Download 1. What is the HR diagram? 1a. The HR diagram is a plot of a star`s

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1. What is the HR diagram?
1a. The HR diagram is a plot of a star’s luminosity on the vertical axis against the star’s temperature on
the horizontal axis.
2. What is a stellar evolutionary track?
2a. A stellar evolutionary track is a plot of the values of luminosity and temperature that a star has at
different times in its life.
3. What happens to the pressure and temperature and density of a contracting gas? How about an
expanding gas?
3a. Pressure and temperature of a contracting gas increase. Pressure and Temperature of an expanding gas
4. What is the definition of a star?
4a. A star is an object which supports itself against gravitational collapse by generating energy from nuclear
5. Whats the definition of a star on the main sequence?
5a. A star on the main sequence supports itself from gravitational collapse by generating energy from nulcear
fusion by burning hydrogen in the core.
6. What generates the pressure that holds up a star against its own gravitational pull?
6a. Nuclear fusion.
7. The processes that you describe in 6) - what happens to their efficiency if the temperature goes up and
7a. The efficiency goes up/down as temperature goes up/down.
8. During the main sequence, what process generates energy and where in the star does this happen?
8a. This is nuclear burning of hydrogen and it occurs in the core of the star.
9. So during the main sequence whats happening to the amount of hydrogen and helium in the star?
9a. Amount of hydrogen going down and the amount of helium going up.
10. Whats the raw fuel for nuclear burning of hydrogen in the core - hence say when nuclear burning in the
core stops.
10a Hydrogen. Hydrogen burning stops when there is no more hydrogen in the core.
11. When this occurs, does the star stop shining? If not, what powers the star since nuclear burning has
11a. When this occurs the star does not stop shining. The star keeps on shining by using energy released
from slight contractions of the star.
12. At this point, why is the star contracting? If the star is contracting, whats happening to the temperature
of the core?
12a. Its contracting because there is not enough energy being generated to hold itself up against gravity. The
temperature of the core is going up.
13. Whats happening to the temperature of a shell around the core? Whats the main component of this
13a. The temperature of a shell around the core is going up.
14. Eventually what will start happening in this shell around the core?
14a. Nuclear burning of hydrogen when the temperature gets hot enough.
15. At this point, whats the main constitent of the core? Is there any energy generation in the core at this
15a. Its Helium. No energy generation in the core at this point.
16. When hydrogen shell burning starts, whats happening to the envelope and to the luminosity of the star
as a whole - justfy your answer with the Stefan-Boltzmann law. Whats happening to the core?
16a. Envelope is expanding and luminosity is going up - Stefan-Boltzman law says that the luminosity of a
star depends on its radius and temperature.
17. The star moves up the Red Giant branch - why is it called the Red Giant Branch?
17a. Its the Red Giant branch because the envelop is cool enough to be in the red range of the spectrum and
the stars are expanding and getting bigger in size along this branch - hence their increase in luminosity.
18. On the Red Giant Branch, whats happening to the temperature of the core - is it going up or down?
18a. Its going up slowly.
What temperature does helium burning require.
About 100 × 106 Kelvin.
What is the Helium Flash?
The explosive start to Helium burning in the core for low mass stars.
On the horizontal branch, how is the star powered? What burns where?
Helium burning in the core. No real shell burning at this stage.
On the asymptotic giant branch (AGB), can you ever get a helium burning shell outside a hydrogen
burning shell? If not, why not?
No because Helium burning requires a higher temperature than hydrogen burning.
On the AGB, whats the main component of the core?
Helium and Carbon.
Whats the planetary nebula stage?
Where the star blows of its outer envelope.
Does a white dwarf produce any energy? What is the main consitituent of a white dwarf?
A white dwarf does not produce any energy. Mainly consists of carbon.
Why cant a low mass star burn carbon to produce energy?
It can never get hot enough to burn Carbon.
Why can a high mass star burn carbon to produce energy?
It can contract enough to get hot enough to burn Carbon.
Is there a Helium flash in these high mass stars?
There is a gentle start to Helium burning in high mass stars but no Helium flash which is an explosive
start to Helium burning in low mass stars.
How is the evolution of a high mass star similar to the above and different to the above?
SImilar in that its always trying to shine and burn something to stop itself collapsing against gravity.
It burns He in a shell and H in shell. Its different in that it can burn elements all the way to Iron.
What is the end point in the life of a low mass star and the life of a high mass star.
Low Mass: WHite Dwarf. High Mass: Neutron star or black hole.
Which comes first; the AGB stage or the Red Giant Stage?
Red Giant.
Which comes first; the Planetary Nebula stage or the White Dwarf stage?
Planetary Nebula stage.
Which comes first; the Supernova stage or the Main Sequence stage?
Main Sequence.
Which spends longer on the main sequence: a 2 solar mass star or a 5 solar mass star?
a 2 solar mass star.
Does a red main sequence star have more or less mass than a blue main sequence star?
Less. Blue implies hot implies more luminous implies more massive.
Which of the following stars does not have nuclear fusion occuring in its core: a) red giant, b) blue main
sequence star c) red main sequence star?
Red Giant.