The unreasonable effectiveness of experiments in constraining nova nucleosynthesis

Classical nova explosions arise from thermonuclear ignition in the envelopes of accreting white dwarfs in close binary star systems. Detailed observations of novae have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. These phenomena are unusual in nuclear astrophysics because most of the thermonuclear reaction rates thought to be involved are constrained by experimental measurements. This situation allows for rather precise statements to be made about which measurements are still necessary to improve the nuclear physics input to astrophysical models. We briefly discuss desired measurements in these environments with an emphasis on recent experimental progress made to better determine key rates.Postprint (published version

Non-extensive statistics to the cosmological lithium problem

Big Bang nucleosynthesis (BBN) theory predicts the abundances of the light elements D, 3He, 4He, and 7Li produced in the early universe. The primordial abundances of D and 4He inferred from observational data are in good agreement with predictions, however, BBN theory overestimates the primordial 7Li abundance by about a factor of three. This is the so-calledPeer ReviewedPostprint (author's final draft

Recent advances in the modelling of classical novae and type I X-ray bursts

Classical nova outbursts and type I X-ray bursts are thermonuclear stellar explosions driven by charged-particle reactions. Extensive numerical simulations of nova explosions have shown that the accreted envelopes attain peak temperatures between 0.1 and 0.4 GK, for about several hundred seconds, and therefore, their ejecta is expected to show signatures of significant nuclear activity. Indeed, it has been claimed that novae play some role in the enrichment of the interstellar medium through a number of intermediate-mass elements. This includes 17O, 15N, and 13C, systematically overproduced in huge amounts with respect to solar abundances, with a lower contribution to a number of species with A<40, such as 7Li, 19F, or 26Al. In this review, we present new 1-D hydrodynamic models of classical nova outbursts, from the onset of accretion up to the explosion and ejection phases. Special emphasis is put on their gross observational properties (including constraints from meteoritic presolar grains and potential gamma-ray signatures) and on their associated nucleosynthesis. Multidimensional models of mixing at the core-envelope interface during outbursts will also be presented. The impact of nuclear uncertainties on the final yields will be also outlined. Detailed analysis of the relevant reactions along the main nuclear path for type I X-ray bursts has only been scarcely addressed, mainly in the context of parameterized one-zone models. Here, we present a detailed study of the nucleosynthesis and nuclear processes powering type I X-ray bursts. The reported bursts have been computed by means of a spherically symmetric (1D), Lagrangian, hydrodynamic code, linked to a nuclear reaction network that contains 325 isotopes (from 1H to 107Te), and 1392 nuclear processes. These evolutionary sequences, followed from the onset of accretion up to the explosion and expansion stages, have been performed for two different metallicities to explore the dependence between the extension of the main nuclear flow and the initial metal content. We carefully analyze the physical parameters that determine the light curve (including recurrence times, ratios between persistent and burst luminosities, or the extent of the envelope expansion). Results are in qualitative agreement with the observed properties of some well-studied bursting sources.Postprint (published version

Binary systems and their nuclear explosions

Peer ReviewedPreprin

The unreasonable effectiveness of experiments in constraining nova nucleosynthesis

Classical nova explosions arise from thermonuclear ignition in the envelopes of accreting white dwarfs in close binary star systems. Detailed observations of novae have stimulated numerous studies in theoretical astrophysics and experimental nuclear physics. These phenomena are unusual in nuclear astrophysics because most of the thermonuclear reaction rates thought to be involved are constrained by experimental measurements. This situation allows for rather precise statements to be made about which measurements are still necessary to improve the nuclear physics input to astrophysical models. We briefly discuss desired measurements in these environments with an emphasis on recent experimental progress made to better determine key rates

Reaction Rates of 64Ge(p,g)65As and 65As(p,g)66Se and the Extent of Nucleosynthesis in Type I X-Ray Bursts

The extent of nucleosynthesis in models of type I X-ray bursts (XRBs) and the associated impact on the energy released in these explosive events are sensitive to nuclear masses and reaction rates around the 64Ge waiting point. Using the well known mass of 64Ge, the recently measured 65As mass, and large-scale shell model calculations, we have determined new thermonuclear rates of the 64Ge(p,¿)65As and 65As(p,¿)66Se reactions with reliable uncertainties. The new reaction rates differ significantly from previously published rates. Using the new data, we analyze the impact of the new rates and the remaining nuclear physics uncertainties on the 64Ge waiting point in a number of representative one-zone XRB models. We find that in contrast to previous work, when all relevant uncertainties are considered, a strong 64Ge rp-process waiting point cannot be ruled out. The nuclear physics uncertainties strongly affect XRB model predictions of the synthesis of 64Zn, the synthesis of nuclei beyond A = 64, the energy generation, and the burst light curve. We also identify key nuclear uncertainties that need to be addressed to determine the role of the 64Ge waiting point in XRBs. These include the remaining uncertainty in the 65As mass, the uncertainty of the 66Se mass, and the remaining uncertainty in the 65As(p,¿)66Se reaction rate, which mainly originates from uncertain resonance energieSPeer Reviewe

