Type IIb Supernova Progenitors in 3D: Variability and Episodic Mass Loss Revealed by Radiation Hydrodynamics Simulations

The Astrophysical Journal Letters · 2026-02-04

Abstract We present the first 3D radiation hydrodynamics simulations of partially stripped ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">core</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>10</mml:mn> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> , M env ∼ 0.1–1 M ⊙ ) yellow supergiant ( L ∼ 10 5 L ⊙ , T eff ≈ 5000–8000 K) envelopes, constructed with Athena++ . These envelope models represent the progenitors of type IIb supernovae (SNe IIb), which have lost a substantial fraction of their H-rich envelope before undergoing core collapse. The luminosity-to-mass ratio is high in these extended envelopes, and convection is strongly driven by hydrogen and helium opacity peaks. This surface convection, coupled with changes in the opacity, sustains large-amplitude low-azimuthal-order radial pulsations, creating order-of-magnitude variability in the stellar luminosity on a timescale of tens of days. If persistent prior to the SN, these variations will be detectable with dedicated monitoring of SN IIb progenitor candidates in nearby galaxies and within deep all-sky time-domain surveys, such as the Vera Rubin Observatory’s Legacy Survey of Space and Time. Supersonic fluid motions across the outer layers of the star lead to both successful and failed mass-ejection events, which shape the circumstellar environment and drive episodic mass loss (∼10 −6 –10 −5 M ⊙ yr −1 , in outbursts). The resulting 3D gas distribution in the outer atmosphere, responsible for early-time SN shock-breakout and shock-cooling emission, shows orders-of-magnitude fluctuations in both space and time at any given radial location. This intrinsically complex halo of bound and unbound material complicates predictions for early SN IIb light curves relative to spherically symmetric models. However, it does provide a natural, self-consistent explanation for the presence and diversity of dense circumstellar material observed or inferred around pulsating evolved stars.

Aspherical Remnants of Triple and Quadruple Detonations in Binary White Dwarfs

The Astrophysical Journal · 2026-01-12 · 1 citations

Abstract White dwarfs which explode by the double-detonation mechanism may have a binary white dwarf donor which is subsequently ignited by its collision with the ejecta. This results in the destruction of the donor via either the triple- or quadruple-detonation mechanism, adding significant mass to the resulting ejecta as well as modifying its structure and composition. We simulate the evolution of supernova remnants resulting from such detonations in a variety of binary progenitors and compare them against a double detonation with a surviving donor. Because of the time delay between the detonations of the two white dwarfs, high-velocity ejecta from the first explosion govern the first few centuries of remnant evolution, whereas at later times the dense core resulting from the donor detonation drives both the forward and reverse shocks to larger radii. The collision between the highest-velocity ejecta of the primary explosion and the donor carves a conical wake into the ejecta, which persists into the remnant phase regardless of whether or not the donor detonates. Our suite of simulated remnants is found to exhibit multiple distinguishing features of the explosion properties: a distinct X-ray morphology in the thermal emission and iron lines for triple detonations and smaller remnants with centrally concentrated emission for double detonations. The remnants are also varied in their elemental abundances and distributions, particularly for lighter elements, but these have limited observational utility and are sensitive to the properties of the progenitor binary.

Type IIb Supernova Progenitors in 3D: Variability and Episodic Mass Loss revealed by Radiation-Hydrodynamics Simulations

ArXiv.org · 2025-08-17

We present the first 3D Radiation-Hydrodynamics simulations of partially-stripped ($M_\mathrm{core}\sim10M_\odot$, $M_\mathrm{env}\sim0.1-1M_\odot$) Yellow Supergiant ($L\sim10^5$, $T_\mathrm{eff}\approx5000-8000$K) envelopes, constructed with Athena++. These envelope models represent the progenitors of Type IIb supernovae (SNe-IIb), which have lost a substantial fraction of their H-rich envelope before undergoing core-collapse. The luminosity-to-mass ratio is high in these extended envelopes, and convection is strongly driven by Hydrogen and Helium opacity peaks. This surface convection, coupled with changes in the opacity, sustains large-amplitude low-azimuthal-order radial pulsations, creating order-of-magnitude variability in the stellar luminosity on a timescale of tens of days. If persistent prior to a SN-IIb, these variations could herald the upcoming explosion. Supersonic fluid motions across the outer layers of the star lead to both successful and failed mass ejection events, which shape the circumstellar environment and drive episodic mass loss ($\sim10^{-6}-10^{-5}M_\odot/$yr, in outbursts). The resulting 3D gas distribution in the outer atmosphere, responsible for early-time supernova shock-breakout and shock-cooling emission, shows orders-of-magnitude fluctuations in both space and time at any given radial location. This intrinsically complex halo of bound and unbound material complicates predictions for early SN-IIb lightcurves relative to spherically-symmetric models. However, it does provide a natural, self-consistent explanation for the presence and diversity of dense circumstellar material observed or inferred around pulsating evolved stars.

