Exam 2
Descriptive Astronomy
UCA

2000 November 3

Multiple Choice: Each question is worth 2 points for a total of 50 points possible.

1. Granulation is seen in this layer of the Sun's atmosphere:

a. chromosphere

b. core

c. corona

d. photosphere

2. If a stellar core is not producing energy via nuclear fusion

a. it will contract and turn to water.

b. it will contract and heat up.

c. it will heat up and expand.

d. it will expand and cool.

3. The lighthouse model explains

a. the sunspot cycle.

b. gamma ray bursts.

c. pulsars.

d. the event horizon.

4. Sunspots are slightly cooler than the rest of the photosphere because of

a. the proton-proton chain.

b. strong magnetic fields.

c. helioseismology.

d. granulation.

5. In the H-R diagram, 90 percent of all stars are

a. in the giant region.

b. on the main sequence.

c. in the supergiant region.

d. among the B stars.

e. among the Z stars.

Use the following HR diagram to answer the next question.

6. Which star in the diagram above has the lowest surface temperature?

a. Alnilam

b. Antares

c. Arcturus

d. HR 5337

e. Sirius B

7. A star will experience a helium flash if

a. its core is degenerate when helium begins to fuse.

b. it is more massive than about 6 solar masses.

c. its core contains oxygen and helium.

d. its mass on the main sequence was less than 0.1 solar masses.

8. To determine the orbital speed of a spectroscopic binary, we must measure

a. temperature.

b. brightness.

c. position.

d. a Doppler shift.

e. luminosity.

9. The layer of the Sun's atmosphere that reaches a temperature of approximately 3 million degrees Kelvin:

a. chromosphere

b. core

c. corona

d. photosphere

10. The _____________ of a star is a measure of the total energy radiated by the star in one second.

a. luminosity

b. absolute visual magnitude

c. apparent visual magnitude

d. spectral type

11. The density of a neutron star is

a. about the same as that of the sun.

b. about the same as an atomic nucleus.

c. about the same as that of a white dwarf.

d. about the same as a water molecule.

12. The proton-proton chain needs high temperature because

a. the neutrinos carry more energy away than the reaction produces.

b. of the ground state energy of the hydrogen atom.

c. of the presence of helium atoms.

d. the protons must overcome the electric repulsion.

e. of the need for low density.

13. Interstellar gas clouds may collapse to form stars if they

a. have very low temperatures.

b. encounter a shock wave.

c. rotate very slowly.

d. all of the above.

e. none of the above.

14. The interstellar gas is composed mainly of:

a. iron

b. hydrogen and helium

c. carbon

d. ammonia, methane, and water

15. The differential rotation of the Sun and its magnetic field causes

a. the sunspot cycle.

b. the Earth to revolve around the Sun.

c. the Earth's magnetic field.

d. the proton-proton chain.

16. What defines a main-sequence star?

a. the apparent brightness

b. rapid rotation and strong stellar winds

c. fusion of hydrogen into helium in the core

d. the surface temperature

17. The endpoint in the evolution of the Sun will be

a. an oxygen white dwarf.

b. a carbon white dwarf.

c. a supernova.

d. an ordinary nova.

18. An iron core cannot support a star because:

a. iron is too dense

b. iron rusts

c. iron cannot fuse with other nuclei to produce energy

d. iron supplies too much pressure

19. The evolution of binary stars can be complex

a. if they are close enough to exchange mass.

b. since they are moving around a center of mass.

c. because tidal forces cause fusion to proceed faster.

d. because they can eclipse.

20. The more distant a star is from Earth

a. the smaller the parallax.

b. the larger the parallax.

c. the brighter the star appears.

d. the more massive the star appears.

21. The search for black holes involves searching for

a. x-ray binaries where the compact companion has a mass in excess of 3 solar masses.

b. large spherical regions from which no light is detected.

c. single isolated stars that emit large amounts of x-rays.

d. pulsars with periods less than one millisecond.

22. The escape velocity at the event horizon of a black hole is

a. twice the speed of light

b. the speed of light

c. 100 m/sec

d. 1000 m/sec

23. The layer of the Sun's atmosphere best seen in filtergrams of emission lines such as Ha and Hb:

a. chromosphere

b. core

c. corona

d. photosphere

24. If a star is in hydrostatic equilibrium then

a. the force of gravity equals the internal pressure everywhere in the star.

b. the mass of the star equals the mass of the core.

c. the force of gravity is greater than the internal pressure in the star.

d. the force of gravity is less than the internal pressure in the star.

25. Observing someone near the event horizon of a black hole you would notice

a. their clock is moving slower than yours.

b. any light signals they are sending are blueshifted.

c. their clock is faster than yours.

d. they are moving twice the speed of light.

Problems and Short Answer Questions: Each question is worth 10 points for a total of 50 points possible.

1. Observing the Sun: Below are recent SOHO data. On the left is the visible light image and on the right is the magnetogram.

a. What are the features in the visible light image and why are they darker than the rest of the photosphere?

b. What is a magnetogram a map of and what does it indicate about the underlying nature of the features seen in the visible light image?

2. Photoelectric Photometry of Stars:

a. When measuring the brightnesses of stars with a photometer, why is it important to first measure the brightness of just the sky?

b. Why for most stars are their apparent magnitudes different from their absolute magnitudes?

c. A star has an apparent magnitude (m) of 12 and an absolute magnitude (M) of 2 what is the distance to this star given
where d is in parsecs (Note: calculator is not necessary).

3. Stellar Spectra:

a. Which star is to coolest, which is the hottest?

b. What would you estimate the spectral types to be?

4. Binary Stars:

a. For an eclipsing binary system why does the apparent brightness of the system periodically dim?

b. Why don't all binary star system appear to be eclipsing binary stars?

c. What effect allows binary stars to be detected spectroscopically?

5. Pulsars: What is the evidence that links neutron stars to pulsars?