Nova Nucleosynthesis Calculations: Robust Uncertainties, Sensitivities, and Radioactive Ion Beam Measurements (original) (raw)

A New 17 F( p , γ) 18 Ne Reaction Rate and Its Implications for Nova Nucleosynthesis

The Astrophysical Journal, 2003

Proton capture by 17 F plays an important role in the synthesis of nuclei in nova explosions. A revised rate for this reaction, based on a measurement of the 1 H( 17 F,p) 17 F excitation function using a radioactive 17 F beam at ORNL's Holifield Radioactive Ion Beam Facility, is used to calculate the nucleosynthesis in nova outbursts on the surfaces of 1.25 M ⊙ and 1.35 M ⊙ ONeMg white dwarfs and a 1.00 M ⊙ CO white dwarf. We find that the new 17 F (p,γ) 18 Ne reaction rate changes the abundances of some nuclides (e.g., 17 O) synthesized in the hottest zones of an explosion on a 1.35 M ⊙ white dwarf by more than a factor of 10 4 compared to calculations using some previous estimates for this reaction rate, and by more than a factor of 3 when the entire exploding envelope is considered. In a 1.25 M ⊙ white dwarf nova explosion, this new rate changes the abundances of some nuclides synthesized in the hottest zones by more than a factor of 600, and by more than a factor of 2 when the entire exploding envelope is considered. Calculations for the 1.00 M ⊙ white dwarf nova show that this new rate changes the abundance of 18 Ne by 21%, but has negligible effect on all other nuclides. Comparison of model predictions with observations is also discussed.

Reaction Rate of 17F(p,γ)18Ne and Its Implications for Nova Nucleosynthesis

2001

The rate of the 17 F(p,γ) 18 Ne reaction has a profound effect on the abundances of several isotopes produced during a nova outburst. In 1999 a new rate for 17 F(p,γ) 18 Ne was determined from a measurement of the excitation function for the 1 H(17 F,p) 17 F reaction at Oak Ridge National Laboratory's (hereafter ORNL) Holifield Radioactive Ion Beam Facility[1]. This experiment yielded the first definite evidence of a J π =3 + state in 18 Ne. This state provided a new resonance in the 17 F +p capture, which could, depending on its properties, dominate the rate of 17 F(p,γ) 18 Ne at stellar explosive temperatures. The new rate for 17 F(p,γ) 18 Ne was determined from these parameters and several other resonance parameters that had been previously determined [2]. A nuclear reaction network was used to calculate abundances produced during a nova outburst. The network required the input of an initial abundance profile, a reaction rate library and a set of hydrodynamic trajectories for each nova. The reaction network was run with the new 17 F(p,γ) 18 Ne rate placed in the reaction rate library and also with three previous determination of the rate by Wiescher et al., Sherr et al. and Garcia et al. [3][4][5]. Abundances for 169 isotopes from hydrogen to chromium were calculated. The final abundances produced by each earlier rate were compared to the final abundances produced by the new ORNL rate. This was done for simulations of novae occurring on a 1.35 M ⊙ ONeMg white dwarf, a 1.25 M ⊙ ONeMg white dwarf, and a 1.00 M ⊙ CO white dwarf. iv The hotter 1.35 M ⊙ white dwarf nova simulation showed the greatest variation in the abundance patterns produced by the four rates. In this simulation, the new ORNL rate changed the abundances of some nuclei, such as 17 O, that are synthesized in the hottest zones of the nova by up to 15,000 times, when compared to the network results with the Wiescher rate and up to 4 times, when compared to the network results with the Wiescher rate when all zones of the nova were considered. Similar results were achieved for the ORNL to Wiescher rate comparisons for the l.25 M ⊙ WD nova nucleosynthesis calculations, with differences of up to 600 times for the hottest zones and up to 2 times when all zones of the nova were considered. For both the 1.35 M ⊙ and 1.25 M ⊙ white dwarf nova nucleosynthesis calculations the abundance patterns produced by the networks with the Sherr and Garcia rates were similar to those of the network with the new ORNL rate, with the exception of small differences for a few key isotopes such as 17 O and 15 N. The 1.00 M ⊙ WD nova calculations showed that there was little variation in the abundance patterns produced by the networks with the four rates, even in the hottest zones. v TABLE OF CONTENTS CHAPTER

New constraints on the F18(p,α)O15 rate in novae from the (d,p) reaction

Physical Review C, 2005

The degree to which the (p, γ) and (p, α) reactions destroy 18 F at temperatures 1-4×10 8 K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide 18 F, a target of γ-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the 18 F+p threshold (E x =6.411 MeV in 19 Ne). To gain further information about these resonances, we have used a radioactive 18 F beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in 19 F via the inverse 2 H(18 F, p) 19 F neutron transfer reaction. Neutron spectroscopic factors were measured for states in 19 F in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in 19 Ne were calculated using a Woods-Saxon potential. The results imply significantly lower 18 F(p, γ) 19 Ne and 18 F(p, α) 15 O reaction rates than reported previously, thereby increasing the prospect of observing the 511-keV annihilation radiation associated with the decay of 18 F in the ashes ejected from novae.

