Astronomy 210 Quiz 6, spring semester 2018
Cuesta College, San Luis Obispo, CA
A star cluster with medium-mass main sequence stars would also have __________ at the same time.
(A) red dwarfs.
(B) supergiants.
(C) white dwarfs.
(D) giants.
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. Medium-mass stars start out as protostars, then reach their main sequence stage, and subsequently become giants, planetary nebulae, and then white dwarfs. So a star cluster with medium-mass main sequence stars cannot have giants nor white dwarfs at the same time, as these are stages that follow the main sequence lifetime of a medium-mass star.
A red dwarf is a low-mass star that has evolved from its protostar stage to its main sequence stage; this takes much longer for a medium-mass star to evolve from its protostar stage to its main sequence lifetime. So a star cluster with medium-mass main sequence stars cannot have red dwarfs at the same time.
A supergiant is a massive star that has evolved from its protostar stage to its main sequence stage, and subsequently used up all of its core hydrogen exit its main sequence stage. Since massive stars evolve much more rapidly than medium-mass stars, then it is plausible that a star cluster with medium-mass main sequence stars can have supergiants at the same time.
Section 30674
Exam code: quiz06nG4s
(A) : 8 students
(B) : 5 students
(C) : 4 students
(D) : 6 students
Success level: 28% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43
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