Probing type Ia supernovae through simulations and observations

Type Ia supernovae result when carbon-oxygen white dwarfs in binary systems accrete mass from companion stars, reach a critical mass and explode. The near uniformity of their light curves makes these supernovae good 'standard candles' for measuring cosmic expansion, but a correction must be applied to account for the fact that the brighter ones have broader light curves. One-dimensional modelling, with a certain choice of parameters, can reproduce this general trend in the width-luminosity relation; but the processes of ignition and detonation have recently been shown to be intrinsically asymmetric, so parameterization must have its limits. Here we report multi-dimensional modelling of the explosion physics and radiative transfer, which reveals that the breaking of spherical symmetry is a critical factor in determining both the width-luminosity relation and the observed scatter about it. The deviation from spherical symmetry can also explain the finite polarization detected in the light from some supernovae. The slope and normalization of the width-luminosity relation has a weak dependence on certain properties of the white dwarf progenitor, in particular the trace abundances of elements other than carbon and oxygen. Failing to correct for this effect could lead to systematic overestimates of up to 2 per cent in the distance to remote supernovae.

The progenitors of Type Ia Supernovae (SNe Ia) are still unknown, despite significant progress during the last years in theory and observations. Violent mergers of two carbon--oxygen (CO) white dwarfs (WDs) are one candidate suggested to be responsible for at least a significant fraction of normal SNe Ia. Here, we simulate the merger of two CO WDs using a moving-mesh code that allows for the inclusion of thin helium (He) shells (0.01\,\msun) on top of the WDs, at an unprecedented numerical resolution. The accretion of He onto the primary WD leads to the formation of a detonation in its He shell. This detonation propagates around the CO WD and sends a converging shock wave into its core, known to robustly trigger a second detonation, as in the well-known double-detonation scenario for He-accreting CO WDs. However, in contrast to that scenario where a massive He shell is required to form a detonation through thermal instability, here the He detonation is ignited dynamically. Accordingly the required He-shell mass is significantly smaller, and hence its burning products are unlikely to affect the optical display of the explosion. We show that this scenario, which works for CO primary WDs with CO- as well as He-WD companions, has the potential to explain the different brightness distributions, delay times and relative rates of normal and fast declining SNe Ia. Finally, we discuss extensions to our unified merger model needed to obtain a comprehensive picture of the full observed diversity of SNe Ia.

view Abstract Citations (253) References (120) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Models for Type I Supernova. I. Detonations in White Dwarfs Woosley, S. E. ; Taam, R. E. ; Weaver, T. A. Abstract In a series of papers, the properties of white dwarfs provoked into nuclear instability by accretion will be explored. The results bear many close similarities to the observed properties of Type I supernovae, especially their energetics, light curves, nucleosynthesis, and spectra. In this paper a class of "detonating white dwarfs" is explored. The final evolution of carbon-oxygen white dwarfs in binary systems undergoing mass exchange at rates in the range 10-9 to 10-8M_sun;yr-1 is considered. Three models are constructed having initial carbon-oxygen core masses 0.5, 0.8, and 1.2 M_sun; and accreting helium at rates of 10-8, 2×10-9, and 10-9M_sun;yr-1, respectively. In all cases continued evolution leads to the accumulation of a thick helium layer surrounding the core, degenerate helium ignition, detonation and mass ejection. Detailed isotopic nucleosynthesis has also been computed for these models and implications for Galactic chemical evolution and γ-line astronomy are discussed. At present, the class of detonating models does not agree well with spectroscopic constraints upon common Type I events. Publication: The Astrophysical Journal Pub Date: February 1986 DOI: 10.1086/163926 Bibcode: 1986ApJ...301..601W Keywords: Binary Stars; Nuclear Fusion; Stellar Evolution; Stellar Physics; Supernovae; White Dwarf Stars; Density Distribution; Detonation; Hydrodynamics; Light Curve; Stellar Envelopes; Stellar Gravitation; Stellar Luminosity; Stellar Mass Accretion; Stellar Models; Stellar Oscillations; Astrophysics; GAMMA RAYS: GENERAL; NUCLEOSYNTHESIS; STARS: BINARIES; STARS: INTERIORS; STARS: SUPERNOVAE; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (2)

