The correlation between C/O ratio, metallicity, and the initial WD mass for SNe Ia^⋆

¹ School of Physics and Chemistry, Henan Polytechnic University, Jiaozuo 454000, PR China
e-mail: xiangcunmeng@hotmail.com
² Department of Astronomy, Beijing Normal University, Beijing 100875, PR China

Received: 15 December 2010
Accepted: 12 May 2011

Abstract

Context. When type Ia supernovae (SNe Ia) were chosen as distance indicators to measure cosmological parameters, the Phillips relation was applied. However, the origin of the scatter in the maximum luminosity of SNe Ia (or the variation in the production of ⁵⁶Ni) remains unclear. Both the metallicity in general and the carbon abundance of a white dwarf (WD) before a supernova explosion are important parameters, but neither has the ability to interpret the scatter in the maximum luminosity of SNe Ia.

Aims. We attempt to check whether or not the carbon abundance can be affected by initial metallicity.

Methods. We calculated a series of stellar evolution models with various masses and metallicities.

Results. We found that when Z ≤ 0.02, the carbon abundance is almost independent of metallicity if it is plotted against the initial WD mass. However, when Z > 0.02, the carbon abundance is not only a function of the initial WD mass, but also metallicity, i.e. for a given initial WD mass, the higher the metallicity, the lower the carbon abundance. On the basis of some previous studies, i.e. which find that both a high metallicity and a low carbon abundance lead to a lower production of ⁵⁶Ni being formed during a SN Ia explosion, the effects of the carbon abundance and the metallicity on the amount of ⁵⁶Ni are enhanced by each other, which may account, at least qualitatively, for the variation in the maximum luminosity of SNe Ia.

Conclusions. Since the central density of WD before a supernova explosion may also play a role in the production of ⁵⁶Ni and the parameters (the carbon abundance, the metallicity, and the central density) are all determined by the initial parameters of the progenitor system, i.e. the initial WD mass, metallicity, orbital period and secondary mass, the amount of ⁵⁶Ni might be a function of the initial parameters. Then, our results might construct a bridge linking the progenitor model to the explosion model of SNe Ia.