Kavli Affiliate: Lars Bildsten
| First 5 Authors: Jared A. Goldberg, Jared A. Goldberg, , ,
| Summary:
We present the first 3D Radiation-Hydrodynamics simulations of
partially-stripped ($M_mathrmcoresim10M_odot$,
$M_mathrmenvsim0.1-1M_odot$) Yellow Supergiant ($Lsim10^5$,
$T_mathrmeffapprox5000-8000$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
($sim10^-6-10^-5M_odot/$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.
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