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

Although most neutron stars are believed to form in core-collapse supernovae, some fraction of them may form in less well-known sites. We investigate evolutionary pathways leading to neutron stars formed through the collapse of oxygen-neon white dwarf (ONe WD) stars in interacting binaries. We consider are (1) non-dynamical mass transfer where an ONe WD approaches the Chandrasekhar mass via stable mass transfer leading to accretion-induced collapse (AIC) and (2) dynamical timescale merger-induced collapse (MIC) between an ONe WD and another WD. We present rates, delay times, and progenitor properties for two different treatments of common envelope evolution. We show that AIC neutron stars are formed via many different channels and the most dominant channel depends on the adopted common envelope physics. Most AIC and MIC neutron stars are born shortly after star formation, though some have delay times >10 Gyr. The shortest delay time (25-50 Myr) AIC neutron stars have stripped-envelope, compact, helium-burning star donors, though many AIC neutron stars with delay times of 50-100 Myr form via wind-accretion from an asymptotic giant branch star. The longest delay time AIC neutron stars, which may be observed as young milli-second pulsars among globular clusters, have a red giant donor at the time of NS formation and will eventually evolve into NS + helium WD binaries. We also discuss MIC progenitors as potential gravitational wave sources for future space-based missions. The formation of neutron stars from interacting WDs in binaries is likely to be a key mechanism for the production of LIGO/Virgo gravitational wave sources (NS-NS and BH-NS mergers) in globular clusters.