Astronomy in-class activity: monolithic collapse hypothesis, stellar populations

Astronomy 210 In-class activity 22 v.16.05.04, spring semester 2016
Cuesta College, San Luis Obispo, CA

Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to discuss different metallicities and ages of stars in the monolithic collapse hypothesis of the Milky Way.

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):

Astronomy midterm question: globular cluster metallicity

Astronomy 210 Midterm 2, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

[20 points.] Discuss whether globular cluster stars in the halo of the Milky Way are expected to be metal-rich or metal-poor, and why. Explain using the properties of mass and stellar lifetimes, and the Milky Way.

Solution and grading rubric:

• p = 20/20:
  Correct. Globular cluster stars in the halo are the old first-generation stars that formed when the Milky Way was spherical in shape and are composed primarily of hydrogen with little metal content, as metal content increases over time due to stars fusing and releasing fusion products to subsequent generations.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Complete explanation of why metal-poor stars are older than metal-rich stars, but discussion of why the halo is the oldest part of the Milky Way is problematic, or vice versa.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. As (r), but discussion of why the halo is the oldest part of the Milky Way is missing, or vice versa.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Has only problematic discussion of how metal-poor stars are old stars (e.g., metals are used up by stars over time).
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Implausible evidence/methods/discussion.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70158
p: 14 students
r: 6 students
t: 9 students
v: 22 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 9221), with a fanciful depiction of increasing metallicity in subsequent generations of stars:

A more conventional sample "p" response (from student 1520):

Another sample "p" response (from student 1204), illustrating the monolithic collapse model:

A sample "v" response (from student 6636), typically discussing how stars use up metals over time to eventually become old and metal-poor: