Modeling S tex2html_wrap_inline12 Cometary Fluorescence Spectra

C. Laffont (Observatoire de Besançon), D.C. Boice (Southwest Research Institute)

We present synthetic cometary fluorescence spectra of the tex2html_wrap_inline14 system of S tex2html_wrap_inline12 , calculated as a function of exposure time of the molecule to the solar irradiation. The model S tex2html_wrap_inline12 molecule contains 36 vibrational levels. To solve the 36 evolution equations governing the population of these levels, we used the Gear method for still differential equation systems where time constants vary by many orders of magnitude.

The initial population of the vibrational levels is obtained with a Boltzmann temperature of about 200 K, typical of expanding gas at the surface of a cometary nucleus in the inner solar system. We calculated fluorescence spectra as a function of time after release of the molecule from the nucleus, from very short times (several ns) to the steady state (about 700 s). The synthetic S tex2html_wrap_inline12 spectra obtained using this method are compared to previous modeling efforts and to IUE spectra of comets IRAS-Araki-Alcock and Hyakutake.