Sam M. Austin Mitchell 4/14/06 Supernovae, Their Collapsing Cores and Nuclear Physics Nature of Supernova Progenitors Their sensitivity to nuclear properties How these properties are determined Ongoing experiments

Sam M. Austin Mitchell 4/14/06 Evolution of Stellar Core for Heavy Stars After initial formation A gravitational collapse, interrupted by long nuclear burning stages. Eventually form “Fe”core, and no further nuclear energy available. Log Central Density Woosley & Janke--Nature Temperature vs Density

Sam M. Austin Mitchell 4/14/06 Problem since Baade/Zwicky in 1930’s suggested SN powered by gravitational energy from collapse of normal star to neutron-star "Fe" core Collapses Bounce-- Form Shock Wave Shock moves out Loses energy. Fe  p's, n's in outer part of Fe core; neutrino emission Stalls Time Supernovae Core Collapse—The Mechanism

Sam M. Austin Mitchell 4/14/06 Difficulty Of The Supernova Problem A comment Insufficient knowledge of nuclear physics properties causes changes at the 1-few% level Dangerous to assume that the effects are always cancelled by negative feedback processes Nature of the energetics—the 1% problem? Only 1% of the available gravitational energy (10 53 ergs) is emitted as explosion energy, rest as neutrinos. (Burrows argues it’s a 10% problem--90% of gravitational energy emitted prior to critical phase). But, either way, it may mean we have to do things very well. What’s been trie d Delayed shock– re-energized by neutrinos from proto-neutron star Better neutrino transport, better weak interactions, 2 and 3-D (limitations), acoustic coupling, …… Scheck, Janka

Sam M. Austin Mitchell 4/14/06 Triple  makes 12 C, 12 C(  ) 16 O turns it into 16 O. Their ratio determines the amounts of C and O made and affects the nature of a star and of its iron core An Example--Helium Burning Rehm-ANL 10:10 WMU-MSU

Sam M. Austin Mitchell 4/14/06 SNII--Pre-collapse Fe Core Size Pre-supernova evolution Vary rate of 12 C(  ) 16 O (or Triple alpha)? All else constant Fe core mass changes by >0.2 M  over the interesting range Important? Naively, yes. If homologous core mass constant, need 3 x erg to dissociate extra 0.2 M  to nucleons Fe Core Size (Solar Masses) C(  ) 16 O Multiplier or 1/Triple alpha? 25 M  Heger, Woosley, Boyes Need ratio of rates to 10% (  ) 160 ±40 keV b Brune alpha Fynbo 2006

Sam M. Austin Mitchell 4/14/06 Element Production in a Supernovae Shell Burning When He is exhausted in the core the core collapses, T increases, core carbon and oxygen burning begin. H and He burning in shells The successive core stages are H  He, gravity He  C,O, gravity C,O  Mg, Si--gravity, Si  Fe. He Burning Core T=10 8 K  = 10 7 kg/m 3 The Result (Stellar Onion) SN blows off outer layers Need detailed element distribution/abundances to predict SN element production

Sam M. Austin Mitchell 4/14/06 Detailed Models-Heger and Woosley 2001 It’s more complex than the onion even in 1D: M= 22 M sun. Along the x-axis sequential episodes of convective carbon, neon, oxygen, and silicon burning. Affected by rates of He-burning reactions.

Sam M. Austin Mitchell 4/14/06 SNII Nucleosynthesis A= C(  ) 16 O Multiplier (xBuchmann 1996) Production Factor Heger, Woosley, Boyes 25 M  Explosion of 25 M  star Vary rate of 12 C(  ) 16 O All else same Production Factor “Same” PF for 1.2 x standard 12 C(  ) 16 O rate 170 keV b

Sam M. Austin Mitchell 4/14/06 Weak Strength and Supernovae Core Collapse Gamow-Teller (GT) Strength? Mediates  -decay, electron capture(EC), n induced reactions GT (allowed) Strength S=1; L = 0, e.g. 0 +  1 +; GT +,GT - Lies in giant resonances (n,p) (p,n) GT + dominates process Situation After silicon burning, T core  3.3 x 10 9 K, density  10 8 g/cm 3. e - Fermi energy allows capture into GT +. Reduces e - pressure emits neutrinos. Speeds collapse. At higher T, GT + thermally populated,  - decays back to ground state.  -  E.C.

Sam M. Austin Mitchell 4/14/06 Effects of Changed Weak Rates- Heger et al. Ap.J. 560 (2001) Time till collapse (s)    d Y e d t  ( s  1 ) LMP-EC LMP-  Y e WW LMP 15 M URCA IPM vs Shell Model WW standard Wallace-Weaver rates based on independent particle model (FFN) LMP-from large basis shell model calculations. (Langanke and Martinez-Pinedo) Significant differences Larger, lower entropy "Fe" pre- collapse core More e-'s (Y e larger), lower T core. Larger homologous core 

Sam M. Austin Mitchell 4/14/06 Important Electron Capture Nuclei Pre-Collapse: Nuclei in the Fe-Ni region Collapse: Heavier nuclei are important, including many with N>40

Sam M. Austin Mitchell 4/14/06 Do (N>40) Nuclei Undergo Electron Capture? From Martinez-Pinedo Independent particle model: No for N>40 Transitions Pauli blocked Shell model at finite T: Blocking removed—Has important effects

