The "turnoff" point for a star cluster is the point in the H-R diagram occupied by the:
A)highest-mass main-sequence stars in the cluster.
B)stars undergoing (or about to undergo) the helium flash.
C)lowest-mass main-sequence stars in the cluster.
D)highest-mass stars that have not yet reached the main sequence.

Question

Quizplus · Accepted Answer

The "turnoff" point in a star cluster's H-R diagram is where the highest-mass main-sequence stars have exhausted their hydrogen fuel and are leaving the main sequence. This point helps determine the cluster's age.

The "Turnoff" Point for a Star Cluster Is the Point