We present a nucleosynthesis calculation of a 25 solar mass star of solar
composition that includes all relevant isotopes up to polonium. In particular,
all stable isotopes and necessary nuclear reaction rates are covered. We follow
the stellar evolution from hydrogen burning till iron core collapse and
simulate the explosion using a ``piston'' approach. We discuss the influence of
two key nuclear reaction rates, C12(a,g) and Ne22(a,n), on stellar evolution
and nucleosynthesis. The former significantly influences the resulting core
sizes (iron, silicon, oxygen) and the overall presupernova structure of the
star. It thus has significant consequences for the supernova explosion itself
and the compact remnant formed. The later rate considerably affects the
s-process in massive stars and we demonstrate the changes that different
currently suggested values for this rate cause.Comment: 6 pages, including 4 PostScript figures, to appear in Proc.
  "Astronomy with Radioactivities III", New Astronomy Review

A Heger

Angulo

Buchmann

Costa

Hoffman

Imbriani

Jaeger

Kunz

Käppeler

M.M Boyes

R.D Hoffman

S.E Woosley

T Rauscher

New Astronomy Reviews

English

arXiv

We present a nucleosynthesis calculation of a 25 M-circle dot star of solar composition that includes all relevant isotopes up to polonium. We follow the stellar evolution from hydrogen burning till iron core collapse and simulate the explosion using a `piston` approach. We discuss the influence of two key nuclear reaction rates, C-12(alpha, gamma)O-16 and Ne-22(alpha, n)Mg-25, on stellar evolution and nucleosynthesis. The former significantly influences the resulting core sizes (iron, silicon, oxygen) and the overall presupernova structure of the star. It thus has significant consequences for the supernova explosion itself and the compact remnant formed. The later rate considerably affects the s-process in massive stars and we demonstrate the changes that different currently suggested values for this rate cause. (C) 2002 Elsevier Science B.V. All rights reserved

Heger, A.

Woosley, S. E.

Rauscher, T.

Hoffman, R. D.

Boyes, M. M.

edoc

Massive star evolution : nucleosynthesis and nuclear reaction rate uncertainties

We present a nucleosynthesis calculation of a 25 M-circle dot star of solar composition that includes all relevant isotopes up to polonium. We follow the stellar evolution from hydrogen burning till iron core collapse and simulate the explosion using a 'piston' approach. We discuss the influence of two key nuclear reaction rates, C-12(alpha, gamma)O-16 and Ne-22(alpha, n)Mg-25, on stellar evolution and nucleosynthesis. The former significantly influences the resulting core sizes (iron, silicon, oxygen) and the overall presupernova structure of the star. It thus has significant consequences for the supernova explosion itself and the compact remnant formed. The later rate considerably affects the s-process in massive stars and we demonstrate the changes that different currently suggested values for this rate cause. (C) 2002 Elsevier Science B.V. All rights reserved.Peer reviewe

Woosley, S.E.

Boyes, M.M.

