Detection of the 62 , urn crystalline HZ 0 ice feature in emission toward HH 7 with ISO-LWSo

We report the detection of the 62 p m feature of crystalline water ice in . emission towards the bow-shaped Herbig-Haro object HH 7. Significant amounts of far infrared continuum emission are also detected between 10 and 200 pm, suggesting that Herbig-Haro objects cease to be pure emission-line objects at FIR wavelengths. The formation of crystalline water ice mantles requires grain temperatures T,, ,> 100 K at the time of mantle formation, suggesting that we are seeing material processed by the HH 7 shock front. The deduced ice mass is N 2 x Ma corresponding to a water column density N(H2O)10" cm-2; an estimate of the [H,O]/[H] abundance yields values close to the interstellar gas-phase oxygen abundance. The relatively high dust temperature and the copious amounts of gas-phase water needed to produce the observed quantity of crystalline water ice, suggest a scenario where both dissociative and non-dissociative shocks co-exist. The timescale for ice mantle formation is of the order of N 400 years, so that the importance of gas-phase water cooling as a shock diagnostic is greatly diminished. /ir?kXSh=[&med:m Subject headings: (ISM:) dust, extinction ISM: Herbig-Haro objects ISM: individual (HH 7 ) ISM: lines and bands infrared: ISM: continuum infrared: ISM: lines and bands