Engineering topics

Woosley, S. E.

Publications and source records attributed to Woosley, S. E..

At least 19 records

DOE OSTI2023

Multidimensional Radiation Hydrodynamics Simulations of Pulsational Pair-instability Supernovae

Stars with masses of 80–130 M ⊙ can encounter pulsational pair-instability at the end of their lives, which triggers consecutive episodes of explosive burning that eject multiple massive shells. Collisions between these shells produce bright transients known as pulsational pair-instability supernovae (PPI SNe) that may explain some extreme supernovae. In this paper, we present the first 2D and 3D radiation hydrodynamics simulations of PPI SNe with the CASTRO code. Radiative cooling causes the collided shells to evolve into thin, dense structures with hot spots that can enhance the peak luminosity of the SN by factors of 2–3. The light curve peaks at 1.9–2.1 × 10 43 erg s -1 for 50 days and then plateaus at 2–3 × 10 42 erg s -1 for 200 days, depending on the viewing angle. The presence of 12 C and 16 O and the absence of 28 Si and 56 Fe in its spectra can uniquely identify this transient as a PPI SN in follow-up observations. Our models suggest that multidimensional radiation hydrodynamics is required to model the evolution and light curves of all shell-collision SNe, such as Type IIne, not just PPI SNe.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Model Light Curves for Type Ib and Ic Supernovae

Using the Monte Carlo code SEDONA, multiband photometry and spectra are calculated for supernovae derived from stripped helium stars with presupernova masses of 2.2 to 10.0 M ⊙ . The models are representative of evolution in close binaries and have previously been exploded using a parameterized one-dimensional model for neutrino transport. A subset, those with presupernova masses in the range of 2.2–5.6 M⊙, have many properties in common with observed Type Ib and Ic supernovae, including a median ejected mass near 2 M ⊙ , explosion energies near 1 × 10 51 erg, typical 56 Ni masses of 0.07–0.09 M ⊙ , peak times of about 20 days, and a narrow range for the V - R color index 10 days post-V-maximum near 0.3 mag. The median peak bolometric luminosity, near 10 42.3 erg s -1 , is fainter, however, than several observational tabulations, and the brightest explosion has a bolometric luminosity of only 10 42.50 erg s -1 . The brightest absolute B, V, and R magnitudes at peak are -17.2, -17.8, and -18.0. These limits are fainter than some allegedly typical Type Ib and Ic supernovae and could reflect problems in our models or in the observational analysis. Helium stars with lower and higher masses also produce interesting transients that may have been observed, including fast, faint, blue transients and long, red, faint Type Ic supernovae. New models are specifically presented for SN 2007Y, SN 2007gr, SN 2009jf, LSQ 13abf, SN 2008D, and SN 2010X.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

GRB 161219B/SN 2016jca: a powerful stellar collapse

ABSTRACT We report observations and analysis of the nearby gamma-ray burst GRB 161219B (redshift z = 0.1475) and the associated Type Ic supernova (SN) 2016jca. GRB 161219B had an isotropic gamma-ray energy of ∼1.6 × 1050 erg. Its afterglow is likely refreshed at an epoch preceding the first photometric points (0.6 d), which slows down the decay rates. Combined analysis of the SN light curve and multiwavelength observations of the afterglow suggest that the GRB jet was broad during the afterglow phase (full opening angle ∼42° ± 3°). Our spectral series shows broad absorption lines typical of GRB supernovae (SNe), which testify to the presence of material with velocities up to ∼0.25c. The spectrum at 3.73 d allows for the very early identification of an SN associated with a GRB. Reproducing it requires a large photospheric velocity ($35\, 000 \pm 7000$ km s−1). The kinetic energy of the SN is estimated through models to be Ekin≈4 × 1052 erg in spherical symmetry. The ejected mass in the explosion was Mej≈6.5 ± 1.5 M⊙, much less than that of other GRB-SNe, demonstrating diversity among these events. The total amount of 56Ni in the explosion was 0.27 ± 0.05 M⊙. The observed spectra require the presence of freshly synthesized 56Ni at the highest velocities, at least three times more than a standard GRB-SN. We also find evidence for a decreasing 56Ni abundance as a function of decreasing velocity. This suggests that SN 2016jca was a highly aspherical explosion viewed close to on-axis, powered by a compact remnant. Applying a typical correction for asymmetry, the energy of SN 2016jca was ∼(1–3) × 1052 erg, confirming that most of the energy produced by GRB-SNe goes into the kinetic energy of the SN ejecta.

