Exploring the spectral diversity of low-redshift Type Ia supernovae using the Palomar Transient Factory

We present an investigation of the optical spectra of 264 low-redshift (z <\n0.2) Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory,\nan untargeted transient survey. We focus on velocity and pseudo-equivalent\nwidth measurements of the Si II 4130, 5972, and 6355 A lines, as well those of\nthe Ca II near-infrared (NIR) triplet, up to +5 days relative to the SN B-band\nmaximum light. We find that a high-velocity component of the Ca II NIR triplet\nis needed to explain the spectrum in ~95 per cent of SNe Ia observed before -5\ndays, decreasing to ~80 per cent at maximum. The average velocity of the Ca II\nhigh-velocity component is ~8500 km/s higher than the photospheric component.\nWe confirm previous results that SNe Ia around maximum light with a larger\ncontribution from the high-velocity component relative to the photospheric\ncomponent in their Ca II NIR feature have, on average, broader light curves and\nlower Ca II NIR photospheric velocities. We find that these relations are\ndriven by both a stronger high-velocity component and a weaker contribution\nfrom the photospheric Ca II NIR component in broader light curve SNe Ia. We\nidentify the presence of C II in very-early-time SN Ia spectra (before -10\ndays), finding that >40 per cent of SNe Ia observed at these phases show signs\nof unburnt material in their spectra, and that C II features are more likely to\nbe found in SNe Ia having narrower light curves.\n