when you observe the temperature change?
Select the “Temperature” icon and run the simulation again. Describe what happens to the temperature as the star evolves.
Consider the relationship between brightness and luminosity. Predict how you think the brightness will change as the star evolves.
Select the “Brightness” icon and run the simulation again. Describe what happens to the brightness as the star evolves.
Now let’s look at the information the clock tells us. Select the “Clock” icon and run the simulation again. Notice the various stages take very different
amounts of time to pass. Which stage takes the longest?
What is meant by the “Hertzsprung gap”?
How many years pass, in total, before the star reaches the upper right corner for the second time?
What happens to the star in the long term, after it passes the corner on the left?
Select the “Scale” icon and run the simulation again. Describe what happens to the mass as the star evolves.
2. Record the lifetime up to the point where the star reaches the upper right corner for the second time in the table below. Run the simulation for the other masses and record those values.
Mass (Solar mass)
Lifetime (million years)
0.2
0.65
1
2
4
6
10
20
30
40
Describe the trend you see with your data. What happens to the lifetime as the star mass increases?
Run the simulation for a 10 solar mass star. Describe the difference in the main shape of the evolutionary track on the luminosity vs. temperature plot.
Describe the difference you see with the size and color evolution of the massive star.
Notice that there is no late stage evolution, as with a sun-like star. It does not turn a corner on the left and decrease luminosity. Why is there no late stage shown for the massive star’s evolution?
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Part III.
Watch videos showing simulations as three different mass evolve:
1 solar mass:
https://www.youtube.com/watch?v=kXdr1viKB-o&feature=youtu.be
10 solar mass:
https://www.youtube.com/watch?v=8qOgY81p1JI&feature=youtu.be
20 solar mass:
https://www.youtube.com/watch?time_continue=7&v=T7ue3hoWhNU
Describe in your own words, the differences between evolution of a sun-like star and that of a massive star. Describe any new information you learned from watching these videos. Please write at least 250 words in your description.