Ashall, C.↗

DOE OSTI2018

A UV resonance line echo from a shell around a hydrogen-poor superluminous supernova

Hydrogen-poor superluminous supernovae (SLSN-I) are a class of rare and energetic explosions discovered in untargeted transient surveys in the past decade. The progenitor stars and the physical mechanism behind their large radiated energies ($\sim10^{51}$ erg) are both debated, with one class of models primarily requiring a large rotational energy, while the other requires very massive progenitors to either convert kinetic energy into radiation via interaction with circumstellar material (CSM), or engender a pair-instability explosion. Observing the structure of the CSM around SLSN-I offers a powerful test of some scenarios, though direct observations are scarce. Here, we present a series of spectroscopic observations of the SLSN-I iPTF16eh, which reveal both absorption and time- and frequency-variable emission in the Mg II resonance doublet. We show that these observations are naturally explained as a resonance scattering light echo from a circumstellar shell. Modeling the evolution of the emission, we find a shell radius of 0.1 pc and velocity of 3300 km s$^{-1}$, implying the shell was ejected three decades prior to the supernova explosion. These properties match theoretical predictions of pulsational pair-instability shell ejections, and imply the progenitor had a He core mass of $\sim 50-55~{\rm M}_{\odot}$, corresponding to an initial mass of $\sim 115~{\rm M}_{\odot}$.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Very Low-energy Supernovae: Light Curves and Spectra of Shock Breakout

The brief transient emitted as a shock wave erupts through the surface of a pre-supernova star carrying information about the stellar radius and explosion energy. Here, the CASTRO code, which treats radiation transport using multigroup flux-limited diffusion, is used to simulate the light curves and spectra of shock breakout in very low-energy supernovae (VLE SNe), explosions in giant stars with final kinetic energy much less than 10{sup 51} erg. VLE SN light curves, computed here with the KEPLER code, are distinctively faint, red, and long-lived, making them challenging to find with transient surveys. The accompanying shock breakouts are brighter, though briefer, and potentially easier to detect. Previous analytic work provides general guidance, but numerical simulations are challenging, due to the range of conditions and lack of equilibration between color and effective temperatures. We consider previous analytic work and extend discussions of color temperature and opacity to the lower energy range explored by these events. Since this is the first application of the CASTRO code to shock breakout, test simulations of normal energy shock breakout of SN 1987A are carried out and compared with the literature. A set of breakout light curves and spectra are then calculated for VLE SNe with final kinetic energies in the range 10{sup 47}--10{sup 50} erg for red supergiants with main-sequence masses of 15 and 25 M{sub ⊙}. The importance of uncertainties in stellar atmosphere model, opacity, and ambient medium is discussed, as are observational prospects with current and forthcoming missions.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Low-energy Population III supernovae and the origin of extremely metal-poor stars

Some ancient, dim, metal-poor stars may have formed in the ashes of the first supernovae (SNe). If their chemical abundances can be reconciled with the elemental yields of specific Population III (Pop III) explosions, they could reveal the properties of primordial stars. But multidimensional simulations of such explosions are needed to predict their yields because dynamical instabilities can dredge material up from deep in the ejecta that would otherwise be predicted to fall back on to the central remnant and be lost in one-dimensional (1D) models. We have performed two-dimensional (2D) numerical simulations of two low-energy Pop III SNe, a 12.4 M ⊙ explosion and a 60 M ⊙ explosion, and find that they produce elemental yields that are a good fit to those measured in the most iron-poor star discovered to date, SMSS J031300.36-670839.3 (J031300). Fallback on to the compact remnant in these weak explosions accounts for the lack of measurable iron in J031300 and its low iron-group abundances in general. Our 2D explosions produce higher abundances of heavy elements (atomic number Z > 20) than their 1D counterparts due to dredge-up by fluid instabilities. Since almost no 56 Ni is ejected by these weak SNe, their low luminosities will prevent their detection in the near-infrared with the James Webb Space Telescope and future 30-m telescopes on the ground. The only evidence that they ever occurred will remain in the fossil abundance record

