Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
[3.0 points.] Which one of the following choices best explains why the Roche lobes of two stars in a close-pair (mass-exchanging) binary system get smaller as they begin to orbit closer to each other?
(A) Gravitational forces get weaker.
(B) Centrifugal forces get stronger.
(C) Degeneracy pressure increases.
(D) Hydrogen is transferred slowly.
(E) Repeated nova explosions disrupts hydrogen transfer.
Correct answer: (B)
Due to conservation of angular momentum, the orbital speeds of the stars will increase as their separation distance decreases (as they would during hydrogen transfer from a more massive star to a less massive star). This will increase the centrifugal forces exerted on them, decreasing the size of their Roche lobes.
Student responses
Section 5166
(A) : 5 students
(B) : 29 students
(C) : 4 students
(D) : 7 students
(E) : 2 students
Related post:
Astronomy in-class activity: mass transfer in close-pair binaries.
Showing posts with label Roche lobe. Show all posts
Showing posts with label Roche lobe. Show all posts
20080509
Astronomy quiz question: mass transfer in close-pair binaries
Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
[3.0 points.] Which one of the following statements best explains why the transfer of hydrogen in a close-pair binary system from a less massive star to a more massive star happens very slowly?
(A) There is not much hydrogen left in the less massive star.
(B) They move farther apart from each other.
(C) The less massive star has not yet ended its main sequence lifetime.
(D) The more massive star produces strong winds.
(E) (None of above choices (A)-(D), as it is not possible for hydrogen to be transferred from a less massive star to a more massive star.)
Correct answer: (B)
When a less massive star is transferring hydrogen to a more massive star, their masses become more unequal, such that their separation distance increases. This decreases their orbital speeds, decreasing centrifugal forces, resulting in enlarging their Roche lobes, making it more difficult for the less-massive star to overflow its Roche lobe. This will slow down, and eventually stop the transfer of hydrogen from the less massive to the more massive star.
Student responses
Section 4160
(A) : 11 students
(B) : 11 students
(C) : 6 students
(D) : 1 student
(E) : 5 students
Related post:
Astronomy in-class activity: mass transfer in close-pair binaries.
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
[3.0 points.] Which one of the following statements best explains why the transfer of hydrogen in a close-pair binary system from a less massive star to a more massive star happens very slowly?
(A) There is not much hydrogen left in the less massive star.
(B) They move farther apart from each other.
(C) The less massive star has not yet ended its main sequence lifetime.
(D) The more massive star produces strong winds.
(E) (None of above choices (A)-(D), as it is not possible for hydrogen to be transferred from a less massive star to a more massive star.)
Correct answer: (B)
When a less massive star is transferring hydrogen to a more massive star, their masses become more unequal, such that their separation distance increases. This decreases their orbital speeds, decreasing centrifugal forces, resulting in enlarging their Roche lobes, making it more difficult for the less-massive star to overflow its Roche lobe. This will slow down, and eventually stop the transfer of hydrogen from the less massive to the more massive star.
Student responses
Section 4160
(A) : 11 students
(B) : 11 students
(C) : 6 students
(D) : 1 student
(E) : 5 students
Related post:
Astronomy in-class activity: mass transfer in close-pair binaries.
20080506
Astronomy clicker question: close-pair binary star system observations
Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
Students were asked the following clicker question (Classroom Performance System, einstruction.com) near the end of their learning cycle (specifically, following the astronomy in-class activity: mass transfer in close-pair binaries).
[0.3 points.] If you were to survey every visible close pair (mass-exchanging) binary star system, which one of the choices (A)-(D) would best describe your observations?
(B) You would see (I) just as often as (II).
(C) You would see (II) more often than (I).
(D) You would only be able to see (I), as it is impossible for (II) to occur.
Correct answer: (C)
Student responses
Section 4160
(A) : 7 students
(B) : 13 students
(C) : 10 students
(D) : 0 students
Section 5166
(A) : 4 students
(B) : 10 students
(C) : 8 students
(D) : 10 students
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
Students were asked the following clicker question (Classroom Performance System, einstruction.com) near the end of their learning cycle (specifically, following the astronomy in-class activity: mass transfer in close-pair binaries).
[0.3 points.] If you were to survey every visible close pair (mass-exchanging) binary star system, which one of the choices (A)-(D) would best describe your observations?
I. Mass being transferred from a more-massive star to a less-massive star.(A) You would see (I) more often than (II).
II. Mass being transferred from a less-massive star to a more-massive star.
(B) You would see (I) just as often as (II).
