Chemistry in circumsellar shells. I - Chromospheric radiation fields and dust formation in optically thin shells of M-giants

Details Chemistry in circumsellar shells. I - Chromospheric radiation fields and dust formation in optically thin shells of M-giants Chemistry in circumsellar shells. I - Chromospheric radiation fields and dust formation in optically thin shells of M-giants

Nov 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...265..626b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 265, no. 2, p. 626-642.

Astronomy and Astrophysics

Astrophysics

34

Interstellar Chemistry, Late Stars, Stellar Envelopes, Astronomical Models, Hydroxyl Radicals, Interstellar Matter, Photodissociation, Stellar Atmospheres, Sulfur, Ultraviolet Radiation

Scientific paper

We investigate the nonequilibrium chemistry in the inner regions of oxygen-rich circumstellar shells of late-type stars. Special attention is directed to the important influence of the stellar chromospheric UV-radiation field on the local chemistry. Our calculations suggest that in the presence of chromospheric radiation photoions and radicals determine the chemical structure of the shell also in the innermost region where hydrogen turns out to be predominantly atomic. As a consequence the main modes of molecule formation are involving charge-exchange, exothermal ion-radical, radiative dissociation, and radiative association reactions. Even in this environment, characterized by extreme nonequilibrium conditions for the chemistry, the CO molecule decides whether the carbon or the oxygen chemistry dominates. In spite of strong chromospheric UV radiation fields substantial amounts of dust could be generated by forming SiO-clusters as nucleation seeds.

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