NAME ______________________________________________

Astronomy 122
Test 2
November 16, 2006

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Formulas
W = 3x10⁷/T(K) Angstroms
F = constant T⁴ [power per unit area]
L = 12.6 constant R²T⁴ [power]
F = L/(12.6 D²) [power per unit area]
E = mc²

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30 Multiple Choice Questions @ 2 points per question -- Select the best answer

1. A feature all Main Sequence stars have in common is _______.

a. they are supported by degenerate pressure
*b. they convert hydrogen to helium in their cores
c. they show strong water lines in their spectra
d. they possess helium shell sources
e. all are found in the spiral arms in our galaxy

2. The least massive Main Sequence stars have masses of 0.1 M_Sun. The lower limit on a star's mass arises because ______.

a. in high mass stars, helium burning sets in before hydrogen burning
b. the ignition of nuclear fusion in a protostar is not quiet; the ignition leads to an intense stellar wind that disrupts the star forming cloud, halting the star formation process
*c. the electrons in the star's core become degenerate preventing the fusion of hydrogen into helium, halting the star formation process
d. the development of a large convection zone around the core of the star halts the star formation process
e. the GMCs in our galaxy have maximum masses of 100 times the mass of the Sun

3. Star formation happens ______.

*a. in GMCs
b. in H I regions
c. in the coronal gas in the ISM
d. just after a planetary nebula forms
e. just before the Helium Flash

4. When a star first enters the red giant branch, its internal structure consists of _______.

a. a carbon and oxygen core surrounded by a helium burning shell and a hydrogen burning shell
*b. a helium core surrounded by a hydrogen burning shell
c. an iron core surrounded by a silicon burning shell and a helium burning shell
d. an iron core surrounded by an oxygen burning shell and a helium burning shell
e. a hydrogen core surrounded by a helium burning shell

5. The point where a star is born (when the protostar phase ends) is marked by _______.

a. the formation of a planetary nebula
b. passage through a spiral arm that triggers the collapse of an ISM cloud
c. the formation of a brown dwarf
*d. the onset of nuclear fusion in the core of the protostar
e. the appearance of a giant molecular cloud

6. A brown dwarf is _______.

a. a low mass main sequence star
b. a dirty low mass main sequence star
*c. a failed star; an object that never got hot enough to ignite nuclear fusion in its core
d. a planet like the Earth
e. a smallish unusually cold sunspot

7. The dimming of the visible light from distant stars is caused primarily by _______.

a. hydrogen atoms
*b. dust particles
c. molecules such as carbon monoxide
d. ice crystals (clouds)
e. the blocking of the distant stars by foreground stars

8. The bright red emission nebulas known as H II regions form _______.

a. around stars like the Sun
b. in regions where you typically find planets
c. around binary star systems
*d. around massive, hot stars
e. around every protostar we have seen

9. The steps in the evolution of a star 25 times as massive as the Sun are _____.

a. protostar, main sequence, red giant, planetary nebula
b. brown dwarf, main sequence, red giant, supernova
*c. protostar, main sequence, red giant, AGB, supernova
d. protostar, brown dwarf, main sequence, red giant, AGB, planetary nebula
e. protostar, brown dwarf, main sequence, red giant, AGB, supernova

10. The _______ while it is on the Main Sequence.

*a. Sun's luminosity slowly increases
b. Sun's mass slowly increases
c. Sun converts helium to carbon and oxygen in a thin shell outside of its core
d. Sun’s surface temperature doubles
e. Sun’s luminosity varies periodically by 50 % every 22 years

11. Which of the following statements about the initial chemical composition of Main Sequence stars is correct?

a. Most are composed primarily of hydrogen and oxygen
*b. Most are composed of hydrogen and helium
c. Most are composed of nitrogen and oxygen
d. Massive stars are composed primarily of hydrogen and carbon
e. Low mass stars are pure hydrogen gas spheres

12. The coolest layer in the Sun’s atmosphere occur in the _______.

a. magnetosphere
b. photosphere
*c. chromosphere
d. convective layer
e. corona

13. An annihilation is when _______.

*a. a matter particle and its anti-matter twin collide and are converted into energy (radiation)
b. a massive nucleus fissions into two smaller nuclei
c. sunspots collide and coalesce on the Sun during Solar maximum
d. four hydrogen nuclei are fused to form one helium nucleus
e. an electron neutrino is transformed into a tau neutrino

14. Whether astronomers consider a star a high mass star or a low mass star is determined by ______.

a. where the star was born. Low mass stars are not born in the spiral arms of our galaxy
b. the fact that only low mass stars can produce reflection nebulae
*c. whether the stars end their lives through Type II Supernovae or through the formation of a Planetary Nebulae
d. whether the star burns carbon in its core during its Main Sequence lifetime or whether it burns hydrogen in its core during its Main Sequence lifetime
e. whether the star is able to become a Red Giant

