The Magnetized White Dwarf + Helium star Binary Evolution with Accretion-induced Collapse

Abstract: Accretion-induced collapse (AIC) from oxygen/neon/magnesium composition white dwarf (ONeMg WD) + stripped helium (He) star binaries is one promising channel to form peculiar neutron star objects. It has been discussed that the WD's magnetic field may alter the accretion phase in the WD binary evolution. By considering non-magnetic and sufficiently magnetized WDs, we investigate the evolution of ONeMg WD + He star binaries with detailed stellar evolution and binary population synthesis simulations. The role of the magnetically confined accretion in the possible formation pathway for like millisecond pulsars (MSPs) and magnetars is also studied. Comparing with the case of spherically symmetric accretion, the mass accumulation efficiency of the WDs is enhanced at low mass transfer rate under the magnetic confinement model. The initial parameter space of the potential AIC progenitor systems moves toward shorter orbital period and lower donor mass (but not so significantly) due to the effect of the magnetic confinement. This also allows final MSPs to have lower-mass WD companions and shorter orbital periods. There is no significant difference between the Galactic birthrates of the AIC derived with and without the magnetic confinement, which implies that the magnetic field of the WD does not dramatically change the number of ONeMg WD + He star binaries which can produce AIC. It is worth noting that these conclusions can be applied for the CO (carbon/oxgen) WD + He star binaries as progenitors of type Ia supernovae, because the accretion phases of ONeMg WDs and CO WDs are similar. The Galactic rate of magnetars possibly formed via AIC of highly magnetized WDs is $0.34\times10^{-4}\,{\rm yr}^{-1}$.