Sternentwicklung Stellar evolution

1
SternentwicklungStellar evolution

• Vorlesung Spätstadien der Sternentwicklung, WS
  07/08
• Lebzelter Hron

2
Early concepts
Lord Kelvin source of solar energy is
gravitational contraction. Age of the sun is 100
million years Charles Darwin age of the earth
is several billion years. Ernest Rutherford
Radium possible long time energy source
O. Gingerich, 1999, ApSS 267, 3
3
Early concepts
Star form out of meteoritic particles, become
first red giants, contract (hot stars), and then
cool down (red dwarfs). Lockyer (1890), Russell
(1925)
4
Milestones

• Understanding of the stellar structure
  (Eddington)
• Understanding of the stars composition (Payne,
  Unsöld)
• Understanding of the energy source(Atkinson,
  Bethe, von Weizsäcker)

5
What is a star?
6
Energy Production
7
Nuclear Timescale
10 of the sun involved
E m c2
0.7 of the mass of a hydrogen core will be
converted into energy
tnuclear 1010 years
8
core hydrogen burning
9
Effect of hydrogen burning

• 4 H transformed into 1 He
• mean molecular weight increases
• according to the ideal gas law density and T have
  to increase
• core contracts ? energy production increases and
  opacity decreases ? L, R, T increase

10
Iben 1967
11
(No Transcript)
12
Core after H burning

• no H ? no energy production
• energy production in shell, core becomes
  isothermic
• H burning shell ? core increases in mass
• maximum core mass 10 stellar mass ? core
  collapse
• low mass starscore degenerates first

13
(No Transcript)
14
Core and Envelope

• Lbottom Lout ? star is in TE
• Lbottom increases ? Lout has to increase
• R increases ? more surface ? more L can be
  emitted ? again TE
• R increases ? T decreases ? at some point opacity
  increases ? NO TE ? star becomes red giant
  (Hertzsprung-gap!)
• Runaway stops at Hayashi-track

15
Hayashi line TE
runaway phase
convection
Energy trapped no TE
TE
TE
16
Iben 1967
17
First Dredge Up

• Convective zone reaches layers with processed
  material
• Abundance changes on the surface12C
  decreases Li decreases14N increases 3He
  increasesO constant
• 12C/13C drops from 90 (solar) to 20

18
Evolution on the RGB

• Luminosity provided almost exclusively by thin H
  burning shell (0.001 0.0001 Msolar)
• burning rate of H shell determined by size and
  mass of core
• ? He core mass luminosity relation

19
Helium core flash

• core T increases until He ignition temperature
  (108 K) approx. 0.5 Msolar
• core material degenerated ? gas pressure not
  sensitive to T ? no cooling by extension ?
  thermonuclear runaway
• Duration approx. 1 Mio years
• Most of the E does not reach the surface
• not for stars above 2.25 Msolar

20
Helium Burning
21
Helium Burning

• 4He 4He ? 8Be8Be 4He ? 12C
• Energy production ? T40
• Energy release per nucleus one order of magnitude
  less than for H burning
• 12C ? ? 16O ?16O ? ? 20Ne ?

22
He exhausted ? 2nd ascent on the giant branch
(Asymptotic Giant Branch, AGB)
23
(No Transcript)
24
Our Sun
12.4 Billion years
Ejection of outer shell
Aus Sackmann et al. 1993

1. 4500 4000 3200

25
CMD of Stellar Clusters
26
Isochrones
Bertelli et al. 2000
27
Isochrones
28
Literature

• Salaris Cassisi Evolution of Stars and Stellar
  Populations
• Kippenhahn Weigert Stellar Structure and
  Evolution
• Renzini et al. 1992, ApJ 400, 280

29
Miras Innenleben
30
(No Transcript)
31
helium burning
32
Aus James Kaler, Sterne
33
Beiträge zum ISM
Sedlmayr 1994
34
Thermische Pulse
PDCZ...Pulse driven convection zone
35
Thermische Pulse
continuous line...surface luminosity dashed
line...H-burning luminosity dotted
line...He-burning luminosity Wood Zarro 1981
36
Vassiliadis Wood 1993
37
Wood Zarro 1981
38
shell hydrogen burning