The single-degenerate model for the progenitors of accretion-induced collapse events

Abstract

It has been suggested that the accretion-induced collapse (AIC) of an oxygen-neon white dwarf (ONe WD) to a neutron star is a theoretically predicted outcome in stellar evolution, likely relating to the formation of some neutron star systems. However, the progenitor models of AIC events are still not well studied, and recent studies indicated that CO WD+He star systems may also contribute to the formation of neutron star systems through AIC process when off-centre carbon ignition happens on the surface of the CO WD. In this work, I studied the single-degenerate (SD) model of AIC events in a systematic way, including the contribution of the CO WD+He star channel and the ONe WD+MS/RG/He star channels. Firstly, I gave the initial parameter space of these SD channels for producing AIC events in the orbital period-secondary mass plane based on detailed binary evolution computations. Then, according to a binary population synthesis approach, I gave the rates and delay times of AIC events for these SD channels based on their initial parameter space. I found that the rates of AIC events in our galaxy are in the range of ∼ 0.3 − 0.9 × 10 −3 yr −1 , and that their delay times are >30 Myr. I also found that the ONe WD+He star channel is the main way to produce AIC events, and that the CO WD+He star channel cannot be ignored when studying the progenitors of AIC events.

On the formation of neutron stars via accretion-induced collapse in binaries

“…As noted in the Results, we do not produce any AIC NSs via the formation channel where a CO WD is produced first, then evolves into an ONe WD via accretion and subsequent carbon shell flashes, though we estimate the contribution from this channel to be on the order of 20%. This COWD-to-AIC scenario was discussed in Brooks et al (2017) (see also Wang 2018), and Brooks et al (2017) state that this may be a significant formation channel leading to AIC events. In our simulations, all AIC progenitors of ONe WDs have masses above 7 M on the ZAMS and, at the base of the AGB, their cores are above the minimum value (threshold between forming CO core and ONe core) that is needed to form an ONe WD (in StarTrack).…”

Accretion-induced Collapse of Dark Matter Admixed White Dwarfs. II. Rotation and Gravitational-wave Signals

“…The GWs have a broad frequency contribution from ∼ 200 Hz to ∼ 1500 Hz and several peaks in-between, which lie in the most sensitive detection band of LIGO. However, from binary population synthesis calculations, the Galactic AIC rate is expected to be 10 −4 −10 −3 yr −1 summing over all possible progenitor scenarios (Wang 2018;Ruiter et al 2019), which disfavors the detection of an AIC event. We estimated that with the proposed sensitivity of the Einstein Telescope (Hild et al 2011), the detection distance can be increased to ∼ 1 Mpc, which will boost the detection possibility significantly.…”

The formation of single neutron stars from double white-dwarf mergers via accretion-induced collapse

“…That means the Galactic rates of AIC events from double WD mergers is about 10% to 2 times of the observed SN Ia rate. Wang (2018a) also present that the Galactic rates of AIC events from the SD model are in the range of ∼0.3−0.9 ×10 −3 yr −1 . Hence, the total Galactic rates of AIC events from both the SD model and the DD model are ∼1.8−9.8 × 10 −3 yr −1 , or in the range of ∼0.6−4.7 × 10 −3 yr −1 when double CO WD merger is not considered.…”

“…The ONe WDs in the binaries indicated by squares will increase their masses to the Chandrasekhar limit by accreting He-rich material from the He companions, i.e. the SD model for producing AIC events (see Liu et al 2018b;Wang 2018a). Binaries marked by open circles will undergo a dynamical unstable mass transfer process when the He subgiants fill their Roche-lobe, leading to common envelope (CE) phases.…”