W. R. Hix

Reexpansion pulmonary edema.

Unilateral reexpansion pulmonary edema (RPE) is a rare complication of the treatment of lung collapse secondary to pneumothorax, pleural effusion, or atelectasis. Although RPE generally is believed to occur only when a chronically collapsed lung is rapidly reexpanded by evacuation of large amounts of air or fluid, in this review 15 of 47 cases of RPE available for assessment occurred when the pulmonary collapse was of short duration or when the lung was reexpanded without suction. The pathogenesis of RPE is unknown and is probably multifactorial. Implicated in the etiological process of RPE are chronicity of collapse, technique of reexpansion, increased pulmonary vascular permeability, airway obstruction, loss of surfactant, and pulmonary artery pressure changes. Since the outcome of RPE was fatal in 11 of 53 cases reviewed (20%), physicians treating lung collapse must be aware of the possible causes and endeavor to prevent the occurrence of this complication.

Electron capture rates on nuclei and implications for stellar core collapse

Supernova simulations to date have assumed that during core collapse electron captures occur dominantly on free protons, while captures on heavy nuclei are Pauli blocked and are ignored. We have calculated rates for electron capture on nuclei with mass numbers A=65-112 for the temperatures and densities appropriate for core collapse. We find that these rates are large enough so that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations.

Surface Hydrogen-burning Modeling of Supersoft X-Ray Binaries: Are They Type Ia Supernova Progenitors?

Nova explosions occur on the white dwarf (WD) component of a cataclysmic variable stellar system that is accreting matter lost by a companion. A Type Ia supernova (SN Ia) explosion is thought to result when a WD, in a similar binary configuration, grows in mass to the Chandrasekhar limit. Here, we present calculations of accretion of solar matter, at a variety of mass accretion rates, onto hot (2.3 × 105 K), luminous (30 L☉), massive (1.25, 1.35 M☉) carbon-oxygen WDs. In contrast to our nova simulations, where the WD has a low initial luminosity and a thermonuclear runaway (TNR) occurs and ejects material, these simulations do not eject material (or only a small fraction of the accreted material), and the WD grows in mass. A hydrogen TNR does not occur because hydrogen fuses to helium in the surface layers, and we call this process surface hydrogen burning (SHB). As the helium layer grows in mass, it gradually fuses either to carbon and oxygen or to more massive nuclei, depending on the WD mass and mass accretion rate. If such a WD were to explode in a SN Ia event, therefore, it would show neither hydrogen nor helium in its spectrum as is observed. Moreover, the luminosities and effective temperatures of our simulations agree with the observations of some of the supersoft X-ray binary sources, and therefore, our results strengthen previous speculation that some of them (CAL 83 and CAL 87, for example) are probably progenitors of SN Ia explosions. Finally, we have achieved SHB for values of the mass accretion rate that almost span the observed values of the cataclysmic variables.

THE EFFECTS OF THE pep NUCLEAR REACTION AND OTHER IMPROVEMENTS IN THE NUCLEAR REACTION RATE LIBRARY ON SIMULATIONS OF THE CLASSICAL NOVA OUTBURST

Nova explosions occur on the white dwarf (WD) component of a cataclysmic variable binary stellar system which is accreting matter lost by its companion. When sufficient material has been accreted by the WD, a thermonuclear runaway (TNR) occurs and ejects material in what is observed as a classical nova (CN) explosion. We have continued our studies of TNRs on 1.25 M ☉ and 1.35 M ☉ WDs (ONeMg composition) under conditions which produce mass ejection and a rapid increase in the emitted light, by examining the effects of changes in the nuclear reaction rates on both the observable features and the nucleosynthesis during the outburst. In order to improve our calculations over previous work, we have incorporated a modern nuclear reaction network into our one-dimensional, fully implicit, hydrodynamic computer code. We find that the updates in the nuclear reaction rate libraries change the amount of ejected mass, peak luminosity, and the resulting nucleosynthesis. Because the evolutionary sequences on the 1.35 M ☉ WD reach higher temperatures, the effects of library changes are more important for this mass. In addition, as a result of our improvements, we discovered that the pep reaction (p + e – + p → d + ν) was not included in our previous studies of CN explosions (or to the best of our knowledge those of other investigators). Although the energy production from this reaction is not important in the Sun, the densities in WD envelopes can exceed 104 g cm–3 and the presence of this reaction increases the energy generation during the time that the p-p chain is operating. Since it is only the p-p chain that is operating during most of the accretion phase prior to the final rise to the TNR, the effect of the increased energy generation is to reduce the evolution time to the peak of the TNR and, thereby, the accreted mass as compared to the evolutionary sequences done without this reaction included. As expected from our previous work, the reduction in accreted mass has important consequences on the characteristics of the resulting TNR and is discussed in this paper.

Strong neutrino cooling by cycles of electron capture and β- decay in neutron star crusts.

The temperature in the crust of an accreting neutron star, which comprises its outermost kilometre, is set by heating from nuclear reactions at large densities, neutrino cooling and heat transport from the interior. The heated crust has been thought to affect observable phenomena at shallower depths, such as thermonuclear bursts in the accreted envelope. Here we report that cycles of electron capture and its inverse, β− decay, involving neutron-rich nuclei at a typical depth of about 150u2009metres, cool the outer neutron star crust by emitting neutrinos while also thermally decoupling the surface layers from the deeper crust. This ‘Urca’ mechanism has been studied in the context of white dwarfs and type Ia supernovae, but hitherto was not considered in neutron stars, because previous models computed the crust reactions using a zero-temperature approximation and assumed that only a single nuclear species was present at any given depth. The thermal decoupling means that X-ray bursts and other surface phenomena are largely independent of the strength of deep crustal heating. The unexpectedly short recurrence times, of the order of years, observed for very energetic thermonuclear superbursts are therefore not an indicator of a hot crust, but may point instead to an unknown local heating mechanism near the neutron star surface.

The neutrino signal in stellar core collapse and postbounce evolution

Abstract General relativistic multi-group and multi-flavor Boltzmann neutrino transport in spherical symmetry adds a new level of detail to the numerical bridge between microscopic nuclear and weak interaction physics and the macroscopic evolution of the astrophysical object. Although no supernova explosions are obtained, we investigate the neutrino luminosities in various phases of the postbounce evolution for a wide range of progenitor stars between 13 and 40 solar masses. The signal probes the dynamics of material layered in and around the protoneutron star and is, within narrow limits, sensitive to improvements in the weak interaction physics. Only changes that dramatically exceed physical limitations allow experiments with exploding models. We discuss the differences in the neutrino signal and find the electron fraction in the innermost eject to exceed 0.5 as a consequence of thermal balance and weak equilibrium at the masscut.

Neutral-current neutrino–nucleus cross sections for A∼50–65 nuclei

Abstract We study neutral-current neutrino–nucleus reaction cross sections for Mn, Fe, Co and Ni isotopes. An earlier study for a few selected nuclei has shown that in the supernova environment the cross sections are increased for low energy neutrinos due to finite-temperature effects. Our work supports this finding for a much larger set of nuclei. Furthermore we extend previous work to higher neutrino energies considering allowed and forbidden multipole contributions to the cross sections. The allowed contributions are derived from large-scale shell model calculations of the Gamow–Teller strength, while the other multipole contributions are calculated within the random phase approximation. We present the cross sections as functions of initial and final neutrino energies and for a range of supernova-relevant temperatures. These cross sections will allow improved estimates of inelastic neutrino reactions on nuclei in supernova simulations.

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

Proton capture by 17F plays an important role in the synthesis of nuclei in nova explosions. A revised rate for this reaction, based on a measurement of the 1H(17F, p)17F excitation function using a radioactive 17F beam at Oak Ridge National Laboratorys Holifield Radioactive Ion Beam Facility, is used to calculate the nucleosynthesis in nova outbursts on the surfaces of 1.25 and 1.35 M☉ ONeMg white dwarfs and a 1.00 M☉ CO white dwarf. We find that the new 17F (p, γ)18Ne reaction rate changes the abundances of some nuclides (e.g., 17O) synthesized in the hottest zones of an explosion on a 1.35 M☉ white dwarf by more than a factor of 104 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 18Ne by 21% but has negligible effect on all other nuclides. Comparison of model predictions with observations is also discussed.

Impact of nuclear reaction rate uncertainties on Nova models

Abstract We have, for the first time, determined the effect of nuclear reactions rate uncertainties on nova model predictions by simultaneously considering uncertainties in all relevant reaction rates. Our unique Monte Carlo approach enables a robust determination of uncertainties of nuclear origin in predictions of synthetized abundances, including radioisotopes which may be observable. This technique also enables us to identify which reactions most influence the production of each isotope, thereby guiding future measurements.

The thermonuclear runaway and the classical nova outburst

Nova explosions occur on the white dwarf component of a Cataclysmic Variable binary stellar system that is accreting matter lost by its companion. When sufficient material has been accreted by the white dwarf, a thermonuclear runaway occurs and ejects material in what is observed as a Classical Nova explosion. We describe both the recent advances in our understanding of the progress of the outburst and outline some of the puzzles that are still outstanding. We report on the effects of improving both the nuclear reaction rate library and including a modern nuclear reaction network in our one-dimensional, fully implicit, hydrodynamic computer code. In addition, there has been progress in observational studies of Supernovae Ia with implications about the progenitors and we discuss that in this review.