The white dwarf’s carbon fraction as a secondary parameter of Type Ia supernovae

Abstract

Context. Binary stellar evolution calculations predict that Chandrasekhar-mass carbon/oxygen white dwarfs (WDs) show a radially varying profile for the composition with a carbon depleted core. Many recent multi-dimensional simulations of Type Ia supernovae (SNe Ia), however, assume the progenitor WD has a homogeneous chemical composition. Aims. In this work, we explore the impact of different initial carbon profiles of the progenitor WD on the explosion phase and on synthetic observables in the Chandrasekhar-mass delayed detonation model. Spectra and light curves are compared to observations to judge the validity of the model. Methods. The explosion phase is simulated using the finite volume supernova code L, which is extended to treat different compositions of the progenitor WD. The synthetic observables are computed with the Monte Carlo radiative transfer code A. Results. Differences in binding energies of carbon and oxygen lead to a lower nuclear energy release for carbon depleted material; thus, the burning fronts that develop are weaker and the total nuclear energy release is smaller. For otherwise identical conditions, carbon depleted models produce less 56 Ni. Comparing different models with similar 56 Ni yields shows lower kinetic energies in the ejecta for carbon depleted models, but only small differences in velocity distributions and line velocities in spectra. The light curve width-luminosity relation (WLR) obtained for models with differing carbon depletion is roughly perpendicular to the observed WLR, hence the carbon mass fraction is probably only a secondary parameter in the family of SNe Ia.

LATE-TIME PHOTOMETRY OF TYPE IA SUPERNOVA SN 2012cg REVEALS THE RADIOACTIVE DECAY OF 57Co

“…Under this approximation, the mass ratio we measure here is roughly twice the corresponding 57 Fe/ 56 Fe ratio measured for the Sun (Asplund et al 2009). This value is slightly higher than the predictions of near-M Ch explosion models: W7 of Iwamoto et al (1999) predicts 1.7 times Solar, the pure turbulent deflagration models of Fink et al (2014) predict ∼1.5 times Solar, the delayeddetonation models of CO WDs of Seitenzahl et al (2013) predict ∼1.3 times Solar, the delayed-detonation models of WDs with carbon-depleted cores of Ohlmann et al (2014) predict ∼1.1 times Solar, and the gravitationally confined detonation models of Meakin et al (2009) …”

“…where B=0.235 is the scaling factor described above; A is the atomic number of the decaying nucleus; λ A is the inverse of the half-life time of the decay chain; q A is the average energy per decay carried by charged leptons and X-rays; t is the time since explosion; and we fit for the masses, M(A), of 56 Co and 57 Co. Our late-time measurements are not precise enough to also fit for the mass of 55 Fe, so we set its mass by using a ratio of M( 57 Co)/M( 55 Fe)≈0.8 (model rpc32; Ohlmann et al 2014). The values of λ A and q A used here are enumerated in For 57 Co, we also take into account the energy emitted by the decay through the 14.4 keV line (1.32 keV per decay).…”

Do electron-capture supernovae make neutron stars?

“…The NSE abundances are tabulated with the density of the fuel being burned as the independent variable. The tables are produced by iteratively writing the abundance tables from postprocessing nuclear network calculations and simulating the deflagration in 2D (the same method as used by Fink et al 2010, for detonations andOhlmann et al 2014, for deflagrations). Thermal neutrino losses are also included in the simulations using the formulae by Itoh et al (1996), as described in Seitenzahl et al (2015).…”

Late-time Flattening of Type Ia Supernova Light Curves: Constraints from SN 2014J in M82

“…where C is a scaling factor, A gives the corresponding atomic number, λ A is the inverse mean lifetime (λ A = τ −1 A = ln(2)/t 1/2,A ), M(A) is the total mass of a certain decaying element, q l A and q X A are the average energies per decay carried by charged leptons and Xrays, respectively, and t e is the time since explosion. Due to the limited data points in our late-time photometry, we used a ratio of M( 57 Co)/M( 55 F e) ≈ 0.8 (model rpc32 ;Ohlmann et al 2014). The values of λ A , q l A and q X A used here are obtained from Table 1 of Seitenzahl et al (2009) and Table 2 of Seitenzahl et al (2014).…”