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Date and Time of the Query: 2019-08-17 T16:42:04 PDT
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For refcode 2014MNRAS.437..338C:
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Copyright by Royal Astronomical Society. 2014MNRAS.437..338C High-velocity features in Type Ia supernova spectra Childress, Michael J.; Filippenko, Alexei V.; Ganeshalingam, Mohan; Schmidt, Brian P. Abstract. We use a sample of 58 low-redshift (z <= 0.03) Type Ia supernovae (SNe Ia) having well-sampled light curves and spectra near maximum light to examine the behaviour of high-velocity features (HVFs) in SN Ia spectra. We take advantage of the fact that Si II lambda6355 is free of HVFs at maximum light in all SNe Ia, while HVFs are still strong in the Ca II near-infrared feature in many SNe, allowing us to quantify the strength of HVFs by comparing the structure of these two lines. We find that the average HVF strength increases with decreasing light-curve decline rate, and rapidly declining SNe Ia (Deltam_15_(B) >= 1.4 mag) show no HVFs in their maximum-light spectra. Comparison of HVF strength to the light-curve colour of the SNe Ia in our sample shows no evidence of correlation. We find a correlation of HVF strength with the velocity of Si II lambda6355 at maximum light (v_Si_), such that SNe Ia with lower v_Si_ have stronger HVFs, while those SNe Ia firmly in the 'high-velocity' (i.e. v_Si_ >= 12 000 km s^-1^) subclass exhibit no HVFs in their maximum-light spectra. While v_Si_ and Deltam_15_(B) show no correlation in the full sample of SNe Ia, we find a significant correlation between these quantities in the subset of SNe Ia having weak HVFs. In general, we find that slowly declining (low Deltam_15_(B)) SNe Ia, which are more luminous and more energetic than average SNe Ia, tend to produce either high photospheric ejecta velocities (i.e. high v_Si_) or strong HVFs at maximum light, but not both. Finally, we examine the evolution of HVF strength for a sample of SNe Ia having extensive pre-maximum spectroscopic coverage and find significant diversity of the pre-maximum HVF behaviour. Key words: supernovae: general
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