STUDY OF AN UNKNOWN TYPE OF DUST

about 18% of the sources observed with the iras low resolution spectrometer (lrs) have dust emission which shows no features in the 8 to 23 micron range. excluding those cases where the star is known to be carbonrich, there are still about 2000 sources with such spectra many of which are associated with normal mtype stars. these stars, being oxygenrich, would normally be expected to have silicate dust and show the 10 micron emission feature. the mtype stars with featureless lrs spectra seem to have a different type of circumstellar dust. this dust has been suggested to be due to ca or al oxides but its real nature has not been determined. we request iso time to observe a set of 7 stars selected with the following criteria: (1) featureless lrs spectra; (2) low colour temperatures (or high optical depths in the circumstellar envelope so that they are not just mtype stars with little circumstellar dust); (3) not carbon stars (either associated with known m stars, or if no optical counterparts, have lrs spectra unlike that of carbon stars. sws01 and lws01 observations are requested for all of these objects to search for dust features which may identify the chemical composition of the dust, and to allow the dust emission and the stellar emission to be well separated. iso is needed for these observations because the dust emission is seen only at midinfrared wavelengths which cannot be studied from the ground, and the kao does not provide nearly enough resolution for good quality data to be obtained. the objects chosen for study are all bright infrared sources. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]