Astronomy final exam question: type II supernovae in star cluster with white dwarfs?

Astronomy 210 Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

Pdg: Can there be type II supernovae explosions seen in a star cluster that also has white dwarfs at the same time? Would it have to be a really old or young star cluster?
spota: Yes, if the star cluster is old enough to contain white dwarf stars it will still be young enough to have hydrogen-burning massive stars that can undergo type II supernova explosions.

Discuss why this answer is incorrect, and how you know this. Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

[*] answers.yahoo.com/question/index?qid=20171117015031AAqCPQo.

Solution and grading rubric:

• p:
  Correct. Understands that star cluster cannot have type II supernovae explosions at the same time as having white dwarfs:
  1. medium-mass stars become white dwarfs well after the end of their main-sequence lifetimes (approximately 10 billion years); and
  2. massive stars will explode as type II supernovae after the end of their main-sequence lifetimes (less than a million years); such that
  3. a star cluster with white dwarfs, will not have any supergiants remaining that can explode as type II supernovae; or a star cluster with supergiants exploding as type II supernovae will have medium-mass stars that have not yet reached the end of their main-sequence lifetimes.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors.
• 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. May discuss type Ia supernovae or lookback time.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30674
Exam code: finaln3sT
p: 6 students
r: 3 students
t: 5 students
v: 4 students
x: 1 student
y: 0 students
z: 1 student

Section 30676
Exam code: finalSuB1
p: 13 students
r: 6 students
t: 6 students
v: 6 students
x: 3 student
y: 1 student
z: 1 student

A sample "p" response (from student 1777):
A sample "p" response (from student 1217), discussing the house party model of determining star cluster ages:
A sample "y" response (from student 7237):