Optical Interferometry of Giants and Supergiants

Over the last several decades optical interferometers have made substantial gains in ability, evolving from simple two-telescope arrays with 10-m baselines that primarily measured the angular diameters of stars, to four- to six-telescope arrays with 300-m baselines that are capable of imaging objects at high spatial resolution (0.3 milli-arcseconds) and high spectral resolution (R ∼ 30, 000). This chapter highlights how optical interferometers have been used during the last three decades to study single and binary systems containing giant and supergiant stars. It reviews diameter measurements and astrometry for single and binary stars, discusses the asymmetric mass-loss processes seen in asymptotic giant-branch stars, shows how resolving stellar disks is helping to solve long-standing problems related to carbon stars, and summarizes some of the state-of-the-art techniques that are now being used to image spots and convective cells on supergiants.