University of Hertfordshire Research Archive

arXiv:astro-ph/0110015v1  30 Sep 2001Massive Star Evolution: Nucleosynthesis andNuclear Reaction Rate UncertaintiesA. Heger a, S.E. Woosley a, T. Rauscher b, R.D. Hoffman c,& M.M. Boyes aaDepartment of Astronomy and Astropyhsics, University of California, SantaCruz, CA 95064bDepartment of Physics and Astronomy, University of Basel, Basel, SwitzerlandcNuclear Theory and Modeling Group, Lawrence Livermore National Laboratory,Livermore, CA 94550AbstractWe present a nucleosynthesis calculation of a 25M⊙ star of solar composition thatincludes all relevant isotopes up to polonium. In particular, all stable isotopes andnecessary nuclear reaction rates are covered. We follow the stellar evolution fromhydrogen burning till iron core collapse and simulate the explosion using a “piston”approach. We discuss the influence of two key nuclear reaction rates, 12C(α, γ)and 22Ne(α,n), on stellar evolution and nucleosynthesis. The former significantlyinfluences the resulting core sizes (iron, silicon, oxygen) and the overall presupernovastructure of the star. It thus has significant consequences for the supernova explosionitself and the compact remnant formed. The later rate considerably affects the s-process in massive stars and we demonstrate the changes that different currentlysuggested values for this rate cause.Key words: stars: massive, evolution, nucleosynthesis, nuclear physics:uncertainties1 IntroductionMassive stars of more than 8M⊙ are the main source of oxygen and heavierelements in the universe. Availability of (theoretical and experimental) reac-tion rate data and computational resources make it now possible to followEmail address: alex@ucolick.org (A. Heger).Preprint submitted to Elsevier Science 1 February 2008the complete nucleosynthesis in massive stars from hydrogen burning till corecollapse and through the supernova explosion (§2). However, significant un-certainties in several key nuclear reaction rates still exist. In §3 we discuss theinfluence of the 22Ne(α, n) rate on the s-process in massive stars and in §4 wedemonstrate the influence of the 12C(α, γ) rate on the presupernova structure.2 Complete nucleosynthesis studyWe present the first calculations to follow the complete nucleosynthesis inmassive stars from hydrogen ignition till onset of iron core collapse and throughthe supernova explosion. Figure 1 shows the average abundance of all ejecta,including stellar wind mass loss, relative to their solar values (productionfactor). The dashed line indicates the production factor for 16O, the dominant“metal” produced by massive stars, and the dotted lines indicate twice and halfthe production factor. The supernova explosion is simulated by a piston thatresulted in ∼ 1.7×1052 erg kinetic energy of the ejecta. The mass cut is thendetermined self-consistently from the hydrodynamical simulation. Note thatFig. 1 does not include a possible r-process contribution due to the neutrinowind from the nascent neutron star.In the 25M⊙ star of Fig. 1, most isotopes from oxygen to the iron groupare produced in about solar ratios relative to oxygen. The iron group itselfis somewhat underproduced, due to fall-back during the explosion. Stars of∼ 15M⊙ typically contribute more here and Type Ia supernovae have addedto the solar abundance in the region. The s-process isotopes above the irongroup till ∼ A = 90 are slightly overproduced. Stars of lower mass and/orlower metallicity produce less here. Therefore these high yields are required toproduce the solar abundances over the lifetime of the Galaxy. Above A & 100many p-isotopes are produced by the γ-process in about solar abundancesrelative to 16O. For more details please refer to Rauscher et al. (2001).3 The 22Ne(α, n) rateThe 22Ne(α, n) rate is the most important source of neutrons for the s-processin massive stars in the region 60 . A . 90. Figure 1 shows the result for thelower limit given by Ka¨ppeler et al. (1994) (as used by Hoffman et al., 2000).In Fig. 2 we show the results for the same star, except that we use the low,high, and recommended values by Jaeger et al. (2001). The abundance ratio ofthe s-process does not change much by this; the abundances only shifting to aslightly higher absolute value. The lower panel shows the result when using thehigh limit given by Angulo et al. (1999) (and the rest of their rate set as well,2Fig. 1. Production factors of isotopes in ejecta, including wind, relative to solarabundances for a 25M⊙ star of solar composition. We use 1.2× the12C(α, γ) rateof Buchmann (1996) (cf. Kunz et al., 2001) and the low 22Ne(α,n) rate of Ka¨ppeleret al. (1994); (as used by Hoffman et al., 2000).which makes only a minor difference as compared to 22Ne(α, n)). The largeoverproduction of the s-process here cannot be balanced by galactochemicalevolution. Even so, we do not find significant production of p-isotopes of Moand Ru (cf. Costa, 2000). For more details please refer to Heger et al. (2001).3Fig. 2. Comparison of the production factors (see Fig. 1) for different 22Ne(α,n)rates. The first three panels give the results for the lower limit, recommended value,and upper limit of Jaeger et al. (2001). The bottom panel uses the reaction rate setby Angulo et al. (1999) with their upper limit for the 22Ne(α,n) rate.4 The 12C(α, γ) rateThe uncertainty of the 12C(α, γ) rate has significant influence on the late timeevolution of massive stars (cf. Imbriani et al., 2001). It determines how much12C is left after core helium exhaustion (Fig. 3). Only for a sufficiently high4Fig. 3. Central carbon mass fraction after core helium exhaustion as a function ofa multiplier on the 12C(α, γ) rate of Buchmann (1996, , 2000 priv. com.) for 15M⊙(dashed line), 20M⊙ (dotted line), and 25M⊙ (solid line) stars.value central carbon burning proceeds convectively while otherwise it burnsradiatively. Similarly, the extent and duration of the carbon shell burningphases are affected. They set the stage for the later burning phases in thatthey produce carbon-free cores of different sizes, as a non-monotonous functionof the carbon abundance. In Fig. 4 the iron core size varies by up to 30%!Therefore the 12C(α, γ) rate determines whether a neutron star or a black holeis formed. For more details please refer to Boyes et al. (2001).5 Conclusions & outlookThe current extent of uncertainties in key nuclear reaction rates still has signifi-cant influence on stellar evolution and nucleosynthesis. Other major uncertain-ties comprise our understanding of mixing processes, rotation, and magneticfields in stars. Some of these uncertainties are currently under re-investigation.The combined effort of refined rate determinations and stellar modeling allowsboth fields to profit from the synergy effects.Acknowledgments: This research was supported, in part, by the DOE (W-7405-ENG-48), the National Science Foundation (AST 97-31569, INT-9726315), the Alexan-der von Humboldt Foundation (FLF-1065004), and the Swiss National Science Foun-5Fig. 4. Helium (squares), carbon-oxygen (rotated squares), neon-oxygen (triangles),silicon (crosses), and “iron” (asterisks) core masses as a function of a multiplier onthe 12C(α, γ) rate of Buchmann (1996)dation (2000-061822.00). T.R. acknowledges support by a PROFIL professorshipfrom the Swiss National Science Foundation (2124-055832.98).ReferencesAngulo, C., et al. 1999, Nuc. Phys. A, 656, 3Boyes, M. M., Heger, A., Woosley, S. E. 2001, in prep.Buchmann, L. 1996, ApJL, 468, 127Costa, V., Rayet, M., Zappala`, R. A., Arnould, M. (2000), 358, L67-L70Heger, A., Woosley, S. E., Hoffman, R. D., Rauscher, T. 2001, in prep.Hoffman, R. D., Woosley, S. E., & Weaver, T. A. 2000, ApJ, 549, 1085Imbriani, G., Limongi, M., Gialanella, L., Terrasi, F., Straniero, O., Chieffi,A. (2001), ApJ, acceptedJaeger, M., Kunz, R., Mayer, A., Hammer, J. W., Staudt, Kratz, K.-L., Pfeif-fer, B. 2001, PRL, in press.Ka¨ppeler, F., et al. (1994), ApJ, 437, 396Kunz, R., Jaeger, M., Mayer, A., Hammer, J. W., Staudt, G., Harissopulos,S., & Paradellis, T. 2001, PRL, in press.Rauscher, T., Heger, A., Hoffman, R. D., Woosley, S. E. 2001, in prep.6

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Massive Star Evolution: Nucleosynthesis and Nuclear Reaction Rate Uncertainties

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