All stars with a stellar mass of about 0.8–8 solar masses will end their lives as asymptotic giant branch (AGB) stars. Through their extensive mass loss the AGB stars constitute an important source of nuclear processed material. They also provide us with fascinating systems where an interchange of different physical and chemical processes occur, making them excellent astrophysical laboratories.

Being the most important process for the evolution of an AGB star, the mass loss is well established, but its details are less well known. On the AGB, the mass-loss rate can span several orders of magnitude, reaching 0.0001 solar masses per year towards the end of the AGB. In the first part of the thesis the reliability of mass-loss rate estimates is evaluated. This is important, since the mass-loss rate affects the derived abundances of other molecules in the circumstellar envelope and therefore the estimates of the amount and composition of the recycled material.

The second part of the thesis focuses on a particular chemical type of AGB stars: the S-type. The S-stars are believed to have approximately the same amount of carbon as oxygen in the photosphere, and might give important clues to the mass-loss mechanisms and to the chemical evolution along the AGB. The analysis comprises estimates of the mass-loss rates and abundances of chemically important molecules for a sample of 40 S-stars.

Time:

Thursday, June 4, 10.00
Place: FB42, AlbaNova University Centre, Roslagstullsbacken 21

Link:
Thesis information Contact:

Sofia Ramstedt, Tel: 08-5537 8550, sofia@astro.su.se