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

TL;DR

This study uses 3D radiation-hydrodynamics simulations to explore the variability, pulsations, and episodic mass loss in progenitors of Type IIb supernovae, revealing complex circumstellar environments that influence early supernova observations.

Contribution

First 3D simulations of partially-stripped Yellow Supergiant envelopes, showing pulsations and episodic mass loss relevant to Type IIb supernova progenitors.

Findings

Large-amplitude luminosity variability driven by surface convection.

Supersonic motions cause both successful and failed mass ejections.

Complex, fluctuating circumstellar material affects early supernova lightcurves.

Abstract

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.