star 989). ⊙ M Internal structure of a 3 which has reached the early Asymptotic Giant Branch. Maeder & Meynet, 1989 star to the early Asymptotic Giant Branch (Maeder & Meynet, 1 ⊙ M Evolution of the structure of a 3 26 27 3–21 3–22 stars): ⊙ M before ve that: CNO α K (1.5 ars. 6 but are energetically l moves deeper into 10 × γ γ γ + + + ) O Ne Mg 17 16 20 24 ) T 5 → → → T ∝ ǫ . ∝ ( He He He 4 4 4 ǫ ( + + + : Simulations show existence of two regimes: C ) reach threshold temperature for 3 O Ne ⊙ 12 16 20 since energy generation from CNO cycle strongly M 5 pp-chain CNO-cycle . : for central temperatures of 18 1 : stars have structure similar to Sun: H shell burning Stellar Evolution: Massive Stars Stellar Evolution: Massive Stars & alpha reactions radiative hull radiative core convective core inner peaked towards center. energy generation: outer convective hull energy generation: ALEX inner ALEX O AN O AN C D C D I R I R R R He just starts to burn.
E I E I
N D A N D A I I
E E
R R
− pp-chain and CNO-cycle produce equal amountsdominates. of energy. Abo − − − − − F F
S S
I I
G G E E
I I A A
I I L L
L
L ⇒
M M
V V
E E
M M
D D A A C C A A Outer layers continue core, can mix fusion products into outer layers. During evolution of star on red giant branch: convective hul Structure on the Main Sequence lower main sequence Evolution of the Sun Evolution of the Sun upper main sequence Evolution on MS similar, however, faster than for low mass st More massive stars ( In these objects, higher order fusion processes can kick in ( unimportant): reaching degeneracy = Kippenhahn et al. (1965): Evolution of the internal structure of a 5 M⊙ star. Evolution of the structure of a 7 M⊙ star to the carbon burning phase (Maeder & Meynet, 1989).
Internal structure of a 7 M⊙ star
Kippenhahn et al. (1965) which just starts its carbon burning Evolution of a 5 M⊙ star in the HRD. phase.
Maeder & Meynet, 1989 36 3–30 age 12...13 billion years ∼ GCs are oldest objects in the universe! ⇒ determination Predicted evolution of HRD from globular clusters can reproduce their HRDs, allows Result: = Stellar Evolution: Massive Stars
ALEX O AN IC D R R
E I D A N I
E
R
F
S
I
G E
I A
I L
L
M
V
E
M
D A C A (M68; Straniero et al., 1997; Fig. 11) Evolution of the Sun 34 35 !), ⊙ yr; 3–29 3–30 6 N/A M 25 ⊙ 01 N/A last much . M 0 age 5 ⇒ (units of 10 . = Coulomb barrier ⊙ ∞ ∞ 01 . M 0 1 . C 12 0.6 He 10000 94 6.4 PN WD → C+C 0.01 → He H shorter than hydrogen burning. Evolution of stars in the HRD from main sequence to death Typical timescales less energy release Schaller et al. 1992): Post-H-burning burning: need higher core temperatures ( determination Predicted evolution of HRD from globular clusters can reproduce their HRDs, allows
absolute Magnitude −7.5 −5.0 −2.5 +2.5 +5.0 +7.5 0.0 −10.0 AGB RGB PN Core Helium Flash Ejection 5000 H He Supernova II AGB 1 Msun He C+O C+C Stellar Evolution: Massive Stars Stellar Evolution: Massive Stars 10000 log T 4.0 3.8 3.6 3.4 Horizontal Branch Temperature [K] H He He C+O stars only Low metallicity 20000 To White Dwarf (0.85 Msun) To White Dwarf (0.6 Msun) 0.00 Gyr 0.02 Gyr 0.10 Gyr 0.32 Gyr 1.00 Gyr He C+O 5 Msun Cooling C−O 10.00 Gyr 19.95 Gyr
H He White Dwarf (0.6 Msun) PN lights up 30000 25 Msun Age = ALEXA ALEXA O N 4.6 4.4 4.2 O N IC D IC D R R R R I I
E 5 4 3 2 1 0 E
N D A N D A I I −1 0 5
E E
R R
F F
S S
−5
I I
G G E E
bol
I I A
A 10 10 10 10 10 10
I I L (Lsun) Luminosity L
10 M
L L
M M
V V
E E
M M
D D A A C C A A after Iben, 1991 Evolution of the Sun after Bertelli et al. (1994) Evolution of the Sun