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Comins DEU 3e Ch 08 Quiz 2 completed
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1. In the spectrum of a particular star, helium absorption lines are
stronger than hydrogen absorption lines, and there are very few spectral
lines present from any other elements. What is the approximate
temperature of this star?
• Very high, about 30,000 K or hotter, hot enough to ionize most of the hydrogen atoms so they cannot absorb
light in the Balmer series
• Quite low, about 6000 K or less, cool enough that most of the hydrogen atoms are in the ground state, so they
cannot absorb light in the Balmer series
• Moderate temperature, about 10,000 K, so that most of the hydrogen atoms that are not in the ground state are
ionized, leaving few to absorb in the Balmer series
2. In the spectrum of a particular star, helium absorption lines are
stronger than hydrogen absorption lines, and there are very few spectral
lines present from any other elements. What is the spectral class of
this star?
• O
• M
• A
3. What does the spectrum of a K-type star look like?
• Relatively strong lines due to hydrogen and helium; lines of all other elements very faint or not present
• Lots of absorption lines due to elements like iron and calcium; hydrogen lines very faint; no helium lines
• Strong hydrogen lines; faint lines due to elements like iron and calcium; no helium lines
4. Which of the following stars has a higher surface temperature than a
star of spectral class F5?
• F2
• F8
• K5
5. Which of the following sequences of stellar classification types
shows stars in order of increasing surface temperatures?
• K0, G6, G9, B2
• K0, G9, G6, B2
• B2, G6, G9, K0
6. A Hertzsprung-Russell diagram shows
•
•
•
the brightnesses of stars plotted against time.
the masses of stars plotted against their brightness or luminosity.
the brightnesses of stars plotted against their temperature or spectral class.
7. Why is the main sequence so named?
• It contains the biggest and brightest stars.
• It contains the greatest number of stars.
• It consists almost entirely of hot, bright stars.
8. A certain star is seen to have a relatively low surface temperature
but a very high luminosity. What can we conclude from these observations?
• The star is a main-sequence star, about the size of the Sun.
• The star must be very large.
• The star is a small but very bright red dwarf.
9. When their absolute magnitude and spectral class are plotted in a
Hertzsprung-Russell diagram, star X is found to be to the lower left of
star Y. From this, we know that star X is
• cooler, fainter, and smaller than star Y.
• cooler, brighter, and larger than star Y.
• hotter, fainter, and smaller than star Y.
10. A distant star of spectral type M is found to be very bright, easily
visible from the Earth. How would you describe it, and what would be its
place in the Hertzsprung-Russell diagram?
• Red supergiant: upper right-hand corner of the H-R diagram
• Red dwarf on the main sequence: lower right-hand corner of the H-R diagram
• Blue supergiant on the main sequence: upper left-hand corner of the H-R diagram
11. Blue dwarfs, white dwarfs, and red dwarfs are three categories of
stars. Which one of the three statements below about these stars is
CORRECT?
• They are all main-sequence stars and are quite similar to the Sun and to each other except for size.
• White dwarfs and red dwarfs are main-sequence stars quite similar to the Sun except for size, but blue dwarfs
are fundamentally different.
• Blue dwarfs and red dwarfs are main-sequence stars quite similar to the Sun except for size, but white dwarfs
are fundamentally different.
12. If a star is found to evolve (or change) so that it moves from the
main sequence (near the Sun's position on the main sequence) to the red
giant area of the Hertzsprung-Russell diagram, which of the following
changes will have occurred?
• The star's surface temperature will have increased.
• The star's mass will have become greater.
• The star will have expanded.
13. How do astronomers measure the luminosity class of a star?
• From the observed size of the star
• From the brightness of the star in the sky
• From the absorption lines in the star's spectrum
14. Aldebaran, a star in the constellation Taurus, has a
spectral-luminosity class of K5 III. This tells us that Aldebaran is
• a hot supergiant.
• a cool supergiant.
• a cool giant.
15. An astronomer classifies a particular star as luminosity class III.
From this information alone, we know that the star is
• much more massive than the Sun.
• much larger than the Sun.
• much cooler than the Sun.
16. What is the method of finding the distances to very distant stars
that works for the largest number of stars?
• Measuring the Doppler shift as the Earth moves alternately toward and away from the star over 1 year
• Combining the star's luminosity class, obtained from its spectrum, with its apparent magnitude, a technique
known as spectroscopic parallax
• Measuring the change in position of the star as the Earth orbits the Sun, a technique known as trigonometric
parallax
17. Most stars in the vicinity of our Sun are
• alone, like our Sun.
• members of a multi-star grouping such as a cluster.
• members of a binary system.
18. The masses of stars are most easily determined
• by their gravitational effect on companion stars.
• from their luminosities because luminosity is related directly to mass for all types of stars.
• by the effect on the spectrum from the stars, the so-called gravitational redshift.
19. Which star is more massive, a B3 V star or an F8 V?
• The F8 V star
• It is not possible to tell from the information given.
• The B3 V star
20. According to the mass-luminosity relation (Figure 8-11 of
/Discovering the Essential Universe/, 3rd Ed.), what is the luminosity
of a main-sequence star that has half the mass of the Sun?
• 1/50 Lu
•
•
1/10 Lu
1/2 Lu
21. Two stars are sufficiently far away from the Earth that they cannot
be resolved as separate stars but orbit each other with a large
separation between them compared to the stars' radii. Furthermore, their
orbital plane is inclined at 45∞ to the direction to the Earth from the
star system. What observation shows us that there are two stars orbiting
each other?
• Detection of slight positional change in the brightest region of the star system
• Periodic movement of spectral lines
• Periodic decreases in overall light intensity of the star system
22. What condition is necessary in order for a binary star system to
appear as an eclipsing binary?
• The line of sight from the Earth to the binary star must be close to the perpendicular to the star system's orbital
plane.
• The line of sight from the Earth to the binary star must be in or almost in the binary star orbital plane.
• The binary star system must be close to the ecliptic plane in the sky in order for eclipses to be seen from the
Earth.
23. An astronomer who wants to measure the sizes and masses of stars
will get the most information by studying
• bright single stars because companion stars interfere with the measurement.
• single-line spectroscopic binary stars.
• eclipsing spectroscopic binary stars.
24. The light curve of an eclipsing binary star is obtained by plotting
the variation in
• the brightness of the star system over one full orbit.
• the positions of the spectral lines over one full orbit.
• the relative positions of the two stars over one full orbit.