The influence of the initial composition of the exploding white dwarf on the nucleosynthesis, light curves and spectra of Type Ia supernovae has been studied in order to evaluate the size of evolutionary effects on cosmological time scales, how the effects can be recognized and how one may be able to correct for them.The calculations are based on a set of delayed detonation models which give a good account of the optical and infrared light curves and of the spectral evolution. The explosions and light curves are calculated using a one-dimensional Lagrangian radiation-hydro code including a nuclear network. Spectra are computed for various epochs using the structure resulting from the light curve code. Our NLTE code solves the relativistic radiation transport equations in the comoving frame consistently with the statistical equations and ionization due to γ radiation for the most important elements (C, O, Ne, Na, Mg, Si, S, Ca, Fe, Co, Ni). About 1,000,000 additional lines are included assuming LTE-level populations and an equivalent-two-level approach for the source functions.Changing the initial metallicity Z from Population I to II alters the isotopic composition of the outer layers of the ejecta that have undergone explosive O burning. Especially important is the increase of the 54 Fe production with metallicity. The influence on the resulting rest frame visual and blue light curves is found to be small. Detailed analysis of spectral evolution should permit a determination of the progenitor metallicity.Mixing 56 N i into the outer layers during the explosion can produce effects similar to an increased initial metallicity. Mixing can be distinguished from metallicity effects by means of the strong cobalt and nickel lines, by a change of the calcium lines in the optical and IR spectra and, in principle, by γ-ray observations.As the C/O ratio of the WD is decreased, the explosion energy and the 56 Ni production are reduced and the Si-rich layers are more confined in velocity space. A reduction of C/O by about 60 % gives slower rise times by about 3 days, an increased luminosity at maximum light, a somewhat faster post-maximum decline and a larger ratio between maximum light and 56 Ni tail. A reduction of the C/O ratio has a similar effect on the colors, light curve shapes and element distribution as a reduction in the deflagration to detonation transition density but, for the same light curve shape, the absolute brightness is larger for smaller C/O. An independent determination of the initial C/O ratio and the transition density is possible for local SN if detailed analyses of both the spectra and light curves are performed simultaneously.Because the spectra are shifted into different color bands at different redshifts, the effect of metallicity Z on a given observed color is a strong function of redshift. A change of Z by a factor of 3 or the C/O ratio by 33 % alters the peak magnitudes in the optical wavelength range by up to ≈ 0.3 m for z ≥ 0.2. These variations are comparable to the effect of changes of Ω M a...

We outline the possible physical processes, associated timescales, and energetics that could lead to the production of pulsars, jets, asymmetric supernovae, and weak γ-ray bursts in routine circumstances and to a 10 16 G magnetar and perhaps stronger γ-ray burst in more extreme circumstances in the collapse of the bare core of a massive star. The production of a LeBlanc-Wilson MHD jet could provide an asymmetric supernova and result in a weak γ-ray burst when the jet accelerates down the stellar density gradient of a hydrogen-poor photosphere. The matter-dominated jet would be formed promptly, but requires 5 to 10 s to reach the surface of the progenitor of a Type Ib/c supernova. During this time, the newly-born neutron star could contract, spin up, and wind up field lines or turn on an α − Ω dynamo. In addition, the light cylinder will contract from a radius large compared to the Alfvén radius to a size comparable to that of the neutron star. This will disrupt the structure of any organized dipole field and promote the generation of ultrarelativistic MHD Waves (UMHDW) at high density and Large Amplitude Electromagnetic Waves (LAEMW) at low density. The generation of these waves would be delayed by the cooling time of the neutron star ≃ 5 to 10 seconds, but the propagation time is short so the UMHDW could arrive at the surface at about the same time as the matter jet. In the density gradient of the star and the matter jet, the intense flux of UMHDW and LAEMW could drive shocks, generate pions by proton-proton collision, or create electron/positron pairs depending on the circumstances. The UMHDW and LAEMW could influence the dynamics of the explosion and might also tend to flow out the rotation axis to produce a collimated γ-ray burst.

Near-infrared (NIR) spectra of the subluminous Type Ia supernova SN 1999by are presented which cover the time evolution from about 4 days before to 2 weeks after maximum light. Analysis of these data was accomplished through the construction of an extended set of delayed detonation (DD) models covering the entire range of normal to subluminous SNe Ia. The explosion, light curves (LC), and the time evolution of the synthetic spectra were calculated self-consistently for each model with the only free parameters being the initial structure of the white dwarf (WD) and the description of the nuclear burning front during the explosion. From these, one model was selected for SN 1999by by matching the synthetic and observed optical light curves, principly the rapid brightness decline. DD models require a minimum amount of burning during the deflagration phase which implies a lower limit for the 56 N i mass of about 0.1M ⊙ and consequently a lower limit for the SN brightness. The models which best match the optical light curve of SN 1999by were those with a 56