Astronomy clicker question: spiral arm with supergiants and red dwarfs

Astronomy 210, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle:

It is possible for red dwarfs and supergiants to be found within the same spiral arm if:
(A) they began their main sequence lives in different spiral arms.
(B) the supergiants have already exploded as type II supernovae, but this light has not yet reached the Earth.
(C) they contain different concentrations of metals (elements heavier than hydrogen and helium).
(D) they are both remnants of medium mass main sequence stars.
(E) (I'm lost, and don't know how to answer this.)

Section 70158
(A) : 25 students
(B) : 7 students
(C) : 6 students
(D) : 13 students
(E) : 1 student

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Section 70158
(A) : 38 students
(B) : 5 students
(C) : 3 students
(D) : 8 students
(E) : 0 students

Correct answer: (A)

Massive stars live for a brief amount of time, evolving rapidly from protostars to main sequence stars to supergiants to type II supernovae. At the other extreme, low mass stars live for an inordinately long time, evolving from protostars to the main sequence, where they all still exist to this day as red dwarfs. So in order for a supergiant to be located in the same spiral arm as a red dwarf, they must have been born in separate locations--the massive star is born, lives, and dies within the same spiral arm, while the red dwarf is on its nth round trip, passing through the spiral arm. Responses (B) and (C) are not an important factors, while response (D) is obviously false.

Pre- to post- peer-interaction gains:
pre-interaction correct = 48%
post-interaction correct = 70%
Hake (normalized) gain <g> = 43%

Section 70160 (pre-)
(A) : 14 students
(B) : 7 students
(C) : 3 students
(D) : 4 students
(E) : 0 students

Section 70160 (post-)
(A) : 20 students
(B) : 8 students
(C) : 0 students
(D) : 0 students
(E) : 0 students

Pre- to post- peer-interaction gains:
pre-interaction correct = 50%
post-interaction correct = 71%
Hake (normalized) gain <g> = 43%