Investigation of the dust formation and violent mass loss of evolved stars

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Evolved stars are the major source of stellar dust in our Galaxy, returning matter to the interstellarmedium and providing material for new star and planet formation. As such, their violent mass loss process is under intense investigation. The main motivation of the project is to study the strong mass loss occurring during the late stages of stellar evolution, which is still poorly understood. In particular, we want to focus on answering the following questions: How is the pulsation of stars on the Asymptotic Giant Branch (AGB) related to the dust condensation sequence and thus to the mass loss? What are the main differences between AGB stars and the more massive Red SuperGiant stars (RSGs)? How does the mass loss of oxygen-rich stars differ from that of carbon-rich stars? To answer these questions, the project focuses on studying evolved stars of different masses and chemical compositions observed with the highest available angular resolution, using the AMBER and MIDI instrument at the Very Large Telescope Interferometer (VLTI). The data will be exploited by using different theoretical codes: radiative transfer codes, an image reconstruction code, and a multidimensional hydrodynamical code. The scientific projects in this proposal are based on observations with AMBER and MIDI, the first generation interferometric instruments installed at the VLTI. However, part of the project is also dedicated to the next generation mid-infrared interferometric instrument MATISSE. MATISSE will open two new observing windows in the L and M bands. For the very first time, it will combine beams of 4 telescopes, allowing imaging in the mid-infrared band. This part of the project focuses on assisting with the preparation of user-friendly image reconstruction code, and on the implementation of the second generationfringe tracker. These tasks are of high importance since the first light from MATISSE is expected in 2016.