Polarimetry of binary stars

Abstract

Astronomical polarimetry is a powerful technique that can provide physical information sometimes difficult or impossible to obtain by any other type of observation. Almost every class of binary star can benefit from polarimetric observations: pre-main-sequence objects, close or contact binaries, mass-transfer systems, evolved binaries, cataclysmic variables, eclipsing binaries, etc. In these systems, polarimetry can help determine the geometry of the circumstellar or circumbinary matter distribution, yield information on asymmetries and anisotropies, identify obscured sources, map starspots, detect magnetic fields, and establish orbital parameters, to name just a few examples. The orbital inclination in particular is a very important piece of information for a binary system because it can lead to the determination of the components' masses, the fundamental parameter that determines a star's initial structure and subsequent evolution. This review will illustrate the usefulness of polarimetric techniques for the study of binary stars, with examples of results obtained for a variety of binary systems, and an overview of models, including those used to retrieve the orbital inclination.