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

TL;DR

This study investigates how magnetic fields in white dwarf + helium star binaries influence accretion-induced collapse, affecting the formation of neutron stars like MSPs and magnetars, with detailed simulations showing minimal impact on overall birthrates.

Contribution

It introduces a detailed analysis of magnetic confinement effects on white dwarf binary evolution and AIC outcomes, expanding understanding of neutron star formation pathways.

Findings

Magnetic confinement enhances WD mass accumulation efficiency at low transfer rates.

Magnetic effects shift progenitor parameter space toward shorter orbital periods.

Galactic AIC birthrates are similar with or without magnetic confinement.

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 $0.34\times10^{-4}\,{\rm yr}^{-1}$.