Self - consistent treatment of dynamics and chemistry in the winds from carbon-rich AGB stars. I. Tests of the equilibrium and kinetic chemical codes

摘要

The main aim of the paper was performing test of our (chemical and kinetic)codes, which will be used during self-consistent modelling of dynamics andchemistry in the winds from C-rich AGB stars. We use the thermodynamicalequilibrium code to test the different databases of dissociation constants. Wealso calculate the equilibrium content of the gas using the kinetic code, whichincludes the chemical network of neutral--neutral reactions studied by Willacy& Cherchneff (1998). The influence of reaction rates updated using the UMISTdatabase for Astrochemistry 2005 (UDFA05), was tested. The local thermodynamical equilibrium calculations have shown that the NISTdatabase reproduces fairly well equilibrium concentrations of Willacy &Cherchneff (1998), while agreement in case of Tsuji (1973) dissociationconstants is much worse. The most important finding is that the steady statesolution obtained with the kinetic code for reaction network of Willacy &Cherchneff (1998) is different from the thermodynamical equilibrium solution.In particular, CN and C2, which are important opacity sources are underabundantrelative to hermodynamical equilibrium, while O-bearing molecules (like SiO,H2O, and OH) are overabundant. After updating the reaction rates by data fromthe UDFA05 database consistency in O-bearing species becomes much better,however the disagreement in C-bearing species is still present.