Conditions for accretion disc formation and observability of wind-accreting X-ray binaries

Abstract

We explore the effect of anisotropic wind driving on the properties of accretion onto black holes in close binaries. We specifically focus on line-driven winds, which are common in high-mass X-ray binaries. In close binary systems, the tidal force from the companion star can modify the wind structure in two different ways. One is the reduction of wind terminal velocity due to the weaker effective surface gravity. The other is the reduction in mass flux due to gravity darkening. We incorporate these effects into the so-called CAK theory in a simple way and investigate the wind flow around the accretor on the orbital scale. We find that a focused accretion stream is naturally formed when the Roche lobe filling factor is $\gtrsim 0.8$-0.9, analogous to that of wind Roche lobe overflow, but only when the velocity reduction is taken into account. The formation of a stream is necessary to bring in sufficient angular momentum to form an accretion disc around the black hole. Gravity darkening effects reduce the amount of accreted angular momentum, but not enough to prevent the formation of a disc. Based on these results, we expect there to be a discrete step in the observability of high-mass X-ray binaries depending on whether the donor Roche lobe filling factor is below or above $\sim$0.8-0.9.

accepted for publication in the Publications of the Astronomical Society of Australia

References in corpus (22)

• Catalogue of high-mass X-ray binaries in the Galaxy ($4^{th}$ edition)
• A 15.65 solar mass black hole in an eclipsing binary in the nearby spiral galaxy Messier 33
• Superorbital variability of X-ray and radio emission of Cyg X-1 - II. Dependence of the orbital modulation and spectral hardness on the superorbital phase
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• A consistent solution for the velocity field and mass-loss rate of massive stars
• Re-estimating the Spin Parameter of the Black Hole in Cygnus X-1
• Simulating the formation of $\eta$ Carinae's surrounding nebula through unstable triple evolution and stellar merger-induced eruption
• Wind mass-loss rates of stripped stars inferred from Cygnus X-1
• The INTEGRAL view on Black Hole X-ray Binaries
• Critical angular velocity and anisotropic mass loss of rotating stars with radiation-driven winds
• X-ray emission from BH+O star binaries expected to descend from the observed galactic WR+O binaries
• Stellar wind accretion and accretion disk formation: applications to neutron star high mass X-ray binaries
• Black hole spin of Cyg X-1 determined from the softest state ever observed
• An Updated Formalism For Line-Driven Radiative Acceleration and Implications for Stellar Mass Loss
• Stellar wind in state transitions of high-mass X-ray binaries
• Wind accretion: Theory and Observations
• Hydrodynamic Winds From Twin-Star Binaries
• Ultraviolet observations of the X-ray photoionized wind of Cygnus X-1 during X-ray soft/high state
• Bimodality of Wind-fed Accretion in High Mass X-ray Binaries
• Spin evolution of neutron stars in wind-fed high mass X-ray binaries
• Clumpy wind accretion in Cygnus X-1
• Orbital modulations of X-ray light curves of Cyg X-1 in its low/hard and high/soft states