Astronomy quiz question: F0 white dwarf vs. K5 main-sequence star

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

An F0 white dwarf will be __________ compared to a K5 main-sequence star.
(A) cooler and dimmer.
(B) cooler and brighter.
(C) hotter and dimmer.
(D) hotter and brighter.

Correct answer: (C)

Using a blank H-R diagram provided on this quiz (to be filled in by the students with the given information as below), the F0 white dwarf is hotter (7,000 K vs. 4,000 K), smaller (0.02 R_Sun vs. 0.6 R_Sun), and dimmer (0.0005 L_Sun vs. 0.1 L_Sun) than the K5 main-sequence star.

Section 30674
Exam code: quiz04Ni7E
(A) : 5 students
(B) : 1 student
(C) : 17 students
(D) : 5 students

Success level: 64% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.63

Section 30676
Exam code: quiz04sGf6
(A) : 9 students
(B) : 1 student
(C) : 19 students
(D) : 13 students

Success level: 50% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.45