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The P-Process of Stellar Nucleosynthesis: Astrophysics and Nuclear Physics Status

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The P-Process of Stellar Nucleosynthesis: Astrophysics and Nuclear Physics Status Available online at www.sciencedirect.com Physics Reports 384 (2003) 1–84 www.elsevier.com/locate/physrep The p-process of stellar nucleosynthesis: astrophysics and nuclear physics status M. Arnould∗, S. Goriely Campus de la Plaine, Institut d’Astronomie et d’Astrophysique, Universite Libre de Bruxelles, CP226, 1050 Brussels, Belgium Accepted 4 June 2003 editor: M.P. Kamionkowski Abstract The p-process of stellar nucleosynthesis is aimed at explaining the production of the stable neutron-deÿcient nuclidesheavier thanironthat are observed up to nowinthe solar system exclusively. Various scenarios have been proposed to account for the bulk p-nuclide content of the solar system, as well as for deviations (‘anomalies’) with respect to the bulk p-isotope composition of some elements discovered in primitive mete- orites. The astrophysics of these models is reviewed, and the involved nuclear physics is discussed, including a brief account of recent experimental e3orts. Already published results are complemented with new ones. A speciÿc attention is paid to the very rare odd–odd nuclides 138La and 180Tam, as well as to the puzzling case of the light Mo and Ru isotopes. Astrophysics and nuclear physics prospects of improvements in the p-process modeling are presented. c 2003 Elsevier B.V. All rights reserved. PACS: 24.60.−k; 26.30.+k; 26.45.+h; 96.10.+i Keywords: Solar system: composition; Stellar nucleosynthesis: p-process; Nuclear reactions; Statistical model Contents 1. Introduction ....................................................................................... 2 2. Observed abundances of the heavy nuclides in the solar system .......................................... 5 2.1. The bulk solar-system composition .............................................................. 5 2.2. Isotopic anomalies in the solar composition ....................................................... 10 3. The nuclear physics of relevance to the p-process ...................................................... 13 ∗ Corresponding author. E-mail address: marcel [email protected] (M. Arnould). 0370-1573/03/$ - see front matter c 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0370-1573(03)00242-4 2 M. Arnould, S. Goriely / Physics Reports 384 (2003) 1–84 3.1. Captures of neutrons and photoreactions: experimental situation ..................................... 14 3.2. Captures of charged particles: experimental situation ............................................... 16 3.3. Theoretical evaluationof reactionrates ........................................................... 17 3.3.1. Reaction rate calculations: general framework .............................................. 17 3.3.2. Ground state properties .................................................................. 20 3.3.3. Nuclear level densities .................................................................. 21 3.3.4. Optical potentials ....................................................................... 24 3.3.5. -ray strength function................................................................... 26 3.4. A confrontation between measured and calculated reaction rates ..................................... 27 3.5. Rate prediction uncertainties evaluated from the use of di3erent sets of nuclear inputs .................. 32 3.6. The nuclear reaction network used in the p-process modeling ....................................... 33 4. Massive stars: the pre-Type II supernova production of the p-nuclides .................................... 34 4.1. Some pedestrian considerations about the evolution of massive stars leading to Type II supernovae ...... 34 4.2. The seeds for the p-process ..................................................................... 36 4.3. Some comments on the non-explosive p-process in massive stars .................................... 37 5. Massive stars: the SNII productionof the p-nuclides .................................................... 39 5.1. Some commentsonthe mainp-process nuclearDows .............................................. 42 5.2. Predicted p-nuclide abundances: inDuence of the SNII mass, and IMF-averaged yields .................. 45 5.3. Predicted p-nuclide abundances: inDuence of the 12C(;)16O rate and of the explosion energy .......... 46 5.4. Predicted p-nuclide abundances: inDuence of metallicity ............................................ 47 5.5. Impact of changesinreactionrate estimates onthe predicted p-nuclideyields ......................... 47 5.6. A comparison between two sets of p-nuclide abundances predicted by di3erent authors using di3erent astrophysics and nuclear physics inputs .............................................. 49 6. Anexaminationofsome puzzlingcases ............................................................... 50 6.1. The underproduction of the light Mo and Ru isotopes: is the s-process a troublemaker? ................ 50 6.2. The puzzle of the originof the rare nuclide 138La: a nuclear physics solution? ........................ 52 6.3. The p-process character of 180Tam ............................................................... 54 7. The p-process invery massive stars explodingas pair-creationsupernovae ................................. 57 7.1. A sketch of the evolutionof very massive stars ................................................... 57 7.2. The p-process ina PCSN ...................................................................... 58 8. The p-process inType I supernovae .................................................................. 60 8.1. The case of the Type Ia explosions .............................................................. 60 8.2. The case of the Type Ib/Ic explosions ........................................................... 66 8.3. The case of the sub-Chandrasekhar white dwarf explosions ......................................... 66 9. The p-process isotopic anomalies and chronometry ..................................................... 71 9.1. The Xe-HL anomaly ........................................................................... 72 9.2. 92Nbg inthe early solar system .................................................................. 74 9.3. 146Sm: a short-lived p-process chronometer? ...................................................... 75 10. Summary and prospects ............................................................................. 76 Acknowledgements ..................................................................................... 79 References ............................................................................................ 79 1. Introduction The observational foundation of the theory of nucleosynthesis rests largely upon the determination of elemental and isotopic abundances in the broadest possible variety of cosmic objects, as well as uponthe study of the most complete set of available observables that help characterizingthe M. Arnould, S. Goriely / Physics Reports 384 (2003) 1–84 3 objects. This knowledge relies almost entirely on the detailed study of the light (possibly at various wavelengths) originating from a large diversity of emitting locations: our Galaxy (non-exploding or exploding stars of various types, the interstellar medium), external galaxies, and perhaps even the early Universe. The studies of the electromagnetic radiation are complemented with the careful analysis of the minute amount of matter of the Universe accessible to humankind. This matter is comprised for its very largest part invarious types of solar system solids. The rest is inthe form of (extra-)galactic cosmic rays. The myriad of observations of the aforementioned types leads in particular to a more and more complete, and at the same time increasingly complex, picture of the abundances in a variety of constituents of the Universe with di3erent locations and ages. This concerns in particular the heavy elements we are dealing with in this review, these elements being deÿned here as those having charge numbers in excess of the value Z = 26 corresponding to iron. Despite the spectacular progress made in astronomical abundance observations, the solar system continues to provide a body of abundance data whose quantity, quality and coherence remain unmatched. This concerns especially isotopic compositions, which are the prime ÿngerprints of astrophysical nuclear processes. This is even more so for the heavy elements, the stable isotopes of which cannot be separated even by the most performant stellar spectroscopic techniques available today. From the early days of the development of the theory of nucleosynthesis (e.g. [1]), the main observational foundation of which was the solar system composition, especially in the heavy element domain, it has proved operationally most rewarding to introduce three categories of heavy nuclides referred to as s-, p-, and r-nuclides. This splitting is not a mere game. It corresponds instead to the ‘topology’ of the chart of the nuclides, which exhibits three categories of stable heavy nuclides: those located at the bottom of the valley of nuclear stability, called the s-nuclides, and those situated on the neutron-deÿcient or neutron-rich side of the valley, named the p- or r-nuclides, respectively. Three di3erent mechanisms are called for to account for the production of these three types of stable nuclides. They are naturally referred to as the s-, r-, and p-processes. We are concerned here with a review of the p-process (the reader is referred to e.g. [2] for lim- ited comments on the s- and r-processes, [3] for
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