Explosive Burning Research Articles

16O(p,α)13N makes explosive oxygen burning sensitive to the metallicity of the progenitors of type Ia supernovae

Even though the main nucleosynthetic products of type Ia supernovae belong to the iron-group, intermediate-mass alpha-nuclei (silicon, sulfur, argon, and calcium) stand out in their spectra up to several weeks past maximum brightness. Recent measurements of the abundances of calcium, argon, and sulfur in type Ia supernova remnants have been interpreted in terms of metallicity-dependent oxygen burning, in accordance with previous theoretical predictions. It is known that α-rich oxygen burning results from 16O→12C followed by efficient 12C+12C fusion reaction, as compared to oxygen consumption by 16O fusion reactions, but the precise mechanism of dependence on the progenitor metallicity has remained unidentified so far. I show that the chain 16O(p,α)13N(γ,p)12C boosts α-rich oxygen burning when the proton abundance is large, increasing the synthesis of argon and calcium with respect to sulfur and silicon. For high-metallicity progenitors, the presence of free neutrons leads to a drop in the proton abundance and the above chain is not efficient. Although the rate of 16O(p,α)13N can be found in astrophysical reaction rate libraries, its uncertainty is unconstrained. Assuming that all reaction rates other than 16O(p,α)13N retain their standard values, an increase by a factor of approximately seven of the 16O(p,α)13N rate at temperatures in the order 3−5 × 109 K is enough to explain the whole range of calcium-to-sulfur mass ratios measured in Milky Way and LMC supernova remnants. These same measurements provide a lower limit to the 16O(p,α)13N rate in the mentioned temperature range, on the order of a factor of 0.5 with respect to the rate reported in widely used literature tabulations.

Initiation Thresholds and Dynamic Characteristics of an Explosion for Thin Samples of PETN-Al Composites under Laser Irradiation

In this paper, we measured thresholds Hcr of explosive decomposition of thin (h = 1 mm) samples of PETN-Al composites with densities in the range of ρ = 0.9–1.7 g/cm3 and variations in the concentration of aluminum inclusions in the range of 0.025–1.0 wt % upon exposure to pulses of a neodymium laser (λ = 1064 nm, 14 ns). For each ρ, inclusion concentrations nopt, at which the threshold for explosive decomposition of Hcr is minimal, are obtained. The velocities of air shock waves (ASWs) were determined depending on sample density ρ, and the times of the start of explosive decomposition were determined depending on the inclusion concentration. The amplitude (in relative units) and time shift of the maximal pressure of an ASW at the piezodetector are determined depending on sample density. It is concluded that the explosion is governed by the SW mechanism at high densities. As sample ρ decreases, the completeness of the explosion increases, with the most likely mechanism for small ρ being explosive burning. The efficiency of explosive decomposition is higher for samples with lower densities.

Role of ozone doping in the explosion limits of hydrogen-oxygen mixtures: Multiplicity and catalyticity

Effects of ozone doping on the Z-shaped explosion boundary of stoichiometric hydrogen-oxygen mixtures are computationally studied. Results show that with increasing ozone doping and within a small range of increment, the explosion limit transitions from the Z-shaped response with two turning points to responses exhibiting four, six, four, two and none turning points. By modifying the rate coefficients of the sensitive reactions within the ozone sub-mechanism, four reactions are identified to control the above highly non-monotonic behavior, and that the system transitions to the H2O3 chemistry as the limit becomes monotonic and overall more explosive. The practical implication is that there exists a critical range of ozone doping such that the mixture is more sensitive to unstable burning for lower levels of doping, with the associated multiple transition states, while the facilitating role of ozone catalyticity is fully realized with just slightly higher levels of doping, resulting in overall stronger explosive burning.

