Can the Helium-detonation Model Explain the Observed Diversity of Type Ia Supernovae?
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AbstractWe study a sample of 16 Type Ia supernovae (SNe Ia) having both spectroscopic and photometric observations within 23 days after the first light. The early BV colors of such a sample tend to show a continuous distribution. For objects with normal ejecta velocity (NV), the Cii6580 feature is always visible in the early spectra, while it is absent or very weak in the high-velocity (HV) counterpart. Moreover, the velocities of the detached high-velocity features (HVFs) of the CaII near-IR triplet (CaIR3) above the photosphere are found to be much higher in HV objects than in NV objects, with typical values exceeding 30,000 km s1 at 23 days. We further analyze the relation between the velocity shift of late-time [Fe II] lines (v[Fe II]) and host galaxy mass. We find that all HV objects have redshifted v[Fe II], while NV objects have both blue- and redshifted v[Fe II]. It is interesting to point out that the objects with redshifted v[Fe II] are all located in massive galaxies, implying that HV and a portion of NV objects may have similar progenitor metallicities and explosion mechanisms. We propose that, with a geometric/projected effect, the He-detonation model may account for the similarity in birthplace environment and the differences seen in some SNe Ia, including BV colors, CII features, CaIR3 HVFs at early times, and v[Fe II] in the nebular phase. Nevertheless, some features predicted by He-detonation simulation, such as the rapidly decreasing light curve, deviate from the observations, and some NV objects with blueshifted nebular v[Fe II] may involve other explosion mechanisms.
