Dr Rhodri Evans outlines how the SOFIA telescope, mounted in a Boeing 747, will help us better photograph infrared radiation in space.
The infrared is one of the most important parts of the electromagnetic spectrum for astronomy. With wavelengths longer than visible light, the infrared allows us to study cool and obscured regions, such as sites of star formation, which we cannot see in visible light. Most of the infrared radiation from space, however, does not get through the atmosphere because of atmospheric absorption. Although satellites are used to get around this problem, an alternative is SOFIA – the Stratospheric Observatory For Infrared Astronomy – a 2.5 metre telescope mounted in a Boeing 747.
SOFIA operates out of NASA’s Armstrong Flight Research Center in Palmdale, California, and is equipped with a suite of different cameras and spectrographs to study the heavens in many different ways. One of SOFIA’s most important instruments is a far infrared camera – HAWC – which has been developed at the University of Chicago. I became involved in this instrument in 1997 when I worked at Chicago, and have maintained that involvement since moving to Cardiff University.
Other people in Cardiff have also played a vital role in developing the HAWC camera; the Astronomical Instrumentation Group at the university provided the lenses and filters which play a key part in the detector’s operation. HAWC is able to image objects at four different wavelengths, and at each of these four wavelengths a filter ensures that only that particular wavelength reaches the detector, with the accompanying lens ensuring the sharpest image possible is achieved.
The filters for HAWC were built in the university’s laboratories and consist of a fine wire mesh; some examples are shown in the accompanying photograph. These wire meshes can be tuned to only allow a particular range of wavelengths of infrared light to pass through. They can also be adapted to act as a dichroic, allowing radiation longer than a certain value to pass through and that at shorter wavelengths to be reflected (or vice-versa). The Cardiff group has become a world-leader in fabricating such high precision filters and dichroics, and have supplied them to many instruments on telescopes around the world and in space.
SOFIA went into operation in 2010, and is projected to have a 20-year lifetime. Over this lifetime its suite of cameras and spectrographs will be regularly updated; in 2015 NASA called for proposals to be made for the third generation of instruments which will keep the observatory’s capabilities at the cutting edge of technology. Astronomers from throughout the world have access to SOFIA, and each time they use HAWC they are depending on technology which was developed and built in Cardiff.
For more information about SOFIA go to http://www.sofia.usra.edu. For more information about the Cardiff Astronomical Instrumentation Group filters go to http://www.astro.cf.ac.uk/research/astro/instr/researchareas/metamaterials