Cool stars winds and chromospheres

Red giant and supergiant stars with weak pulsations are surrounded by a hot layer called chromosphere. The recent UV Hubble Space Telescope (HST) data indicate that this region plays a crucial role in driving the mass loss in these stars. However, the physical mechanisms responsible for the mass loss remain a major open question in the field of cool, evolved stars. In a recent work I demonstrated that combining in a systematic way interferometric, spectroscopic and photometric data, provides important constraints for models of mass losing pulsating red giants. I propose now to extend this novel line of work to giants with chromospheres to reveal the role of the chromosphere in driving the winds of these stars. I will accomplish this with observations from the International Ultraviolet Explorer (IUE) satellite and from the Hubble Space Telescope (HST) spectrographs including the Goddard High Resolution Spectrograph (GHRS), the Space Telescope Imaging Spectrograph (STIS), and the Cosmic Origins Spectrograph (COS). I will investigate the dynamics of the outer atmospheres (flow and turbulent velocities), line profiles and formation, will compute theoretical models, and will derive thermodynamic constraints for those. In addition, ground-based high-angular resolution measurements from the visible into the infrared range, will be used to test the geometrical extent of the chromospheres and to better understand the behavior of the outer atmospheres at various spatial scales. To analyze the observed line profiles and visibilities I will use state-of-the-art chromosphere models. In this way I will be able to infer wind and chromospheric parameters, mass-loss rates, and fundamental stellar parameters. This multi-wavelength, multi-technique approach will enable the first complete, self-consistent test of the stellar mass loss scenarios for giants with chromospheres. These results are key ingredients for improving our knowledge of the enrichment of the interstellar medium with chemical elements like carbon and oxygen as well as dust. Therefore this work will contribute to a final understanding of the origin and evolution of stars and the formation of planets.