We consider the evolution of stellar hierarchical quadruple systems in the 2+2 (two binaries orbiting each other's barycentre) and 3+1 (triple orbited by a fourth star) configurations. In our simulations, we take into account the effects of secular dynamical evolution, stellar evolution, tidal evolution and encounters with passing stars. We focus on type Ia supernovae (SNe Ia) driven by collisions of carbon-oxygen (CO) white dwarfs (WDs). Such collisions can arise from several channels: (1) collisions due to extremely high eccentricities induced by secular evolution, (2) collisions following a dynamical instability of the system, and (3) collisions driven by semisecular evolution. The systems considered here have initially wide inner orbits, with initial semilatus recti larger than 12 AU, implying no interaction if the orbits were isolated. However, taking into account dynamical evolution, we find that $\approx 0.4$ ($\approx 0.6$) of 2+2 (3+1) systems interact. In particular, Roche Lobe overflow can be triggered possibly in highly eccentric orbits, dynamical instability can ensue due to mass-loss-driven orbital expansion or secular evolution, or a semisecular regime can be entered. We compute the delay-time distributions (DTDs) of collision-induced SNe Ia, and find that they are flatter compared to the observed DTD. Moreover, our combined SNe Ia rates are $(3.7\pm0.7) \times 10^{-6} \,\mathrm{M}_\odot^{-1}$ and $(1.3\pm0.2) \times 10^{-6} \,\mathrm{M}_\odot^{-1}$ for 2+2 and 3+1 systems, respectively, three orders of magnitude lower compared to the observed rate, of order $10^{-3} \, \mathrm{M}_\odot^{-1}$. The low rates can be ascribed to interactions before the stars evolve to CO WDs. However, our results are lower limits given that we considered a subset of quadruple systems.

Observations of main sequence stars conducted over the last several decades have clearly shown that something like 50 per cent of stars of spectral types G and F occur in multiple systems. For earlier spectral types, the incidence of multiplicity is even higher. Thus, a volume limited sample of white dwarfs should reflect the percentage of binarity observed in stars of F to late B spectral types, which are their Main Sequence progenitors. However, a study of the local volume limited sample of white dwarfs (20 pc from the Sun) conducted by Holberg has shown that a white dwarf has a probability of only $\sim 32$ per cent of occurring in a binary system, in stark contrast to the observations of multiplicity of Main Sequence stars. Others studies have also led to the same conclusion. In this paper, we argue that the "hidden" white dwarfs are either in double white dwarf systems or in Sirius-like systems. We also show that the white dwarf progenitors of the SDSS white dwarf - M dwarf wide binaries are distributed according to Salpeter's IMF. However, they cannot be paired with secondary stars which are also drawn from this IMF, since such a pairing would produce a percentage of white dwarf-M dwarfs systems that is several times larger than observed.

Context. Stars with masses ranging from 3 to 11 M ⊙ exhibit multiple evolutionary paths. Less massive stars in this range conclude their evolution as carbon-oxygen (CO) white dwarfs (COWDs). However, stars that achieve carbon ignition before the pressure induced by the degenerate electron halts the core contraction would either form massive CONe or ONe WDs, or they might undergo an electron-capture supernova (ECSN). Alternatively, they could photo-disintegrate neon and proceed with further thermonuclear burning, ultimately leading to the formation of a gravitationally unstable iron core. Aims. An evaluation of the impact of the energy loss caused by the production of axion-like-particles (ALPs) on the evolution and final destiny of these stars is the main objective. Methods. We computed various sets of stellar models, all with solar initial composition, varying the strengths of the ALP coupling with photons and electrons. Results. As a consequence of an ALP thermal production, the critical masses for off-center C and Ne ignitions are both shifted upward. When the current bounds for the ALP coupling strengths are assumed, the maximum mass for CO WD progenitors is about 1.1 M ⊙ heavier than that obtained without the ALP energy loss, while the minimum mass for a core collapse supernova (CCSN) progenitor is 0.7 M ⊙ higher. Conclusions. Current constraints from observed type II-P supernova light curves and pre-explosive luminosity do not exclude an ALP production within the current bounds. However, the maximum age of CCSN progenitors, as deduced from the star formation rate of the parent stellar population, would require a lower minimum mass. This discrepancy can be explained by assuming a moderate extra mixing (as due to core overshooting or rotational induced mixing) above the fully convective core that develops during the main sequence.

