Chapter 13: Measuring the Properties of Stars (30 points) Name: ________________

Chapter 13: Measuring the Properties of Stars (30 points) Name: ____________________________
Multiple Choice (16 points):
1. What is parallax?
A. The distance to an object, measured in parsecs
B. The difference between the apparent and absolute magnitude
C. The apparent shift in angular position of an object as the object moves through space
D. The apparent shift in position of an object caused by a change in the observer’s position
2. In the HR diagram on the horizontal (i.e., x-axis) the temperature increases _____.
A. Toward left B. Toward right C. In both directions D. Arbitrarily
3. Luminosity (absolute brightness) of a star depends on its ___________.
A. Temperature B. Distance from us C. Radius
D. Both A and C E. Both A and B
4. A star has a parallax angle of 0.05 arcseconds. It is therefore at a distance of
A. 20 light years B. 20 parsecs C. 4 parsecs D. 4 light years
5. The star Aldebaran is a red giant, and is much more luminous than the Sun. What conclusions can be
drawn from this fact?
A. Aldebaran is cooler and much more massive than the Sun
B. Aldebaran is hotter and has a larger diameter than the Sun
C. In the HR diagram, Aldebaran is above and to the left of the Sun
D. Aldebaran is a binary star
E. None of the above
6. How can we explain the fact that hydrogen Balmer lines are essentially absent in the hot O type and the
cool M stars?
A. O type stars do not contain hydrogen
B. In O stars hydrogen is ionized and in M stars the electrons of hydrogen are in level 1, not level 2
C. In cool stars hydrogen combines to form large molecules
D. All of the above
E. Only A and B above account for the absence of hydrogen lines
7. A visual binary star system has rotation period P = 10 years. The semi-major axis of the orbit of one of
the stars is 10 AU. What is the combined mass of the binary star system?
A. 1,000 solar masses B. 100 solar masses C. 10 solar masses D. 10,000 solar masses
8. Which of the following is not true for a pulsating star?
A. They are members of an eclipsing binary star system
B. The outer layers of a pulsating star expand and contract periodically
C. The luminosity changes periodically
D. The surface temperature of a pulsating star changes periodically
E. They show periodic shifts in their spectral lines
9. _____ can be used to measure the _____ of nearby stars.
A. Parallax measurements; radius
B. Interferometry; radius
C. The method of standard candles; brightness
D. All of the above methods can be used
10. A star’s luminosity varies in an irregular pattern therefore ________.
A. the star is very young B. the star is very old
C. the star is rotating D. the star is either very old or very young
11. A light source at a distance of 1 meter that emits 100 Watts of visible radiation has the same ____ as a
source emitting 400 Watts when it is located ____.
A. Luminosity; 4 meters away
B. Luminosity; 2 meters away
C. Apparent brightness; 4 meters away
D. Apparent brightness; 2 meters away
12. Analysis of stellar spectra shows that most stars consist of 71% ___, 27% ___ and a 2% mix of the other
elements.
A. Hydrogen; oxygen B. Helium; hydrogen
C. Oxygen; nitrogen D. Hydrogen; helium
13. Lines from molecules are strongest in the cool ___ type stars.
A. A B. F C. M D. K E. O
14. The hydrogen absorption lines are the strongest in ___ type stars.
A. A B. B C. O D. G E. F
15. A main sequence star has 2 times the mass of the Sun. Using ____ we find that the star is ___ times
more luminous than the Sun.
A. The mass-luminosity relation; 8 (approximately 11.3 if corrected)
B. The Stefan-Boltzmann law; 2 (exact)
C. The mass-luminosity relation; 2 (exact)
D. Wien’s law; 16 (exact)
E. The inverse-square law; 4
16. White dwarfs have ____ spectral lines than red giants.
A. Wider B. Stronger C. Weaker D. Narrower
True / False (7 points):
17. The coolest (O and B type) stars are usually binary stars, while the hottest (M type) stars are usually
single stars.
18. Astronomers cannot determine the radius and distance of the star based on luminosity.
19. One light year is equal to 3.26 parsecs.
20. A star moving away from the Earth will show spectral lines that are shifted to longer wavelengths.
21. The mass-luminosity relation applies to all stars that have been observed to date.
22. The luminosity class of a star can be determined from the width of the spectral lines of the star.
23. The H-R diagram shows that stars begin their life as red giants, contract and heat-up with age and
progress from right to left along the main sequence.
Short Answer Questions (partial answers will only be rewarded with particle credit):
Choose 7 of the 9 questions below → 7 points
24. How is the parsec defined? How big is a parsec compared with a light-year?
25. How do astronomers triangulate a star’s distance?
26. How do astronomers measure a star’s temperature?
27. What distinguishes the spectral classes of stars?
28. Why are binary stars useful to astronomers?
29. What is the H-R diagram? Make sure to identify the axes.
30. What is the main sequence on the HR diagram?
31. What is the mass-luminosity relation?
32. What is meant by the period of a variable star?