Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pasp..104..383k&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.104, p.383
Astronomy and Astrophysics
Astronomy
Scientific paper
Mass-losing red-giant stars represent links between the late stages of stellar evolution and the chemical evolution of the galaxy. In this dissertation, I address the mechanisms which lead to profuse mass loss, and estimate the global rate of mass return to the interstellar medium (ISM) by red giants. From a model of the circumstellar envelope based on that used by Knapp and Morris (1985), but employing a self-consistent treatment of the kinetic temperature of the gas and revised estimates of CO photodissociation radii, I estimate mass-loss rates in gas (M_g) for 150 red giants in the solar neighborhood, most of these detected during a survey for CO emission conducted by Zuckerman and Dyck. Analysis of the mass-loss rates indicated that between 0.3 and 0.7 solar mass per year is returned to the ISM by evolved stars in the Galaxy, similar to an estimate of the global mass-loss rate based on the white-dwarf birthrate. In the solar neighborhood, rouhgly equal amounts are contributed by carbon-rich adn oxygen-rich red giants. Comparison of M_g with mass-loss rate, outflow velocity, and dust-to-gas ratio are discussed. In related studies, I present the results of a search for massive carbon stars in the Galaxy and of near-IR imaging polarimetry of the reflection nebulosities around four preplanetary nebulae. In the former program, CO emission has been detected for the first time from 46 evolved stars. Preliminary analysis suggests that some of the carbon stars among them are luminous, with masses 4 solar mass. In the latter study, polarization maps of CRL 2688, CRL 618, OH 213.8+4.2, and IRC +10216 (the last employing a coronagraph) indicate that the imaged near-IR flux is, in each case, scattered emission from embedded central sources. From a simple model, I estimate dust-density gradients and total dust masses for each object. (SECTION: Dissertation Abstracts)
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