A&A 445, 387-402 (2006)
DOI: 10.1051/0004-6361:20053552

Spectroscopy of twelve type Ia supernovae at intermediate redshift

C. Balland^{1, 2, 3}, M. Mouchet^{2, 4}, R. Pain¹, N. A. Walton⁵, R. Amanullah⁶, P. Astier¹, R. S. Ellis^{5, 7}, S. Fabbro⁸, A. Goobar⁶, D. Hardin¹, I. M. Hook⁹, M. J. Irwin⁵, R. G. McMahon⁵, J. M. Mendez^{10, 11}, P. Ruiz-Lapuente¹⁰, G. Sainton¹, K. Schahmaneche¹ and V. Stanishev<sup>6

1</sup>  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 z=0.178 to z=0.493, 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.

Key words: cosmology: observations -- supernovae: general

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