Hot star polarimetric variability and the nature of wind inhomogeneities

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)