Upper limit for circumstellar gas around the type Ia SN 2000cx

¹ European Organization for Astronomical Research in the Southern Hemisphere; K. Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: fpatat@eso.org
² INAF - Osservatorio Astronomico di Padova, v. Osservatorio n. 5, 35122 Padova, Italy
³ Department of Astrophysics, University of Oxford, Oxford OX1 3RH, UK
⁴ Max-Planck-Institut fuer Astrophysik, K. Schwarzschild Str. 2, 85748 Garching, Germany
⁵ INAF - Osservatorio Astronomico di Trieste, v. Tiepolo 11, 34131 Trieste, Italy
⁶ INAF - Osservatorio Astronomico di Arcetri, Largo E. Fermi n. 5, Firenze, Italy
⁷ Astronomy Department, MS 105-24, California Institute of Technology, Pasadena, CA 91125, USA

Received: 1 August 2007
Accepted: 27 August 2007

Abstract

Context.The nature of the companion stars in type Ia Supernova (SNe) progenitor systems remains unclear. One possible way to discriminate between different scenarios is the presence (or absence) of circumstellar material, the left overs from the progenitor evolution that may be revealed by their interaction with the SN.

Aims.A new method to probe the circumstellar environment has been exploited for the normal type Ia SN 2006X, leading for the first time to the direct detection of material which escaped the progenitor system. In this paper we apply the same analysis to the peculiar type Ia SN 2000cx, with the aim of constraining the properties of its progenitor system.

Methods.Using multi-epoch, high-resolution spectroscopy we have studied the spectral region where narrow, time-variable Na ID absorption features are expected in case circumstellar material is present along the line of sight.

Results.No Na ID absorption is detected in the rest-frame of the host galaxy to a level of a few mÅ, setting a stringent upper limit to the column density of the absorbing material (N(NaI) ≤ 2 10¹⁰ cm^-2).

Conclusions.In this respect the peculiar type Ia SN 2000cx is different from the normal Ia SN 2006X. Whether this is to be attributed to a different progenitor system, to viewing-angle effects or to a low metallicity remains to be clarified.