Astronomy quiz question: stellar evolution states in star cluster

Astronomy 210 Quiz 6, spring semester 2017
Cuesta College, San Luis Obispo, CA

At right is an H-R diagram of a star cluster. The stars in the dashed box are __________ stars that have __________ their main-sequence life.
(A) massive; not yet begun.
(B) massive; already ended.
(C) low-mass; not yet begun.
(D) low-mass; already ended.

Correct answer (highlight to unhide): (B)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. The luminous stars at the top of the H-R diagram are massive stars that evolve faster than medium-mass and low mass stars, so a star cluster containing medium-mass stars that are in their main-sequence stage (and low mass stars that have not reached the main-sequence) will have massive stars that have already left the main-sequence.

Section 30674
Exam code: quiz06n4cI
(A) : 3 students
(B) : 16 students
(C) : 0 students
(D) : 1 student

Success level: 82% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.40

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