Time Dependent Radiation Driven Winds

TL;DR

This study investigates how time-dependent radiation influences line-driven winds, revealing resonance effects and phase-dependent velocity variations through simulations extending classic wind theory.

Contribution

It introduces a novel analysis of wind response to sinusoidal radiation variations, highlighting resonance phenomena near the dynamical frequency.

Findings

Winds reach a periodic state after a relaxation time.

High-frequency radiation drives winds like stationary models.

Resonance near the dynamical frequency significantly alters velocities.

Abstract

We study temporal variability of radiation driven winds using one dimensional, time dependent simulations and an extension of the classic theory of line driven winds developed by Castor Abbott and Klein. We drive the wind with a sinusoidally varying radiation field and find that after a relaxation time, determined by the propagation time for waves to move out of the acceleration zone of the wind, the solution settles into a periodic state. Winds driven at frequencies much higher than the dynamical frequency behave like stationary winds with time averaged radiation flux whereas winds driven at much lower frequencies oscillate between the high and low flux stationary states. Most interestingly, we find a resonance frequency near the dynamical frequency which results in velocity being enhanced or suppressed by a factor comparable to the amplitude of the flux variation. Whether the velocity is enhanced or suppressed depends on the relative phase between the radiation and the dynamical variables. These results suggest that a time-varying radiation source can induce density and velocity perturbations in the acceleration zones of line driven winds.