A proper description of clumping in hot star winds: the key to obtaining reliable mass-loss rates?

TL;DR

This paper introduces an improved model of clumping in hot star winds, addressing underestimation of mass-loss rates by traditional methods and reconciling observations with theoretical predictions.

Contribution

It presents a new description of wind clumping that improves mass-loss rate estimates and discusses limitations of current simulation-based structures.

Findings

Microclumping underestimates mass-loss rates in O stars.

New wind models reconcile observational data with line-driven wind theory.

Current simulations cannot fully fit UV and optical lines simultaneously.

Abstract

Small-scale inhomogeneities, or `clumping', in the winds of hot, massive stars are conventionally included in spectral analyses by assuming optically thin clumps. To reconcile investigations of different diagnostics using this microclumping technique, very low mass-loss rates must be invoked for O stars. Recently it has been suggested that by using the microclumping approximation one may actually drastically underestimate the mass-loss rates. Here we demonstrate this, present a new, improved description of clumpy winds, and show how corresponding models, in a combined UV and optical analysis, can alleviate discrepancies between previously derived rates and those predicted by the line-driven wind theory. Furthermore, we show that the structures obtained in time-dependent, radiation-hydrodynamic simulations of the intrinsic line-driven instability of such winds, which are the basis to our current understanding of clumping, in their present-day form seem unable to provide a fully self-consistent, simultaneous fit to both UV and optical lines. The reasons for this are discussed.