Type Ia supernovae from exploding oxygen-neon white dwarfs

¹ Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Campus Hubland Nord, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
e-mail: kmarquardt@astro.uni-wuerzburg.de
² Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
³ School of Mathematics and Physics, Queen’s University Belfast University Road Belfast, Northern Ireland BT7 1NN, UK
⁴ ARC Centre of Excellence for All-Sky Astrophysics (CAASTRO)  
⁵ Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Weston Creek, ACT 2611, Australia
⁶ The Oskar Klein Centre & Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
⁷ Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Philosophenweg 12, 69120 Heidelberg, Germany

Received: 28 January 2015
Accepted: 2 May 2015

Abstract

Context. The progenitor problem of Type Ia supernovae (SNe Ia) is still unsolved. Most of these events are thought to be explosions of carbon-oxygen (CO) white dwarfs (WDs), but for many of the explosion scenarios, particularly those involving the externally triggered detonation of a sub-Chandrasekhar mass WD (sub-M_Ch WD), there is also a possibility of having an oxygen-neon (ONe) WD as progenitor.

Aims. We simulate detonations of ONe WDs and calculate synthetic observables from these models. The results are compared with detonations in CO WDs of similar mass and observational data of SNe Ia.

Methods. We perform hydrodynamic explosion simulations of detonations in initially hydrostatic ONe WDs for a range of masses below the Chandrasekhar mass (M_Ch), followed by detailed nucleosynthetic postprocessing with a 384-isotope nuclear reaction network. The results are used to calculate synthetic spectra and light curves, which are then compared with observations of SNe Ia. We also perform binary evolution calculations to determine the number of SNe Ia involving ONe WDs relative to the number of other promising progenitor channels.

Results. The ejecta structures of our simulated detonations in sub-M_Ch ONe WDs are similar to those from CO WDs. There are, however, small systematic deviations in the mass fractions and the ejecta velocities. These lead to spectral features that are systematically less blueshifted. Nevertheless, the synthetic observables of our ONe WD explosions are similar to those obtained from CO models.

Conclusions. Our binary evolution calculations show that a significant fraction (3–10%) of potential progenitor systems should contain an ONe WD. The comparison of our ONe models with our CO models of comparable mass (~1.2 M_⊙) shows that the less blueshifted spectral features fit the observations better, although they are too bright for normal SNe Ia.