Dr Eric Dunford is a space scientist from RAL. We do get great support from RAL and even though the topics sometimes overlap there is always much knowledge of interest to be had. This time the subject was ‘Infra-Red Astronomy from Space’.
Dr Dunford started working on astronomical satellites in the late 60s and he gave us a run through of the various IR spaceborne observatories that have had a European and personal interest to him.There are problems with observing in IR, in that the atmosphere’s water vapour stops most wavelengths of IR, and also that spaceborne observatories will in themselves give off heat radiation, some of which will be IR. This makes it essential for these satellites to have sunshields, and detectors have to be supercooled so that their own radiation doesn’t mess up the observations.
The first, and very successful one was the Infra-Red Astronomical Satellite (IRAS) in 1983. This was in the days before CCDs, and it had lots of different detectors of three different wavelengths. The mirror was 33 cm in diameter and the instruments were kept at a temperature of 2.5 kelvin, thanks to the gradual evaporation of a helium jacket. The data was downloaded every 12 hours and the helium evaporation ended up keeping IRAS going for 319 days, leaving us with observations of 400,000 objects. It is still out there, orbiting at 900km from Earth. It also discovered a comet which was also discovered visually, Comet IRAS-Araki-Alcock. Vega was used as a calibration object but it turned out to be a flop because it had a protoplanetary system around it so was not a stellar point source.
The IR Space Observatory (ISO) survived for about 2.5 years and had a 60 cm mirror and detectors giving 1000x more sensitivity than IRAS. Dr Dunford then explained that it was very difficult to do any testing on these kinds of gadgets prior to launch as you had to test them cold, i.e. 2.5 kelvin on Earth, and that made all the materials brittle.
Herschel was the next IR telescope with European interests and was launched in May 2009.It is still the largest mirror we have put into space, 3.5m. It was launched with Planck (a far IR and submillimetre telescope he did not touch on) on an Ariane 5 rocket. It moves around in the L2 point (in a line from the Sun through the Earth/Moon). It had three detectors (SPIRE) observing in wavelengths longer than what IRAS used, going into far infra-red to submillimetre wavelengths. It was able to detect water on Mars.
The PACS detector looked at shorter wavelengths (70 to 160 microns) and were used more to look at stars and galaxies. The resolution of M31 and the Rosette Nebula was stunning. The ground based James Clerk Maxwell Telescope in Hawaii was able to observe in these wavelengths but its field of view was minute in comparison. Herschel ran out of fuel in April 2013 but the data is still being analysed.
The James Webb Space Telescope, about which we heard much in our January speaker meeting, will also be observing in the near infra-red. Dr Dunford was pleased to tell us that the last telescope segment was installed in the week before his talk.