Astronomy quiz question: halo vs. disk star absorption lines

Astronomy 210 Quiz 6, spring semester 2012
Cuesta College, San Luis Obispo, CA

[Version 1]
Halo stars with fewer absorption lines than disk stars provides evidence:
(A) that the Milky Way became thinner and flatter as it evolved.
(B) that halo stars are younger than disk stars.
(C) of the Milky Way's spiral arm structure.
(D) of unequal amounts of matter and antimatter.

Correct answer: (A)

Halo stars with fewer absorption lines contain less metals and are thus older than younger stars in the disk, which have more absorption lines, which contain more metals inherited from previous generation stars.

Section 30674
Exam code: quiz06niLl
(A) : 11 students
(B) : 17 students
(C) : 4 students
(D) : 0 students

"Success level": 38% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.22

[Version 2]
Halo stars with fewer absorption lines than disk stars provides evidence:
(A) that the Milky Way became thinner and flatter as it evolved.
(B) that halo stars are younger than disk stars.
(C) of dark matter in the halo.
(D) of unequal amounts of matter and antimatter.

Correct answer: (A)

Section 30676
Exam code: quiz06suE7
(A) : 15 students
(B) : 14 students
(C) : 1 student
(D) : 5 students

"Success level": 48% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.53