Astronomy quiz question: Cepheid variable stars

Astronomy 210 Quiz 6, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

Cepheid variable stars are used to determine the distances to globular clusters in the Milky Way halo because these stars:
(A) are companion stars of neutron stars or black holes.
(B) have periods are correlated with their luminosities.
(C) contain trace amounts of dark matter.
(D) are brighter than O- and B-type main sequence stars.

Correct answer: (B)

Since Cepheids have periods are correlated with their luminosities (as they go through their instability phase in their giant stage), then their "true brightness" (absolute magnitudes) can be used with their apparent magnitudes, in order to determine their distances.

Section 70158
(A) : 5 students
(B) : 27 students
(C) : 2 students
(D) : 8 students

Success level: 68% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.70

Section 70160
(A) : 2 students
(B) : 27 students
(C) : 2 students
(D) : 9 students
(Blank: 1 student)

Success level: 68% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50