Astronomy quiz question: O5 main-sequence star vs. M5 giant

Astronomy 210 Quiz 4, spring semester 2013
Cuesta College, San Luis Obispo, CA

An O5 main-sequence star will be __________ compared to a M5 giant.
(A) smaller and dimmer.
(B) smaller and brighter.
(C) larger and dimmer.
(D) larger and brighter.

Correct answer: (B)

Using an H-R diagram (provided on this quiz, to be filled in by the students with the given information as below), the O5 white dwarf is smaller (10 R_Sun vs. 110 R_Sun), brighter (1,000,000 L_Sun vs. 1,000 L_Sun), and hotter (50,000 K vs. 2,500 K), than the M5 giant.

Section 30674
Exam code: quiz04Ni7E
(A) : 1 student
(B) : 16 students
(C) : 3 students
(D) : 7 students
(No response: 1 student)

Success level: 60% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50

Section 30676
Exam code: quiz04sGf6
(A) : 6 students
(B) : 24 students
(C) : 2 students
(D) : 10 students

Success level: 60% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73