He-Burning in massive Stars

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 3 + 7.6 MeV

Red Giant Evolution in HR diagram http://www.maths.monash.edu.au/~johnl/stellarevolnv/mz0/hb_h+hrdhmovie.gif http://www.maths.monash.edu.au/~johnl/stellarevolnv/mz0/hb_hemovie.gif http://www.maths.monash.edu.au/~johnl/stellarevolnv/mz0/shb_h+hrdhmovie.gif http://www.maths.monash.edu.au/~johnl/stellarevolnv/mz0/shb_omovie.gif

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

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

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

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

Geometry of cluster configurations

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

etwork for stellar Helium burning ( ) ), ( ), ( ), ( 3 3 ), ( ), ( ), ( ), ( ), ( ), ( 3 3 6 6 6 8 8 6 6 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 + +

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

The case of: 3- and (,γ) 6 O Reaction rates determined by cluster state configurations providing strong resonances! θ θ 0.0 MeV 0 + 7.65 MeV 0 + -.0 MeV 7.367 MeV θ 0.7.580 MeV - θ 0.3 7.6 MeV 7.7 MeV - 6.7 MeV + θ 0.8 He 8 Be 6 O

The () Reaction as two step process first step! Q0.0 MeV 8 Be 0 + He+ T / ( 8 Be).7 0-7 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

Example for 8 Be equilibrium abundance: ase of typical He-burning: T0.GK T 0.; ρ0 5 g/cm 3 ( 8 Be).068 35 3/ T 60 T e ( 8 ) 38 Be.0 ρ X i i X ( 8 Be) X.30 ~ one 8 Be nucleus for 0 particles

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 +

The Resonance Strength ( ) ev mev ev e e tot rad e e e e µ ωγ γ γ γ 3. 60.6 0. 0.5 3.58.08 8.0 ± Γ Γ Γ ± Γ ± Γ + Γ + Γ Γ + Γ Γ Γ + + + % 0 3.58 ± MeV ωγ

The 8 Be+ reaction rate reaction rate.e-0.e-08.e- 8 Be (, γ ) 6.( T ) 3/ 3.33 T e.e-0 0.05 0.5 0.5 0.35 0.5 0.55 0.65 0.75 0.85 0.5 temperature [GK]

The total <> rate r X ρ 8 Be(, γ ) 8 Be Step Step 8 ( Be) 60 35 T 3/ e.068 T 8 Be (, γ ) 6.( T ) 3/ e 3.33 T r.60 + δ 56 3 T 3 e ( 0.0 0.78).605 + T r.380 5 3 ρ X 3 T 3 e. T 3 [ cm s ]

Energy production in He burning s g erg e T X erg MeV Q r Q T. 3 3 8 5 0.5 0.6 7.7 ρ ε ρ ε

Example: ρ0 5 g/cm 3 energy production [erg/gs].00e+0.00e+0.00e-0.00e-08.00e-.00e-0 ε ε 0 6 0 8.0 0 0. 0. 0.6 0.8. temperature [GK] 8 L ρ erg g s X 3 ( 0.T ) 0 T-dependent main energy source for stellar He-burning

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

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

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

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)

(,γ) 6 O reaction rate 6.0 8 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!

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!

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 0 6 8 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

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!

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 0..0 0.0 temperature [GK] (,γ) rate dominates over the 6 O(,γ) rate at typical He-burning temperatures T~0.-0.3 GK.

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-07 0..0 0.0 temperature [GK]

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 F88 0-3 3.e+.e+.3e+.5e+ Time (s) He Type II Supernova shock-front nucleosynthesis in and He shells of pre-supernova star

Summary Several important experiments are being discussed Possible improvement in the accuracy of the 7.65 0 + 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