Mass Loss and Subsequent Thermal Evolution of Surviving Helium White Dwarfs Shocked by Thermonuclear Supernovae

ArXiv.org · 2025-08-17

Following a type Ia supernova (SN Ia) in a double white dwarf (WD) binary, a surviving WD companion leaves at its orbital velocity $\approx 1$,000 - 3,000 km/s. The Gaia mission has discovered seven such hypervelocity WDs with inflated radii indicative of shock heating by SN ejecta. We study the interaction between SN ejecta and Roche lobe-filling 0.08 - 0.45 $M_{\odot}$ helium WD companions using three-dimensional hydrodynamical simulations with Athena++. Given the importance of the later thermal evolution, we include an accurate equation-of-state for the degenerate helium WD donor. We show that a lower-mass, larger-radius WD companion is more strongly impacted by SN ejecta and undergoes substantial mass loss. We find a tight relation between the fractional mass loss and the ratio between the ejecta ram pressure and donor volume-averaged pressure, which can be used for predicting mass loss in other systems. In the most extreme case, the companion becomes a very inflated $\approx0.02\,M_{\odot}$ object. We find helium mass loss $\approx 0.005 - 0.06\,M_{\odot}$ with velocities $\approx $ 1,000$-$4,000 km/s, which may lead to emission lines in the nebular phase. The surviving helium WD receives a kick velocity, but its final velocity is essentially determined by its orbital velocity $\lesssim$ 1,600 km/s. We model the post-explosion evolution of the shock-heated companions using MESA, and find reasonable agreement with the hypervelocity stars D6-2, J0546+0836, J1332-3541 &amp; SDSS J1637+3631. A surviving $\gtrsim 0.3\,M_{\odot}$ helium WD can be ruled out in SN1972E &amp; SN2011fe, and any surviving helium WD is likely ruled out in SN remnants 0509-67.5 &amp; SN1006.

Wakes from Companion Interactions in Type Ia Supernovae Nebular Emission Line Profiles

ArXiv.org · 2025-07-08

Thermonuclear supernovae (SNe) are the result of the nuclear transformation of carbon/oxygen (C/O) white dwarfs (WDs) to the radioactive element $^{56}\mathrm{Ni}$ and intermediate mass elements (IMEs) like Ca, Ar, etc. Most progenitor scenarios involve a companion star which donates matter to the exploding white dwarf, implying a fundamental prediction: the formation of a wake in the explosive ejecta as it runs into and moves past the companion star. This wake leaves an indelible imprint on the ejecta's density, velocity, and composition structure that remains fixed as the ejecta reaches homologous expansion. We simulate the interaction of the ejecta and Roche-lobe filling donor in a double degenerate double detonation Type Ia progenitor scenario and explore the detectability of this imprint in late-time nebular phase spectroscopy of Type Ia SNe under the assumption of local heating ($t &gt; 200$ days). At these times, the velocity profiles of forbidden emission lines reflect the velocity distribution of all of the ejecta and the critical electron density for that forbidden line. We explicitly calculate line shapes for the [Co III] $11.89 μ\mathrm{m}$ line that traces the initial $^{56}\mathrm{Ni}$ distribution and the [Ar III] $8.99 μ\mathrm{m}$ line, which traces a typical intermediate mass element. We predict the viewing angle dependence of the line shape, present a tool to quickly calculate optically thin line shapes for various 3D density-velocity profiles and discuss JWST observations.

The First Day of a Type Ia Supernova from a Double-degenerate Binary

The Astrophysical Journal · 2025-10-01 · 3 citations

Abstract Supernovae in binary star systems involve a hydrodynamical interaction between the ejecta and a binary companion. This collision results in shock heating and a modified density structure for the ejecta, both of which affect the light curve. As highlighted by D. Kasen, these considerations are particularly relevant for Type Ia supernovae, as the companion is expected to be Roche-lobe filling at the time of the explosion. We simulate here the interaction between Type Ia supernova ejecta and a white dwarf donor using Athena++, finding the formation of a low-density wake extending to higher velocities than the unperturbed ejecta. Radiation hydrodynamics is then used to generate synthetic light curves for the first day after the explosion for a range of viewing angles. We find that the hot, high-velocity, shocked ejecta yield L &gt; 10 40 erg s −1 over half the sky in the first few hours. The photosphere within the shock-heated ejecta cools and recedes in velocity space, partially obscuring it from view, as heating from radioactive nickel becomes increasingly important in driving the supernova’s luminosity. By one day after the explosion, the luminosity measured by observers looking directly into the wake is dimmer than that of a normal Type Ia supernova by 15% due to the modified density structure.

