Cuesta College, San Luis Obispo, CA
Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
(The following question was asked prior to, and then following the lecture on stellar populations and Milky Way history.)
Which type of stars is more abundant in metals (elements heavier than hydrogen and helium) in their outermost layers? (Graded for completion.)
(A) Extremely old stars that formed a long time ago.
(B) Young stars that formed very recently.
(C) (Both types of stars have equal amounts of metals.)
(D) (Neither type of stars, as outer layers of stars cannot have metals.)
(E) (I'm lost, and don't know how to answer this.)
Student responses (pre-instruction)
Section 70158
(A) : 16 students
(B) : 7 students
(C) : 1 student
(D) : 7 students
(E) : 2 students
Student responses (post-instruction)
Section 70158
(A) : 3 students
(B) : 25 students
(C) : 1 student
(D) : 1 student
(E) : 1 student
Correct answer: (B)
Stars fuse hydrogen into heavier elements in their cores. When short-lived massive stars die in type II supernova explosions, these heavy elements are incorporated into the next generation of stars that form from interstellar matter, and thus newer stars will have more metals in their outer layers.
Pre- to post- instruction gains:
pre-interaction correct = 21%
post-interaction correct = 81%
Hake, or normalized gain
(Students were then prompted to fill in a text box online to justify their answer for the post-instruction online reading assignment.)
Briefly explain your answer for the above question (which stars are more metal-abundant). (Graded for completion.)
The following are all of the student responses to this question, verbatim and unedited.
"Young stars are population I stars are relatively metal rich."
"old=poor in metals. new=rich in metals."
"young stars have less helium"
"because young stars are picking up metal made from old stars"
"ninja tag!!!"
"because they use more energy"
"young stars are abundant in metals because they are using fusion and old stars do not."
"Population 1 stars are younger because they are in the disc, and population 1 stars are more metal rich because of recycled pollution of metal in the air. So the newer the star, the more metal."
"old stars blow up and shed their metals to the younger generations"
"New stars are more abundant because they have absorbed the metals expelled by older stars."
"Stars begin with a lot of metals and release them into space as they grow older."
"old stars may have already used up their hydrogen"
"Old stars have begun to fuse atoms into larger elements because they have already fused all of their hydrogen together to make helium"
"Young starts are made from the excess junk left by dead starts."
"there's no metals in old stars..."
"We talked about it in class."
"Both have metals on the inner core because they first use up the elements with the least work needed to be done."
"I just think it's the bigger stars because they leave metal behind to form younger stars."
"the small stars are buliding too become bigger stars in that prosess the sallow up all the metals that the bigger stars lose over time."
"thats what my notes say"
"Older stars formed at a time when the galaxy was poor in metals. Since that time, the galaxy has become more rich in these metals, so the newer stars forming in the galaxy are likewise more rich in metals."
"the book"
"sorry i don't know why.."
"Young stars are more abundant in metal because the elements of hydrogen and helium become more heavier and become the proportion of the young star
because the old stars already used all the hydrogen and imploded or exploded giving all the metals to the newly forming stars."
"Older stars have shuffed off their metals."
"cuz they start with all this metal and so thats how it is"
"Because they haven't expended any yet"
"They form from all the dust and other stuff in the universe."
"..."
"The younger stars because they are collecting more rapidly..."
"older=more"
1 comment:
Astronomy 210, Fall Semester 2009
Cuesta College, San Luis Obispo, CA
Student responses (pre-instruction only)
Section 70160
(A) : 7 students
(B) : 14 students
(C) : 2 students
(D) : 1 student
(E) : 3 students
Correct answer: (B)
(Students were then prompted to fill in a text box online to justify their answer for the pre-instruction online reading assignment.)
Briefly explain your answer for the above question (which stars are more metal-abundant). (Graded for completion.)
The following are all of the student responses to this question, verbatim and unedited.
"Young stars are population I stars are relatively metal rich."
"DONT KNOW"
"Older stars have lower metallicities than young stars like the Sun."
"They havnt burned yet"
"Old small stars that formed long ago have gone through many stage and because they are small their convection currents travel all the way to the core thus they have more friction and heavier metals are created."
"Not sure which, but I would guess the young stars."
"disk population stars (young stars) formed within the last few billion years contain the more abundant metals."
"just a guess"
"Younger stars haven't had an opportunity to burn off or use up as many of its elements as a old star would have."
"the young are formed from the remnants of the old stars, and the old stars use up all their hydrogen and helium towards the end of their life."
"The older stars have had more time to fuse all these different elements."
"jldsjfisdjf dsjflksjd fijldcldsjfsd"
"because i said so"
"I think the older starts have gone through a process ultimately leading to higher levesl iron"
"When stars form they have a lot of metal!"
"cuz they are newer and the metal crap hasn't fallen off yet"
"newer stars are more abundent in metals because they are formed out of older interstellar gas clouds, which are enriched through the explosion of older stars."
"Stars become less abundant as they age"
"well according to the big bang theory the universe was comprised primarily of hydrogen+helium so the older stars would have larger amounts of it rather than metals (this is of course assuming that you are referring to any other elements than hydrogen/helium as metals)"
"Metals are to hard to fuse i think"
"I dont know"
"I don't really know the reason, but its something about the early universe consisting mostly of Hydrogen."
"The older stars formed earlier in the history of the galaxy when it was not as metal-abundant."
"After the first stars died, their novae enriched the interstellar gas with metals for later stars."
"extreamly old stars would more meatal abundant because the core would always be able to burn the hydrogen gas allowing it to absorb more elements"
"Yeah, i wont lie, i have no idea."
"elements past helium and hydrogen are not as old as the universe"
"I don't know"
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