Astronomy midterm question: low-mass stars in young star cluster?

Astronomy 210 Midterm 2, spring semester 2012
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...]?
Twizard113: ...[Continuing] to shine as...main sequence stars...
Decide whether or not if this answer is correct, and how you know this. Explain using the properties and evolution of stars.

*Source: http://answers.yahoo.com/question/index?qid=20081119115729AA2IQ67.

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:
Grading distribution:
Section 30676
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:

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