Astronomy quiz question: metal-rich vs. metal-poor stars

Astronomy 210 Quiz 7, spring semester 2014
Cuesta College, San Luis Obispo, CA

Older stars are metal-poor, while newer stars are metal-rich because:
(A) older stars have longer lifetimes.
(B) older stars break down their metals.
(C) newer stars contain less dark matter.
(D) newer stars contain metals produced by older stars.

Correct answer (highlight to unhide): (D)

Stars produce metals (elements heavier than hydrogen and helium) in their cores during their giant/supergiant phases, up through type Ia/II supernovae explosions. Along with their unused hydrogen, these metals are then scattered into the interstellar medium, which are then incorporated into later generations of stars. An old, early generation star will have metals only in its core, while a young, later generation star will have metals sprinkled in its outer layers as well as in the core.

Section 30674
Exam code: quiz07nU7e
(A) : 0 students
(B) : 3 students
(C) : 0 students
(D) : 23 students

Success level: 89% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43

Section 30676
Exam code: quiz07s1Rp
(A) : 1 student
(B) : 9 students
(C) : 1 student
(D) : 23 students

Success level: 70% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.70