Пороги инициирования и динамические характеристики взрыва для тонких образцов композитов ТЭН-Al при лазерном воздействии

AbstractIn this paper, we measured thresholds H _cr of explosive decomposition of thin ( h = 1 mm) samples of PETN-Al composites with densities in the range of ρ = 0.9–1.7 g/cm^3 and variations in the concentration of aluminum inclusions in the range of 0.025–1.0 wt % upon exposure to pulses of a neodymium laser (λ = 1064 nm, 14 ns). For each ρ, inclusion concentrations n _opt, at which the threshold for explosive decomposition of H _cr is minimal, are obtained. The velocities of air shock waves (ASWs) were determined depending on sample density ρ, and the times of the start of explosive decomposition were determined depending on the inclusion concentration. The amplitude (in relative units) and time shift of the maximal pressure of an ASW at the piezodetector are determined depending on sample density. It is concluded that the explosion is governed by the SW mechanism at high densities. As sample ρ decreases, the completeness of the explosion increases, with the most likely mechanism for small ρ being explosive burning. The efficiency of explosive decomposition is higher for samples with lower densities.

Detonation of Low-Density Explosives

Electromagnetic measurements of the particle velocity are performed in a situation when the detonation wave reaches the interface between a powdered high explosive (HE) and a window made of an inert material (Plexiglas). PETN, RDX, and HMX with densities close to the natural bulk density are studied. In order to measure not only the averaged velocity profile, but also possible fluctuations at scales of the order of the HE grain size, small sensors with the working arm length approximately 1 mm are used. In most experiments, profiles with clear chemical spikes are obtained; in some of the measured results, however, the chemical spike cannot be detected on the background of strong signal oscillations, which may be considered as manifestation of the nonclassical mechanism of wave propagation (explosive burning suggested by Apin). Along withour previous study, the present results suggest parallel operation of the shock and convective mechanisms with domination of each mechanism at different segments of the wave front.

Gamma-ray observations of Nova Sgr 2015 No. 2 with INTEGRAL

Context. INTEGRAL observed Nova Sgr 2015 No. 2 (V5668 Sgr) around the time of its optical emission maximum on 21 March 2015. Studies at UV wavelengths showed spectral lines of freshly produced 7Be. This could also be measurable in gamma rays at 478 keV from the decay to 7Li. Novae are also expected to synthesise 22Na which decays to 22Ne, emitting a 1275 keV photon. About one week before the optical maximum, a strong gamma-ray flash on timescales of hours is expected from short-lived radioactive nuclei such as 13N and 18F. These nuclei are β+-unstable, and should yield emission of up to 511 keV, but this emission has never been observed from any nova. Aims. The SPectrometer on INTEGRAL (SPI) pointed towards V5668 Sgr by chance. We use these observations to search for possible gamma-ray emission of decaying 7Be, and to directly measure the synthesised mass during explosive burning. We also aim to constrain possible burst-like emission days to weeks before the optical maximum using the SPI anticoincidence shield (ACS), i.e. at times when SPI was not pointing to the source. Methods. We extracted spectral and temporal information to determine the fluxes of gamma-ray lines at 478 keV, 511 keV, and 1275 keV. Using distance and radioactive decay, a measured flux converts into the 7Be amount produced in the nova. The SPI-ACS rates are analysed for burst-like emission using a nova model light curve. For the obtained nova flash candidate events, we discuss possible origins using directional, spectral, and temporal information. Results. No significant excess for the 478 keV, the 511 keV, or the 1275 keV lines is found. Our upper limits (3σ) on the synthesised 7Be and 22Na mass depend on the uncertainties of the distance to V5668 Sgr: the 7Be mass is constrained to less than 4.8 × 10−9 (dkpc−1)2 M⊙, and the 22Na mass to less than 2.4 × 10−8 (dkpc−1)2 M⊙. For the 7Be mass estimate from UV studies, the distance to V5668 Sgr must be greater than 1.2 kpc (3σ). During the three weeks before the optical maximum, we find 23 burst-like events in the ACS rate, of which 6 could possibly be associated with V5668.

How were the heavy chemical elements beyond iron made in the Universe?

Nuclear astrophysics, which is an interdisciplinary branch of nuclear physics (micro scale) and astrophysics (macro scale), addresses some of the most compelling questions in the universe. Research efforts have been devoted to many topics such as the origins of the chemical elements, the unique conditions of earth that makes life possible, and the formation and evolution of the sun, stars, and galaxies. Nuclear processes play an extremely important role in cosmic evolution after the Big Bang, and they are the only known mechanisms that synthesize heavy elements, in addition to providing the energy for stars to resist the force of gravity. Over the past 50 years, scientists have developed a deep understanding of Big-Bang primordial nucleosynthesis and the mechanisms for synthesizing heavy elements. However, the astrophysical models have yet to adequately reproduce the observed solar abundances of those elements beyond iron (referred to as ultra-iron elements). It is widely believed that these ultra-iron elements were primarily synthesized via the slow neutron capture process (s-process) and the fast neutron capture process (r-process). The fundamental s-process component is thought to originate from thermally pulsing low-mass AGB stars, with reaction pathways closed after the stable nuclides. About half of the heavy elements (up to bismuth) were produced via the s-process. The r-process is thought to occur in the explosive burning of core-collapse supernova and/or neutron-star mergers. Although the r-process site remains a mystery, experts believe that more than half of the ultra-iron elements (up to thorium and uranium) were produced via the r-process. In addition, there are 35 neutron-deficient stable isotopes, which are present in significantly less abundance in our solar system. These so-called p-nuclei are likely produced in Type II supernova, through the photo-dissociation (referred to as p-process or r-process) of existing s- or r-process seeds, or through the recently proposed neutrino-proton v p-process. Astrophysical models require a huge amount of nuclear-physics input data. The most essential data include nuclear mass, structure, decay and fission characteristics, and related nuclide cross-sections along the various nucleosynthesis paths. Thus far, the lack of systematic and precise nuclear inputs is one of the main reasons scientists have not been able to reproduce the observed solar abundances of ultra-iron elements. Published by Discover magazine in 2002, the American National Research Council ranked the question, how were the heavy elements from iron to uranium made? as one of the 11 Greatest Unanswered Questions of Physics in this Century . More complete and precise nuclear physics inputs are therefore urgently needed to improve astrophysical models and decode the observations. This paper introduces the most important nucleosynthesis processes that are responsible for the ultra-iron elements production in the universe, while also summarizing the relevant key nuclear-physics inputs required in the astrophysical models. Finally, the frontier in this field study includes the origins of ultra-iron elements, and the future of nuclear astrophysics research in China is examined.

Direct measurement of resonance strengths inS34(α,γ)Ar38at astrophysically relevant energies using the DRAGON recoil separator

Background: Nucleosynthesis of mid-mass elements is thought to occur under hot and explosive astrophysical conditions. Radiative α capture on S34 has been shown to impact nucleosynthesis in several such conditions, including core and shell oxygen burning, explosive oxygen burning, and type Ia supernovae. Purpose: Broad uncertainties exist in the literature for the strengths of three resonances within the astrophysically relevant energy range (ECM=1.94-3.42MeV at T=2.2GK). Further, there are several states in Ar38 within this energy range which have not been previously measured. This work aimed to remeasure the resonance strengths of states for which broad uncertainty existed as well as to measure the resonance strengths and energies of previously unmeasured states. Methods: Resonance strengths and energies of eight narrow resonances (five of which had not been previously studied) were measured in inverse kinematics with the DRAGON facility at TRIUMF by impinging an isotopically pure beam of S34 ions on a windowless He4 gas target. Prompt γ emissions of de-exciting Ar38 recoils were detected in an array of bismuth germanate scintillators in coincidence with recoil nuclei, which were separated from unreacted beam ions by an electromagnetic mass separator and detected by a time-of-flight system and a multianode ionization chamber. Results: The present measurements agree with previous results. Broad uncertainty in the resonance strength of the ECM=2709keV resonance persists. Resonance strengths and energies were determined for five low-energy resonances which had not been studied previously, and their strengths were determined to be significantly weaker than those of previously measured resonances. Conclusions: The five previously unmeasured resonances were found not to contribute significantly to the total thermonuclear reaction rate. A median total thermonuclear reaction rate calculated using data from the present work along with existing literature values using the STARLIB rate calculator agrees with the NON-SMOKER statistical model calculation as well as the REACLIB and STARLIB library rates at explosive and nonexplosive oxygen-burning temperatures (T=3-4GK and T=1.5-2.7GK, respectively).

The History and Impact of the CNO Cycles in Nuclear Astrophysics

The carbon cycle, or Bethe-Weizsacker cycle, plays an important role in astrophysics as one of the most important energy sources for quiescent and explosive hydrogen burning in stars. This paper presents the intellectual and historical background of the idea of the correlation between stellar energy production and the synthesis of the chemical elements in stars on the example of this cycle. In particular, it addresses the contributions of Carl Friedrich von Weizsacker and Hans Bethe, who provided the first predictions of the carbon cycle. Further, the experimental verification of the predicted process as it developed over the following decades is discussed, as well as the extension of the initial carbon cycle to the carbon-nitrogen-oxygen (CNO) multi-cycles and the hot CNO cycles. This development emerged from the detailed experimental studies of the associated nuclear reactions over more than seven decades. Finally, the impact of the experimental and theoretical results on our present understanding of hydrogen burning in different stellar environments is presented, as well as the impact on our understanding of the chemical evolution of our universe.

Experimental Approach to Explosive Hydrogen Burning in X-Ray Bursts and Core-Collapse Supernovae

Recent experimental challenges to study the explosive hydrogen burning at extremely high temperatures are discussed. Along the nucleosynthetic pathway, discussions were made especially for the medium mass region, where we have possible waiting points and bottle necks which influence not only the light curve but also the production of heavy elements including the anomalously abundant p-nuclei at A = 80-100. Two approaches were discussed for the problem; one is the precision mass measurements and the other one is the half-live measurement of very short lived isotopes. A scope of the field is also discussed.

Role of nuclear reactions on stellar evolution of intermediate-mass stars

The evolution of intermediate-mass stars (8 - 12 solar masses) represents one of the most challenging subjects in nuclear astrophysics. Their final fate is highly uncertain and strongly model dependent. They can become white dwarfs, they can undergo electron-capture or core-collapse supernovae or they might even proceed towards explosive oxygen burning and a subsequent thermonuclear explosion. We believe that an accurate description of nuclear reactions is crucial for the determination of the pre-supernova structure of these stars. We argue that due to the possible development of an oxygen-deflagration, a hydrodynamic description has to be used. We implement a nuclear reaction network with ∼200 nuclear species into the implicit hydrodynamic code AGILE. The reaction network considers all relevant nuclear electron captures and beta-decays. For selected relevant nuclear species, we include a set of updated reaction rates, for which we discuss the role for the evolution of the stellar core, at the example of selected stellar models. We find that the final fate of these intermediate-mass stars depends sensitively on the density threshold for weak processes that deleptonize the core.

Study of the Characteristics of Elementary Processes in a Chain Hydrogen Burning Reaction in Oxygen

The characteristics of possible chain explosive hydrogen burning reactions in an oxidizing medium are calculated on the potential energy surface. Specifically, reactions H2 + O2 → H2O + O, H2 + O2 → HO2 + H, and H2 + O2 → OH + OH are considered. Special attention is devoted to the production of a pair of fast highly reactive OH radicals. Because of the high activation threshold, this reaction is often excluded from the known kinetic scheme of hydrogen burning. However, a spread in estimates of kinetic characteristics and a disagreement between theoretical predictions with experimental results suggest that the kinetic scheme should be refined.

Mass retention efficiencies of He accretion onto carbon-oxygen white dwarfs and type Ia supernovae

Type Ia supernovae (SNe Ia) play a crucial role in studying cosmology and galactic chemical evolution. They are thought to be thermonuclear explosions of carbon-oxygen white dwarfs (CO WDs) when their masses reach the Chandrasekar mass limit in binaries. Previous studies have suggested that He novae may be progenitor candidates of SNe Ia. However, the mass retention efficiencies during He nova outbursts are still uncertain. In this article, we aim to study the mass retention efficiencies of He nova outbursts and to investigate whether SNe Ia can be produced through He nova outbursts. Using the stellar evolution code Modules for Experiments in Stellar Astrophysics, we simulated a series of multicycle He-layer flashes, in which the initial WD masses range from 0.7 to 1.35 Msun with various accretion rates. We obtained the mass retention efficiencies of He nova outbursts for various initial WD masses, which can be used in the binary population synthesis studies. In our simulations, He nova outbursts can increase the mass of the WD to the Chandrasekar mass limit and the explosive carbon burning can be triggered in the center of the WD; this suggests that He nova outbursts can produce SNe Ia. Meanwhile, the mass retention efficiencies in the present work are lower than those of previous studies, which leads to a lower birthrates of SNe Ia through the WD + He star channel. Furthermore, we obtained the elemental abundances distribution at the moment of explosive carbon burning, which can be used as the initial input parameters in studying explosion models of SNe Ia.

Helium ignition in rotating magnetized CO white dwarfs leading to fast and faint rather than classical Type Ia supernovae

Based mostly on stellar models which do not include rotation, CO white dwarfs which accrete helium at rates of about $\sim 10^{-8}~\mathrm{M}_\odot/\mathrm{yr}$ have been put forward as candidate progenitors for a number of transient astrophysical phenomena, including supernovae of Type Ia, and the peculiar and fainter Type Iax supernovae. Here we study the impact of accretion-induced spin-up including the subsequent magnetic field generation, angular momentum transport, and viscous heating on the white dwarf evolution up to the point of helium ignition. We resolve the structure of the helium accreting white dwarf models with a one dimensional Langrangian hydrodynamic code, modified to include rotational and magnetic effects. We find magnetic angular momentum transport, which leads to quasi solid-body rotation, profoundly impacts the evolution of the white dwarf models. Our rotating lower mass ($0.54$ and $0.82~\mathrm{M}_\odot$) models accrete up to 50\% more mass up to ignition compared to the non-rotating case and the opposite for our more massive models. Furthermore, we find that rotation leads to up to 10-times smaller helium ignition densities, except for the lowest adopted initial white dwarf mass. Ignition densities of order $10^6\,\mathrm{g/cm}^3$ are only found for the lowest accretion rates and for large amounts of accreted helium $\gtrsim 0.4\,\mathrm{M}_\odot$. However, correspondingly massive donor stars would transfer mass at much higher rates. We expect explosive He-shell burning to mostly occur as deflagrations and at $\dot{M}>2\cdot10^{-8}~\mathrm{M}_\odot/\mathrm{yr}$, regardless of white dwarf mass. Our results imply that helium accretion onto CO white dwarfs at the considered rates is unlikely to lead to explosions of the CO core or to classical Type,Ia supernovae, but may instead produce events like faint and fast hydrogen-free supernovae.

Does Explosive Nuclear Burning Occur in Tidal Disruption Events of White Dwarfs by Intermediate-mass Black Holes?

Abstract We investigate nucleosynthesis in tidal disruption events (TDEs) of white dwarfs (WDs) by intermediate-mass black holes. We consider various types of WDs with different masses and compositions by means of three-dimensional (3D) smoothed particle hydrodynamics (SPH) simulations. We model these WDs with different numbers of SPH particles, N, from a few 104 to a few 107 in order to check mass resolution convergence, where SPH simulations with N > 107 (or a space resolution of several 106 cm) have unprecedentedly high resolution in this kind of simulation. We find that nuclear reactions become less active with increasing N and that these nuclear reactions are excited by spurious heating due to low resolution. Moreover, we find no shock wave generation. In order to investigate the reason for the absence of a shock wave, we additionally perform one-dimensional (1D) SPH and mesh-based simulations with a space resolution ranging from 104 to 107 cm, using a characteristic flow structure extracted from the 3D SPH simulations. We find shock waves in these 1D high-resolution simulations, one of which triggers a detonation wave. However, we must be careful of the fact that, if the shock wave emerged in an outer region, it could not trigger the detonation wave due to low density. Note that the 1D initial conditions lack accuracy to precisely determine where a shock wave emerges. We need to perform 3D simulations with ≲106 cm space resolution in order to conclude that WD TDEs become optical transients powered by radioactive nuclei.

Physics with post accelerated beams: nuclear astrophysics

In this article, recent studies so far conducted with post accelerated beams at the ISOLDE facility in the area of nuclear astrophysics are reviewed. Two experiments in particular are highlighted, that each feature novelty and innovation. Three future experiments are also briefly presented. Collectively, these works advance our understanding of big bang nucleosynthesis, quiescent and explosive burning in novae and x-ray bursts, and core-collapse supernovae, both in terms of the underlying explosion mechanism and gamma-ray satellite observable radioisotopes.

The Synthesis of 44Ti and 56Ni in Massive Stars

Abstract We discuss the influence of rotation on the combined synthesis of and in massive stars. While is significantly produced by both complete and incomplete explosive Si burning, is mainly produced by complete explosive Si burning, with a minor contribution (in standard non-rotating models) from incomplete explosive Si burning and O burning (both explosive and hydrostatic). We find that, in most cases, the thickness of the region exposed to incomplete explosive Si burning increases in rotating models (initial velocity, v ini = 300 km s−1) and since is significantly produced in this zone, the fraction of mass coming from the complete explosive Si burning zone necessary to get the required amount of reduces. Therefore the amount of ejected for a given fixed amount of decreases in rotating models. However, some rotating models at [Fe/H] = −1 develop a very extended O convective shell in which a consistent amount of is formed, preserved, and ejected in the interstellar medium. Hence a better modeling of the thermal instabilities (convection) in the advanced burning phases together with a critical analysis of the cross sections of the nuclear reactions operating in O burning are relevant for the understanding of the synthesis of .

THE ORIGIN OF THE IRON-RICH KNOT IN TYCHO’S SUPERNOVA REMNANT

ABSTRACT X-ray observations of supernova remnants (SNRs) allow us to investigate the chemical inhomogeneity of ejecta, offering unique insight into the nucleosynthesis in supernova explosions. Here we present detailed imaging and spectroscopic studies of the “Fe knot” located along the eastern rim of the Type Ia SNR Tycho (SN 1572) using Suzaku and Chandra long-exposure data. Surprisingly, the Suzaku spectrum of this knot shows no emission from Cr, Mn, or Ni, which is unusual for the Fe-rich regions in this SNR. Within the framework of the canonical delayed-detonation models for SN Ia, the observed mass ratios , , and (at 90% confidence) can only be achieved for a peak temperature of (5.3–5.7) K and a neutron excess of . These constraints rule out the deep, dense core of a Chandrasekhar-mass white dwarf as the origin of the Fe knot and favor either incomplete Si burning or an α-rich freeze-out regime, probably close to the boundary. An explosive He burning regime is a possible alternative, although this hypothesis is in conflict with the main properties of this SNR.

IMPACT OF NEW GAMOW–TELLER STRENGTHS ON EXPLOSIVE TYPE IA SUPERNOVA NUCLEOSYNTHESIS

ABSTRACT Recent experimental results have confirmed a possible reduction in the Gamow–Teller (GT+) strengths of pf-shell nuclei. These proton-rich nuclei are of relevance in the deflagration and explosive burning phases of SNe Ia. While prior GT strengths result in nucleosynthesis predictions with a lower-than-expected electron fraction, a reduction in the GT+ strength can result in a slightly increased electron fraction compared to previous shell model predictions, though the enhancement is not as large as previous enhancements in going from rates computed by Fuller, Fowler, and Newman based on an independent particle model. A shell model parametrization has been developed that more closely matches experimental GT strengths. The resultant electron-capture rates are used in nucleosynthesis calculations for carbon deflagration and explosion phases of SNe Ia, and the final mass fractions are compared to those obtained using more commonly used rates.

Detection of burning ashes from thermonuclear X-ray bursts

Abstract When neutron stars (NS) accrete gas from low-mass binary companions, explosive nuclear burning reactions in the NS envelope fuse hydrogen and helium into heavier elements. The resulting thermonuclear (type-I) X-ray bursts produce energy spectra that are fit well with black bodies, but a significant number of burst observations show deviations from Planck spectra. Here we present our analysis of RXTE/PCA observations of X-ray bursts from the NS low-mass X-ray binary HETE J1900.1-2455. We have discovered that the non-Planckian spectra are caused by photoionization edges. The anticorrelation between the strength of the edges and the colour temperature suggests that the edges are produced by the nuclear burning ashes that have been transported upwards by convection and become exposed at the photosphere. The atmosphere model fits show that occasionally the photosphere can consist entirely of metals, and that the peculiar changes in blackbody temperature and radius can be attributed to the emergence and disappearance of metals in the photosphere. As the metals are detected already in the Eddington-limited phase, it is possible that a radiatively driven wind ejects some of the burning ashes into the interstellar space.