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Abstract:

A KP devoted to study molecular emission from evolved stars. The first data obtained by the HIFISTARS consortium will be discussed. The purpose of the key program HIFISTARS is to carry out a comprehensive study of circumstellar envelopes around evolved stars (namely O-and C-rich AGB stars, young planetary nebulae, red supergiants, and yellow hypergiants), systematically observing molecular lines with the high-resolution spec-trometer HIFI. The HIFI first observations confirm that our objects show lines with large S/N ratios and that HIFI provides the expected high-quality study of evolved stars. The circumstellar shells in these objects show very rich structure and dynamics, whose study is basic to understand their evolution, since the formation of the nebulae is due to the gas ejection by the central star and the interaction between different wind phases. The observed line profiles allow the study of the dynamics in our objects thanks to the high spectral resolution provided by HIFI. Very intense water vapor lines are found in O-rich AGB stars and young PNe, as well as in certain C-rich objects. Strong FIR lines of CO and other abundant molecules have been also observed. The different lines contain information on different aspects of the physical and chemical conditions in our objects. A summary of the observations and a first analysis of the data, including modeling, are discussed.