Astronomy 122&, Fall 2009

Homework E: Due Friday, October 16.

Part I: Multiple choice. On your scantron fill out your NAME, STUDENT NUMBER, and NETWORK ID both in writing and in the bubbles. In addition, fill out "FORM E."

1. A 2nd magnitude star is how many times brighter than a 12th magnitude star?
a) 10 b) 100 c) 1000 d) 10,000 e) 100,000

2. The absolute magnitude of a star is what the apparent magnitude would be at how many parsecs?
a) 1 b) 10 c) 100 d) 1000 e) 10,000

3. The primary distances to the stars are found by
a) sending spacecraft to them
b) radar
c) how fast they move
d) their colors
e) parallax

4. The parallax of a star is 0.02 seconds of arc. What is its distance?
a) 0.5 pc b) 5 pc c) 50 pc d) 20 pc e) 200 pc

5. What characterizes the spectrum of an A star?
a) titanium oxide
b) strong hydrogen
c) ionized calcium
d) ionized helium
e) molybdenum

6. What characterizes the spectrum of an M star?
a) titanium oxide
b) strong hydrogen
c) ionized calcium
d) argon
e) molybdenum

7. The Sun has what absolute magnitude and is of what spectral class?
a) +10, K5
b) +15, A3
c) +5, G2
d) +3, M2
e) +12, B5

8. A class F dwarf star (ignoring the core) is typically made mostly of
a) fluorine
b) calcium
c) iron
d) helium
e) hydrogen

9. The standard spectral sequence is a result of
a) different stellar temperatures
b) differences in the amounts of hydrogen
c) differences in the amounts of helium
d) differences in the amounts of metal atoms
e) differences in the radii, hence densities, of the stars

10. The most luminous and hottest dwarf stars below are of class
a) O b) B c) G d) K e) M

11. The most common stars are
a) O dwarfs
b) M giants
c) K giants
d) white dwarfs
e) M, L, and T dwarfs

12. White dwarfs are typically about the size of
a) Champaign-Urbana
b) Chicago
c) Earth
d) the Sun
e) the inner planetary system

13. We know that supergiants are really larger than giants because supergiants
a) move slower than giants through space as they are more affected by gravity
b) are brighter than giants that have the same temperatures
c) are hotter than giants that have the same luminosities
d) have destroyed their planetary systems whereas giants have not
e) rotate slower than giants

14. Stellar masses are found from
a) variable stars
b) double stars
c) star clusters
d) planets in orbit around other stars
e) their neutrino emission

15. As you go down the main sequence from class A, stellar masses
a) stay the same
b) decrease
c) increase
d) increase then decrease
e) decrease then increase

16. What is the minimum mass for a star that will run full hydrogen fusion (in solar units)?
a) .001 b) 0.01 c) 0.08 d) 0.22 e) 0.53

17. The masses of white dwarfs are similar to that of
a) Champaign-Urbana
b) Chicago
c) Earth
d) the Sun
e) Jupiter

18. The coolest and brightest M supergiants are about at big as the orbit of
a) Venus
b) Earth
c) Mars
d) Jupiter, even approaching that of Saturn
e) Pluto

19. Brown dwarfs are
a) stars below the proton-proton chain mass cutoff
b) planetary satellites
c) supermassive stars
d) large interstellar dust grains
e) earth-like planets

20. The spectra of class T stars are characterized by
a) methane
b) ammonia
c) hydrogen
d) titanium oxide
e) nothing

Part II. Show all your work.

1. Make a table for the Alpha stars of the constellations listed below. Give their full spectral classes (including luminosity classes), what prominent spectrum lines you would expect to find, and their effective temperatures. (See Tables 13.3 and Figures 13.11 and 13.12)
a) Lyra
b) Cygnus
c) Orion
d) Bootes

2. What is the luminosity (in solar units) of a star with a temperature of 60,000 K and a radius 5 times that of the Sun? (In this question and in question 4, round the solar temperature off to the nearest thousand degrees.)

3. What is the radius (in solar units) of a star with a temperature of 3000 K and a luminosity 1/10,000 that of the Sun?

4. Draw your own H-R diagram with all the appropriate parts labelled. On the diagram place ten stars from each of Tables 13.1 and 13.3 using different symbols for the different tables. Comment briefly on the difference between the two.