Stellar wind accretion and accretion disk formation: Applications to neutron star high-mass X-ray binaries

Recent X-ray observations have revealed the complexity and diversity of high-mass X-ray binaries (HMXBs). This diversity challenges a classical understanding of the accretion process on to the compact objects. In this study, we reinforce the conventional concept of the nature of wind-fed accretion on to a neutron star considering the geometrical effect of radiatively accelerated wind, and re-evaluate the transported angular momentum by using a simple wind model. Our results suggest that even in an OB-type HMXB fed by stellar wind, a large amount of angular momentum could be transported to form an accretion disk due to the wind-inhomogeneity, if the binary separation is tight enough and/or the stellar wind is slow. We apply our model to actual systems such as LMC X-4 and OAO 1657−415, and discuss the possibility of disk formations in these systems.