The following document lists the file abstract/MHAAS_MORESTAR.abs
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===================================================================== ==> This proposal requests an upgrade from Priority 3 for some of the ==> observations in MHAAS.EVOLSTAR ==> In addition, more time is being requested to complete and extend ==> the work begun in the proposal MHAAS.EVOLSTAR ===================================================================== The mass loss suffered by evolved stars controls their evolutionary fate and provides a significant fraction of the total metal-enriched gas returned to the ISM. Stellar winds also represent a major birthing site for interstellar grains -- both the wind acceleration mechanism and the dust formation process continue to be of intense theoretical and observational interest. We propose to study these phenomena in nearby supergiants and other well-known, evolved stars by observing the fine-structure lines of FeII(26,35um), SiII(35um), OI(63,146um), and CII(158um). These lines are believed to originate in the inner or trans- ition regions of the circumstellar envelopes of evolved stars, in the very region where molecules and dust are expected to form and the stellar winds are presumably accelerated. For the archetypal supergiant alpha Ori, we propose to measure the brightest lines at high resolution (Fabry-Perot) to obtain dynamical information about the outflowing gas. This will help to establish the nature of the emitting region and will also provide information on the gas-phase abundances, temperature, and density of the gas, as well as the stellar mass- loss rate and incident UV field. The FeII(26), SiII(35), and OI(63) lines will be observed in grating mode for an additional 18 evolved stars to determine total masses of atomic gas, mass-loss rates, and the gas-phase abundances as a function of spectral type, dust-to-gas ratio, and dust formation history. Since neither dust formation nor wind acceleration is well understood and effective tracers of this warm, atomic gas are limited, these FIR observations are crucial to our understanding of these enigmatic processes.