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 final exam question: relative metallicities of red dwarfs

Astronomy 210 Final Exam, fall semester 2014
Cuesta College, San Luis Obispo, CA

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

Pd: What differences are there between a star born a long time ago, from a star born a short time ago? Both stars have the same mass.
qcl: A red dwarf born long ago will consist of fewer metals than a red dwarf born a short time ago.

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=20141206170547AAKawke.

Solution and grading rubric:

• p:
  Correct. Understands that:
  1. metals are formed only by medium-mass and massive stars during their giant and supergiant phases, and these would be released out to universe during a type Ia or type II supernova explosion;
  2. a star that formed a long time ago in the early universe would start out metal-poor, while a star that formed more recently would be metal-rich, having formed from hydrogen enriched with metals produced by previous generation stars;
  3. and red dwarfs are extremely long-lived main-sequence stars that fuse hydrogen into helium, so they cannot make metals regardless of its age, which means that any metal content must come from the material that it formed from.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Two of the three points (1)-(3) correct, the third is problematic/incomplete.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Only one of the three points (1)-(3) correct, other two are problematic/incomplete.
• 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.
• 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:
  Blank.

Grading distribution:
Section 70158
Exam code: finalst0P
p: 0 students
r: 17 students
t: 12 students
v: 4 students
x: 1 student
y: 0 students
z: 0 students

Section 70160
Exam code: finaln3rF
p: 1 student
r: 9 student
t: 12 students
v: 5 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 3314):
A sample "r" response (from student 9999):
A sample "v" response (from student 0620):
Another sample "v" response (from student 0902):
Another sample "v" response (from student 1717):
Another sample "v" response (from student 3980):

Astronomy final exam question: giant versus supergiant metallicity

Astronomy 210 Final Exam, spring semester 2014
Cuesta College, San Luis Obispo, CA

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

Pd: Right now, which would be more metal-rich in its outermost layers today: a giant or a supergiant?
th: The correct answer is a giant.

Discuss why this answer is incorrect, and how you know this. Explain using the properties and evolution of stars.

[*] answers.yahoo.com/question/index?qid=20140405002159AARyDpo.

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; and (2) supergiants are the end-stage of massive stars, which have evolved rapidly (having short main-sequence lifetimes), such that they had formed very recently than giants (end-stage of medium-mass stars, which have longer main-sequence lifetimes), and are thus 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.
• 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. Discusses factors other than relevant to Hubble's law, redshifts/recession velocities, expansion of space, big bang, etc. Discussion not based on metallicity and evolution rates of stars.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30674
Exam code: finaln0oN
p: 5 students
r: 1 student
t: 9 students
v: 8 students
x: 1 student
y: 0 students
z: 0 students

Section 30676
Exam code: finals0N6
p: 5 students
r: 2 students
t: 16 students
v: 7 students
x: 1 student
y: 1 student
z: 2 students

A sample "p" response (from student 0923):
Another sample "p" response (from student 6288), using the "house party" analogy of stellar evolution rates:
A sample "t" response (from student 1920), only explaining how giants are younger than supergiants:
Another sample "t" response (from student 6124), only explaining how younger stars inherit the metals from previous-generation stars that have gone supernovae:

Astronomy quiz question: halo vs. disk star absorption lines

Astronomy 210 Quiz 6, spring semester 2012
Cuesta College, San Luis Obispo, CA

[Version 1]
Halo stars with fewer absorption lines than disk stars provides evidence:
(A) that the Milky Way became thinner and flatter as it evolved.
(B) that halo stars are younger than disk stars.
(C) of the Milky Way's spiral arm structure.
(D) of unequal amounts of matter and antimatter.

Correct answer: (A)

Halo stars with fewer absorption lines contain less metals and are thus older than younger stars in the disk, which have more absorption lines, which contain more metals inherited from previous generation stars.

Section 30674
Exam code: quiz06niLl
(A) : 11 students
(B) : 17 students
(C) : 4 students
(D) : 0 students

"Success level": 38% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.22

[Version 2]
Halo stars with fewer absorption lines than disk stars provides evidence:
(A) that the Milky Way became thinner and flatter as it evolved.
(B) that halo stars are younger than disk stars.
(C) of dark matter in the halo.
(D) of unequal amounts of matter and antimatter.

