The following document lists the file abstract/MHAAS_EVOLSTAR.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
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 transition 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 one or two nearby supergiants, we propose to measure all six lines and also examine the velocity distribution and time variability of the emission. This will establish the nature of the emitting regions and provide information on the gas-phase abundances, temperatures, and densities of the gas, as well as the stellar mass-loss rates and incident UV fields. About a dozen additional evolved stars will also be observed 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. ISO's SWS and LWS are the only present or near-term instruments capable of obtaining these data.