Characterization of the carbon component in cometary Stardust samples by means of infrared and Raman spectroscopy

Aims. We attempt to ellucidate the structure and chemical composition of the carbon bulk detected in cometary Stardust particles. We determine if the carbon material observed spectroscopically is of true cometary origin and whether or not it was formed by direct UV-photoprocessing of icy grain mantles in the local dense cloud and/or the solar nebula. Methods. We acquire infrared spectroscopy of ten Stardust cometary particles from track 35 and the aerogel inside and outside the particle track. Using infrared and Raman spectroscopy, the dominant carbon component in cometary Stardust particles was compared to IDPs and organics made from UV-photoprocessing of interstellar/circumstellar ice analogs in the laboratory. The Raman spectra of Stardust particles used in this comparison are adapted from the literature. Results. As indicated in previous works, it is found that the collecting aerogel medium, processed during particle impact, poses serious problems for the infrared analysis of the Stardust cometary particles reported in this paper. We identify the structure of the carbon bulk of the organic material retrieved from the aerogel with a form of (hydrogenated) amorphous carbon. It is found that this material is not a direct product of ice photoprocessing.