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California Digital Library · 2025-01-01

Stochastic low-frequency variability of 50 massive stars in the Cygnus OB associations and the Small Magellanic Cloud

ArXiv.org · 2025-04-22

In recent years, high-precision high-cadence space photometry has revealed that stochastic low frequency (SLF) variability is common in the light curves of massive stars. We use the data from the Transiting Exoplanet Survey Satellite (TESS) to study and characterize the SLF variability found in a sample of 49 O- and B-type main-sequence stars across six Cygnus OB~associations and one low-metallicity SMC star AV~232. We compare these results to 53 previously studied SLF variables. We adopt two different methods for characterizing the signal. In the first, we follow earlier work and fit a Lorentzian-like profile to the power density spectrum of the residual light curve to derive the amplitude $α_0$, characteristic frequency $ν_{\rm char}$, and slope $γ$ of the variability. In our second model-independent method, we calculate the root-mean-square (RMS) of the photometric variability as well as the frequency at 50\% of the accumulated power spectral density, $ν_{50\%}$, and the width of the cumulative integrated power density, $w$. For the full sample of 103 SLF variables, we find that $α_0$, $γ$, RMS, $ν_{50\%}$, and $w$ correlate with the spectroscopic luminosity of the stars. Both $α_0$ and RMS appear to increase for more evolved stars whereas $ν_{\rm char}$ and $ν_{50\%}$ both decrease. Finally, we compare our results to 2-D and 3-D simulations of subsurface convection, core-generated internal gravity waves, and surface stellar winds, and find good agreement between the observed $ν_{\rm char}$ of our sample and predictions from sub-surface convection.

Ejecta Wakes from Companion Interaction in Type Ia Supernova Remnants

The Astrophysical Journal · 2025-03-19 · 7 citations

Abstract Type Ia supernovae are triggered by accretion onto a white dwarf from a companion that is most likely Roche lobe–filling at the time of the explosion. The collision between the ejecta and a surviving companion carves out a conical wake, which could manifest as an asymmetry when the ejecta reaches the remnant phase. We simulate the companion interaction using the Athena++ hydrodynamics solver to determine the ejecta structure for a double-degenerate type Ia supernova. Ejecta in the wake is of lower density and higher velocity than the unperturbed ejecta. We then evolve the ejecta for several thousand years using the expanding-grid code Sprout. The forward shock within the wake is initially indented, but becomes spherical after roughly a thousand years due to transverse motion of shocked ejecta that fills the wake. The reverse shock travels quickly within the wake, leading to an off-center convergence of the reverse shock and leaving the remnant with an asymmetrical core. This also draws material from the interstellar medium deep into the remnant, eventually reaching the center. Large Rayleigh–Taylor plumes are found around the edge of the wake, creating a toroidal structure composed primarily of ejecta. Estimates of the thermal X-ray emission show that such remnants exhibit observable asymmetries for thousands of years.

Stochastic low-frequency variability of 50 massive stars in the Cygnus OB associations and the Small Magellanic Cloud

Monthly Notices of the Royal Astronomical Society · 2025-04-25 · 4 citations

ABSTRACT In recent years, high-precision high-cadence space photometry has revealed that stochastic low-frequency (SLF) variability is common in the light curves of massive stars. We use the data from the Transiting Exoplanet Survey Satellite to study and characterize the SLF variability found in a sample of 49 O- and B-type main-sequence stars across six Cygnus OB associations and one low-metallicity Small Magellanic Cloud star AV 232. We compare these results to 53 previously studied SLF variables. We adopt two different methods for characterizing the signal. In the first, we follow earlier work and fit a Lorentzian-like profile to the power density spectrum of the residual light curve to derive the amplitude $\alpha _0$, characteristic frequency $\nu _{\rm char}$, and slope $\gamma$ of the variability. In our second model-independent method, we calculate the root mean square (RMS) of the photometric variability as well as the frequency at 50 per cent of the accumulated power spectral density, $\nu _{50~{{\ \rm per\ cent}}}$, and the width of the cumulative integrated power density, w. For the full sample of 103 SLF variables, we find that $\alpha _0$, $\gamma$, RMS, $\nu _{50~{{\ \rm per\ cent}}}$, and w correlate with the spectroscopic luminosity of the stars. Both $\alpha _0$ and RMS appear to increase for more evolved stars, whereas $\nu _{\rm char}$ and $\nu _{50~{{\ \rm per\ cent}}}$ both decrease. Finally, we compare our results to 2D and 3D simulations of subsurface convection, core-generated internal gravity waves, and surface stellar winds, and find good agreement between the observed $\nu _{\rm char}$ of our sample and predictions from subsurface convection.