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

We numerically studied the explosion of a supernova caused by supersonic jets present in its center. The jets are assumed to be generated by a magneto-rotational mechanism when a stellar core collapses into a neutron star. We simulated the process of the jet propagation through the star, jet breakthrough, and the ejection of the supernova envelope by the lateral shocks generated during jet propagation. The end result of the interaction is a highly nonspherical supernova explosion with two high-velocity jets of material moving in polar directions, and a slower moving, oblate, highly distorted ejecta containing most of the supernova material.

We discuss the optical spectropolarimetry of several core-collapse supernovae, SN 1996cb (Type IIB), SN 1997X (Type Ic), and SN 1998S (Type IIn). The data show polarization evolution of several spectral features at levels from 0.5% to above 4%. The observed line polarization is intrinsic to the supernovae and not of interstellar origin. These data suggest that the distribution of ejected matter is highly aspherical. In the case of the Type IIn SN 1998S, the major-to-minor axis ratio must be larger than 2.5 if the polarization is 3% from an oblate spheroidal ejecta seen edge-on. A well-deÐned symmetry axis can be deduced from spectropolarimetry for SN 1998S, but the Type IIB events SN 1993J and SN 1996cb seem to possess much more complicated geometries with polarization position angles showing larger irregular variations across spectral features ; the latter may be associated with large-scale clumpiness of the ejecta. The observed degree of polarization of the Type Ic SN 1997X is above 4%. The data reveal a trend that the degree of polarization increases with decreasing envelope mass and with the depth within the ejecta. The high axial ratio of the ejecta is difficult to explain in terms of the conventional neutrino-driven corecollapse models for Type II explosions. Highly asymmetric explosion mechanisms such as the formation of bipolar jets during core collapse may be a necessary ingredient for models of all core-collapse supernovae.

High-quality spectropolarimetry (range 417-860 nm; spectral resolution 1.27 nm and 0.265 nm/pixel) of the SN Ia 2001el were obtained with the ESO Very Large Telescope Melipal (+ FORS1) at 5 epochs. The spectra a week before maximum and around maximum indicate photospheric expansion velocities of about 10,000 km s −1 . Prior to optical maximum, the linear polarization of the continuum was ≈ 0.2 − 0.3% with a constant position angle, showing that SN 2001el has a well-defined axis of symmetry. The polarization was nearly undetectable a week after optical maximum.The spectra are similar to those of the normally-bright SN 1994D with the exception of a strong double-troughed absorption feature seen around 800 nm (FWHM about 22 nm). The 800 nm feature is probably due to the Ca II IR triplet at very high velocities (20,000 -26,000 km s −1 ) involving ∼ 0.004 M ⊙ of calcium and perhaps 0.1 M ⊙ total mass. The 800 nm feature is distinct in velocity space from the photospheric Ca II IR triplet and has a significantly higher

We present mid-infrared (MIR) observations of the Type II-plateau supernova (SN) 2004et, obtained with the Spitzer Space Telescope between 64 and 1406 days past explosion. Late-time optical spectra are also presented. For the period 300-795 days past explosion, we argue that the spectral energy distribution (SED) of SN 2004et comprises (1) a hot component due to emission from optically thick gas, as well as free-bound radiation; (2) a warm component due to newly formed, radioactively heated dust in the ejecta; and (3) a cold component due to an IR echo from the interstellar-medium dust of the host galaxy, NGC 6946. There may also have been a small contribution to the IR SED due to free-free emission from ionized gas in the ejecta. We reveal the first-ever spectroscopic evidence for silicate dust formed in the ejecta of a supernova. This is supported by our detection of a large, but progressively declining, mass of SiO. However, we conclude that the mass of directly detected ejecta dust grew to no more than a few times 10 −4 M . We also provide evidence that the ejecta dust formed in comoving clumps of fixed size. We argue that, after about two years past explosion, the appearance of wide, box-shaped optical line profiles was due to the impact of the ejecta on the progenitor circumstellar medium and that the subsequent formation of a cool, dense shell was responsible for a later rise in the MIR flux. This study demonstrates the rich, multifaceted ways in which a typical core-collapse supernova and its progenitor can produce and/or interact with dust grains. The work presented here adds to the growing number of studies that do not support the contention that SNe are responsible for the large mass of observed dust in high-redshift galaxies.

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