Type Ia supernovae (SNe Ia) are likely the thermonuclear explosions of carbon–oxygen (CO) white-dwarf (WD) stars, but their progenitor systems remain elusive. Recent studies have suggested that a propagating detonation within a thin helium shell surrounding a sub-Chandrasekhar mass CO core can subsequently trigger a detonation within the core (the double-detonation model, DDM). The outcome of this explosion is similar to a central ignition of a sub-Chandrasekhar mass CO WD (SCD). While SCD is consistent with some observational properties of SNe Ia, several computational challenges prohibit a robust comparison to the observations. We focus on the observed t0−MNi56 relation, where t0 (the γ-rays’ escape time from the ejecta) is positively correlated with MNi56 (the synthesized 56Ni mass). We apply our recently developed numerical scheme to calculate SCD and show that the calculated t0−MNi56 relation, which does not require radiation transfer calculations, converges to an accuracy of a few per cent. We find a clear tension between our calculations and the observed t0−MNi56 relation. SCD predicts an anticorrelation between t0 and MNi56, with $t_0\approx 30\, \textrm{d}$ for luminous ($M_\text{Ni56}\gtrsim 0.5\, \mathrm{ M}_{\odot }$) SNe Ia, while the observed t0 is in the range of $35\!-\!45\, \textrm{d}$. We show that this tension is larger than the uncertainty of the results, and that it exists in all previous studies of the problem. Our results hint that more complicated models are required, but we argue that DDM is unlikely to resolve the tension with the observations.

Type Ia supernovae (SNe Ia) often show high-velocity absorption features (HVFs) in their early phase spectra; however the origin of the HVFs is unknown. We show that a near-Chandrasekhar-mass white dwarf (WD) develops a silicon-rich layer on a carbon-oxygen (CO) core before it explodes as an SN Ia. We calculated the nuclear yields in successive helium shell flashes for 1.0 $M_\odot$, 1.2 $M_\odot$, and 1.35 $M_\odot$ CO WDs accreting helium-rich matter with several mass-accretion rates ranging from $1 \times 10^{-7}~M_\odot$ yr$^{-1}$ to $7.5 \times 10^{-7}~M_\odot$ yr$^{-1}$. For the $1.35~M_\odot$ WD with the accretion rate of $1.6 \times 10^{-7}~M_\odot$ yr$^{-1}$, the surface layer developed as helium burning ash and consisted of 40% $^{24}$Mg, 33% $^{12}$C, 23% $^{28}$Si, and a few percent of $^{20}$Ne by weight. For a higher mass accretion rate of $7.5 \times 10^{-7}~M_\odot$ yr$^{-1}$, the surface layer consisted of 58% $^{12}$C, 31% $^{24}$Mg, and 0.43% $^{28}$Si. For the $1.2~M_\odot$ WDs, silicon is produced only for lower mass accretion rates (2% for $1.6 \times 10^{-7}~M_\odot$ yr$^{-1}$). No substantial silicon ($< 0.07%$) is produced on the $1.0~M_\odot$ WD independently of the mass-accretion rate. If the silicon-rich surface layer is the origin of Si II HVFs, its characteristics are consistent with that of mass increasing WDs. We also discuss possible Ca production on very massive WDs ($ \gtrsim 1.38~M_\odot$).

