Heavy Element Abundances in the Photospheres of Cool Supergiants
Abstract
We report on a program to determine the chemical composition of massive, cool supergiant photospheres. We concentrate on elements heavier than the iron group, addressing the question of whether nuclear by-products from the weak s-process have been brought to the surface by convective processes. For massive stars, atoms with mass up to approximately A = 100 are thought to be formed by neutron capture via the weak s-process. The abundances of these elements have been calculated by other researchers to be a function of stellar mass.
Our initial work has concentrated on the identification of useful atomic spectral lines at infrared wavelengths, where absorption from molecular species is reduced relative to that at optical wavelengths for M-type stars. Abundances are determined by synthetic spectrum fitting to line profiles in high-resolution spectra. We present results for the cool, supergiant Betelgeuse (M2 Iab). Abundances are determined for a number of heavy elements, and despite large uncertainties attributed to the available atomic data (oscillator strengths), a distinct enhancement of Sr is determined after correcting for non-LTE effects. Such an enhancement is predicted by models of interior nucleosynthesis via neutron capture. Our results illuminate the problems that must be overcome before being able to derive abundances with the accuracy required for rigorous comparison with theoretical calculations. We also present our approach to applying the results for Betelgeuse to additional cool supergiants.- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AAS...209.9304W