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Founded January 1970
Julian Date: 2459009.16
2019-2020: CLXII
THE DAILY ASTRONOMER
Monday, June 8, 2020
Remote Planetarium 49: Week 10 Quiz
Happy Monday!
We realize that beginning your week with a quiz is borderline cruel, but recent events compelled us to alter our schedule. On the bright side, we'll be offering another quiz this Friday. Today's 20-question examination covers last week's topics about the H-R Diagram and stellar evolution.
Good luck!
1. The absolute magnitude of the star Aldebaran is -0.64. What can we conclude about Aldebaran?
a. it is intrinsically brighter than the Sun
b. it is closer than Sirius
c. it is hotter than the Sun
d. none of the above
2. The star Antares' absolute magnitude is -5.28 and its spectral type is M1.5 . Where would it appear on the H-R Diagram?
a. lower left
b. upper left
c. lower right
d. upper right
3. Omicron Scorpii's luminosity class is II, meaning that it is a _____________.
a. hypergiant
b. subgiant
c. bright giant
d. dwarfs
4. Which of the following is an absolute magnitude value one would expect for a white dwarf?
a. -9.0
b. -2.4
c. 4.85
d. 11.1
5. If a star has a luminosity class V, which of the following statements can you make about it? (Could be more or less than one.)
a. it is a dwarf star
b. it belongs on the main sequence
c. it is hotter than the Sun
d. it is cooler than the Sun.
6. If star A's radius is 3 times that of star B, how much larger is A than B in terms of volume?
a. 3 times
b. 9 times
c. 27 times
d 81 times
7. If a star's radius is one-tenth that of the Sun, where on the H-R Diagram would it be found?
a. at the upper right
b. at the lower right
c. at the lower left
d. at the upper left
e. either b or c
8. According to the mass-luminosity relation, the more massive stars will also be _________________.
a. less luminous
b. more luminous
c. neither a nor b
d. smaller
9. If a star is between 2 and 55 times more massive than the Sun, its luminosity relative to the Sun's will be proportional to its mass relative to the Sun's by the power of _____.
a. 2
b. 3.5
c. 4
d. 8.3
10. Star A is on the main sequence. So, too, is Star B. Star A is four times more massive than Star B. Which of the following statements about these two stars is/are true?
a. Star A is more luminous than Star B
b. Star A will remain on the main sequence longer than Star B
c. Star A will remain on the main sequence for less time than Star B
d. none of the above.
11. At the end of its life, the Sun will become a _____________.
a. pulsar
b. neutron star
c. black hole
d. white dwarf
12. According to current estimates, Earth will become too hot to sustain life in approximately ________________ years.
a. 1.1 billion
b. 3 billion
c. 5 billion
d. 8 billion
13. After it exhausts its core hydrogen reserves, the Sun's core will consist mainly of helium. Eventually, the helium will start fusing to produce_____________.
a. carbon
b. iron
c. manganese
d. silicon
14. After the Sun exhausts its core helium reserves, it will fuse carbon to produce _________.
a. oxygen
b. silicon
c. iron
d. none of the above
15. Once the Sun leaves the main sequence on the H-R Diagram, it will start moving_____________.
a. toward the upper right
b. toward the lower left
c. directly downward
d. none of the above
16. A 10 solar mass star will remain on the main sequence for approximately _____________years.
a. 10 million
b. 32 million
c. 140 million
d. 2.1 billion
17. The Sun is a Population _____ star, meaning that it is metal-____.
a. I; rich
b. I; poor
c. III; poor
d. II; rich
18. Only stars at least ______times as massive as the Sun can possibly become black holes.
a. 10
b. 15
c. 20
d. 25
19. When a star's core consists of _______, it is doomed as the star cannot fuse that element into anything heavier.
a. silicon
b. oxygen
c. gold
d. iron
20. Which of the following statements about Population III stars is/are true?
a. they are devoid of metals
b. they have been observed only in the Andromeda Galaxy
c. they are only within the spiral arms of our galaxy
d. none of the above.
ANSWERS
1. The absolute magnitude of the star Aldebaran is -0.64. What can we conclude about Aldebaran?
a. it is intrinsically brighter than the Sun
The Sun's absolute magnitude is 4.83. The absolute magnitude (M) is equal to the star's apparent magnitude if it were at a distance of 10 parsecs. Aldebaran is 439 times more luminous than the Sun. The absolute magnitude alone will not give us information about the star's distance or temperature.
2. The star Antares' absolute magnitude is -5.28 and its spectral type is M1.5 . Where would it appear on the H-R Diagram?
d. upper right
As seen below, the star Antares appears at the upper right of the H-R Diagram. Antares' spectral type is M1.5, meaning that it is "cool" and therefore at the right of the H-R Diagram. With an absolute magnitude of -5.28, the star is also very luminous and so at the upper region of the H-R Diagram.
