DUST FORMATION IN THE CASSIOPEIA-A SUPERNOVA

High angular resolution (6'') spectre-imaging observations of Cassiope ia A, the youngest supernova remnant of our galaxy, were performed wit h ISOCAM, the mid-infrared camera on board of the Infrared Space Obser vatory (ISO). The remnant was fully mapped with the LW8 filter (10.7-1 2 mu m), which probes mainly dust thermal emission. Emission is seen b oth from the blast wave region and the inner region; the north-eastern jet region outside the nominal radius of the remnant is also detected . Additional spectre-imaging observations of the northern part of the remnant were done in order to better characterise the dust and its lin k to the gas. The gaseous ionic emission lines of sulphur (SIV at 10.5 mu m) and of neon (NeII at 12.8 mu m) were observed with the ISOCAM C ircular Variable Filter at a spectral resolution of 40. The gas emissi on is spatially well correlated with the so-called fast moving knots s een in the optical and which are known to be made of nuclear burning p roducts from the progenitor star. The dust continuum was observed at 9 .8, 11.3 and 12 mu m. The LW9 filter (14-16 mu m) was also used. A ver y good spatial correlation between gas and dust emission is revealed b y the observations. This is a good hint that dust formation took place in the knots and that we are observing supernova grains in the evapor ating interfaces between cool optical knots and the hot supernova cavi ty gas.