Aspherical ejecta of type Ia supernovae inferred from high velocity features

Spectral synthesis in 3-dimensional space for the early phase spectra of Type Ia supernovae is presented. In particular, the high velocity absorption features that ubiquitously exist at the earliest epochs (∼ 10 days before maximum light) are investigated. The increasing number of early spectra available allows statistical study on the geometry of the ejecta. The observed diversity in the strength of the high velocity features (HVFs) can be reproduced through a "covering factor", which represents the fraction of the projected photosphere that is concealed by high velocity material. Various geometrical models involving high velocity material with a clumpy structure or a thick torus can naturally account for the observed statistics of HVFs. Models with 1 or 2 blobs, as well as a thin torus or disk-like enhancement seem to be unlikely as a standard situation.