Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280e..20c&link_type=abstract
The Molecular Universe, Proceedings of the 280th Symposium of the International Astronomical Union held in Toledo, Spain, May 30
Astronomy and Astrophysics
Astronomy
Scientific paper
The study of the chemical evolution of evolved stars is one of the more complex areas of Astrochemistry. The physical conditions of the gas and dust grains change from very high gas densities (>1010 cm-3) and temperatures (TK>1500 K) where chemistry is dominated by processes under thermodynamical equilibrium, to those of the interstellar medium, i.e., low densities and TK≃10-20 K. Hence, molecules are submitted to very different pumping mechanism through the whole envelope and molecular abundances are changing by several orders of magnitude. Consequently, the only procedure to characterize the chemistry and to derive reasonable accurate physical conditions is through a systematic frequency coverage of the molecular emission, i.e., through the observation of line surveys at all wavelengths. I will present recent results obtained from ground based telescopes and the 30m IRAM radio telescope, the Herschel satellite, and the TEXES instrument installed at the IRTF telescope. These data cover the frequency domain 100-2000 GHz with high spectral resolution (3 km s-1), 2-6 THz with medium spectral resolution (PACS instrument onboard Herschel), and 21-26 THz (spectral resolution of 4 km s-1). The analysis of the data shows how complex the chemistry can be in carbon-and oxygen-rich AGB and post-AGB stars. These line surveys provided also an excellent tool to explore which molecules are produced in the dust formation zone and the effects of molecular condensation on the dust grains. Finally, the spatial distribution of the gas is analyzed in the prototypical carbon-rich star IRC+10216.
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