Out of the shadows: unveiling circumstellar structure with optical wavelength spectro-polarimetric interferometry.

Abstract

Interferometry is the ultimate exercise in information theory. In performing interferometry a trade is made – fewer observables are obtained than from a direct image but each may have intrinsically higher resolution and signal to noise. However, this trade is not free – from a restricted number of observables, information recovery techniques are required to fit models and reconstruct images of the underlying scene for astrophysical inference.

A powerful observational technique is found in the combination of interferometry with spectro-polarimetry – optical wavelength spectro-polarised interferometric measurement provides a high resolution spatio-spectral probe of the geometry, chemistry and grain size of the dust within inner-most circumstellar

environments.

Observing the circumstellar environments of evolved stars remains a core pursuit of modern stellar astrophysics, as these regions encode information on the physical mechanisms driving the intense stellar mass loss that enriches the interstellar medium. Whilst information recovery techniques for traditional optical interferometric observables have a long history, techniques applicable to optical spectro-polarised interferometry have so far been restricted to simple scattering regimes and symmetric geometries, leaving significant room for technical development.

This thesis pursues three core goals: (1) the development of novel astronomical instrumentation – the spectro-polarimetric interferometry mode of the VAMPIRES instrument, (2) the creation of a suite of modelling and image reconstruction tools for spectro-polarised interferometric observables which significantly advance upon existing techniques and (3) the application of these methods to µ Cephei as a test case, to characterise its circumstellar environment.