Abstract (eng)
Low to intermediate-mass stars (~0.8-8 solar masses) spend a short but eventful time on the asymptotic giant branch (AGB). Due to the low temperatures, molecules and, in the outermost layers, even solid particles (dust) can form, which are eventually injected into the environment by heavy matter outflows. Since more than 90 percent of the stars become AGB objects, their dusty winds contribute significantly to the enrichment of the interstellar medium with processed elements. Thus, it is of great importance for the understanding of the cosmic matter cycle to comprehend the mechanisms of the mass-loss process.
For this work, photometric data of the two carbon stars TT Cygni and UX Draconis, obtained with the Photodetector Array Camera and Spectrometer (PACS) on-board the Herschel satellite in the course of the MESS (Mass-loss of Evolved StarS) program, were studied. The photometric measurements were used to derive basic parameters of the circumstellar structures. Additionally, radiative transfer calculations were carried out using the radiative transfer code DUSTY, in order to estimate properties of the mass-loss process.
For TT Cyg a geometrically thin and remarkably spherically symmetric detached dust shell was detected. A co-spatial gas equivalent was already found in previous sub-mm observations. Around UX Dra a previously unobserved structure was identified.