Astronomy quiz question: O5 main-sequence star versus K2 main-sequence star

Astronomy 210 Quiz 4, fall semester 2012
Cuesta College, San Luis Obispo, CA

An O5 main-sequence star will be __________ compared to a K2 main-sequence star.
(A) cooler and dimmer.
(B) cooler and brighter.
(C) hotter and dimmer.
(D) hotter and brighter.

Correct answer: (D)

On the OBAFGKM spectral type sequence, O-type stars are hotter than K-type stars, while on an H-R diagram, the O-type main sequence stars are brighter than the K-type main sequence stars.

Section 70158
Exam code: quiz04Spr6
(A) : 4 students
(B) : 0 students
(C) : 9 students
(D) : 22 students

Success level: 65% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.89

Section 70160
Exam code: quiz04nNm5
(A) : 2 student
(B) : 1 student
(C) : 4 students
(D) : 19 students

Success level: 75% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.14