Other
Scientific paper
Mar 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt..........r&link_type=abstract
Acta Universitatis Upsaliensis. Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 515.
Other
3
Agb Stars, Stellar Evolution, Late-Type Stars, Mass Loss, Circumstellar Matter, Stellar Winds, Infrared Spectroscopy
Scientific paper
Spectroscopic investigations of stellar winds from red giants are of interest for several reasons. The discussion on the cosmic build-up of elements needs information based on such investigations. Asymptotic Giant Branch (AGB) stars have a large mass loss which expels newly synthesised elements and enriches the interstellar medium from which a new generation of stars is formed. The circumstellar envelopes of AGB stars are also of interest in their own right. In recent years it has been possible to extend this research into the infrared wavelength regions as a result of the recent developments in space and detector technology. In our work, new infrared probes of the physical conditions in the envelopes surrounding AGB stars have been shown to be useful tools in the study of stellar winds. The detection of gaseous, circumstellar CO2 has initiated a discussion concerning the wind regions very close to AGB stars. It is suggested that the CO2 bands probably are formed in two separate parts of the envelopes at different distances from the star. More information on the circumstellar envelopes can be obtained by simultaneously modelling radio and far-IR observations of CO rotational lines, in a fashion resembling archaeology, studying different layers of the envelopes at different wavelengths. This method was applied for the first time to IRAS 15194-5115, a star of unknown evolutionary status. The history of the mass-loss rate of AGB stars is imprinted in the circumstellar envelopes and its variations can be studied and can provide clues to the evolutionary stage of the star. Another way of studying the winds is to investigate spatially resolved, photospheric light scattered in infrared, vib-rot lines of CO, such as the observations of the circumstellar envelope of the AGB star Mira Ceti. The discussion and modelling of these observations has shed some light onto the inner regions (< 100 stellar radii) of the winds, for which little observational knowledge is available today. The scientific approach of combining observations (of high spectral and spatial resolution) of vib-rot transitions of CO, radio and FIR observations with a circumstellar wind model has proved to be powerful. Thus, further investigations along the same lines as those discussed in this thesis would certainly be rewarding.
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