The Physics of Wind-Fed Accretion

TL;DR

This paper reviews the physical processes of wind-fed accretion in high-mass X-ray binaries, and develops advanced models combining photoionization, hydrodynamics, and radiation transport to better understand these systems.

Contribution

It introduces comprehensive global models of photoionized winds and accretion flows in HMXBs, integrating multiple simulation techniques for the first time.

Findings

Generated 2D and 3D maps of wind properties and X-ray emission lines.

Produced synthetic X-ray spectra to compare with observations.

Enhanced understanding of wind properties affecting binary evolution.

Abstract

We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-1. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.