A SYSTEMATIC STUDY OF CARBON–OXYGEN WHITE DWARF MERGERS: MASS COMBINATIONS FOR TYPE Ia SUPERNOVAE

Abstract

Mergers of two carbon-oxygen (CO) white dwarfs (WDs) have been considered to be progenitors of Type Ia supernovae (SNe Ia). Based on smoothed particle hydrodynamics (SPH) simulations, previous studies have claimed that mergers of CO WDs lead to SN Ia explosions either in the dynamical merger phase or the stationary rotating merger remnant phase. However, the mass range of CO WDs that lead to SNe Ia has notyet been clearly identified. In the present work, we perform systematic SPH merger simulations for the WD masses ranging from M 0.5  to M 1.1  with higher resolutions than the previous systematic surveys and examine whether or not carbon burning occurs dynamically or quiescently in each phase. We further study the possibility of SNe Ia explosions and estimate the mass range of CO WDs that lead to SNe Ia. We found that when both WDs are massive, i.e., in the mass range of ⩽ ⩽ and the total mass exceeds M 1.38  , they can finally explode in the stationary rotating merger remnant phase. We estimate the contribution of CO WD mergers to the entire SN Ia rate in our galaxy to be of 9%  . Thus, it might be difficult to explain all galactic SNe Ia with CO WD mergers.

The Critical Mass Ratio of Double White Dwarf Binaries for Violent Merger-Induced Type Ia Supernova Explosions

“…Our CO WD models have auniform composition of 50% carbon and 50% oxygen in mass. Sato et al (2015) simulated mergers of CO WDs whose masses were 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 1.1 M e .…”

“…We add M 2 = 0. 725, 0.75, 0.775, 0.825, 0.85, and 0.875 M e for each M 1 = 0.75, 0.8, 0.9, 1.0, and 1.1 M e , because q cr seems to be in this mass range (see Figure5 of Sato et al 2015). The numerical resolution is 500 k per solar mass (k≡1,024).…”

“…Our SPH scheme derives the temperature of a particle from the density and internal energy through the EOS. The estimations of density and internal energy have some numerical noises, and the derived temperature is also fluctuated (Dan et al 2012;Sato et al 2015;Tanikawa et al 2015).…”

“…After Benz et al (1990) first performed three-dimensional (3D) hydrodynamical simulations of CO WD mergers with their smoothed particle hydrodynamics (SPH) code (e.g., Gingold & Monaghan 1982;Monaghan 2005;Rosswog 2009), similar merger simulations have been performed by various groups (e.g., Rasio & Shapiro 1995;Segretain et al 1997;Guerrero et al 2004;D'Souza et al 2006;Motl et al 2007;Yoon et al 2007;Lorén-Aguilar et al 2009;Fryer et al 2010;Pakmor et al 2010Pakmor et al , 2011Pakmor et al , 2012aPakmor et al , 2012bDan et al 2011Dan et al , 2012Dan et al , 2014Raskin et al 2012Raskin et al , 2014Zhu et al 2013;Moll et al 2014;Kashyap et al 2015;Sato et al 2015;Tanikawa et al 2015). These studies showed that a CO WD merger could lead to an SN Ia if several conditions are satisfied.…”

“…They investigated whether or not dynamical carbon burning would occur during the merger. Pakmor et al (2012a) and Sato et al (2015) showed that the numerical resolution is another important factor in studying the violent merger scenario, and Sato et al (2015) suggested that it should be ☉  -M 500,000 1 (see also Tanikawa et al 2015).…”