Simulation of the cometary 10 μm band by laboratory data. II. Extension to spectra available for different comets

Recent observations have shown that the presence of emission bands at 9.8 and 11.3 μm is a characteristic of many comets. Although their attribution to silicates is commonly accepted, a wide debate is open to identify the actual species responsible for the two bands. In a previous paper (Colangeli et al. 1995a) we fitted emission spectra from comets P/Halley 1986 III and Levy 1990 XX in the 10 μm band region by using spectroscopic data obtained in our laboratory on various silicate samples. In the present work we extend the simulation to available cometary spectra showing similar bands. We show that combinations of pyroxene-type and olivine-type submicron grains produce satisfactory fits. Despite the limited number of observational data available in the literature, our results evidence that spectral variations can be interpreted in terms of intrinsic and/or evolutionary differences among the comets.