3. Omicron Scorpii's luminosity class is II, meaning that it is a _____________.
c. bright giant
Still highly luminous, but not considered supergiants due to their spectra. Luminosity thousands of times greater than the Sun's.
4. Which of the following is an absolute magnitude value one would expect for a white dwarf?
d. 11.1
White dwarfs are stellar remnants created when stars up to eight times more massive than the Sun reach the end of their life cycles. Although they are quite hot, these stars are so small they are quite dim.
5. If a star has a luminosity class V, which of the following statements can you make about it? (Could be more or less than one.)
a. it is a dwarf star
b. it belongs on the main sequence
All V stars are dwarf stars.
All dwarf stars belong on the main sequence.
All dwarf stars belong on the main sequence.
Some dwarf stars will be hotter than the Sun.
Some dwarf stars will cooler than the Sun
Some dwarf stars will cooler than the Sun
Some dwarf stars will be the same temperature as the Sun because the Sun, itself, is a dwarf star.
6. If star A's radius is 3 times that of star B, how much larger is A than B in terms of volume?
c. 27 times
A sphere's volume is proportional to the cube of its radius. If star A's radius is three times greater than star B, its volume will be 3 x 3 x 3 = 27 times greater than star B.
7. If a star's radius is one-tenth that of the Sun, where on the H-R Diagram would it be found?
e. either b or c
Stars that are much smaller than the Sun could be along the lower left or lower right. One would find white dwarfs at the left and red dwarfs at the right.
8. According to the mass-luminosity relation, the more massive stars will also be _________________.
b. more luminous
The mass luminosity relation tells us that the more massive the star, the more luminous it will be.
9. If a star is between 2 and 55 times more massive than the Sun, its luminosity relative to the Sun's will be proportional to its mass relative to the Sun's by the power of _____.
b. 3.5
We can see below that the mass luminosity relation varies with stellar mass. The luminosity of stars between 2 - 55 solar masses will be proportional to their masses raised to the power of 3.5
10. Star A is on the main sequence. So, too, is Star B. Star A is four times more massive than Star B. Which of the following statements about these two stars is/are true?
a. Star A is more luminous than Star B
c. Star A will remain on the main sequence for less time than Star B
The mass-luminosity relation tells us that the more massive star will be more luminous. Also, the more massive stars have shorter life spans.
11. At the end of its life, the Sun will become a _____________.
d. white dwarf
The Sun, like all stars with masses less than or equal to nine solar masses, will become a white dwarf. A white dwarf is a highly dense, ultra hot stellar remnant. It will slowly cool over billions of years to become a black dwarf.
12. According to current estimates, Earth will become too hot to sustain life in approximately ________________ years.
a. 1.1 billion
The Sun's luminosity increases by about one percent every 100 million years. In approximately 1.1 billion years, Earth will become too hot to sustain life due to the Sun's increased luminosity.
13. After it exhausts its core hydrogen reserves, the Sun's core will consist mainly of helium. Eventually, the helium will start fusing to produce_____________.
a. carbon
For approximately 100 million years, helium will fuse in the Sun's core to produce carbon. The core will be surrounded by a "hydrogen burning shell" in which hydrogen will fuse to produce helium.
14. After the Sun exhausts its core helium reserves, it will fuse carbon to produce _________.
d. none of the above
The Sun is not massive enough to produce the pressures and temperatures necessary to fuse carbon into any heavier element. The helium fusion is the final stage for the Sun and all solar mass stars.
15. Once the Sun leaves the main sequence on the H-R Diagram, it will start moving_____________.
a. toward the upper right
When the Sun leaves the main sequence, it will become cooler, larger and more luminous. So, it will shift toward the right and upwards.
16. A 10 solar mass star will remain on the main sequence for approximately _____________years.
b. 32 million
The more massive the star, the shorter the lifespan. A 10 solar mass star's main sequence lifetime is 0.32% that of the Sun's.
17. The Sun is a Population _____ star, meaning that it is metal-____.
a. I; rich
The Sun consists of many "metals," elements heavier than helium, because much of its material was once part of another star.
18. Only stars at least ______times as massive as the Sun can possibly become black holes.
d. 25
Stars between 25 - 40 times more massive than the Sun can either become neutron stars or black holes by fallback. The star's metallicity determines its fate: stars with higher metallicities in this range will become neutron stars; the others black holes.
19. When a star's core consists of _______, it is doomed as the star cannot fuse that element into anything heavier.
d. iron
Iron fusion is an endothermic process: the amount of energy it imparts into the star is less than the energy the star requires to produce those reactions. Once a star develops an iron core, it will soon perish to become a neutron star or a black hole.
20. Which of the following statements about Population III stars is/are true?
a. they are devoid of metals
Population III stars were the first population of stars and so formed from material devoid of metals, those elements heavier than iron. No Population III star has yet to have been observed and so this population is hypothetical.
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