Detection of solid ammonia, methanol, and methane with ISOPHOT

We report on a search for the NH3 inversion band at 9.0 mum, the CH4 band at 7.7 mum, and the CH3OH band at 9.7 mum in the spectra of 10 heavily obscured stellar objects taken with the spectrophotometer ISOPHOT-S aboard the Infrared Space Observatory (ISO). Four of them show indications of the NH3 inversion band at 9.0 mum superimposed on the always strong silicate band. The results show that ammonia ice may be abundant in some cool and dense molecular circumstellar regions. The 9.7 mum band of solid CH3OH was detected in 5 of the sources, and also the 7.7 mum band of solid CH4 was found in 5 sources. The PHT-S detections were cross-checked against ISO-SWS spectra from archive data. Considering the different beam sizes (24 x 24 square versus 14 x 20 square), there is good agreement.