Paul J. Barr

The Infrared Space Observatory (ISO)

Abstract The Infrared Space Observatory (ISO), a fully approved and funded project of the European Space Agency (ESA), will operate at wavelengths from 2.5 to 200 μm. ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to the most distant extragalactic sources. The satellite essentially consists of a large liquid-helium cryostat, a telescope with a 60-cm diameter primary mirror and four scientific instruments. The instrument complement is: an imaging photo-polarimeter (2.5–200 μm), a camera (2.5–17 μm), a short wavelength spectrometer (2.5–45 μm) and a long wavelength spectrometer (45–180 μm). These instruments are being built by international consortia of scientific institutes and will be delivered to ESA for in-orbit operations. ISO is scheduled to be launched in 1995 and will be operational for at least 18 months. In keeping with ISOs role as an observatory, two-thirds of its observing time will be made available to the general astronomical community.

ISO Observations of Symbiotic Stars

A number of symbiotic stars have been observed with ISO. In addition to a number of emission lines, SWS observations of the symbiotic novae RR Tel and V1016 Cyg reveal prominent, broad 10 & 18 µm silicate dust features. The 10 µm, features are similar to the crystalline silicate profiles seen in classical novae. There is some evidence that the silicate brightness in V1016 Cyg varies with Mira-component phase. However, the silicate feature in RR Tel also showed some variation even though observations were made at very similar Mira-component phases. PHT observations of S-type symbiotic stars show the IR emission to be dominated by the red-giant component. However, an excess in the PHT-P filters from 10 to 15 µm is evident in all the stars, and there may be a broad 3.2 µm absorption feature or a broad 3.8 µm emission feature. At this time we have no adequate physical explanations for any of these features.

ISO Observations of Classical Novae

We describe the ISO programme to observe classical novae. The programme includes observations of novae during and shortly after eruption, and old novae. ISO observations of far infrared fine structure lines are providing us with information about physical conditions in nova ejecta which complement and extend knowledge obtained from ground-based observations. Surprisingly, we are getting little information about dust in nova systems, despite the fact that many novae are prolific dust-producers.