Toward concordance of Ex and JPi values for proton unbound 31S states

Nucleosynthesis in classical novae on oxygen-neon white dwarfs is sensitive to the poorly constrained thermonuclear rate of the 30P(p,¿)31S reaction. In order to improve this situation, a variety of experiments have been performed over the past decade to determine the properties of proton unbound 31S levels up to an excitation energy of ˜6.7 MeV. Inconsistencies in the energies and Jp values for these levels have made it difficult to produce a useful 30P(p,¿)31S reaction rate based on experimental information. In the present work, we revisit a subset of published data on the structure of 31S in order to shed light on these problems. First, we present an alternative calibration of 31P(3He, t)31S spectra using newly available high-precision data in order to address discrepant 31S excitation energies. Second, we apply a similar method to a recently acquired 32S(d, t)31S spectrum. Third, for a different 31P(3He, t)31S experiment in which angular distributions were acquired, we present alternative fits to the experimental data in order to address discrepant 31S Jp values. Finally, we compare the Jp values from 31P(3He, t)31S to those reported from in beam ¿-ray spectroscopy experiments in order to search for potential resolutions to the inconsistencies. Overall, viable new solutions to some of the problems emerge, but other problems persist.Peer Reviewe

Spectroscopy of Ne 19 for the thermonuclear O 15 (alfa,gamma) Ne 19 and F 18 (pi,alfa) O 15 reaction rates

Uncertainties in the thermonuclear rates of the O15(a,¿)19Ne and 18F(p,a)15O reactions affect model predictions of light curves from type I x-ray bursts and the amount of the observable radioisotope F18 produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of Ne19 over Ex=4.0-5.1 and 6.1-7.3 MeV using the F19(He3,t)Ne19 reaction. We find the Jp values of the 4.14- and 4.20-MeV levels to be consistent with 9/2- and 7/2-, respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86-MeV state. Higher resolution experiments are urgently needed to further clarify the structure of Ne19 around the proton threshold before a reliable 18F(p,a)15O rate for nova models can be determined.Peer Reviewe

Reaction Rates of 64Ge(p,g)65As and 65As(p,g)66Se and the Extent of Nucleosynthesis in Type I X-Ray Bursts

The extent of nucleosynthesis in models of type I X-ray bursts (XRBs) and the associated impact on the energy released in these explosive events are sensitive to nuclear masses and reaction rates around the 64Ge waiting point. Using the well known mass of 64Ge, the recently measured 65As mass, and large-scale shell model calculations, we have determined new thermonuclear rates of the 64Ge(p,¿)65As and 65As(p,¿)66Se reactions with reliable uncertainties. The new reaction rates differ significantly from previously published rates. Using the new data, we analyze the impact of the new rates and the remaining nuclear physics uncertainties on the 64Ge waiting point in a number of representative one-zone XRB models. We find that in contrast to previous work, when all relevant uncertainties are considered, a strong 64Ge rp-process waiting point cannot be ruled out. The nuclear physics uncertainties strongly affect XRB model predictions of the synthesis of 64Zn, the synthesis of nuclei beyond A = 64, the energy generation, and the burst light curve. We also identify key nuclear uncertainties that need to be addressed to determine the role of the 64Ge waiting point in XRBs. These include the remaining uncertainty in the 65As mass, the uncertainty of the 66Se mass, and the remaining uncertainty in the 65As(p,¿)66Se reaction rate, which mainly originates from uncertain resonance energieSPeer Reviewe

The 20Ne(d,p)21Ne transfer reaction in relation to the s-process abundances

Nuclear Physics in Astrophysics VI (NPA6) , 19–24 May 2013, Lisbon, PortugalA study of the 20Ne(d,p)21Ne transfer reaction was performed using the Quadrupole Dipole Dipole Dipole (Q3D) magnetic spectrograph in Garching, Germany. The experiment probed excitation energies in 21Ne ranging from 6.9 MeV to 8.5 MeV. The aim was to investigate the spectroscopic information of 21Ne within the Gamow window of core helium burning in massive stars. Further information in this region will help reduce the uncertainties on the extrapolation down to Gamow window cross sections of the 17 O(alfa,gamma)21Ne reaction. In low metallicity stars, this reaction has a direct impact on s-process abundances by determining the fate of 16O as either a neutron poison or a neutron absorber. The experiment used a 22-MeV deuteron beam, with intensities varying from 0.5-1 miA, and an implanted target of 20Ne of 7 microg/cm2 in 40 microg/cm2 carbon foils. Sixteen 21Ne peaks have been identified in the Ex = 6.9-8.5 MeV range, of which only thirteen peaks correspond to known states. Only the previously-known Ex = 7.960 MeV state was observed within the Gamow window.Peer Reviewe