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

MAGNETAR-POWERED SUPERNOVAE IN TWO DIMENSIONS. I. SUPERLUMINOUS SUPERNOVAE

Previous studies have shown that the radiation emitted by a rapidly rotating magnetar embedded in a young supernova can greatly amplify its luminosity. These one-dimensional studies have also revealed the existence of an instability arising from the piling up of radiatively accelerated matter in a thin dense shell deep inside the supernova. Here, we examine the problem in two dimensions and find that, while instabilities cause mixing and fracture this shell into filamentary structures that reduce the density contrast, the concentration of matter in a hollow shell persists. The extent of the mixing depends upon the relative energy input by the magnetar and the kinetic energy of the inner ejecta. The light curve and spectrum of the resulting supernova will be appreciably altered, as will the appearance of the supernova remnant, which will be shellular and filamentary. A similar pile up and mixing might characterize other events where energy is input over an extended period by a centrally concentrated source, e.g., a pulsar, radioactive decay, a neutrino-powered wind, or colliding shells. The relevance of our models to the recent luminous transient ASASSN-15lh is briefly discussed.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Core-collapse supernovae from 9 to 120 solar masses based on neutrino-powered explosions

Nucleosynthesis, light curves, explosion energies, and remnant masses are calculated for a grid of supernovae (SNe) resulting from massive stars with solar metallicity and masses from 9.0 to 120 M{sub ⊙}. The full evolution is followed using an adaptive reaction network of up to 2000 nuclei. A novel aspect of the survey is the use of a one-dimensional neutrino transport model for the explosion. This explosion model has been calibrated to give the observed energy for SN 1987A, using five standard progenitors, and for the Crab SN using a 9.6 M{sub ⊙} progenitor. As a result of using a calibrated central engine, the final kinetic energy of the SN is variable and sensitive to the structure of each pre-SN star. Many progenitors with extended core structures do not explode, but become black holes (BHs), and the masses of exploding stars do not form a simply connected set. The resulting nucleosynthesis agrees reasonably well with the Sun provided that a reasonable contribution from SNe Ia is also allowed, but with a deficiency of light s-process isotopes. The resulting neutron star initial mass function has a mean gravitational mass near 1.4 M{sub ⊙}. The average BH mass is about 9 M{sub ⊙} if only the helium core implodes, and 14 M{sub ⊙} if the entire pre-SN star collapses. Only ∼10% of SNe come from stars over 20 M{sub ⊙}, and some of these are Type Ib or Ic. Some useful systematics of Type IIp light curves are explored.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

A two-parameter criterion for classifying the explodability of massive stars by the neutrino-driven mechanism

Thus far, judging the fate of a massive star (either a neutron star [NS] or a black hole) solely by its structure prior to core collapse has been ambiguous. Our work and previous attempts find a nonmonotonic variation of successful and failed supernovae with zero-age main-sequence mass, for which no single structural parameter can serve as a good predictive measure. However, we identify two parameters computed from the pre-collapse structure of the progenitor, which in combination allow for a clear separation of exploding and nonexploding cases with only a few exceptions (∼1%–2.5%) in our set of 621 investigated stellar models. One parameter is M{sub 4}, defining the normalized enclosed mass for a dimensionless entropy per nucleon of s = 4, and the other is μ{sub 4}≡(dm/M{sub ⊙})/(dr/1000 km)|{sub s=4}, being the normalized mass derivative at this location. The two parameters μ{sub 4} and M{sub 4}μ{sub 4} can be directly linked to the mass-infall rate, M-dot , of the collapsing star and the electron-type neutrino luminosity of the accreting proto-NS, L{sub ν{sub e}}∝M{sub ns} M-dot , which play a crucial role in the “critical luminosity” concept for the theoretical description of neutrino-driven explosions as runaway phenomena of the stalled accretion shock. All models were evolved employing the approach of Ugliano et al. for simulating neutrino-driven explosions in spherical symmetry. The neutrino emission of the accretion layer is approximated by a gray transport solver, while the uncertain neutrino emission of the 1.1 M{sub ⊙} proto-NS core is parameterized by an analytic model. The free parameters connected to the core-boundary prescription are calibrated to reproduce the observables of SN 1987A for five different progenitor models.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

