  During the late phases of evolution, low-to-intermediate mass stars like our
Sun undergo periods of extensive mass loss, returning up to 80% of their
initial mass to the interstellar medium. This mass loss profoundly affects the
stellar evolutionary history, and the resulting circumstellar ejecta are a
primary source of dust and heavy element enrichment in the Galaxy. However,
many details concerning the physics of late-stage stellar mass loss remain
poorly understood, including the wind launching mechanism(s), the mass loss
geometry and timescales, and the mass loss histories of stars of various
initial masses. These uncertainties have implications not only for stellar
astrophysics, but for fields ranging from star formation to extragalactic
astronomy and cosmology. Observations at centimeter, millimeter, and
submillimeter wavelengths that resolve the radio surfaces and extended
atmospheres of evolved stars in space, time, and frequency are poised to
provide groundbreaking new insights into these questions in the coming decade.