The progenitor systems and explosion mechanism of Type Ia supernovae are still unknown. Currently favoured progenitors include double-degenerate systems consisting of two carbon-oxygen white dwarfs with thin helium shells. In the double-detonation scenario, violent accretion leads to a helium detonation on the more massive primary white dwarf that turns into a carbon detonation in its core and explodes it. We investigate the fate of the secondary white dwarf, focusing on changes of the ejecta and observables of the explosion if the secondary explodes as well rather than survives. We simulate a binary system of a $1.05\, \mathrm{M_\odot }$ and a $0.7\, \mathrm{M_\odot }$ carbon-oxygen white dwarf with $0.03\, \mathrm{M_\odot }$ helium shells each. We follow the system self-consistently from inspiral to ignition, through the explosion, to synthetic observables. We confirm that the primary white dwarf explodes self-consistently. The helium detonation around the secondary white dwarf, however, fails to ignite a carbon detonation. We restart the simulation igniting the carbon detonation in the secondary white dwarf by hand and compare the ejecta and observables of both explosions. We find that the outer ejecta at $v~\gt ~15\, 000$ km s−1 are indistinguishable. Light curves and spectra are very similar until $\sim ~40 \ \mathrm{d}$ after explosion and the ejecta are much more spherical than violent merger models. The inner ejecta differ significantly slowing down the decline rate of the bolometric light curve after maximum of the model with a secondary explosion by ∼20 per cent. We expect future synthetic 3D nebular spectra to confirm or rule out either model.

We present the first linear polarimetric survey of white dwarfs (WDs). Our sample consists of WDs of DA and DC spectral types in the SDSS r magnitude range from 13 to 17. We performed polarimetric observations with the RoboPol polarimeter attached to the 1.3-m telescope at the Skinakas Observatory. We have 74 WDs in our sample, of which almost all are low polarized WDs with polarization degree (PD) smaller than 1%, while only 2 have PD higher than 1%. There is an evidence that on average the isolated WDs of DC type have higher PD (with median PD of 0.78%) than the isolated DA type WDs (with median PD of 0.36%). On the other hand, the median PD of isolated DA type WDs is almost the same, i.e. 0.36% as the median PD of DA type white dwarfs in binary systems with red dwarfs (dM type), i.e. 0.33%. This shows, as expected, that there is no contribution to the PD from the companion if the WD companion is the red dwarf, which is the most common situation for WDs binary systems. We do not find differences in the polarization degree between magnetic and non-magnetic WDs. Because 97% of WDs in our sample have PD lower than 1%, they can be used as faint zero--polarized standard star in the magnitude range from 13 up to 17 of SDSS r filter. They cover the Northern sky between 13 hour to 23 hour in right ascension and from -11 degrees to 78 degrees in declination. Additionally, we found that for low extinction values (< 0.04) the best model that describes the dependence of PD on E(B-V) is given by the equation: PD_{max, ISM}[%] = 0.65 x E(B-V)^{0.12}.

Knowing the late stages of the stellar evolution is crucial for understanding the fate of planets around subdwarfs and white dwarfs. Simulations by (Staff et al.2016) show, that exoplanets engulfed in the extending stellar envelope will quickly spiral down onto the parent star. Therefore, we do not expect to find planets on close by orbits to the subdwarfs (Blokesz et al.2019) or white dwarfs. However, the recent observation of planetary debris around WD 1145+017 white dwarf suggests, there might exists planets farther away from these stars. Using binarograms, O-C diagrams and Fourier transform for the Kepler space telescope data, we investigate a problem of missing planets around white dwarfs in binary systems, single white dwarfs and subdwarfs type B. The last ones, being the only stars which (due to the lack of hydrogen) go directly to the white dwarf cooling track after their red giant phase.

