Nadyozhin, D

Panov, I

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PoS(NIC-IX)147Neutrino-induced nucleosynthesis as a probe intothe mechanism of supernovaeD. Nadyozhin and I. PanovA.I. Alikhanov Institute for Theoretical and Experimental PhysicsE-mail: nadezhin@itep.ru, Igor.Panov@itep.ruThe neutrino nucleosynthesis yields depend on a number of factors. Apart from the onion-likepresupernova chemical structure, they are sensitive to temporal and spectral properties of the neu-trino light curve" and to such hydrodynamic parameters as the supernova explosion energy andthe delay in passing of the shock wave through successive presupernova chemical shells. More-over, possible intrusions of other chemicals into the shells (e.g., hydrogen into the helium shell)can appreciably modify the nal yields. We report the results of our systematic quantitative studyof some of these effects with special attention to the supernova explosion energy and characteristictime of the neutrino ux.International Symposium on Nuclear Astrophysics - Nuclei in the Cosmos - IX25-30 June 2006CERNSpeaker.cCopyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/PoS(NIC-IX)147Neutrino-induced nucleosynthesis and supernova mechanism D. NadyozhinIntroductionThe neutrino-induced nuclear processing in the envelopes of core-collapse supernovae is animportant constituent of the theory of stellar nucleosynthesis. The resulting neutrino-dependentyields are sensitive to a number of parameters coupled both with the presupernova structure andthe properties of not yet finally established details of the supernova mechanism. The most importantones are: The neutrino “light curve" and the neutrino energy and flavor spectra. The supernova total explosion energy Eexp that determines the strength of the shock waveand time it takes to propagate through the presupernova envelope. The properties of the onion-like presupernova chemical structure, especially the distances ofdifferent chemical shells from stellar center.The carbon-oxygen-neon shell and the helium one are good places to verify how the resultingyields depend on the above properties and thereby to obtain constraints on the supernova mecha-nism itself. Here we discuss the results we have obtained for the neutrino-induced nucleosynthesisin the helium shell.Method and Input PhysicsWe have used two nuclear kinetics codes. The first one calculates the nuclear kinetics for thelight nuclides from D, 3H, 3He,    through 24Mg (the L code). The second code (H) controls thenuclear kinetic for the heavier nuclides up to Z  60 (Nd). The L code calculate the kinetics ofabout 160 thermonuclear reactions and beta-decays connecting 40 most important nuclides. TheH code deals with about 1300 isotopes. Both the codes work consistently by exchanging with freeneutrons and protons [1, 2].The presupernova models were taken from [3]. The temporal behavior of the temperature,density, and radius of shocked material were described by analytical formulae from [4].The following neutrino processes were taken into account.Inelastic ν-α scattering:4Heν  ν  n 	 3He, 4Heν  ν  p 	 3H.Inelastic ν scattering off 12C, 14N, 16O, and 20Ne:12Cν  ν  3He 	 9Be,12Cν  ν  n 	 11C, 12Cν  ν  p 	 11B,14Nν  ν  α 	 10B,16Oν  ν  n 	 15O, 16Oν  ν  p 	 15N,20Neν  ν  n 	 19Ne, 20Neν  ν  p 	 19F,where ν stands for µ and τ neutrino and antineutrino.Finally, the ν¯e proton capture was included: pν¯e,e 	 n.2PoS(NIC-IX)147Neutrino-induced nucleosynthesis and supernova mechanism D. NadyozhinThe total (bolometric) neutrino light curve was taken from [5]. The total neutrino energy radi-ated was assumed to be equally distributed among all the 6 neutrino and antineutrino species. Theneutrino cross-sections, averaged over the Fermi–Dirac spectra with the zero chemical potentialand temperature of 8 MeV for µ  τ neutrino and antineutrino and 4 MeV for the electron neutrinoand antineutrino, were taken from [6, 7, 8].ResultsFigure 1 shows how the production factors (PF) change with the explosion energy Eexp. ThePF for 7Li, 11B, 15N, and 19F include the contribution from beta-decays of their radioactive coun-terparts 7Be, 11C, 15O, and 19Ne, respectively. Although the PF dependence on Eexp is noticeable,it is not crucial.The 11B turns out to be always overproduced relative to 7Li. The reason is not yet clearand deserves further investigation in the framework of constraints on presupernova models andsupernova mechanism.The PF for 9Be is small (  0  1). However, there is a hope to get PF(9Be)  1 since the cross-section of the reaction 12Cν  ν  3He 	 9Be is still poorly known and some, otherwise unimportantproperties, of the presupernova structure may be helpful to resolve the problem. Moreover, theneutrino-induced production of 9Be depends strongly on the duration of the neutrino “light" curvewhich in our calculations has a characteristic time of  20s [5] supported by the observations ofSN 1987A. If one used the exponential approximation with the characteristic time 3s the PF(9Be)would be at least by a factor of 10 lower. This occurs because there is not enough time in this casefor the neutrino flux to restore 9Be burned in the shock wave.Figure 2 and 3 show the chemical structure of He-shells for 15M  and 75M  presupernovaof very low metallicity: Z  0  0001Z  . Of special interest are the sub-shells with a rather smalladmixture of elements heavier than 4He which used to absorb free neutrons and thereby prevent tobuild heavy elements from the “Fe" seeds. In terms of the mass coordinate m, the sub-shells arem 3  8  4  1 	 M  and m 32  8  33  7 	 M  for a 15M  and 75M  presupernova, respectively.Figures 4, 5 show the results of our calculation of the neutrino nucleosynthesis in the sub-shellof a 15M  presupernova when all the species (but not the “Fe" seeds!) with the abundances belowlog X  6 are neglected (these abundances are not seen in Fig. 4). The initial abundance of the“Fe" seeds is XFe  3  15  10 8 . Thus in the metal-poor presupernovae, there exists a rather goodsite to obtain a kind of a “weak" r-process up to A  130. Figure 5 demonstrates that the overalltrend in the distribution of elemental abundances obtained in our calculations (a serrated solid line)is in good agreement with the solar and metal-poor star data.If in the sub-shell of a 15M  presupernova the abundances of 12C, 16O, and 20NeXC12 5  5  108 , XO16  1  2  10 8 , XNe20  2  4  10 7	 , dropped out in the previous calculation, areretained, then the neutrino-induced r-process extends to A  80 only (Fig. 6, solid line). The samestory happens with a 75M  presupernova. A bulk of neutrons produced by the ν-He spallationproves to be captured by a relatively abundant 12C (Fig. 3) and only about one neutron being leftfor a “Fe" seed. However, for the 12C abundance decreased by a factor of  104 (in this case it3PoS(NIC-IX)147Neutrino-induced nucleosynthesis and supernova mechanism D. Nadyozhinbecomes comparable with the abundance of 16O) we obtained a limited r-process shown in Fig. 6by a dashed line.ConclusionThe goal of this contribution is to draw the attention of the scientific community to the factthat some details of the presupernova models and of the mechanism of core-collapse supernovaecan be probed by modelling the neutrino induced nucleosynthesis.Three issues seem to be the most challenging for the helium shell: The synthesis of 9Be that strongly depends on the total duration of the neutrino “light" curve. An overproduction of 11B relative to 7Li. The possibility of the neutrino-driven weak r-process in the poor-metal supernova modelsthat depends on the admixture of such neutron poisons as 12C and 14N. Their concentrationsmight be sensitive to details of description of mixing in presupernova models (convectiveand semi-convective diffusion).Acknowledgement. We thank the NIC-9 Organizing Committee for the invitation to attendthe Conference. The work was supported by the grants: RFBR No. 04-02-16793 and SNSFNo. IB7320-110996.References[1] D.K. Nadyozhin, I.V. Panov, and S.I. Blinnikov, The neutrino-induced neutron source in helium shelland r-process nucleosynthesis, Astron. Astrophys. 335, 207 (1998).[2] D.K. Nadyozhin and I.V. Panov, A two-code iterative method to calculate the light and heavy elementsynthesis, Nuclear Phys., A688, 590c (2001).[3] A. Heger and S.E. WoosleyGrids of Stellar Evolution Models. Presupernova Structure Data Files.,http://www.ucolick.org/  alex/stellarevolution/data.shtml[4] D.K. Nadyozhin and A.Yu. Deputovich, An analytical approximation of post-shock conditions in typeII supernova shells, Astron. Astrophys. 386, 711 (2002).[5] D.K. Nadyozhin, The neutrino radiation for a hot neutron star formation and the envelope outburstproblem, Astroph. Sp. Sci., 53, 131 (1978).[6] A. Heger, E. Kolbe, W.C. Haxton et al. Neutrino Nucleosynthesis, Physics Letters, B606, 258 (2005);astro-ph/0307546 v1 31 Jul 2003.[7] S.E. Woosley, D.H. Hartmann, R.D. Hoffman, and W.C. Haxton, The nu-process, Astrophys. J., 356,272 (1990).[8] G.V. Domogatskij and S.V. Imshennik, Production of the 9Be isotope induced by neutrinos generatedthrough gravitational stellar collapse, Sov. Astron. Lett., 8, 190, (1982).[9] J.J. Cowan, C. Sneden, S. Burles et al., The chemical composition and age of the metal-poor halo starBD +17o3248, Astrophys. J., 572, 861 (2002).4PoS(NIC-IX)147Neutrino-induced nucleosynthesis and supernova mechanism D. NadyozhinFigure 1: Production factors versus explosion energy in the helium shell of a 15M  supernova (solarmetallicity).Figure 2: The composition of He-shell for a 15M  presupernova (0  0001Z  ) [3].5PoS(NIC-IX)147Neutrino-induced nucleosynthesis and supernova mechanism D. NadyozhinFigure 3: The composition of He-shell for a 75Mpresupernova (0  0001Z) [3].Figure 4: Heavy nuclides yields versus mass number A for a 15M  supernova (0  0001Z  , Eexp 1  1051 erg). There were captured about 50 neutrons per Fe" seed.6PoS(NIC-IX)147Neutrino-induced nucleosynthesis and supernova mechanism D. NadyozhinFigure 5: Heavy nuclide yields versus atomic number Z for a 15Msupernova (0  0001Z, Eexp 1  1051 erg). Black stars stand for a metal-poor star BD +17o3248 [9], also the solar abundances for somenuclides are shown. All the data are arbitrarily shifted along the vertical axis.Figure 6: Heavy nuclide yields versus mass number A for a 15M  supernova (0  0001Z  , Eexp 1  1051 erg) and a 75M  supernova (0  0001Z  , Eexp  1  1052 erg). About 14 and 17 neutrons werecaptured per Fe" seed, respectively.7

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