Cuesta College, San Luis Obispo, CA
[Version 1]
The H-R diagrams of three possible or impossible star clusters are shown below.
How many of these star cluster H-R diagram(s) is/are possible? (Do not circle the H-R diagrams; clearly circle a response below.)(A) Only one.
(B) Two.
(C) Three.
(D) (None of the star clusters.)
Section 30676
(A) : 7 students
(B) : 6 students
(C) : 5 students
(D) : 0 students
Correct answer: (B) (Star clusters X and Y)
Massive stars will evolve the quickest, reaching the upper part of the main sequence line first, staying there the shortest amount of time, and then leaving first, compared to the low-mass stars, which evolve the slowest, reaching the lower part of the main sequence line last, and then staying there...and remain there, as the universe has not been around long enough for low-mass stars to have exhausted their main-sequence lifetimes. Thus star cluster Z is impossible, as it still has massive stars remaining on the main-sequence at the same time that the low-mass stars are on the main sequence.
[Version 2]
The H-R diagrams of three possible or impossible star clusters are shown below.
How many of these star cluster H-R diagram(s) is/are possible? (Do not circle the H-R diagrams; clearly circle a response below.)(A) Only one.
(B) Two.
(C) Three.
(D) (None of the star clusters.)
Section 30676
(A) : 11 students
(B) : 17 students
(C) : 1 student
(D) : 0 students
Correct answer: (C) (All star clusters are possible)
"Difficulty level": 42% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33
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