Spectroscopy of twelve type Ia supernovae at intermediate redshift

¹ LPNHE, CNRS-IN2P3 and Universities of Paris 6 & 7, 75252 Paris Cedex 05, France e-mail: christophe.balland@ias.u-psud.fr
² APC, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France
³ IAS, UMR 8617 CNRS and Université Paris-Sud 11, 91405 Orsay, France
⁴ LUTH, UMR 8102 CNRS, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁶ Department of Physics, Stockholm University, 10691 Stockholm, Sweden
⁷ California Institute of Technology, Pasadena, CA 91125, USA
⁸ CENTRA-Centro M. de Astrofisica and Department of Physics, IST, Lisbon, Portugal
⁹ Astrophysics, Denys Wilkinson Building, Keble Road, OX1 3RH, Oxford, UK
¹⁰ Department of Astronomy, University of Barcelona, 08028, Barcelona, Spain
¹¹ Isaac Newton Group of Telescopes, Apartado 321, 38700 Santa Cruz de La Palma, Spain

Received: 2 June 2005
Accepted: 28 July 2005

Abstract

We present spectra of twelve type Ia supernovae obtained in 1999 at the William Herschel Telescope and the Nordic Optical Telescope during a search for type Ia supernovae (SN Ia) at intermediate redshift. The spectra range from to , including five high signal-to-noise ratio SN Ia spectra in the still largely unexplored range . Most of the spectra were obtained before or around restframe B-band maximum light. None of them shows the peculiar spectral features found in low-redshift over- or under-luminous SN Ia. Expansion velocities of characteristic spectral absorption features such as Si ii at 6355 Å, S ii at 5640 Å and Ca ii at 3945 Å are found to be consistent with those of their low-z SN Ia  counterparts.