2015/02/17 by J. M. Silverman, Silverman, Jeffrey M., J. Vinkó +13 · 2 citations
Physics and Astronomy · #Gamma-ray bursts and supernovae #Astro and Planetary Science
paper · pdf · doi:10.48550/arxiv.1502.07278
"High-velocity features" (HVFs) are spectral features in Type Ia supernovae\n(SNe Ia) that have minima indicating significantly higher (by greater than\nabout 6000 km/s) velocities than typical "photospheric-velocity features"\n(PVFs). The PVFs are absorption features with minima indicating typical\nphotospheric (i.e., bulk ejecta) velocities (usually ~9000-15,000 km/s near\nB-band maximum brightness). In this work we undertake the most in-depth study\nof HVFs ever performed. The dataset used herein consists of 445 low-resolution\noptical and near-infrared (NIR) spectra (at epochs up to 5 d past maximum\nbrightness) of 210 low-redshift SNe Ia that follow the "Phillips relation." A\nseries of Gaussian functions is fit to the data in order to characterise\npossible HVFs of Ca II H&K, Si II \λ6355, and the Ca II NIR triplet. The\ntemporal evolution of the velocities and strengths of the PVFs and HVFs of\nthese three spectral features is investigated, as are possible correlations\nwith other SN Ia observables. We find that while HVFs of Ca II are regularly\nobserved (except in underluminous SNe Ia, where they are never found), HVFs of\nSi II \λ6355 are significantly rarer, and they tend to exist at the\nearliest epochs and mostly in objects with large photospheric velocities. It is\nalso shown that stronger HVFs of Si II \λ6355 are found in objects that\nlack C II absorption at early times and that have red ultraviolet/optical\ncolours near maximum brightness. These results lead to a self-consistent\nconnection between the presence and strength of HVFs of Si II \λ6355 and\nmany other mutually correlated SN~Ia observables, including photospheric\nvelocity.\n