Today in Astronomy 241: late stellar evolution

1
Today in Astronomy 241 late stellar evolution

• Todays reading Carroll and Ostlie Sec, 13.2, on
• Ascent of the red giant branch fully convective
  stars
• The horizontal branch helium-burning main
  sequence
• The asymptotic giant branch
• Death of low-mass stars

M10, by T. Credner and S. Kohle (Bonn U.)
2
Late stages of stellar evolution

• After the main sequence and the subgiant phase
• Red giant phase
• Core collapse and heating
• Convection zone extends inward (dredge-up)
  eventually star becomes fully convective
• Extreme expansion of envelope of star
• Core temperature reaches 108 K, and triple-a
  begins burning helium efficiently (helium flash
  in stars with Mgt2Msun)
• Horizontal branch
• Core helium burning, shell hydrogen burning

3
Late stages of stellar evolution (continued)

• Asymptotic giant branch
• Further dredge-ups
• Shell helium hydrogen burning, carbon-oxygen core
• Occasional helium shell flashes, from ignition of
  helium passed downwards by the hydrogen-burning
  shell
• Mechanical instabilities, thermal pulses,
  pulsations, and mass loss
• Further evolution of stars with M lt 8Msun
• Low-mass end ejection of stellar envelope,
  leaving degenerate helium or carbon-oxygen core
  planetary nebula and white dwarf remnant
• High-mass end Type I supernova?

4
Post-main-sequence stellar evolution
Post-main-sequence development of a 5 Msun star
(Iben 1967)
Giant branches star mostly convective and
expanding. (Reverse of the Hayashi track.)
5
Post-main-sequence stellar evolution (continued)
Kippenhahn, Thomas and Weigert 1965
Points on last plot 1 2 3 6,7
10 11 13,14
6
An evolved population (globular cluster)
Like all Galactic globular clusters, M3 is about
12000 Myr old. It lies about 10400 pc away.
Image J. Challis (Harvard-Smithsonian CfA).
B-V
7
M3 color-magnitude diagram
AGB
HB
RG
Blue stragglers
SG
MS
MS turnoff
RR Lyrae (pulsating HB stars are highlighted)
Data from J. Hartmann (CfA)