Spectral Surveys of AGB Stars - The rise of the elements
Astronomy and astrophysics
Friday 23 September 2016
to 11:30 at
Elvire de Beck (Onsala Space Observatory / Chalmers)
Understanding the chemical evolution of matter in the Universe requires knowing and understanding the different "polluters". Asymptotic giant branch (AGB) stars, cool evolved stars of low to intermediate birth mass, are among the major contributors. They nucleosynthesise heavy elements and release these in steady stellar winds, depositing up to half of the stellar mass in gas and dust into the ISM. The physical properties of the winds’ gas and dust content are thus crucial to the description of the mass-losing process and evolution of the majority of stars. The chemical characterisation of the winds is crucial to our understanding of the overall chemical enrichment of galaxies.
As a population, the AGB stars also contribute significantly to the light of galaxies and understanding their behaviour is crucial, e.g., in the study of galaxies at a redshift of about 2 where the intermediate-mass stars appear on the scene as luminous AGB stars.
Molecular spectroscopy at (sub)millimeter wavelengths is an extremely powerful tool to study the enormous wealth in gas-phase species present in the circumstellar envelopes (CSEs) of evolved stars. Observations of CO have led to the characterisation of the basic physical properties of these outflows (wind speed, mass-loss rate, and geometry). Targeted observations of other known molecules such as SiO, HCN, and H2O, have helped to further constrain e.g. wind acceleration, geometry, and depletion of certain species from the gas phase.
I will report on unbiased spectral surveys of several AGB stars. Such observations cover large frequency ranges, without targeting specific species in the spectrum. This way, we can detect a large number of lines and species, allowing us to set up an extensive and essentially unbiased molecular inventory, including low-abundance and unexpected species. Surveys of this kind provide a probe of and strongly constrain the immense variety of astrochemical networks active throughout the outflows, connecting gas and dust.