Cuesta College, San Luis Obispo, CA
[20 points.] An astronomy question on an online discussion board(*) was asked and answered:
Eli: In a...young star cluster, if the...massive stars are swelling up into [supergiants], the low mass stars [are...]?Decide whether or not if this answer is correct, and how you know this. Explain using the properties and evolution of stars.
Twizard113: ...[Continuing] to shine as...main sequence stars...
Solution and grading rubric:
- p = 20/20:
Correct. Understands that massive stars evolve faster than low-mass stars, such that by the time massive stars have already gone through their protostar to main sequence to supergiant phases, medium-mass stars are now on the main sequence, but low mass stars are still protostars, and have not yet become red dwarfs on the main sequence.
- r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. As (p), but claims low mass stars would be on main sequence.
- t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands correlation between mass and main sequence lifetime.
- v = 8/20:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
- x = 4/20:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
- y = 2/20:
Irrelevant discussion/effectively blank.
- z = 0/20:
Exam code: midterm02sA4r
p: 13 students
r: 6 students
t: 13 students
v: 3 students
x: 3 students
y: 0 students
z: 0 students
A sample "p" response (from student 4392), showing the star cluster on an H-R diagram:
Another sample "p" response (from student 1014), discussing the relative evolution rates of massive vs. low-mass stars:
Yet another sample "p" response (from student 5040), discussing the "House Party" analogy of stellar evolution: