Initiation of the detonation in the gravitationally confined detonation model of Type Ia supernovae

We study the initiation of the detonation in the gravitationally confined detonation (GCD) model of Type Ia supernovae (SNe Ia). Initiation of the detonation occurs spontaneously in a region where the length scale of the temperature gradient extending from a flow (in which carbon burning is already occurring) into unburned fuel is commensurate to the range of critical length scales which have been derived from 1D simulations that resolve the initiation of a detonation. By increasing the maximum resolution in a truncated cone that encompasses this region, beginning somewhat before initiation of the detonation occurs, we successfully simulate in situ the first gradient-initiated detonation in a whole-star simulation. The detonation emerges when a compression wave overruns a pocket of fuel situated in a Kelvin-Helmholtz cusp at the leading edge of the inwardly directed jet of burning carbon. The compression wave pre-conditions the temperature in the fuel in such a way that the Zel'dovich gradient mechanism can operate and a detonation ensues. We explore the dependence of the length scale of the temperature gradient on spatial resolution and discuss the implications for the robustness of this detonation mechanism. We find that the time and the location at which initiation of the detonation occurs varies with resolution. In particular, initiation of a detonation had not yet occurred in our highest resolution simulation by the time we ended the simulation because of the computational demand it required. We suggest that the turbulent shear layer surrounding the inwardly directed jet provides the most favorable physical conditions, and therefore the most likely location, for initiation of a detonation in the GCD model.Comment: 28 pages, 12 figures, 1 table, accepted to Ap

Mixed configuration-interaction and many-body perturbation theory calculations of energies and oscillator strengths of J=1 odd states of neon

Ab-initio theory is developed for energies of J=1 particle-hole states of neutral neon and for oscillator strengths of transitions from such states to the J=0 ground state. Hole energies of low-Z neonlike ions are evaluated.Comment: 5 pages, 1 figure, 4 table

EUV intercombination transition rates in Be-like nitrogen and oxygen ions measured at a heavy-ion storage ring

The electric dipole intercombination decay rate of the 2s2p 3Po1 level in the Be-like ions N3+ and O4+ has been measured with ions circulating in a heavy-ion storage ring. The observation employed three devices in parallel, two different VUV photon detectors and a residual gas recoil ion detector. The measured transition probabilities of (578 ± 3.3) s-1 for N3+ (level lifetime τ = 1.73 ± 0.01 ms) and of (2315 ± 50) s-1 for O4+ (τ = 0.432 ± 0.009 ms), corroborate the results of recent calculations and improve the precision with which the isoelectronic trend can be established

High Photoluminescence In Erbium-Doped Chalcogenide Thin Films

The spectral properties of the chalcogenide glasses As2S3 and As24S38Se38-doped with Er3+ are presented and discussed. Thin films were formed by thermal evaporation and the erbium doping was obtained by subsequent ion implantation. Strong Er3+ emission at 1.54 μm has been observed. The high refractive index of these chalcogenide glasses lead to Er3+ emission cross-sections (15 × 10-21 cm2) which are two times higher than for doped silica glass. The lifetime of the Er3+ metastable 4I13/2 energy level was measured to be 2.3 ms. This short lifetime is consistent with the high emission cross-section. Furthermore, the very low phonon energies of chalcogenide glasses lead to relatively long lifetimes of the Er3+4I11/2 pump level, which have been measured to be of the order of 0.25 ms. These spectral properties make this glass a good candidate for applications in the field of integrated optics. © 2000 Elsevier Science B.V. All rights reserved