(C) You would see (II) more often than (I).
(D) You would only be able to see (I), as it is impossible for (II) to occur.
Correct answer: (C)
Student responses
Section 4160
(A) : 7 students
(B) : 13 students
(C) : 10 students
(D) : 0 students
Section 5166
(A) : 4 students
(B) : 10 students
(C) : 8 students
(D) : 10 students
20080505
Astronomy in-class activity: mass transfer in close-pair binaries
Astronomy 10 In-class activity 23 v.07.04.30, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to summarize the three stages of initial mass transfer in a close-pair (mass transferring) binary star system.
Star B is more massive than Star A, due to its being closer to the center of mass, and also because of its larger Roche lobes. As a result, Star B will end its main sequence lifetime earlier than Star A, and become a giant or supergiant.
As a result of Star B expanding and filling its Roche lobe up to the "neck" or "pinch point," hydrogen will then be transferred to Star A. This makes their masses become more equal, making their separation distance decrease, while increasing their orbital speeds. As a result, centrifugal forces increase, such that the size of Star B's lobe shrinks (while it is expanding in its giant/supergiant phase), making the "spillage" from Star B to Star A rapid.
Eventually the masses of Star B and Star A equalize; this is when their separation distance is the smallest, and their lobes are equal in size, but the physical size of Star B (still) fills its (smaller) Roche lobe.
As Star B still transfers hydrogen to Star A, this makes their masses become unequal, making their separation distance increase, while decreasing their orbital speeds. As a result, centrifugal forces decrease, such that the size of Star B's lobe expands. This makes it harder for Star B to "spill over" hydrogen out of its Roche lobe, and the transfer of material slows, and eventually stops when Star B is unable to exceed its much larger Roche lobe.
(Transfer from Star A, when it eventually ends its main sequence lifetime, to Star B will eventually occur, but this discussion is outside the scope of this course.)
Thus with all observations of close-pair binary star systems where mass transfer is taking place, it is more likely to see a less-massive star feeding a more-massive star than vice versa.
Follow-up post:
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to summarize the three stages of initial mass transfer in a close-pair (mass transferring) binary star system.
Star B is more massive than Star A, due to its being closer to the center of mass, and also because of its larger Roche lobes. As a result, Star B will end its main sequence lifetime earlier than Star A, and become a giant or supergiant.As a result of Star B expanding and filling its Roche lobe up to the "neck" or "pinch point," hydrogen will then be transferred to Star A. This makes their masses become more equal, making their separation distance decrease, while increasing their orbital speeds. As a result, centrifugal forces increase, such that the size of Star B's lobe shrinks (while it is expanding in its giant/supergiant phase), making the "spillage" from Star B to Star A rapid.
Eventually the masses of Star B and Star A equalize; this is when their separation distance is the smallest, and their lobes are equal in size, but the physical size of Star B (still) fills its (smaller) Roche lobe. As Star B still transfers hydrogen to Star A, this makes their masses become unequal, making their separation distance increase, while decreasing their orbital speeds. As a result, centrifugal forces decrease, such that the size of Star B's lobe expands. This makes it harder for Star B to "spill over" hydrogen out of its Roche lobe, and the transfer of material slows, and eventually stops when Star B is unable to exceed its much larger Roche lobe.
(Transfer from Star A, when it eventually ends its main sequence lifetime, to Star B will eventually occur, but this discussion is outside the scope of this course.)
Thus with all observations of close-pair binary star systems where mass transfer is taking place, it is more likely to see a less-massive star feeding a more-massive star than vice versa.
Follow-up post:
20071227
Astronomy final exam question: close-pair mass transfer
Astronomy 10 Final Exam, Fall Semester 2007
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.3
[15 points.] The stars in a binary star system are a 4 M_Sun main sequence star and a 1 M_Sun giant, where no mass transfer is taking place right now. Discuss which star had originally first transferred mass to the other star, and explain your reasoning.
Solution and grading rubric:
Section 1073
p: 10 students
r: 13 students
t: 4 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students
A sample of a "p" response (from student 1000) is shown below:
Another "p" response (from student 1256):
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.3
[15 points.] The stars in a binary star system are a 4 M_Sun main sequence star and a 1 M_Sun giant, where no mass transfer is taking place right now. Discuss which star had originally first transferred mass to the other star, and explain your reasoning.
