Radiative–Thermal Winds from an Accretion Disk

Abstract

We examine a hydrodynamical wind, which emanates from an accretion disk and is driven by thermal and radiation pressures, under a one-dimensional approximation along supposed streamlines. Such a disk wind is characterized by the disk gravitational and radiation fields, whose behavior is rather different from the spherical case. Along the streamline of winds, the gravitational field produced by the central object generally has a peak at some height, unlike the spherical case where it decreases monotonically. The radiation field produced by the disk, on the other hand, is almost constant near to the disk surface and decreases far from the disk, again unlike the spherical case. Due to these characteristic properties of force fields, disk winds are classified into three patterns: in the cold less-luminous case no wind can blow, in the warm luminous case transonic winds are established, and beyond some critical luminosity disk winds are always supersonic. We found that transonic winds can blow for the parameter range of $a_0 + 2\Gamma_\mathrm{eff} \gtrsim 0.8$, where $a_0$ is the initial sound speed in units of the Keplerian speed at the wind base and $\Gamma_\mathrm{eff}$ the normalized disk luminosity at the wind base. Furthermore, supersonic winds blow for $\Gamma_\mathrm{eff} \gtrsim 0.4$. We derive the terminal speed as a function of $\Gamma_\mathrm{eff}$. A radial extension of the flow is also discussed and applied to mass outflow from several active objects.