Accretion-Induced Collapse From Helium Star + White Dwarf Binaries

Abstract

Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandrasekhar mass ($M_{\mathrm{Ch}}$), reaching central densities that trigger electron captures in the core. Using Modules for Experiments in Stellar Astrophysics ($\text{MESA}$), we present the first true binary simulations of He star + O/Ne WD binaries, focusing on a $1.5M_{\odot }$ He star in a 3 hour orbital period with $1.1-1.3M_{\odot }$ O/Ne WDs. The helium star fills its Roche lobe after core helium burning is completed and donates helium on its thermal timescale to the WD, $\dot{M}\approx 3\times 10^{-6}{M}_{\odot }$/yr, a rate high enough that the accreting helium burns stably on the WD. The accumulated carbon/oxygen ashes from the helium burning undergo an unstable shell flash that initiates an inwardly moving carbon burning flame. This flame is only quenched when it runs out of carbon at the surface of the original O/Ne core. Subsequent accumulation of fresh carbon/oxygen layers also undergo thermal instabilities, but no mass loss is triggered, allowing $M_{\mathrm{WD}}\to M_{\mathrm{Ch}}$, triggering the onset of AIC. We also discuss the scenario of accreting C/O WDs that experience shell carbon ignitions to become O/Ne WDs, and then, under continuing mass transfer, lead to AIC. Studies of the AIC event rate using binary population synthesis should include all of these channels, especially this latter channel, which has been previously neglected but might dominate the rate.

9 pages, 8 figures

References in corpus (5)

• Modules for Experiments in Stellar Astrophysics (MESA)
• On Carbon Burning in Super Asymptotic Giant Branch Stars
• Hybrid C-O-Ne white dwarfs as progenitors of type Ia supernovae: dependence on Urca process and mixing assumptions
• The hybrid CONe WD + He star scenario for the progenitors of type Ia supernovae
• Convection Destroys the Core/Mantle Structure in Hybrid C/O/Ne White Dwarfs

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• Evolution of Magnetized White Dwarf Binaries to Type Ia Supernovae
• Fast and Luminous Transients from the Explosions of Long Lived Massive White Dwarf Merger Remnants
• Evolution of Helium Star - White Dwarf Binaries Leading up to Thermonuclear Supernovae
• HD 49798: Its History of Binary Interaction and Future Evolution
• Off-centre carbon burning in He-accreting carbon-oxygen white dwarfs