Line Driven Acceleration using Multi-Frequency Radiation Hydrodynamics

TL;DR

This paper demonstrates the capabilities of multi-frequency radiation hydrodynamics in simulating radiative acceleration in stellar winds, highlighting the importance of Doppler shifts and re-radiation effects in modeling line-driven winds.

Contribution

It introduces multi-group radiation transfer methods in Athena++ for modeling line-driven stellar winds, incorporating Doppler shifts and re-radiation effects for the first time.

Findings

Force described by Sobolev transfer in supersonic regions

Re-radiation significantly affects outer wind regions

Multi-group methods are computationally feasible for complex models

Abstract

We use multi-frequency radiation hydrodynamics (rad-HD) to simulate radiative acceleration of a spherically symmetric stellar wind. We demonstrate the rad-HD capabilities of Athena++ for a series of test problems with multi-group radiation transfer. We then model the radiative transfer of a single spectral line through a spherically symmetric, isothermal, "CAK"-type line driven wind. We find that correctly accounting for the Doppler shift of the absorbed radiation, the force is well described by the analytic Sobolev line transfer in the supersonic parts of the solution where the flow is stationary and the effects of Abbott waves is negligible. Unlike in the analytic, steady-state solution re-radiation is important and leads to non-trivial radiation energy density and fluxes in the outer parts of the wind. We discuss a variety of applications to these multi-group methods that are currently computationally tractable.