Berkeley Supernova Ia Program - II. Initial analysis of spectra obtained near maximum brightness

In this second paper in a series we present measurements of spectral features\nof 432 low-redshift (z < 0.1) optical spectra of 261 Type Ia supernovae (SNe\nIa) within 20 d of maximum brightness. The data were obtained from 1989 through\nthe end of 2008 as part of the Berkeley SN Ia Program (BSNIP) and are presented\nin BSNIP I (Silverman et al. 2012). We describe in detail our method of\nautomated, robust spectral feature definition and measurement which expands\nupon similar previous studies. Using this procedure, we attempt to measure\nexpansion velocities, pseudo-equivalent widths (pEW), spectral feature depths,\nand fluxes at the centre and endpoints of each of nine major spectral feature\ncomplexes. We investigate how velocity and pEW evolve with time and how they\ncorrelate with each other. Various spectral classification schemes are employed\nand quantitative spectral differences among the subclasses are investigated.\nSeveral ratios of pEW values are calculated and studied. The so-called Si II\nratio, often used as a luminosity indicator (Nugent et al. 1995), is found to\nbe well correlated with the so-called "SiFe" ratio and anticorrelated with the\nanalogous "SSi ratio," confirming the results of previous studies. Furthermore,\nSNe Ia that show strong evidence for interaction with circumstellar material or\nan aspherical explosion are found to have the largest near-maximum expansion\nvelocities and pEWs, possibly linking extreme values of spectral observables\nwith specific progenitor or explosion scenarios. [Abridged]\n