The composition of circumstellar gas and dust in 51 Oph

We analyze ISO archive data of the nearby bright emission-line star 51 Oph, previously classified as a proto-planetary system similar to P Pie. The in frared spectrum reveals the presence of gas-phase emission bands of hot (si milar to 850 K) CO, CO2, H2O and NO. In addition to this, partially crystal line silicate dust is present. The solid-state bands and the energy distrib ution are indicative of dust that has: formed recently, rather than of debr is dust. The presence of hot molecular gas and the composition of the circu mstellar dust are highly unusual for a young star and are reminiscent of wh at is found around evolved (AGB) stars, although we exclude the possibility of 51 Oph belonging to this group. We suggest several explanations for the nature of 51 Oph, including a recent episode of mass loss from a Be star, and the recent destruction of a planet-sized body around a young star.