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An Updated Formalism for Line-Driven Outflows and Consequences for Mass Loss

Presentation #116.02 in the session “Stellar Atmospheres and Winds”.

Published onJan 11, 2021
An Updated Formalism for Line-Driven Outflows and Consequences for Mass Loss

The colloquially-termed “radiation pressure” of line-driven winds plays an important role in driving outflows in various astrophysical environments. Quantification of the associated force is crucial to understanding interactions within these environments. The large number of spectral lines in ay given ion of the outflow material must be tabulated in order to specify this force. Here we provide new calculations of the dimensionless line strength parameter, describing the ratio of radiative acceleration of bound to free electrons, from an updated line list comprised of approximately 4.5 million spectral lines, compiled from four spectral databases. We assume local thermodynamic equilibrium and compute the line strengths for a range of temperatures and densities in a 2D grid. These are combined with dimensionless flux-weighting functions from an assumed Planck-function source to form the canonical line-force multiplier M(t), where t is a fiducial Sobolev optical depth. Historically, M(t) has been described by a power-law function, and we revisit this assumption by fitting alternative functions that include a saturation to a constant value (Gayley’s Q-bar parameter) at low values of t. We find that this alternate form is a better fit than the power-law form, and we use it to calculate mass-loss rates for our density-temperature grid. A sharp drop-off is present in the mass-loss rates when compared to the power-law form, representing a previously undescribed quenching of the wind.

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