Midterm 2.
Astronomy 205
NAME______________________________________
Dr. Edward Rhoads
Section 1: Multiple Choice (20 questions 2 points each)
Note: It is possible for a question to have more than one correct answer. You just have
to pick one of the possible correct answers if that happens.
1) What is the remnant of a star twice the mass of our sun at the end of its lifetime?
A) White Dwarf
B) Neutron Star
C) Black Hole
D) Nothing (it completely destroys itself)
2) What is the remnant of a star five times the mass of our sun at the end of its lifetime?
A) White Dwarf
B) Neutron Star
C) Black Hole
D) Nothing (it completely destroys itself)
3) What is the remnant of a star ten times the mass of our sun at the end of its lifetime?
A) White Dwarf
B) Neutron Star
C) Black Hole
D) Nothing (it completely destroys itself)
4) Which of the following stars will NOT supernova at the end of its lifetime?
• A) a star the mass of the sun
• B) a star ten times the mass of the sun
• C) a star fifty time the mass of the sun
• D) these will all supernova at the end of their lives
5) RR Lyra and Cepheid Variable stars are stars on which part of their lifetime?
• A) main sequence
• B) horizontal branch
• C) protostar
• D) these could occur at any time in their lives as it has nothing to do with the
star’sevolution
6) If you have two variable stars the more massive star will have a greater:
A) period
B) change in brightness
C) apparent brightness
D) all of the above
7) Observing variable stars allow us to determine the distance to the variable stars
because:
• A) Unlike most stars distance affects the color of a variable star
• B) The period of variability allows you to determine its absolute brightness
• C) The time it takes to vary its brightness is determined by how long the light
took to get to us
• D) all of the above
8) If attempting to determine the distance to a nearby galaxy which is the better type of
variable star to use, RR Lyrae or Cepheid Variable?
• A) RR Lyrae
• B) Cepheid Variable
• C) both work equally well
• D) neither one will work for anything outside our galaxy
9) Quasars are typically found?
• A) on the other side of the observable universe (< 4 billion light years)
• B) in the cores of the nearest galaxies to us (less than 100 million light years)
• C) in the cores of nearby galaxy clusters (200 million to 2 billion light years)
• D) Quasars are found equally at all distances from us
10) How much light do you get from the object that is considered to really be the
“Quasar”?
• A) none, it comes from something else
• B) all of it
• C) half from it and half from something else
• D) Quasars are theoretical and have never been observed
11) What can we learn from the Lyman-alpha forest?
A) the masses of quasars
B) about the galaxies and clouds of gas in the path between us and the Lymanalpha forest
C) about what the quasars are made out of
D) all of the above
12) Many Wolf-Rayet stars have no Hydrogen in their spectrum. Why is this?
• A) They have fused all the Hydrogen into Helium for the entire star
• B) They have thrown all of their Hydrogen into space
• C) They formed without having any Hydrogen
• D) Their spectra are so far Doppler shifted that we would never be able to detect
any of the Hydrogen lines.
13) Most of the Carbon, Oxygen, and Nitrogen in out bodies comes from:
A) the birth of our universe (big bang)
B) cores of stars like our sun
C) from the outer parts of massive stars thrown into space
D) fairly equally from all of these three sources
14) When a 50 solar mass star dies what is left over?
A) a white dwarf
B) a neutron star
C) a black hole
D) nothing
15) A star 100 times the mass of our sun when it ends it life theoretically could:
A) create a supernova
B) create a hypernova
C) create a gamma ray burst along its magnetic poles
D) completely collapse upon itself and not even generate a supernova
E) It could theoretically do any of these
16) What is the best method to find the distance to Sirius (8.6 light years away)?
A) parallax
B) variable stars
C) Hubble’s Law
D) star cluster fitting
17) What is the best method to find the distance to Andromeda Galaxy (3 million light
years away)?
A) parallax
B) variable stars
C) Hubble’s Law
D) star cluster fitting
18) What is the best method to find the distance to the Pleiades (an open cluster) (400
light years away)?
A) parallax
B) variable stars
C) Hubble’s Law
D) star cluster fitting
19) Which of the following is the best method to find a distance to a spiral galaxy that is
about 500 million light years away?
A) parallax
B) variable stars
C) Hubble’s Law
D) star cluster fitting
20) Which of the following objects has the greatest mass?
A) Our sun
B) An LBV/Wolf-Rayet star
C) A neutron star
D) A Quasar
Section 2: Short Answer. 40 pts per question lowest score is dropped.
1) A) For a brief period after the Hydrogen in a core of a star is all fused to Helium where
does the energy that a star needs to survive come from (before it starts to fuse Helium)
and how does that affect the size and temperature of the surface of the star?
B) What is the process by which Helium (also known as alpha particles) are fused into
another element and what element is created from this fusion process?
C) For stars like our sun explain what the final two products will be at the end of its life
(the core and everything outside the core what do they become)? For what the core
becomes explain what keeps it from collapsing further.
D) For stars ten times the mass of our sun explain what the final two products will be at
the end of its life (the core and everything outside the core what do they become)? For
what the core becomes explain what keeps it from collapsing further.
2) You will find the following equations useful for this question:
distance = 10 parsecs * 10(x/5)
where x = V - Mv for a given star.
For a Cepheid Variable its absolute magnitude (Mv) = -2.81 log(Period in days) – 1.43
Please note that “Magnitude” for the vertical below is the V magnitude.
A) Find the period of variability for the star.
B) Find the absolute magnitude of the star.
C) Find the distance to the star.
D) What 2 physical mechanisms causes stars like this to vary their brightness (one causes
the cycle to occur and the other is what actually makes the brightness change) and what
part of their variable cycle are they hottest and what part are they brightest?
3) This question examines the post Main Sequence lifetime of the most massive stars (>
25 solar masses).
A) In a few sentences explain what LBV and Wolf-Rayet stars are. One bonus point if
you can name a specific star that is either a LBV or is a Wolf-Rayet star.
B) If you wanted to discover a new LBV or Wolf-Rayet star where would you search and
why?
C) What determines the limit to the maximum brightness that stars can increase to as they
finish up their lifetimes? (Hint, what would happen to the star if it became any brighter
than this, and yes the answer to the hint should be part of your answer).
D) When we look at an LBV or Wolf-Rayet star we see lots of emission lines. What are
we really looking at when we examine this spectrum? Why does that make it difficult to
observe and study these types of stars and how does that affect their brightness over
time?
4) A) When you look at a Quasar what are you really looking at and where is the energy
it is emitting coming from? What is a Quasar actually though?
B) What has to happen to a galaxy (that we scientists seem to think anyway) so that the
galaxy (for some period of time) will have a Quasar? That is to say Quasars seem to
correspond to what kind of event for a galaxy?
C) Approximately what is the mass of a typical Quasar and what is its approximate
physical size?
D) What is the Lyman-Alpha forest, what causes it, and what can we learn about the
universe by studying it?
5) A) How does Astronomical Parallax work for finding distances to stars? About how
far out does it work and what determines what limits this distance?
B) Most methods of finding distances to objects hinge on comparing what two values
(and of course each method has a different way of finding the first of those two values)?
C) What is the difference between Type I and Type II supernovae and why are we able to
use these supernova to determine distances?
D) Astronomers different methods to find distances to objects is referred to as a “distance
ladder”. Why is it called this and what influence do the lowest rungs of the “ladder” such
as parallax have on the other rungs of the ladder. Explain.