Spectropolarimetric determination of circumstellar disc inclinations

Abstract

Inference of the density and velocity structure of rotating/expanding circumstellar discs/winds is of considerable interest in the understanding of stellar mass loss. High resolution line spectropolarimetry creates the possibility of diagnosing such envelope structure much more fully than broad band polarimetry or high resolution spectrometry alone since each element of the scattered spectropolarimetric profile picks out the element of the envelope with the appropriate Doppler shift and provides orientation information on it. This problem has been formulated in detail by Wood, et al (1993) for scattering of a finite width line in a flattened envelope – the spectral shape of the scattered Stokes fluxes being determined by isowavelength–shift contours or surfaces which give the relative wavelength shift of the scattered radiation at different regions in the disc. It was also shown how, in the case of a narrow stellar line scattered in a rotating or expanding flat disc with a simply parametrised density and velocity structure (ignoring the smearing effect of electron thermal motions), it is possible to infer the system inclination and structure model parameters from the resulting spectropolarimetric line profile. This poster presents a method for determining the disc inclination from analysis of the scattered profiles – a parameter which cannot be determined uniquely from spectrometry alone – and thus illustrates the powerful diagnostic potential of high resolution line spectropolarimetry.