15. The large loops of glowing gas seen hanging above the Solar limb are called _______.

a. coronal holes
b. coronal mass ejections (CMEs)
c. flares
*d. prominences
e. Solar streamers

16. The fusion of hydrogen to helium occurs in the cores of stars at temperatures of around _______.

a. 1,000,000-1,500,000 K
*b. 10,000,000-15,000,000 K
c. 10,000,000,000-15,000,000,000 K
d. 200,000,000 K
e. 600,000,000 K

17. Which of the following does not vary over the Solar Activity Cycle?

a. number of sunspots
b. amount of flares
c. coronal streamers
*d. the rotation rate of the Sun
e. the luminosity of the Sun

18. Normal stars spend _____ of their lifetimes as Giant stars.

*a. around 1 %
b. around 10 %
c. 80-90 %
d. 99 %

19. The corona of the Sun has a temperature of _____.

a. 5,800 K
b. 4,500 K
c. 100,000 K
*d. 1,000,000-3,000,000 K
e. 10,000,000-15,000,000 K

20. Of the following, which is the most efficient way to generate energy?

a. gasoline engines
*b. nuclear fusion
c. annihilation
d. coal burning
e. tunneling

21. A Reflection Nebula requires the presence of which of the following?

a. carbon and water
b. a brown dwarf and hydrogen gas
*c. dust and a massive star (an O or B star)
d. dust and a planetary nebula
e. hydrogen and helium gas

22. The Chandrasekhar limit is ______.

*a. the maximum mass a white dwarf may have
b. the minimum mass a main sequence star may have
c. the maximum mass a main sequence star may have
d. the fastest rate at which the Sun can rotate
e. the dividing line between high mass and low mass stars

23. After the carbon burning phase of evolution, most of the energy from nuclear reactions is lost through _____.

a. the emission of light (photons)
b. strong stellar winds
c. CMEs
*d. neutrinos
e. high speed protons

24. Sirius is a bright main sequence star. Sirius has mass of 2.1 times as massive as the Sun. Sirius will eventually wind up as a _____.

a. supernova
b. black hole
c. neutron star
*d. white dwarf
e. brown dwarf

25. The _____ is used to determine the age of the cluster.

a. number of stars in a stellar cluster
b. main sequence turn-off of a stellar cluster
c. number of white dwarfs in a stellar cluster
d. shape of a stellar cluster
e. position in the Milky Way galaxy of a stellar cluster

26. The layer of the Sun’s atmosphere which extends beyond the Earth is the _______.

a. helium burning shell
b. photosphere
c. chromosphere
*d. corona
e. convective layer

27. Which relationship concerning the mass of protostars is false?

a. The more massive protostars reach the main sequence first.
b. The most massive protostars will be the hottest and most luminous stars.
*c. The more massive protostars will be made of the heaviest elements.
d. The more massive protostars will become hot enough to produce H II regions.

28. What inevitably forces a star like the Sun to evolve away from the main sequence?

a. The core begins to fuse iron.
*b. The star uses up the supply of hydrogen in its core.
c. The helium flash ignites the core.
d. The core loses all of its neutrinos and fusion ceases.
e. Hydrogen burning and helium burning shells ignite.

29. Black dwarfs are _____.

a. the lowest mass main sequence stars
b. the end result of the evolution of ultra-massive stars
c. objects not quite massive enough to become stars
d. the material ejected from highly evolved brown dwarfs
*e. the cooled off remnants of white dwarfs

30. Hydrogen burning in the core of a star like the Sun lasts for _____.

a. 200 million years
b. 10 thousand years
*c. 10 billion years
d. 10 trillion years
e. 10 million years

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8 Short Answer Questions @ 5 points per question

Question 1:

Why is the observational study of stellar evolution so difficult? Why are stellar clusters ideally suited for the study of stellar evolution?

Question 2:

What are the triggers for star formation? Why are triggers for star formation needed?

Question 3:

Draw an HR diagram including only the Main Sequence. Next, carefully draw the evolutionary track followed by a star that has the same mass as the Sun. Mark and label the locations on the track where (1) hydrogen burning in the core of the Sun occurs, (2) shell hydrogen burning occurs, (3) the Helium Flash occurs, (4) the planetary nebula phase occurs, and (5) the white dwarf phase.

Question 4:

State the Russell-Vogt Theorem.

Question 5:

What is the most massive element which is made in large quantities during normal stellar evolution? What will be the chemical composition of the white dwarf left by the Sun at the end of its evolution?

Question 6:

Why is nuclear fusion difficult? (What is the major impediment to fusion?) What allows nuclear fusion to occur at the low temperature found in the core of the Sun?

Question 7:

We know that star formation occurs near the spiral arms of our galaxy and that star formation is an ongoing process. How do we know that star formation occurs near the spiral arms of our galaxy and that it is an ongoing process?

Question 8:

Describe a plausible explanation for why there is a maximum mass for Main Sequence stars.

POINTS

Multiple Choice

Short Answer

Total