Spitzer Space Telescope - Guaranteed Time Observer Proposal #30188 Spitzer Observations of Luminous Blue Variables Principal Investigator: Giovanni Fazio Institution: Harvard-Smithsonian Astrophysical Observatory Co-Investigators: Grazia Umana, OACt, Catania, Italy Carla Buemi, INAF Corrado Trigilio, INAF Paolo Leto, INAF Science Category: evolved stars/pn/sne Observing Modes: IracMap IrsStare Hours Approved: 3.7 Abstract: Luminous Blue Variables (LBVs) are luminous, massive stars which as they evolve from the Main Sequence to become Wolf Rayet stars, undergo a period of enhanced mass loss over a very short period of time, leading to the formation of extended circumstellar nebulae. The overall scenario of LBV evolution is still under debate and the nebula formation mechanism, including the intensity, duration and geometry of the mass-loss event, and mechanisms for producing asymmetrical distribution and differences between the gas and dust shells, is still not established. We propose to obtain IRAC images and IRS spectra of seven LBVs and candidate LBVs. The IRAC images will detect and resolve the faint dust shells that have been ejected from the central stars. In conjunction with the radio and mm data, the IRAC images will allow us to determine the SEDs of the nebula and model the gas and dust emission. The IRS spectra will show the relative importance of continuum dust emission, PAH and small grain features, possible silicate absorption and emission features, and atomic and molecular lines in the 5 - 40 µm range. These data will allow us to put together a comprehensive picture of the structure and state of the material in the nebula surrounding the LBVs, and help understand the mechanisms that have led to the asymmetrical shapes and differences between the gas and dust distributions that have been observed in these objects.