Licentiate Thesis: On the importance of being standard. Properties of Type Ia supernovae and implications for cosmology

by Jakob Nordin (SU Fysikum)

Monday 26 Oct 2009, 10:00 → 12:00 Europe/Stockholm

FA:32

Type Ia supernovae are individual objects as bright as galaxies, responsible for the creation of a large fraction of all heavy elements and proving that the expansion of the universe is accelerating. Yet their mechanism is not very well understood. A basic picture where Type Ia supernovae are caused by thermonuclear explosions of white dwarfs is now generally accepted, but the details are still debated, and these uncertainties will propagate into systematic uncertainties for cosmological parameters. We have designed a Monte Carlo framework, SMOCK, to model this error propagation. The package is used both to investigate the sensitivity to systematic errors for current surveys and to design future surveys less sensitive to systematic uncertainties. Optical spectra of Type Ia supernovae contain a wealth of information regarding the nature of these events. This includes possible evolution and the nature of reddening, two of the largest systematic uncertainties (as estimated with SMOCK).We have reduced all spectra observed with the NOT and NTT telescopes in conjunction with the SDSS-II supernova survey in a coherent fashion. We have further studied possible difficulties when performing pseudo-equivalent widths and line velocities measurements on low S/N spectra. Using these results, together with automatic measurement algorithms, we have compared spectral indicators for SNe in the NTT/NOT data sample with a low redshift reference set. No evolution in the SN properties with redshift is detected. Correlations with lightcurve shape are confirmed and possible correlations with lightcurve colour are discussed. The latter would indicate an intrinsic component to the observed reddening.