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Astron. Astrophys. 356, 619-626 (2000)


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Hot star polarimetric variability and the nature of wind inhomogeneities

J.C. Brown 1,2, R. Ignace 1,4 and J.P. Cassinelli 1,3

1 Kelvin Bldg, Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, Scotland, UK
2 Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3 Sterling Hall, Department of Astronomy, University of Wisconsin, Madison, WI 53706-1582, USA
4 Now at Physics and Astronomy, 203 Van Allen Hall, University of Iowa, Iowa City, IA 52245, USA

Received 10 May 1999 / Accepted 1 February 2000

Abstract

The problem is addressed of how much hot star polarisation variability can result from density redistribution processes within the wind as opposed to localised enhancement of stellar mass loss rate, such as ejections of wind inhomogeneities. For optically thin electron scattering, we present a theory for the relative polarisation arising from particle redistribution and consider several specific cases relevant to interpreting observations of wind variability. It is concluded that, allowing for partial cancellation of the contribution from compressed and evacuated regions, density redistribution internal to the wind can produce significant polarisation but only for processes that redistribute wind material over relatively large radial or angular scales. This conclusion favors extended spatial structures (e.g., from strong radiatively driven shocks) over localised condensations (e.g., from radiative instabilities).

Key words: polarization – stars: circumstellar matter – stars: early-type – stars: mass-loss – stars: variables: general

Send offprint requests to: J.C. Brown (john@astro.gla.ac.uk)

© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000

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