1. 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

2. 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

3. 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 7:30pm in Fiske planetarium: Jason Glenn on “Revealing galaxy formation in the early universe”

4. 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

5. 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.

6. Star Birth
Cauldron
NGC 604
in M33
Triangulum

7. What happens to nuclear fusion when the hydrogen in a star’s core runs low?
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

8. Life track in H-R diagram of solar-mass star blow lovely shell
Many 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

9. Overview of what will happen: MS  Red Giant I  Horiz Branch 
Red Giant II
(or Supergiant)
RG II
RG I MS

10. 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

11. MS 
subgiant 
red giant

12. MS  subgiant  red giant
Contracting core in red giant gradually becomes
“electron degenerate” -- what does that mean?

13. Oops!
Thermostat
is missing in
degenerate gas
Could get
exciting!

14. Complex
aside:
“Degeneracy”
pressure

15. Degeneracy pressure analogy Limited quantum mechanical states
(exclusion principle)
(see S4.5)

16. 3: Helium Flash He core burning -- removes electron degeneracy
with thermostat
 “horizontal
branch star”

17. 4: Horizontal branch star He core burning, H shell burning
Short phase,
lasts ~50 MY
Triple-alpha
fusion:
3 He  C

18. Helium flash 
He fusion to C
in core
(horizontal branch)

19. H-R diagram of
globular cluster
Discussion:
What does it
tell us? Why is
it useful?

20. 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

21. Sun in its “far future” ~5+ BY Thermal pulses in red supergiant blow
off outer shells

22. 6. Planetary Nebula Outer shells of red supergiant “puffed off”
Great pictures!
“Naked”
white dwarf
emerges

23. Ring
Nebula

24. NGC 6751

25. Spirograph

26. Life after brief WHITE DWARF “planetary nebula” stage ….
Hot central core
emerges as
WHITE DWARF
Ring Nebula

27. 7. White Dwarf Inert C core, He & H shells Very dense, size of Earth
electron degeneracy
pressure holds it up
Very dense,
size of Earth
max mass of
1.4 MSUN