Modeling DACs in UV Lines of Massive Hot Stars

TL;DR

This paper uses 3D radiative transfer modeling to analyze the structure and variability of Discrete Absorption Components in the UV lines of a massive hot star, revealing the influence of hydrodynamic parameters on wind features.

Contribution

It introduces a detailed 3D modeling approach to interpret UV line variability in massive stars, linking hydrodynamic wind structures to observed spectral features.

Findings

CIR in HD 64760 is caused by a non-corotating density wave.

A small 0.6% increase in mass-loss rate produces observable wind structures.

The model successfully fits observed UV line variability.

Abstract

We apply the 3-dimensional radiative transport code Wind3D to 3D hydrodynamic models of Corotating Interaction Regions to fit the detailed variability of Discrete Absorption Components observed in Si IV UV resonance lines of HD 64760 (B0.5 Ib). We discuss important effects of the hydrodynamic input parameters on these large-scale equatorial wind structures that determine the detailed morphology of the DACs computed with 3D transfer. The best fit model reveals that the CIR in HD 64760 is produced by a source at the base of the wind that lags behind the stellar surface rotation. The non-corotating coherent wind structure is an extended density wave produced by a local increase of only 0.6 % in the smooth symmetric wind mass-loss rate.