FIRST RESULTS FROM ISO SPECTRA OF SUPERNOVA-REMNANTS HEAVILY INTERACTING WITH THE ISM

ISO spectra(1) of the supernova remnant RCW103 are presented. This obj ect is the prototype of a SNR shock heavily interacting with dense ISM (probably a molecular cloud). The spectra are dominated by prominent lines and show very little continuum at lambda < 40 mu m suggesting th at the 12 and 25 mu m IRAS emission from these types of remnant could be dominated by lines rather than continuum emission from warm dust he ated by the shock as generally believed. The ISO data provide for the first time a simple and reliable estimate of the gas phase abundances of Si and Fe which are found to be close to solar relative to non refr actory species such as Ne, S and Ar. This indicates that the shock is very effective in destroying the ISM dust and may therefore explain th e absence of warm dust behind the shock. Like the optical Nickel lines , [NiII]6.63 mu m yields Ni/Fe abundances a factor greater than or equ al to 10 above solar which we conclude results from a large underestim ation of the computed Ni+ collision strengths.