Brief Introduction to IRAS
The Infrared Astronomical Satellite (IRAS) mission was a
collaborative effort by the United States (NASA), the Netherlands (NIVR), and
the United Kingdom (SERC). IRAS contained a liquid helium-cooled 0.6 m
Ritchey-Chretien telescope. It conducted an all-sky survey at wavelengths
ranging from 8 to 120 microns in four broadband photometric channels centered
at 12, 25, 60, and 100 microns. The focal plane contained an array of 62
rectangular infrared detectors. The angular resolution varied between about
0.5' at 12 microns to about 2' at 100 microns. Some 250,000 point sources
were detected down to a limiting flux density, away from confused regions of
the sky, of about 0.5 Jy at 12, 25, and 60 microns and about 1.5 Jy at 100
microns. A catalog of small (< 8') extended sources gives the characteristics
of some 20,000 objects down to flux density levels about a factor of three
brighter than the point source detection limits. An atlas of images covering
the entire sky gives the absolute surface brightness at each of the four
survey wavelengths. The positional accuracy of sources detected by IRAS
depends on their size, brightness and spectral energy distribution but is
usually better than 20". For the all-sky survey the satellite scanned at
3.85' per second along arcs of constant Solar elongation close to 90°.
IRAS also made pointed observations of selected objects with integration times
lasting up to 12 minutes, providing up to a factor of 10 increase in
sensitivity relative to that of the survey.
In addition to the main survey instrument, two other instruments - A Low
Resolution Spectrometer (LRS) and a Chopped Photometric Channel (CPC) - were
colocated with the photometric detector array in the focal plane. The LRS
provided 8-22 micron spectra of approximately 5000 survey sources brighter
than 10 Jy at 12 and 25 microns. The CPC made 50 and 100 micron maps by
scanning in raster fashion with a circular 1.2' diameter aperture, however the
detectors behaved anomalously and yielded data of lower quality than expected.
Following a 10 month long mission, IRAS exhausted its cryogen and ceased
operations on November 21, 1983.
For more detailed information about the IRAS mission, see the
Introduction to IRAS
at IPAC
ADF/IRAS page