Effects of Radiation Field Geometry on Line Driven Disc Winds

TL;DR

This study investigates how the geometry of radiation fields in accretion discs influences line-driven winds, revealing that truncated discs can produce stronger and faster outflows despite similar total luminosity.

Contribution

It demonstrates that the geometry of the radiation field significantly affects wind properties, highlighting the importance of self-consistent disc and wind modeling.

Findings

Truncated discs launch higher mass flux outflows.

Outflow velocity can be approximately 50% faster in truncated discs.

Interior streamlines are unaffected by truncation, carrying similar momentum flux.

Abstract

We study line driven winds for models with different radial intensity profiles: standard Shakura-Sunyaev radiating thin discs, uniform intensity discs and truncated discs where driving radiation is cutoff at some radius. We find that global outflow properties depend primarily on the total system luminosity but truncated discs can launch outflows with $\sim 2$ times higher mass flux and $\sim 50\%$ faster outflow velocity than non-truncated discs with the same total radiation flux. Streamlines interior to the truncation radius are largely unaffected and carry the same momentum flux as non-truncated models whereas those far outside the truncation radius effectively carry no outflow because the local radiation force is too weak to lift matter vertically away from the disc. Near the truncation radius the flow becomes more radial, due to the loss of pressure/radiation support from gas/radiation at larger radii. These models suggest that line driven outflows are sensitive to the geometry of the radiation field driving them, motivating the need for self-consistent disc/wind models.