Correct answer: (A)

Section 30676
Exam code: quiz06suE7
(A) : 15 students
(B) : 14 students
(C) : 1 student
(D) : 5 students

"Success level": 48% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.53

Astronomy midterm question: red dwarf vs. massive main-sequence star metallicity

Astronomy 210 Midterm 2, fall semester 2011
Cuesta College, San Luis Obispo, CA

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

Pdg: Which star today would have more metals: a red dwarf or a massive main-sequence star?
qp: I'm guessing a massive main-sequence star; because a red dwarf is likely very old...

Discuss whether or not if this answer is correct, and how you know this. Explain using the properties and evolution of stars.

[*] answers.yahoo.com/question/index?qid=20110601124741AA76NMC.

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. red dwarfs take a long time to become main sequence stars, such that they had to have started forming a long time ago, are thus are metal-poor, while massive stars take a short time to form, such that they formed recently, and 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) is correct, other is problematic.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Only one of the two points (1)-(2) correct, other is missing, or both are problematic.
• 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.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02s3Ar
p: 9 students
r: 3 students
t: 14 students
v: 8 students
x: 0 students
y: 0 students
z: 0 students

Section 70160
Exam code: midterm02n1cT
p: 9 students
r: 3 students
t: 9 students
v: 6 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 2541):
Another sample "p" response (from student 1863), using a "House Party" analogy:
Yet another sample "p" response (from student 1985), lavishly illustrated:
A sample "v" response (from student 0628), where older stars would have had more time to absorb metals than recent stars:
Another sample "v" response (from student 1226), where older stars have more time to break down metals:
Yet another sample "v" response (from student 1559), where older stars have more time to fuse metals by breaking them down:

Astronomy midterm question: older versus younger stars

Astronomy 210 Midterm 2, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board (http://answers.yahoo.com/question/index?qid=20100510145903AAHVFRG) was asked and answered:

J*rocks: How are older stars different than younger stars?
Smileyface: Older stars have higher percentages of heavier elements than younger stars...

Discuss whether or not if this answer is correct, and how you know this. Explain using the properties and evolution of stars.

Solution and grading rubric:

• p = 20/20:
  Correct. Understands that (a) older stars are metal-poor having formed from essentially just hydrogen but produce metals in their cores; and (b) that newer stars were produced from material from older stars that were released when older stars exploded, making the newer stars metal-rich.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of the two points (a)-(b) is correct, other is problematic.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Only one of the two points (a)-(b) correct, other is missing, or both are problematic.
  
• v = 8/20:
  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 = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. May state answer is incorrect, but without proof; or discussion other than that of the properties and evolution of stars.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 30676
Exam code: midterm02Sys7
p: 20 students
r: 4 students
t: 3 students
v: 18 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 3517):

Another sample "p" response (from student 0701):

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: metal-poor vs. metal-rich stars

Astronomy 210 Midterm 2, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[20 points.] Discuss what observations tell you that a star is metal-poor, and whether this is an old or young star, using the properties and evolution of stars in your explanation.

Solution and grading rubric:

• p = 20/20:
  Correct. Discusses (a) how observations of absorption spectra classify stars as metal-poor, and (b) how production of metals in cores of massive and medium-mass stars is dispersed via type II/type Ia supernovae to be incorporated into the outer layers of subsequent generation stars.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One topic is complete/correct, other other is problematic.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Only one of two discussion topics is complete and correct, the other is missing or has serious errors (typically spectroscopy); or both topics have minor errors.
  
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discusses metal-poor stars as being old, but with conceptual errors; no discussion on spectroscopy.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. May discuss how metals are used to fuel a star; less metals would then indicate an older star that has used up all its metals.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70158
p: 5 students
r: 6 students
t: 23 students
v: 14 students
x: 22 students
y: 1 student
z: 0 students

A sample "p" response (from student 0711):
A sample "t" response (from student 1990):
Another sample "t" response (from student 3259):
A sample "x" response (from student 7027):