EDP Sciences
Free access
Volume 492, Number 2, December III 2008
Page(s) 535 - 544
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:200810675
Published online 27 October 2008

A&A 492, 535-544 (2008)
DOI: 10.1051/0004-6361:200810675

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

V. Arsenijevic, S. Fabbro, A. M. Mourão, and A. J. Rica da Silva

CENTRA - Centro Multidisciplinar de Astrofísica, IST, Avenida Rovisco Pais, 1049 Lisbon, Portugal
    e-mail: arsenije@ist.utl.pt

Received 25 July 2008/ Accepted 17 September 2008

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 Si II 4000 equivalent width (EWw{Si II}). The ability and, especially, the ease in extending the method to SNe at high-z is demonstrated. We applied the method to 110 SNe Ia and found correlations between EWw{Si II} and parameters related to the light-curve shape for 88 supernovae with available photometry. No evidence for evolution of EWw{Si II} with redshift is seen. Three sub-classes of SNe Ia were confirmed using an independent cluster analysis with only light-curve shape, colour, and EWw{Si II}. SNe from high-z samples seem to follow a similar grouping to nearby objects. The EWw{Si II} value measured on a single spectrum may point towards SN Ia sub-classification, avoiding the need for expansion velocity gradient calculations.

Key words: supernovae: general -- methods: data analysis

© ESO 2008