Revealing the Surfaces of Stars with Interferometric Imaging

Since the first stellar diameters were resolved with interferometry in the early twentieth century, the technique has revealed the angular extent of hundreds of stars. Knowing the size of a star on the sky and its distance from Earth has allowed for straight-forward measurements of fundamental stellar parameters. Measuring a stellar diameter can be achieved with just two telescopes which make a single baseline, but today's interferometric arrays allow for multiple baselines to be observed at once. Combining the light from three telescopes at once allows for the observations of closure phases, which highlight asymmetries of the target. By increasing the number of telescopes and observations and the size of baselines, sufficient data can be obtained to not just resolve the size of stars, but image details on their surfaces. In recent years, a number of studies have shown that interferometric imaging is capable of capturing the surface details of a wide variety of stars as they appear on the sky. I will present a review of the images obtained to date, particularly noting those of cool stars, like asymptotic giant, supergiant, and magnetically active stars. I will also detail the advantages of the method compared to other imaging techniques and of utilizing stellar surface images.