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HW #11 Review for Exam #2
There is nothing to turn in this week. Instead spend time reviewing for the
exam.
1) It is important that you understand everything from the first Exam or else it will be very
difficult to apply these concepts to the material for this exam. Review your last exam and
be sure that you understand why certain answers are correct, and others are wrong.
New material for this Exam
2) Understand how binary stars are used to determine stellar masses. This includes the use
of spectroscopic binaries, the Doppler shift, Kepler’s 3rd Law, and how it is possible to
determine orbital period and orbital radius.
3) Be sure to really, truly, understand all aspects of the H-R diagram. What variables are on
the x and y-axes. Which way does temperature increase, which way does luminosity
increase. Where is the main-sequence (V). What are main-Sequences stars. Where are
the super giants (I), the giants (III) and the White Dwarfs. Why do each have the
position that they do o the H-R diagram. For instance, red super giants have cool surface
temperature. So they are on the right side of the diagram. But their luminosity is huge.
This is because their radius is gigantic.
4) Understand spectral typing. Why the hydrogen lines become large as the surface
temperature increases until they reach spectral type A. Then as the temperature increases
the hydrogen lines actually shrink. Also, understand what line strength depends on. It is
the surface temperature and the number of absorbers of a certain element. Understand
why we can use spectroscopy to figure out the amount of processed elements (elements
heavier than helium) in a star.
5) Review the interstellar medium (ISM), and what it is like. What is interstellar dust and
how are molecular clouds different than the normal ISM.
6) Understand the various mechanisms that allow molecular clouds to become compressed
to the point that they start to gravitationally contract. We discussed 2 mechanisms that
initiate star formation, and two mechanisms which continue star formation in the
molecular cloud (self-sustained star formation) Be sure to understand how stellar life
times, especially in the high mass O and B stars are important to self-sustained star
formation.
7) Understand the track that an individual star takes from beginning proto-star phase to main
sequence star. What is happening to the temperature, radius and luminosity? What
process is providing the luminosity and why is a proto-star able to shrink. How does
convection play a part in the proto-star evolution?
8) Understand all aspects of low mass star evolution off the main-sequence. Why a star
leaves the main sequence, what the sub-giant and giant phases are and what is happening
inside the star during these phases. What is happening to the star when helium core
burning is occurring and what is happening during the planetary nebula phase and what is
a white dwarf. Also understand how we can use white dwarf temperatures to estimate the
age of the universe.
9) Understand all aspects of high mass star evolution. How high masses stars move on the
H-R diagram and why. Understand why the core can only produce elements up to Iron.
What happens when the iron core is created. How do supernovas occur and want is a
neutron star, a pulsar. How do super nova help self-sustained star formation and where
do all the other heavy elements in the universe come from.
10) Know what a black hole is, what a singularity is, what the event horizon is. Which stars
form black holes and why black holes are not universal cosmic vacuum cleaners.
11) Also, what are the two postulates of special relativity. Understand why forcing the speed
of light to be the same for all observers means that time cannot be the same for all
observers. Understand how time dilation and length contraction can explain the twin
paradox. Also understand that gravity is not a force and how mass warps space-time
which causes objects to move in curved lines.