Radiato-Magneto-Thermal Winds from an Accretion Disk

Abstract

We examine a hydrodynamical wind, which emanates from an accretion disk and is driven by thermal, magnetic, and radiation pressures, under a one-dimensional approximation along supposed streamlines. The disk gas is assumed to be isothermal, the magnetic field has only a toroidal component, and the radiation field is evaluated along the streamline. Such a disk wind is characterized by an isothermal sound speed, the Alfvén speed at the footpoint, and the strength of radiation fields. Isothermal winds can always blow even in the cold less-luminous case, and transonic winds are established, except for the perfectly cold case without thermal pressure. Beyond some critical luminosity, disk winds are always supersonic, irrespective of the thermal and magnetic pressures. We found that the terminal speed $v_\infty$ is roughly expressed as $(1/2) v_\infty^2 = (1/2) v_0^2-(1/2) (GM/ r_0) + 10.5 a_\mathrm{T}^2 + 0.7 a_\mathrm{A0}^2 + 16 \Gamma_\mathrm{eff} (GM/r_0),$ where $v_0$ is the initial velocity, $M$ the mass of the central object, $r_0$ the radius of the wind base on the disk, $a_\mathrm{T}$ the isothermal sound speed, $a_\mathrm{A0}$ the initial Alfvén speed, and $\Gamma_\mathrm{eff}$ the effective normalized luminosity, although the coefficients depend on the configuration of the streamlines.