As radiant energy diffuses from a star's interior through its surface layers, it interacts with the constituent gases --atoms, ions, and molecules -- in those surface layers and produces a host of absorption and emission lines. These lines constitute a signature that is accessible to terrestrial observation and analysis, telling us a great deal about the temperature, density, and composition structure of stellar atmospheres. This is a particularly rich field of study in the case of cool giant stars, for their light is characterized by an abundance of spectral lines. The Principal Investigator (PI) proposes to use millisecond time resolution spectrophotometry in the observation of cool, bright giant stars during lunar occultations. The goal is to measure the mean depths of the formation of spectral features in the extended atmospheres of these stars and in the inner layers of the dust shells surrounding some of them. Furthermore, the PI will measure the angular diameters of these stars and derive the dependence of angular diameter on absorption features and the stars' colors.
