paper

Diversity of supernovae Ia determined using equivalent widths of Si II 4000

arXiv:0809.3133 · doi:10.1051/0004-6361:200810675

Abstract

Spectroscopic and photometric properties of low and high-z supernovae Ia (SNe Ia) have been analyzed in order to achieve a better understanding of their diversity and to identify possible SN Ia sub-types. We use wavelet transformed spectra in which one can easily measure spectral features. We investigate the \ion{Si}{II} 4000 equivalent width ($EW_w\lbrace\ion{Si}{II}\rbrace$). The ability and, especially, the ease in extending the method to SNe at high- is demonstrated. We applied the method to 110 SNe Ia and found correlations between $EW_w\lbrace\ion{Si}{II}\rbrace$ and parameters related to the light-curve shape for 88 supernovae with available photometry. No evidence for evolution of $EW_w\lbrace\ion{Si}{II}\rbrace$ with redshift is seen. Three sub-classes of SNe Ia were confirmed using an independent cluster analysis with only light-curve shape, colour, and $EW_w\lbrace\ion{Si}{II}\rbrace$. SNe from high- samples seem to follow a similar grouping to nearby objects. The $EW_w\lbrace\ion{Si}{II}\rbrace$ value measured on a single spectrum may point towards SN Ia sub-classification, avoiding the need for expansion velocity gradient calculations.

arXiv comment12 pages, 5 figures

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