Sam M. Austin Mitchell 4/14/06 Results of New Calculations-- Langanke et al PRL Nature of calculations Shell model Monte Carlo + RPA Results Capture on nuclei dominates by x10 Neutrino energies are lower Mass enclosed by the shock is smaller by 0.1 M sun Shock is weaker Ye varies with enclosed mass

Sam M. Austin Mitchell 4/14/06 Reliability of Nuclear Models for e-Capture For pre-collapse calculations Quite good, some problems Further validation of models requires data for unstable isotopes especially odd-odd nuclei : FFN (IPM) : data (n,p) (TRIUMF) : Caurier et al. (1999) Large basis SM : Caurier et al. folded with experimental resolution ? ? ? (Caurier, et al NPA 653, 439(99

Sam M. Austin Mitchell 4/14/06 Reliability of Nuclear Models for e-Capture-cont. For heavier nuclei--less firmly based and not validated General Comment Can’t measure everything, 1000s of transitions, many from thermally excited states But need to do enough checks to have confidence in models Nature of measurements: Hadronic charge exchange reactions Operators similar to  decay operator; (n,p), (d, 2 He), (t, 3 He) measure e-capture strength B(GT) =  CEX (q = 0)/  unit,  unit calibrated from known transitions Accuracies in 10-20% range, better for strong transitions Require energy of >100 MeV/nucleon to minimize 2-step processes Reactions studied: In past (n,p), (d, 2 He), (t, 3 He); presently only (t, 3 He)

Sam M. Austin Mitchell 4/14/06 Charge Exchange Options (t, 3 He) Secondary triton beams /sec at MSU/NSCL, 115 MeV/A tritons Resol: 160 keV achieved Data on 24,26 Mg, 58 Ni, 63 Cu, 94 Mo Unique beam-spectrometer(S800), simple analysis, calibration from ( 3 He, t) reaction at Osaka. More beam nice Future (Zegers, et al.) Develop techniques for using radioactive beams: (p,n), ( 7 Li, 7 Be) in inverse kinematics to study  -decay, electron capture, respectively. Test ( 7 Li, 7 Be) expt in near future.

Sam M. Austin Mitchell 4/14/06 (t, 3 He), ( 3 He,t) vs (p,n) and Shell Model

Sam M. Austin Mitchell 4/14/06 II   Q 2 = -287 keV   + 8 Be Hoyle state Back to The Triple Alpha Process-More Formally Step I:  8 Be Equilibrium abundance of 8 Be Step II: 8 Be +   12 C(7.65) Present Interests—3  and SNII (Iron core size, nucleosynthesis) 5% AGB Stars (Carbon production and carbon stars) 5% Limits on variation of “fundamental” constants r 3   rad ( 7.65 )e - Q/kt  rad =   +  , - Q = Q 1 +Q 2 Rate depends on properties of Hoyle state (7.65), mostly on  rad I Q 1 = -92 keV 

Sam M. Austin Mitchell 4/14/06 How Well Do We Know  rad            rad   2.7% 9.2% 6.4%  2.7%  12% Least well known quantity is    A WMU, MSU collaboration is undertaking a new measurement: WMU Alan Wuosmaa, Jon Lighthall, Scott Marley, Nicholas Goodman MSU/NSCL Clarisse Tur, SMA

Sam M. Austin Mitchell 4/14/06 Measuring    A hard measurement: Branch is small ~6 x New measurement: WMU/MSU WMU Tandem, (p,p’) at 135 o, MeV (strong resonance for 7.65 state)     pairs / #-7.65 protons) Aim: ± 5% accuracy Side View Improved version of Robertson, et al PRC 15,1072(77)

Sam M. Austin Mitchell 4/14/06 WMU-MSU/NSCL Detector

Sam M. Austin Mitchell 4/14/06 Final Comments Discussed two cases were nuclear uncertainties are important Helium burning (expts on 12 C(  and 3alpha rates ongoing) Electron capture (expts ongoing) Others have not been much investigated 12 C+ 12 C reaction rate poorly known—sensitivity of progenitor structure? r-process nucleosynthesis could provide a diagnostic of conditions at its site—nuclear properties need to be better understood

Sam M. Austin Mitchell 4/14/06 Cocktail beam 78 Ni Measured half-life of 78 Ni with 11 events  Acceleration of the r-process  excess of heavy elements with the new shorter 78 Ni half-life Result: ms (Theory: 460 ms) T 1/2 measurement at NSCL Beta Lifetimes are important--Example: doubly magic 78 Ni Energy loss  velocity  r-process calculation P. Hosmer et al (NSCL, Mainz, Maryland collaboration)

Sam M. Austin Mitchell 4/14/06 Some Comments Discussed two cases were nuclear uncertainties are important Helium burning (expts on 12 C(a,g) and 3alpha rates ongoing) Electron capture (expts ongoing) Others have not been much investigated 12 C+ 12 C reaction rate poorly known—sensitivity of progenitor structure? r-process nucleosynthesis could provide a diagnostic of conditions at its site—nuclear properties need to be better understood 2D and 3D calculations of progenitor evolution In their beginning phases Will surely change the nature of the pre-SN star Note: present 1-D models differ somewhat from group to group