The remarkable deaths of 9–11 solar mass stars

The post-helium-burning evolution of stars from 7 M{sub ⊙} to 11 M{sub ⊙} is complicated by the lingering effects of degeneracy and off-center ignition. Here, stars in this mass range are studied using a standard set of stellar physics. Two important aspects of the study are the direct coupling of a reaction network of roughly 220 nuclei to the structure calculation at all stages and the use of a subgrid model to describe the convective bounded flame that develops during neon and oxygen burning. Below 9.0 M{sub ⊙} degenerate oxygen–neon cores form that may become either white dwarfs or electron-capture supernovae. Above 10.3 M{sub ⊙} the evolution proceeds “normally” to iron-core collapse, without composition inversions or degenerate flashes. Emphasis here is upon the stars in between, which typically ignite oxygen burning off-center. After oxygen burns in a convectively bounded flame, silicon burning ignites in a degenerate flash that commences closer to the stellar center and with increasing violence for stars of larger mass. In some cases the silicon flash is so violent that it could lead to the early ejection of the hydrogen envelope. This might have interesting observable consequences. For example, the death of a 10.0 M{sub ⊙} star could produce two supernova-like displays, a faint low-energy event due to the silicon flash, and an unusually bright supernova many months later as the low-energy ejecta from core collapse collides with the previously ejected envelope. The potential relation to the Crab supernova is discussed.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

First Direct Measurement of C 12 ( C 12 , n ) Mg 23 at Stellar Energies

Neutrons produced by the carbon fusion reaction 12 C( 12 C,n) 23 Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. Here in this paper, we present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction 12 C( 12 C,p) 23 Na . The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that 12 C ( 12 C,n) 23 Mg is crucial to the production of Na and Al in pop-III pair instability supernovae. It also plays a nonnegligible role in the production of weak s -process elements, as well as in the production of the important galactic γ-ray emitter 60 Fe.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2015

Distance probes of dark energy

This document presents the results from the Distances subgroup of the Cosmic Frontier Community Planning Study (Snowmass 2013). We summarize the current state of the field as well as future prospects and challenges. In addition to the established probes using Type Ia supernovae and baryon acoustic oscillations, we also consider prospective methods based on clusters, active galactic nuclei, gravitational wave sirens and strong lensing time delays.

Cosmology↗

DOE OSTI2015

The LOFT perspective on neutron star thermonuclear bursts: White paper in support of the mission concept of the large observatory for X-ray timing

The Large Area Detector (LAD) on the Large Observatory For X-ray Timing ( LOFT ), with a 8.5 m 2 photon- collecting area in the 2–30 keV bandpass at CCD-class spectral resolving power (λ/Δλ = 10 – 100), is designed for optimum performance on bright X-ray sources. Thus, it is well-suited to study thermonuclear X-ray bursts from Galactic neutron stars. These bursts will typically yield 2 x 10 5 photon detections per second in the LAD, which is at least 15 times more than with any other instrument past, current or anticipated. The Wide Field Monitor (WFM) foreseen for LOFT uniquely combines 2–50 keV imaging with large (30%) prompt sky coverage. This will enable the detection of tens of thousands of thermonuclear X-ray bursts during a 3-yr mission, including tens of superbursts. Both numbers are similar or more than the current database gathered in 50 years of X-ray astronomy.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Type Ia supernovae from merging white dwarfs. I. Prompt detonations

Merging white dwarfs are a possible progenitor of Type Ia supernovae (SNe Ia). Numerical models suggest that a detonation might be initiated before the stars have coalesced to form a single compact object. Here we study such prompt detonations by means of numerical simulations, modeling the disruption and nucleosynthesis of the stars until the ejecta reach the coasting phase, and generating synthetic light curves and spectra. Three models are considered with primary masses 0.96 M {sub ☉}, 1.06 M {sub ☉}, and 1.20 M {sub ☉}. Of these, the 0.96 M {sub ☉} dwarf merging with a 0.81 M {sub ☉} companion, with an {sup 56}Ni yield of 0.58 M {sub ☉}, is the most promising candidate for reproducing common SNe Ia. The more massive mergers produce unusually luminous SNe Ia with peak luminosities approaching those attributed to 'super-Chandrasekhar' mass SNe Ia. While the synthetic light curves and spectra of some of the models resemble observed SNe Ia, the significant asymmetry of the ejecta leads to large orientation effects. The peak bolometric luminosity varies by more than a factor of two with the viewing angle, and the velocities of the spectral absorption features are lower when observed from angles where the light curve is brightest. The largest orientation effects are seen in the ultraviolet, where the flux varies by more than an order of magnitude. The set of three models roughly obeys a width-luminosity relation, with the brighter light curves declining more slowly in the B band. Spectral features due to unburned carbon from the secondary star are also seen in some cases.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

