the iras low resolution spectrometer detected a small number of sources with featureless spectra of very low colour temperatures (about 200 k) which are not hii regions. the nature of these objects is unknown. subsequent co observations of some of these sources showed that their co properties are typical of mass-losing agb stars. the circumstellar dust shells of these objects are unusual because of the low temperature and because no features are seen. the broad-band iras colours of these sources are similar to those of planetary nebulae, so they may be pns or objects evolving from the agb to the pn phase. in order to identify the nature of these sources we request iso sws observations, and for a few brighter objects, with the lws. such observations would (a) provide us with an accurate picture of the spectral energy distribution of these sources which radiate dominantly in the 15 to 45 micron wavelength range, and (b) open the possibility that dust features or emission lines would be detected. it is also possible that some underlying stellar features might be detected at short wavelengths. the emission from these objects has so far been detected only in the far-infrared and therefore the identification of the nature of these sources can only be done in the 25 micron wavelength range with iso. the featureless nature of the lrs spectra might be explained if the dust were graphitic in nature, or it may be an entirely different type of dust such as that which produces the featureless lrs spectra for m-type stars. with these possibilities in mind it is important to obtain lws data for the brighter of these objects to search for longer wavelength dust features which may allow identification of the type of dust in the event that no features are seen at shorter wavelengths.
Instrument
LWS01 , SWS01
Temporal Coverage
1996-09-17T22:31:59Z/1997-05-31T07:55:10Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the world's first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, 1999, Spectroscopy Of Featureless Comma Low-Temperature Iras Sources, 1.0, European Space Agency, https://doi.org/10.5270/esa-uevq8je
