Line Driven Winds from Variable Accretion Discs

TL;DR

This study uses time-dependent hydrodynamics simulations to analyze how variable accretion rates influence line-driven winds from accretion discs, revealing correlations between luminosity fluctuations and wind mass flux, especially before reaching steady state.

Contribution

It introduces a dynamic model that accounts for local, variable accretion rates in simulating line-driven winds, extending previous static radiation field models.

Findings

Luminosity variations correlate with wind mass flux changes before steady state.

Intrinsic wind variability dominates after steady state, reducing luminosity-flux correlation.

Clump formation near the disc influences wind variability and mass flux.

Abstract

We use numerical hydrodynamics simulations to study line driven winds launched from an accreting alpha-disc. Building on previous work where the driving radiation field is static, we compute a time-dependent radiation flux from the local, variable accretion rate of the disc. We find that prior to the establishment of a steady state in the disc, variations of ~ 15% in disc luminosity correlate with variations of ~ 2-3 in the mass flux of the wind. After a steady state is reached, when luminosity variations drop to ~ 3%, these correlations vanish as the variability in the mass flux is dominated by the intrinsic variability of the winds. This is especially evident in lower luminosity runs where intrinsic variability is higher due to a greater prevalence of failed winds. The changing mass flux occurs primarily due to the formation of clumps and voids near the disc atmosphere that propagate out into the low velocity part of the flow, a process that can be influenced by local variations in disc intensity. By computing the normalised standard deviation of the mass outflow, we show that the impact of luminosity variations on mass outflow is more visible at higher luminosity. However, the absolute change in mass outflow due to luminosity increases is larger for lower luminosity models due to the luminosity-mass flux scaling relation becoming steeper. We further discuss implications for CVs and AGN and observational prospects.