University of Exeter

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Tim Harries
Early-type stars

Introduction

High-mass stars shed material at a prodigious rate. These winds are characterized by small (clumps) and large (disks, plumes) scale asymmetries perhaps arising from stellar rotation or inherent instabilities in the line-driving mechanism. The final evolutionary stages of high-mass stars involves short-lived phases of truly exceptional mass-loss (Wolf-Rayet stars, luminous blue variables, red supergiants) until the star explodes as a supernova. All these later phases show evidence of highly asymmetric mass-loss.

The role of wind structures in mass-loss rate measurements

Large- and small-scale departures from homogeneity in the stellar winds of hot stars increase the effective wind clumping factor, which means that all diagnostics based on free-free or recombination processes will systematically overestimate the mass-loss rate. Using high-resolution time-series spectropolarimetry we are searching for evidence of wind-clumping and rotational modulation of line-profiles and linear polarization, the signature of deep-seated co-rotating structures such as spiral streams. Numerical models are being used to assess the impact of these structures on derived mass-loss rates, and hence stellar evolutions models of the most massive stars, which are critically dependent on the rates adopted.

Numerical simulations of structure winds


The image to the right shows electron-scattering optical depth for an O-supergiant whose wind is distorted by three spiral structures. The image is linked to a movie showing how the spiral structures rotate with the photosphere.
A similar image showing how a clumpy wind might look. The image is linked to an mpeg movie showing how the clumps accelerate out into the wind.

See also Tim Harries' publication list and the Group publications list .

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