Although multidimensional simulations have investigated the processes of double white dwarf (WD) mergers, postmerger evolution only focused on the carbon–oxygen (CO) or helium (He) WD merger remnants. In this work, we investigate for the first time the evolution of the remnants stemming from the merger of oxygen–neon (ONe) WDs with CO WDs. Our simulation results indicate that the merger remnants can evolve to hydrogen- and helium-deficient giants with a maximum radius of about 300 R ⊙. Our models show evidence that merger remnants more massive than 1.95 M ⊙ can ignite Ne before significant mass loss ensues, and they thus would become electron-capture supernovae. However, remnants with initial masses less than 1.90 M ⊙ will experience further core contraction and longer evolutionary time before reaching the conditions for Ne burning. Therefore, their fates are more dependent on mass-loss rates due to stellar winds and thus more uncertain. Relatively high mass-loss rates would cause such remnants to end their lives as ONe WDs. Our evolutionary models can naturally explain the observational properties of the double WD merger remnant IRAS 00500+6713 (J005311). As previously suggested in the literature, we propose and justify that J005311 may be the remnant from the coalescence of an ONe WD and a CO WD. We deduce that the final outcome of J005311 would be a massive ONe WD rather than a supernova explosion. Our investigations may be able to provide possible constraints on the wind mass-loss properties of the giants that have CO-dominant envelopes.

There is increasing evidence that Type I supernovae (SN I) are the main producers of iron-peak elements in the Galaxy. In addition observations of SN I also indicate the existence of appreciable amounts of intermediate elements like O, Mg, Si, S, and Ca in the outer layers of the exploding star. Such an abundance pattern can be produced by carbon deflagration models of accreting carbon-oxygen white dwarfs in binary systems or stars on the asymptotic giant branch (AGB) which ignite central carbon burning explosively. The present study discusses the nucleosynthesis results of those carbon deflagration supernovae in detail. Special emphasis is given to the discussion of burning conditions and corresponding nucleosynthesis products. The overproduction of 54Fe+58Ni, mentioned in earlier publications, is still existing. Assuming that SN I which contributed to the abundances in the solar system, originated from white dwarfs with a metallicity range 0.1<Z/Z⊙<1, might remove this overproduction. This would allow for SN I to be the major contributors of Fe-group nuclei in galactic nucleosynthesis.

The present study is aimed at exploring the effects of hydrogen envelopes on the structure and evolution of low- and intermediate-mass, helium white dwarfs. To this end, we compute the evolution of models of helium white dwarfs with masses ranging from 0.15 to 0.5 M⊙ for low and intermediate effective temperatures. We treat the mass of the hydrogen envelope as a free parameter within the range 10-8≤MH/M≤4×10-3. The calculations are carried out by means of a detailed white dwarf evolutionary code in which updated radiative opacities and equations of state for hydrogen and helium plasmas are considered. The energy transport by convection is described by the full spectrum turbulence theory developed by Canuto, Goldman & Mazzitelli, which has no free parameters. We also take into account both convective mixing in the outer layers occurring at low luminosities and the presence of hydrogen burning at the bottom of the hydrogen-rich envelope by means of the inclusion of a detailed network of thermonuclear reaction rates. Our attention is focused mainly on that phase of evolution where finite-temperature effects are particularly significant. In this respect, we find that thick hydrogen envelopes appreciably modify the radii and surface gravity of the no-hydrogen models, especially in the case of low-mass configurations. In addition, convective mixing in low-luminosity models with thin hydrogen envelopes leads to objects with helium-dominated outer layers. Finally, we find that the role played by hydrogen burning in these stars is strongly dependent on the mass of the hydrogen envelope. The computations presented here represent the most detailed models of helium white dwarfs with hydrogen envelopes presently available. These models should be particularly valuable for the study of the structure and evolutionary status of the recently detected low-mass white dwarfs in binary systems.

Neutron stars can form through core collapse (CC) following a supernova explosion of a massive star, or from a white dwarf that first forms in a binary system and then collapses into a neutron star via accretion induced collapse (AIC). So far, there have been no unambiguous identifications of AIC neutron stars in our Galaxy, although it has been suspected that they may exist among the population of binary millisecond pulsars (BMSPs). We summarise results of new calculations on the expected birth rates of binary systems with AIC neutron stars and discuss the predicted orbital period of systems with He, CO and O-Ne-Mg white dwarfs and main sequence companions. We argue that AIC systems may make an important contribution to the observed population of BMSPs.