An alternative symbiotic channel to Type Ia supernovae

By assuming an aspherical stellar wind with an equatorial disc from a red giant, we investigate the production of Type Ia supernovae (SNe Ia) via a symbiotic channel. We estimate that the Galactic birthrate of SNe Ia via the symbiotic channel is between  1.03 × 10⁻³  and  2.27 × 10⁻⁵ yr⁻¹  , while the delay time of SNe Ia has a wide range from ∼0.07 to 5 Gyr. The results are greatly affected by the outflow velocity and mass-loss rate of the equatorial disc. Using our model, we discuss the progenitors of SN 2002ic and SN 2006X.     

Light curves for off-centre ignition models of Type Ia supernovae

We compare observations of the high-redshift galaxy population to the predictions of the galaxy formation model of Croton et al. and De Lucia & Blaizot. This model, implemented on the Millennium Simulation of the concordance Lambda cold dark matter cosmogony, introduces 'radio mode' feedback from the central galaxies of groups and clusters in order to obtain quantitative agreement with the luminosity, colour, morphology and clustering properties of the present-day galaxy population. Here we construct deep light cone surveys in order to compare model predictions to the observed counts and redshift distributions of distant galaxies, as well as to their inferred luminosity and mass functions out to redshift 5. With the exception of the mass functions, all these properties are sensitive to modelling of dust obscuration. A simple but plausible treatment agrees moderately well with most of the data. The predicted abundance of relatively massive  (∼ M _*)  galaxies appears systematically high at high redshift, suggesting that such galaxies assemble earlier in this model than in the real Universe. An independent galaxy formation model implemented on the same simulation matches the observed mass functions slightly better, so the discrepancy probably reflects incomplete or inaccurate galaxy formation physics rather than problems with the underlying cosmogony.     

Determining the motion of the Solar system relative to the cosmic microwave background using Type Ia supernovae

We estimate the Solar system motion relative to the cosmic microwave background using Type Ia supernovae (SNe) measurements. We take into account the correlations in the error bars of the SNe measurements arising from correlated peculiar velocities. Without accounting for correlations in the peculiar velocities, the SNe data we use appear to detect the peculiar velocity of the Solar system at about the 3.5σ level. However, when the correlations are correctly accounted for, the SNe data only detect the Solar system peculiar velocity at about the 2.5σ level. We forecast that the Solar system peculiar velocity will be detected at the 9σ level by GAIA and the 11σ level by the Large Synoptic Survey Telescope. For these surveys, we find the correlations are much less important as most of the signal comes from higher redshifts where the number density of SNe is insufficient for the correlations to be important.     

Type Ia supernovae and remnant neutron stars

On the basis of the current observational evidence, we put forward the case that the merger of two CO white dwarfs produces both a Type Ia supernova explosion and a stellar remnant, the latter in the form of a magnetar. The estimated occurrence rates raise the possibility that many, if not most, Type Ia supernovae might result from white dwarf mergers.     

Time-dependent three-dimensional spectrum synthesis for Type Ia supernovae

A Monte Carlo code ( artis ) for modelling time-dependent three-dimensional spectral synthesis in chemically inhomogeneous models of Type Ia supernova ejecta is presented. Following the propagation of γ-ray photons, emitted by the radioactive decay of the nucleosynthesis products, energy is deposited in the supernova ejecta and the radiative transfer problem is solved self-consistently, enforcing the constraint of energy conservation in the comoving frame. Assuming a photoionization-dominated plasma, the equations of ionization equilibrium are solved together with the thermal balance equation adopting an approximate treatment of excitation. Since we implement a fully general treatment of line formation, there are no free parameters to adjust. Thus, a direct comparison between synthetic spectra and light curves, calculated from hydrodynamic explosion models, and observations is feasible. The code is applied to the well-known W7 explosion model and the results tested against other studies. Finally, the effect of asymmetric ejecta on broad-band light curves and spectra is illustrated using an elliptical toy model.     

Supersoft X‐ray sources and the progenitors of Type Ia supernovae

Supersoft X‐ray sources have been proposed as one of the major channels to produce Type Ia supernovae (SNe Ia). However, the true nature of the progenitors has remained an unsolved problem. In this review I summarize the present status of our understanding of SN Ia progenitors, the main classes of progenitor models and recent observational constraints. At present, neither the single‐degenerate nor the double‐degenerate model can be ruled out, and indeed more than one channel may be required to explain the observed SN Ia diversity. Finally, I discuss the origin of the lightcurve peak – lightcurve width relation (the ‘Phillips relation’) and show that it is expected to depend on metallicity; this needs to be taken into account in high‐precision cosmological applications (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)