Astronomy final exam question: metallicity of modern-day type II supernovae?

Astronomy 210 Final Exam, fall semester 2013
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
Pdf: Are all of the stars that go type II supernova today metal-rich? Or metal-poor?
Richard: Nearby type II supernovae will in general be of relatively high metallicity.
Discuss why this answer is correct, and how you know this. Explain using the properties and evolution of stars.

[*] answers.yahoo.com/question/index?qid=20131124104506AAsacIr.

Solution and grading rubric:
  • p:
    Correct. Understands that:
    1. older stars are metal-poor having formed from essentially just hydrogen, while newer stars are metal-rich, having formed from hydrogen enriched with metals produced by previous generation stars;
    2. type II supernovae are the end-stage of massive stars, which have evolved rapidly (having short main-sequence lifetimes), such that they had formed very recently, are thus are metal-rich.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of the two points (1)-(2) correct, other is problematic/incomplete.
  • t: Contains right ideas, but discussion is unclear/incomplete or contains major errors. Both points (1)-(2) problematic/incomplete, or one point correct while other is missing. Typically discusses how type II supernovae today are metal-rich relative to the composition when they first formed because of metal production within the star during its supergiant and type II supernovae phases (as opposed to being metal-rich relative to type II supernovae in the past).
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars, such as breaking down of metals; masses and evolution rates.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on metallicity and evolution rates of stars.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
Grading distribution:
Section 70158
Exam code: finals0oB
p: 17 students
r: 9 students
t: 4 students
v: 5 students
x: 3 students
y: 1 student
z: 0 students

Section 70160
Exam code: finaln4A6
p: 5 students
r: 9 students
t: 7 students
v: 1 student
x: 1 student
y: 1 student
z: 1 student

A sample "p" response (from student 0507):

A sample "p" response (from student 2441):

A sample "t" response (from student 1456):

A sample "v" response (from student 2979):

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