The deflagration stage of Chandrasekhar mass models for type Ia supernovae. I. Early evolution

We present high-resolution, full-star simulations of the post-ignition phase of Type Ia supernovae using the compressible hydrodynamics code Castro. Initial conditions, including the turbulent velocity field and ignition site, are imported directly from a simulation of the last few hours of presupernova convection using a low Mach number code, Maestro. Adaptive mesh refinement allows the initial burning front to be modeled with an effective resolution of 36,864{sup 3} zones (136 m zone{sup –1}). The initial rise and expansion of the deflagration front are tracked until burning reaches the star's edge and the role of the background turbulence on the flame is investigated. The effect of artificially moving the ignition location closer to the star's center is explored. The degree to which turbulence affects the burning front decreases with increasing ignition radius since the buoyancy force is stronger at larger radii. Even central ignition—in the presence of a background convective flow field—is rapidly carried off-center as the flame is carried by the flow field. We compare our results to analytic models for burning thermals, and find that they reproduce the general trends of the bubble's size and mass, but underpredict the amount of buoyant acceleration due to simplifying assumptions of the bubble's properties. Overall, we find that the amount of mass that burns prior to flame break out is small, consistent with a gravitationally confined detonation' occurring at a later epoch, but additional burning will occur following breakout that may modify this conclusion.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Finding the first cosmic explosions. III. Pulsational pair-instability supernovae

Population III supernovae have been the focus of growing attention because of their potential to directly probe the properties of the first stars, particularly the most energetic events that can be seen at the edge of the observable universe. But until now pulsational pair-instability supernovae, in which explosive thermonuclear burning in massive stars fails to unbind them but can eject their outer layers into space, have been overlooked as cosmic beacons at the earliest redshifts. These shells can later collide and, like Type IIn supernovae, produce superluminous events in the UV at high redshifts that could be detected in the near infrared today. We present numerical simulations of a 110 M {sub ☉} pulsational pair-instability explosion done with the Los Alamos radiation hydrodynamics code Radiation Adaptive Grid Eulerian. We find that collisions between consecutive pulsations are visible in the near infrared out to z ∼ 15-20 and can probe the earliest stellar populations at cosmic dawn.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

FINDING THE FIRST COSMIC EXPLOSIONS. I. PAIR-INSTABILITY SUPERNOVAE

The first stars are the key to the formation of primitive galaxies, early cosmological reionization and chemical enrichment, and the origin of supermassive black holes. Unfortunately, in spite of their extreme luminosities, individual Population III (Pop III) stars will likely remain beyond the reach of direct observation for decades to come. However, their properties could be revealed by their supernova explosions, which may soon be detected by a new generation of near-IR (NIR) observatories such as JWST and WFIRST. We present light curves and spectra for Pop III pair-instability supernovae calculated with the Los Alamos radiation hydrodynamics code RAGE. Our numerical simulations account for the interaction of the blast with realistic circumstellar envelopes, the opacity of the envelope, and Lyman absorption by the neutral intergalactic medium at high redshift, all of which are crucial to computing the NIR signatures of the first cosmic explosions. We find that JWST will detect pair-instability supernovae out to z ∼> 30, WFIRST will detect them in all-sky surveys out to z ∼ 15-20, and LSST and Pan-STARRS will find them at z ∼< 7-8. The discovery of these ancient explosions will probe the first stellar populations and reveal the existence of primitive galaxies that might not otherwise have been detected.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

MULTI-DIMENSIONAL MODELS FOR DOUBLE DETONATION IN SUB-CHANDRASEKHAR MASS WHITE DWARFS

Using two-dimensional and three-dimensional simulations, we study the ''robustness'' of the double detonation scenario for Type Ia supernovae, in which a detonation in the helium shell of a carbon-oxygen white dwarf induces a secondary detonation in the underlying core. We find that a helium detonation cannot easily descend into the core unless it commences (artificially) well above the hottest layer calculated for the helium shell in current presupernova models. Compressional waves induced by the sliding helium detonation, however, robustly generate hot spots which trigger a detonation in the core. Our simulations show that this is true even for non-axisymmetric initial conditions. If the helium is ignited at multiple points, then the internal waves can pass through one another or be reflected, but this added complexity does not defeat the generation of the hot spot. The ignition of very low-mass helium shells depends on whether a thermonuclear runaway can simultaneously commence in a sufficiently large region.

79 ASTRONOMY AND ASTROPHYSICS↗