Abundance stratification in Type Ia supernovae - III. The normal SN 2003du

The element abundance distributions in the ejecta of Type Ia supernova (SN) is studied by modelling a time series of optical spectra of SN 2003du until ~1 yr after the explosion. Since SN 2003du is a very normal Type Ia SN both photometrically and spectroscopically, the abundance distribution derived for it can be considered as representative of normal Type Ia SNe. We find that the innermost layers are dominated by stable Fe-group elements, with a total mass of ~0.2M⊙, which are synthesized through electron capture. Above the core of stable elements there are thick ⁵⁶Ni-rich layers. The total mass of ⁵⁶Ni is 0.65M⊙. The Si- and S-rich layers are located above the ⁵⁶Ni-rich layers. The dominant element in the outermost layers (M_r⊙ > 1.1M, v > 13 000 km s^-1) is O, with a small amount of Si. Little unburned C remains, with an upper limit of 0.016M⊙. The element distributions in the ejecta are moderately mixed, but not fully mixed as seen in three-dimensional deflagration models.