Solution and grading rubric:
- p = 15/15:
Correct. Massive stars have shorter main sequence lifetimes than more massive stars. Star "B," the 1 M_Sun giant, had to have been the larger star in order to have reached the giant phase first. Since it is now less massive than star "A," the 4 M_Sun main sequence star, star "B" must have transferred mass to star "A." - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 1073
p: 10 students
r: 13 students
t: 4 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students
A sample of a "p" response (from student 1000) is shown below:
Another "p" response (from student 1256):
20070724
Interactive binary star system
Binary Stars Interactive (*.swf)
McGraw-Hill Online Learning Center
Astronomy 10 learning goal Q10.2
Begin with setting M_A = 0.5 solar masses, M_B = 5.0 solar masses, and separation distance = 20 solar radii. Point out that the more massive star B is closer to the center of mass/rotation axis, while the less massive star A is farther away. Ask the students which star will eventually reach the end of its main sequence lifetime first, and why (star B, as it is more massive), and which star will have the larger Roche lobe (star B, as it is both more massive and slower in orbital speed, resulting in less centrifugal force, which counteracts gravity).
If the separation distance is decreased to 7.0 solar radii, the Roche lobes of both stars shrink, as they will both have faster orbital speeds (and thus stronger centrifugal forces, which decreases the volume of space that matter will accelerate in towards either star). The more massive star B still has a larger Roche lobe than star A.
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%::100%::/sites/dl/free/007299181x/78778/Binary_Nav.swf::Binary%20Stars%20Interactive
20070723
Astronomy quiz question: close-binary mass transfer
Astronomy 10 Quiz 10, Summer Session 2007
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
[3.0 points.] Shown at right are the equipotentials of a close pair (mass-exchanging) binary system. Which one of the following choices best describes the transfer of hydrogen in the figure at right?
(A) A giant taking hydrogen from a more massive neutron star.
(B) A giant feeding hydrogen to a more massive neutron star.
(C) A giant taking hydrogen from a less massive neutron star.
(D) A giant feeding hydrogen to a less massive neutron star.
(E) (None of the above choices (A)-(D), as no hydrogen is being transferred.)
Correct answer: (B)
The star on the left has less mass than the star on the right, as the center of mass of the binary star system is closer to the star on the right. The star on the left is in its giant phase, as it has expanded in size to its Roche lobe, and thus is transferring hydrogen to the more massive neutron star on the right.
Student responses
Section 8027
(A) : 3 students
(B) : 6 students
(C) : 3 students
(D) : 1 student
(E) : 0 students
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.2
[3.0 points.] Shown at right are the equipotentials of a close pair (mass-exchanging) binary system. Which one of the following choices best describes the transfer of hydrogen in the figure at right? (A) A giant taking hydrogen from a more massive neutron star.
(B) A giant feeding hydrogen to a more massive neutron star.
(C) A giant taking hydrogen from a less massive neutron star.
(D) A giant feeding hydrogen to a less massive neutron star.
(E) (None of the above choices (A)-(D), as no hydrogen is being transferred.)
Correct answer: (B)
The star on the left has less mass than the star on the right, as the center of mass of the binary star system is closer to the star on the right. The star on the left is in its giant phase, as it has expanded in size to its Roche lobe, and thus is transferring hydrogen to the more massive neutron star on the right.
Student responses
Section 8027
(A) : 3 students
(B) : 6 students
(C) : 3 students
(D) : 1 student
(E) : 0 students
20070601
Astronomy final exam question: novae
Astronomy 10 Final Exam, Spring Semester 2007
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.3
[15 points.] Describe and explain what causes repeated nova explosions.
Solution and grading rubric:
Section 4136
p: 18 students
r: 0 students
t: 3 students
v: 3 students
x: 9 students
y: 0 students
z: 1 student
A portion of a "p" response (from T. B.):
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q10.3
[15 points.] Describe and explain what causes repeated nova explosions.
Solution and grading rubric:
- p = 15/15: Correct.
A giant or supergiant overflows its Roche lobe, depositing hydrogen onto a white dwarf companion, which by itself cannot have fusion. When enough hydrogen gathers onto the surface of the white dwarf, then it will become dense enough and hot enough to undergo fusion. The process then repeats itself, as long as there is hydrogen still being taken from the giant/supergiant. - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least recognizes that hydrogen is transferred between two stars in a close-pair ("mass-exchanging") system. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 4136
p: 18 students
r: 0 students
t: 3 students
v: 3 students
x: 9 students
y: 0 students
z: 1 student
A portion of a "p" response (from T. B.):
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