ASTR%201040%20Accel%20Astro:%20Stars%20

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ASTR 1040 Accel Astro Stars Galaxies
Etched Hourglass Nebula

• Prof. Juri Toomre TAs Ben Brown, Adam Jensen
• Lecture 14 Thur 2 Mar 06
• zeus.colorado.edu/astr1040-toomre

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Today

• Consider red giant (RG I) phase, with H shell
  burning
• Helium flash goes off in shrinking degenerate
  core horizontal branch star with He core
  burning
• Double shell burning (H and He) yields red
  supergiant (RG II), blows off planetary nebula
• Read 18.2 about white dwarfs formed at end of
  evolution of low-mass stars
• Respond to discussion question posted on shapes
  of planetary nebulae
• Monday recitation meets in Duane G116 (computer
  lab) in support of Planet Finder Homework 6
  go there directly

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More news

• Observatory session write-ups are due soon
  would like all by next Thur 9 March
• Very nice public lecture (free to you) tonight at
  730pm in Fiske planetarium Jason Glenn on
  Revealing galaxy formation in the early universe

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Clicker Poll of Advice

• How do you take notes (or listen) during
  lectures?
• A. I get most of it by just listening
• B. I write down some notes, then go back to book
  to look things up
• C. I listen, take some notes, then get copies of
  lecture slides from course website
• D. I enjoy talking with my buddies, and they
  tell me later if I missed anything

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Clicker starbirth what has stuck?

• The vast majority of stars in a newly formed star
  cluster are ________ ?
• A. less massive than the Sun
• B. very high-mass, type O and B stars
• C. red giants
• D. about the same mass as Sun

A.
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Star Birth Cauldron
NGC 604 in M33 Triangulum
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What happens to nuclear fusion when the hydrogen
in a stars core runs low?
E.

• A. It stops
• B. It shifts from the core to a shell around the
  core
• C. Other elements start to fuse
• D. The star goes out of balance and becomes a
  red giant
• E. B and D

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Life track in H-R diagram of solar-mass star Ma
ny meanders, but MS phase longest, red
giant phase(s) shorter, finally white dwarf left
to cool slowly
blow lovely shell
RG II
?
Red Giant I
protostar
white dwarf
ZAMS
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Overview of what will happen
MS ? Red Giant I ? Horiz Branch ? Red Giant
II (or Supergiant)
RG II
RG I
MS
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2 Subgiant to Red Giant (first visit) H
burning in shell, makes much more energy
Vast expansion, RG phase lasts 500 MY Huge
convective envelope
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MS ? subgiant ? red giant
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MS ? subgiant ? red giant
red giant
MS
Contracting core in red giant gradually becomes
electron degenerate -- what does that mean?
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Oops! Thermostat is missing in degenerate gas
Could get exciting!
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Complex aside Degeneracy pressure
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Degeneracy pressure analogy
Limited quantum mechanical states (exclusion
principle) (see S4.5)
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3 Helium Flash He core burning --
removes electron degeneracy
? He core burning with thermostat ?
horizontal branch star
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4 Horizontal branch star He core burning,
H shell burning
Short phase, lasts 50 MY Triple-alpha fusion
3 He ? C
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Helium flash ? He fusion to C in core
(horizontal branch)
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H-R diagram of globular cluster
Discussion What does it tell us? Why is it
useful?
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5. Red Supergiant
Double-shell burning of H and He
Phase could be very short if He burning is
erratic (unstable) -- then lasts only a few MY,
and blows off outer shells
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Sun in its far future 5 BY
Thermal pulses in red supergiant blow off outer
shells
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6. Planetary Nebula
Outer shells of red supergiant puffed
off Great pictures!
Naked white dwarf emerges
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Ring Nebula
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NGC 6751
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Spirograph
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Life after brief planetary nebula stage
. Hot central core emerges as WHITE DWARF
Ring Nebula
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7. White Dwarf
Inert C core, He H shells electron
degeneracy pressure holds it up
Very dense, size of Earth max mass of 1.4 MSUN