Astronomy midterm question: monolithic collapse model

Astronomy 210 Midterm 2, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] Discuss the evidence for the monolithic collapse model of the Milky Way (spherical gas cloud flattening into a disk). Support your answer using the orbit and metal content properties of halo stars versus disk stars.

Solution and grading rubric:

• p = 20/20:
  Correct. Discusses evidence supporting the flattening of the Milky Way's shape by explaining how metal content increases for younger generations of stars, and observations that disk stars are metal-rich compared to the metal-poor halo stars above and below the disk.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least some discussion related to the monolothic collapse model.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the monolithic collapse model.
  y = 2/20: Irrelevant discussion/effectively blank.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70160
p: 17 students
r: 8 students
t: 4 students
v: 6 students
x: 3 students
y: 3 students
z: 0 students

A sample "p" response (from student 1991):