Nucleosynthesis in classical nova explosions

Journal of Physics G: Nuclear and Particle Physics, 2007

Classical novae are fascinating stellar explosions at the crossroads of stellar astrophysics, nuclear physics, and cosmochemistry. In this review, we briefly summarize 30 years of nucleosynthesis studies, with special emphasis on recent advances in nova theory (including multidimensional models) as well as on experimental efforts to reduce nuclear uncertainties affecting critical reaction rates. Among the topics that are covered, we outline the interplay between nova outbursts and the galactic chemical abundances, the synthesis of radioactive nuclei of interest for γ-ray astronomy, such as 7 Li, 22 Na or 26 Al, and the potential discovery of presolar meteoritic grains likely condensed in nova shells.

Prospects in Classical Nova Modeling and Nucleosynthesis

Nuclear Physics A, 2005

Classical novae are fascinating stellar events, at the crossroads of astrophysics, nuclear physics and cosmochemistry. In this review, we outline the history of nova modeling with special emphasis on recent advances and perspectives in multidimensional simulations. Among the topics that are covered, we analyze the interplay between nova outbursts and the Galactic chemical abundances, the synthesis of radioactive nuclei of interest for gamma-ray astronomy, such as 7 Li, 22 Na or 26 Al, and the recent discovery of presolar meteoritic grains, likely condensed in nova shells. 1. Nuclear ashes: Classical novae and Galactic nucleosynthesis Classical novae are close binary systems consisting of a white dwarf, and a large main sequence (or a more evolved) star. The companion overfills its Roche lobe and matter flows through the inner Lagrangian point, leading to the formation of an accretion disk around the compact star. A fraction of this (H-rich) matter ultimately ends up on top of the white dwarf, where it is gradually compressed up to the point when ignition conditions to drive a thermonuclear runaway (hereafter, TNR) are reached. The thermonuclear origin of nova outbursts was first theorized by Schatzman [36,37]. Modern multiwavelength observations and numerical simulations (pioneered by the early hydro models of Starrfield et al. [40]) have drawn a basic picture, usually referred to as the thermonuclear runaway model. Since then, several groups have attempted to improve our understanding of these dramatic stellar events, including state-of-the-art nova nucleosynthesis studies with spherically symmetric (or 1-D) hydro codes (see [26,21,43], and references therein) or preliminary multi-D approaches [13,14,24,25]. Nuclear physics plays a crucial role in the course of the explosion. As material from the accretion disk piles up on top of the (CO or ONe) white dwarf, the first nuclear reactions take place. This follows a rise in temperature since degenerate conditions unable the star to readjust the hydrostatic equilibrium by an envelope expansion and, as a result, a TNR ensues. The triggering reaction is 12 C(p,γ), which initiates the 'cold' CNO cycle. At very early stages of the explosion, the main nuclear activity is driven by 12 C(p, γ) 13 N(β +) 13 C(p, γ) 14 N. But as the temperature rises, the characteristic time for proton capture reactions on 13 N becomes shorther than its β + decay time, initiating the 'hot' CNO cycle. This is accompanyied by proton capture reactions onto 14 N, leading to 15 O, as well as by 16 O(p,γ) 17 F (near peak temperature, T peak). At this stage, the envelope exhibits the presence of significant amounts of 13 N, 14,15 O and 17 F. Indeed, it is the decay of these

UNCERTAINTIES IN THE νp-PROCESS: SUPERNOVA DYNAMICS VERSUS NUCLEAR PHYSICS

The Astrophysical Journal, 2011

We examine how the uncertainties involved in supernova dynamics as well as in nuclear data inputs affect the νp-process in the neutrino-driven winds. For the supernova dynamics, we find that the wind termination by the preceding dense ejecta shell, as well as the electron fraction (Y e,3 ; at 3 × 10 9 K) play a crucial role. A wind termination within the temperature range of (1.5 − 3) × 10 9 K greatly enhances the efficiency of the νp-process. This implies that the early wind phase, when the innermost layer of the preceding supernova ejecta is still ∼ 200 − 1000 km from the center, is most relevant to the νp-process. The outflows with Y e,3 = 0.52 − 0.60 result in the production of the p-nuclei up to A = 108 with interesting amounts. Furthermore, the p-nuclei up to A = 152 can be produced if Y e,3 = 0.65 is achieved. For the nuclear data inputs, we test the sensitivity to the rates relevant to the breakout from the pp-chain region (A < 12), to the (n, p) rates on heavy nuclei, and to the nuclear masses along the νp-process pathway. We find that a small variation of the rates of triple-α and of the (n, p) reaction on 56 Ni leads to a substantial change in the p-nuclei production. We also find that 96 Pd (N = 50) on the νp-process path plays a role as a second seed nucleus for the production of heavier p-nuclei. The uncertainty in the nuclear mass of 82 Zr can lead to a factor of two reduction in the abundance of the p-isotope 84 Sr.

Sensitivity ofp‐Process Nucleosynthesis to Nuclear Reaction Rates in a 25M⊙Supernova Model

The Astrophysical Journal, 2006

The astrophysical p process, which is responsible for the origin of the proton rich stable nuclei heavier than iron, was investigated using a full nuclear reaction network for a type II supernova explosion when the shock front passes through the O/Ne layer. Calculations were performed with a multi-layer model adopting the seed of a pre-explosion evolution of a 25 solar mass star. The reaction flux was calculated to determine the main reaction path and branching points responsible for synthesizing the proton rich nuclei. In order to investigate the impact of nuclear reaction rates on the predicted pprocess abundances, extensive simulations with different sets of collectively and individually modified neutron-, proton-, α-capture and photodisintegration rates have been performed. These results are not only relevant to explore the nuclear physics related uncertainties in p-process calculations but are also important for identifying the strategy and planning of future experiments.