Explosive Nucleosynthesis in Near-Chandrasekhar Mass White Dwarf Models for Type Ia Supernovae: Dependence on Model Parameters

We present two-dimensional hydrodynamics simulations of near-Chandrasekhar mass white dwarf (WD) models for Type Ia supernovae (SNe Ia) using the turbulent deflagration model with deflagration-detonation transition (DDT). We perform a parameter survey for 41 models to study the effects of the initial central density (i.e., WD mass), metallicity, flame shape, DDT criteria, and turbulent flame formula for a much wider parameter space than earlier studies. The final isotopic abundances of $^{11}$C to $^{91}$Tc in these simulations are obtained by post-process nucleosynthesis calculations. The survey includes SNe Ia models with the central density from $5 \times 10^8$ g cm$^{-3}$ to $5 \times 10^9$ g cm$^{-3}$ (WD masses of 1.30 - 1.38 $M_\odot$), metallicity from 0 to 5 $Z_{\odot}$, C/O mass ratio from 0.3 - 1.0 and ignition kernels including centered and off-centered ignition kernels. We present the yield tables of stable isotopes from $^{12}$C to $^{70}$Zn as well as the major radioactive isotopes for 33 models. Observational abundances of $^{55}$Mn, $^{56}$Fe, $^{57}$Fe and $^{58}$Ni obtained from the solar composition, well-observed SNe Ia and SN Ia remnants are used to constrain the explosion models and the supernova progenitor. The connection between the pure turbulent deflagration model and the subluminous SNe Iax is discussed. We find that dependencies of the nucleosynthesis yields on the metallicity and the central density (WD mass) are large. To fit these observational abundances and also for the application of galactic chemical evolution modeling, these dependencies on the metallicity and WD mass should be taken into account.Comment: 53 pages, 43 figures. Accepted for publication in Astrophysical Journal. Tables and figures updated to be consistent with other works. Also table magnified for better visio

A New Versatile Code for Gamma-Ray Monte-Carlo Radiative Transfer

Ongoing MeV telescopes such as INTEGRAL/SPI and Fermi/GBM, and proposed telescopes including the recently accepted COSI and the e-ASTROGAM and AMEGO missions, provide another window in understanding transients. Their signals contain information about the stellar explosion mechanisms and their corresponding nucleosynthesis of short-lived radioactive isotopes. This raises the need of a radiative transfer code which may efficiently explore different types of astrophysical $\gamma$-ray sources and their dependence on model parameters and input physics. In view of this, we present our new Monte-Carlo Radiative Transfer code in Python. The code synthesizes the $\gamma$-ray spectra and light curves suitable for modeling supernova ejecta, including C+O novae, O+Ne novae, Type Ia and core-collapse supernovae. We test the code extensively for reproducing results consistent with analytic models. We also compare our results with similar models in the literature and discuss how our code depends on selected input physics and setting.Comment: 15 pages, 25 figures, published in the Monthly Notices of the Royal Astronomical Society, submitted at 08 May 2022, accepted at 14 Feb 2023, published at 20 Feb 202

Pulsational Pair-instability Supernovae. I. Pre-collapse Evolution and Pulsational Mass Ejection

We calculate the evolution of massive stars, which undergo pulsational pair-instability (PPI) when the O-rich core is formed. The evolution from the main-sequence through the onset of PPI is calculated for stars with the initial masses of $80 - 140$ $M_{\odot}$ and metallicities of $Z = 10^{-3} - 1.0$ $Z_\odot$. Because of mass loss, $Z \leq 0.5$ $Z_\odot$ is necessary for stars to form He cores massive enough (i.e., mass $>40 ~M_\odot$) to undergo PPI. The hydrodynamical phase of evolution from PPI through the beginning of Fe core collapse is calculated for the He cores with masses of $40 - 62 ~M_\odot$ and $Z = 0$. During PPI, electron-positron pair production causes a rapid contraction of the O-rich core which triggers explosive O-burning and a pulsation of the core. We study the mass dependence of the pulsation dynamics, thermodynamics, and nucleosynthesis. The pulsations are stronger for more massive He cores and result in such a large amount of mass ejection such as $3 - 13$ $M_\odot$ for $40 - 62 ~M_\odot$ He cores. These He cores eventually undergo Fe-core collapse. The $64 ~M_\odot$ He core undergoes complete disruption and becomes a pair-instability supernova. The H-free circumstellar matter ejected around these He cores is massive enough for to explain the observed light curve of Type I (H-free) superluminous supernovae with circumstellar interaction. We also note that the mass ejection sets the maximum mass of black holes (BHs) to be $\sim 50$ $M_{\odot}$, which is consistent with the masses of BHs recently detected by VIRGO and aLIGO.Comment: 33 pages, 57 figures, submitted at 29 January 2019, revised at 16 October 2019, accepted at 20 October 2019; published 11 December 2019. References and metadata update

Hydrodynamic Simulations of Pre-supernova Outbursts in Red Supergiants: Asphericity and Mass Loss

The activity of a massive star approaching core-collapse can strongly affect the appearance of the star and its subsequent supernova. Late-phase convective nuclear burning generates waves that propagate toward the stellar surface, heating the envelope and potentially triggering mass loss. In this work, we improve on previous one-dimensional models by performing two-dimensional simulations of the pre-supernova mass ejection phase due to deposition of wave energy. Beginning with stellar evolutionary models of a 15 M_⊙ red supergiant star during core O-burning, we treat the rate and duration of energy deposition as model parameters and examine the mass-loss dependence and the pre-explosion morphology accordingly. Unlike one-dimensional models, density inversions due to wave heating are smoothed by Rayleigh–Taylor instabilities, and the primary effect of wave heating is to radially expand the star's hydrogen envelope. For low heating rates with long durations, the expansion is nearly homologous, whereas high but short-lived heating can generate a shock that drives envelope expansion and results in a qualitatively different density profile at the time of core-collapse. Asymmetries are fairly small, and large amounts of mass loss are unlikely unless the wave heating exceeds expectations. We discuss implications for pre-supernova stellar variability and supernovae light curves

Hydrodynamic Simulations of Pre-Supernova Outbursts in Red Supergiants: Asphericity and Mass Loss

The activity of massive stars approaching core-collapse can strongly affect the appearance of the star and its subsequent supernova. Late-phase convective nuclear burning generates waves that propagate toward the stellar surface, heating the envelope and potentially triggering mass loss. In this work, we improve on previous one-dimensional models by performing two-dimensional simulations of the pre-supernova mass ejection phase due wave heat deposition. Beginning with stellar evolutionary models of a 15 $M_{\odot}$ red supergiant star during core O-burning, we treat the energy deposition rate and duration as model parameters and examine the mass-loss dependence and the pre-explosion morphology accordingly. Unlike one-dimensional models, density inversions due to wave heating are smoothed by Rayleigh-Taylor instabilities, and the primary effect of wave heating is to radially expand the star's hydrogen envelope. For low heating rates with long durations, the expansion is nearly homologous, whereas high but short-lived heating can generate a shock that drives envelope expansion and results in a qualitatively different density profile at the time of core-collapse. Asymmetries are fairly small, and large amounts of mass loss are unlikely unless the wave heating exceeds expectations. We discuss implications for pre-supernova stellar variability and supernovae light curves.Comment: 21 pages, 44 figures. Submitted to Astrophysical Journal at 25 June 2020, accepted at 3 August 2020. Main text and references update