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G. Cremonese (Osservatorio Astronomico, Padova, Italy), D.C. Boice, W.F. Huebner (Southwest Research Institute, San Antonio, USA), H. Rauer (DLR Institut fuer Planetenerkunding)
High resolution spectra were obtained of Comet Hale-Bopp on the nights of April 23 and 24, 1997, showing a diffuse Na-tail superimposed on the dust tail and a separate, narrow Na-tail in a different direction. It had been suggested that two separate reservoirs exists for the two types of Na-tails. We will call them Na d-source (the sodium reservoir of the diffuse tail) and the Na c-source ( the reservoir of the collimated tail), which appears to be a compact source in the inner coma. Analysis of the spectra provided important data to explain the narrow sodium tail, but the source and the processes for the release of sodium from the Na-c source in the coma are still not understood. A further analysis of the spectra suggests fragmentation of large dust particles as a possible Na-c source, but does not yet rule out dissociation of sodium-bearing molecules. In order to define whether a molecular or dust source fits the complex intensity profiles in the coma best, we report rate coefficient (lifetimes) for some sodium-bearing molecules that have been observed in the Solar System and in the interstellar medium. We will present preliminary results of a coma model taking into account these molecules.