THREE-DIMENSIONAL MODELS FOR HIGH-VELOCITY FEATURES IN TYPE Ia SUPERNOVAE

Spectral synthesis in three-dimensional space for the earliest spectra of Type Ia supernovae (SNe Ia) is presented. In particular, the high-velocity absorption features that are commonly seen at the earliest epochs (10 days before maximum light) are investigated by means of a three-dimensional Monte Carlo spectral synthesis code. The increas-ing number of early spectra available allows statistical study of the geometry of the ejecta. The observed diversity in strength of the high-velocity features (HVFs) can be explained in terms of a ‘‘covering factor,’ ’ which represents the fraction of the photosphere that is concealed by high-velocity material. Various geometric models involving high-velocity material with a clumpy structure or a thick torus can naturally account for the observed statistics of HVFs. HVFs may be formed by a combination of density and abundance enhancements. Such enhancements may be pro-duced in the explosion itself or may be the result of interaction with circumstellar material or an accretion disk. Mod-els with one or two blobs, as well as a thin torus or disklike enhancement, are unlikely as a standard situation. Subject headinggs: radiative transfer — supernovae: general Online material: color figures 1