Astronomy quiz question: metallicity

Astronomy 10 Quiz 11, Summer Session 2007
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q11.5

[3.0 points.] All elements heavier than hydrogen and helium are considered to be "metals." Which one of the following statements best explains why metal-poor stars are older than metal-rich stars?
(A) Metal-poor stars gradually become metal-rich stars at the end of their main sequence lifetime.
(B) Metal-poor stars have longer main sequence lifetimes.
(C) Metal-poor stars have fewer lines in their absorption spectra.
(D) Explosion debris from metal-poor stars is then incorporated into metal-rich stars.
(E) When metal-poor stars collide, they produce metal-rich stars.

Correct answer: (D)

"Metals" that are produced in the cores of stars are not detectable in their absorption spectra from their exospheres. However, these heavy elements are released during type II supernova explosions, which can then be incorporated into a subsequent generation of stars, which will then have "metals" in their absorption spectra. Thus each generation of stars gets more and more "polluted" by heavy elements in their exospheres.

Student responses
Section 8027
(A) : 2 students
(B) : 2 students
(C) : 3 students
(D) : 1 student
(E) : 2 students

(Compare to previous post: Astronomy clicker question: metal-rich stars.)

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