He-Burning in massive Stars

Transcription

1 He-Burning in massive Stars He-burning is ignited on the He and ashes of the preceding hydrogen burning phase! Most important reaction -triple alpha process MeV

2 Red Giant Evolution in HR diagram

3 ritical Reactions in He-burning Oxygen-6 Energy source in stellar He burning Energy release determined by associated reaction rates

4 uclear Structure spects for evaluating and interpreting capture reaction rates hydrogen burning depends on capture probability of a proton single particle configuration of final state σ ( E) ψ H ψ + ψ f t p Θ p helium burning depends on capture probability of an particle -cluster configuration of final state

5 -cluster configurations in and Mg Mg luster model predictions for luster and shape configurations For and Mg T0 nuclei

6 lpha luster Structure in T0, nuclei Excitation-Energy Pronounced clustering In T0 nuclei near threshold θ > 0. Mass-umber

7 Geometry of cluster configurations

8 Resonant Reaction Rate σv [ MeV ] µ T 3/.605E T R.50 ωγ e [ MeV ] ωγ ( J + ) Γ Γ in out Γtot ( ) ( ) Γ i i j + j + Γ p T tot at low energy astrophysical conditions: Γ in << Γ out Γ tot Γ in Γ T Θ V, V c l

9 etwork for stellar Helium burning ( ) ), ( ), ( ), ( 3 3 ), ( ), ( ), ( ), ( ), ( ), ( γ γ γ γ γ γ γ γ ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ ρ He He O He O O He He n e He e O He O He O He O He He He dt d dt d dt d dt d + +

10 time [s] bundance evolution in stellar core Decline of He (time-scale) increase in, 6 O equilibrium / 6 O Rapid decline in.

11 The case of: 3- and (,γ) 6 O Reaction rates determined by cluster state configurations providing strong resonances! θ θ 0.0 MeV MeV MeV MeV θ MeV - θ MeV 7.7 MeV MeV + θ 0.8 He 8 Be 6 O

12 The () Reaction as two step process first step! Q0.0 MeV 8 Be 0 + He+ T / ( 8 Be) s Γ 6.8 ev pure cluster configuration fast capture equilibrium between capture and decay 8 /3 R.3.7 fm Interaction time: t 0 s << τ ( v cm E 3.80 fm s µ 3/ pplication of Saha Equation 8 3 π ( Be) e For calculating h 8 Be equilibrium: µ kt Be) Q kt

13 Example for 8 Be equilibrium abundance: ase of typical He-burning: T0.GK T 0.; ρ0 5 g/cm 3 ( 8 Be) / T 60 T e ( 8 ) 38 Be.0 ρ X i i X ( 8 Be) X.30 ~ one 8 Be nucleus for 0 particles

14 Resonant capture on 8 Be The Hoyle resonance! E R 0.87MeV 7.65 MeV 0 + Q7.367 MeV 8 Be+ γ e + e - σv ωγ ( J + ).50 Γin Γ Γ tot ωγ µ T out 3/ e.605e T R.3 MeV + Decay by sequential E γ transitions or internal e + e - pair conversion 0 +

15 The Resonance Strength ( ) ev mev ev e e tot rad e e e e µ ωγ γ γ γ ± Γ Γ Γ ± Γ ± Γ + Γ + Γ Γ + Γ Γ Γ % ± MeV ωγ

16 The 8 Be+ reaction rate reaction rate.e-0.e-08.e- 8 Be (, γ ) 6.( T ) 3/ 3.33 T e.e temperature [GK]

17 The total <> rate r X ρ 8 Be(, γ ) 8 Be Step Step 8 ( Be) T 3/ e.068 T 8 Be (, γ ) 6.( T ) 3/ e 3.33 T r.60 + δ 56 3 T 3 e ( ) T r ρ X 3 T 3 e. T 3 [ cm s ]

18 Energy production in He burning s g erg e T X erg MeV Q r Q T ρ ε ρ ε

19 Example: ρ0 5 g/cm 3 energy production [erg/gs].00e+0.00e+0.00e-0.00e-08.00e-.00e-0 ε ε temperature [GK] 8 L ρ erg g s X 3 ( 0.T ) 0 T-dependent main energy source for stellar He-burning

20 Uncertainty in low energy extrapolation ( (,γ) 6 O, the Holy Grail Level and Interference Structure

21 reaction contributions in (,γ) 6 O Difficulty in the reliability of low energy extrapolation E component - resonances & subthreshold states S-factor E component + resonances & E direct capture

22 R-matrix analysis omplex resonance structure, interfering broad resonances R-matrix analysis R-matrix school Parameters from probing 6 O compound nucleus through elastic scattering β-delayed -decay resonant capture -transfer reaction (,) 6 (β,) (,γ) 6 O ( 7 Li,t) 6 O

23 R-matrix fit examples E-term E-term S E 80 kev barn, S E 85 kev-barn From Kunz et al. PRL 86 (00)

24 (,γ) 6 O reaction rate T /3 S eff [ MeV b] e 3. / 3 T cm s 3 S eff 0.7 [ MeV b].0 8 T /3 e 3. / 3 T cm s 3 Only very crude estimate! E-T dependency needs to be considered!

25 The 6 O(,γ) 0 e reaction mechanism σ res ( E) λ ω π Γ ( E) Γ ( E) Γ tot ( E ) ER γ Only a few single resonances, no strong non-resonant term observed in the excitation curve!

26 Direct capture contributions to the cross section of 6 O(,γ) 0 e ( ) ( )( ) ( )( ) ( ) () () () dr r r u r r u J J E E M Z M Z E b E c f i f t i f dc 0 0 3/ 3 00 Ω l l l l γ µ µ σ M Z M Z o E dc-term For 6 O+ ( ) ( )( ) ( )( ) ( ) () () () dr r r u r r u J J E E M Z M Z E b E c f i f t i f dc 0 0 3/ 5 00 Ω l l l l γ µ µ σ

27 E-dc S-factor term Hahn et al. PR36 (87) Inverse kinematics experiment with TG recoil separator theory prediction exp. data o strong direct capture in E and E observed!

28 Impact of the, 6 O(,γ) rates reaction rate [ccm/s mol].0e+00.0e-05.0e-0.0e-5.0e-0.0e-5.0e-30 Gamow Range 6 O(,γ) 0 e (,γ) 6 O temperature [GK] (,γ) rate dominates over the 6 O(,γ) rate at typical He-burning temperatures T~ GK.

29 the 6 O/ ratio in steady state d 6 6 dt O O 6 O 6 He O(, γ ) (, γ ) ρ.0e+03 6 O(, γ ) + He ρ (, γ ) 0.0E+0 ( )/( 6 O).0E-0.0E-03.0E-05.0E temperature [GK]

30 onsequences of (,γ) 6 O 0-6 O Late Stellar Evolution determines arbon and/or Oxygen phase X / i i i 0 - Type Ia Supernova central carbon burning of /O white dwarf M 3 M.0 F88.3 F e+.e+.3e+.5e+ Time (s) He Type II Supernova shock-front nucleosynthesis in and He shells of pre-supernova star

31 Summary Several important experiments are being discussed Possible improvement in the accuracy of the decay channel Improved low energy data (yield and angular distribution) for (,γ) 6 O R-matrix analysis lternative approaches like 6 O(γ,) to broaden data set and statistics for R-matrix analysis ew resonance and E direct capture study for 6 O(,γ) 0 e