Ice absorption features in the 5-8 mu m range

ISO-SWS spectra (2 - 45 mu m) have been obtained towards a large number of luminous young stellar objects. Here, we present a study of absorption features towards the two objects NGC: 7538:IRS9 and Mon R2:IRS3, for the spectral region 5 - 8 mu m. The shape of these features changes dramatically from source to source. The 6.0 mu m feature varies as a result of the different H2O ice temperatures and also as a direct consequence to the presence of additional absorption in this band for some sources. Furthermore, these new high resolution observations show that the peak position of the 6.85 mu m varies from source to source. The observations draw attention to the fact that hotter sources (Mon R2:IRS3) have a 6.85 mu m band position that is red shifted with respect to colder sources (NGC 7538:IRS9). This gives clues to the as yet unknown origin of this band.