Infrared Array Camera

The Infrared Array Camera (IRAC) is an infrared camera system on the Spitzer Space Telescope which operates in the mid-infrared spectrum.[1] It is composed of four detectors that operate simultaneously at different wavelengths; all four were in use until 15 May 2009 when its cryostat ran out of liquid helium.[2] As of 2017, the spacecraft is operating as a warm extended mission, in which two of the four detectors remain functional.[2]

Infrared observations can see objects hidden in visible light, such as HUDF-JD2 shown. This shows how the Spitzer IRAC camera was able see beyond the wavelengths of Hubble's instruments
Four-band IRAC image of the Trifid Nebula. The wavelengths the camera sees are mapped to the visible spectrum for a false color image that humans can see. Here, the mapping is blue for 3.6 μm, green for 4.5 μm, orange for 5.8 μm, and red for 8.0 μm.
IRAC filters

During its primary mission, IRAC was able to simultaneously operate in four wavelengths: 3.6 μm, 4.5 μm, 5.8 μm, and 8.0 μm.[1][3] Each infrared detector has a resolution of 256×256 pixels—a significant improvement over previous spaceborne infrared telescopes—and each image taken covers 5.12 square arcminutes of sky.[1][4] The detectors operating at 3.6 μm and 4.5 μm were constructed with indium antimonide (InSb), while the 5.8 μm and 8.0 μm detectors were made of silicon doped with arsenic (Si:As).[1][3][5] The telescope's primary and secondary mirrors, along with its supporting structure, were made mostly of beryllium.[4] The telescope was cryogenically cooled to 5.5 K (−268 °C; −450 °F); the 3.6 μm and 4.5 μm detectors operated at 15 K (−258 °C; −433 °F) and the 5.8 μm and 8.0 μm detectors operated at 6 K (−267 °C; −449 °F).[6]

After Spitzer's liquid helium coolant ran out on 15 May 2009, the spacecraft warmed up over several months.[7] IRAC stabilized at its warm mission operating temperature of 28.7 K (−244 °C; −408 °F) on 18 September 2009.[7] This meant that the 5.8 μm and 8.0 μm detectors could not function as they required the cryogenic cooling,[1] but the 3.6 μm and 4.5 μm detectors remained about as sensitive as they were during the primary mission.[8] The other two Spitzer instruments (IRS and MIPS) likewise ceased to function as they worked at longer wavelengths, leaving IRAC as the sole operational instrument.[8]

The cryogenic assembly of IRAC is contained in the Multiple Instrument Chamber (MIC), which also houses the other focal plane elements and the pointing calibration reference sensor. In the MIC is the Infrared Array Camera, Infrared Spectrograph, and Multiband Imaging Photometer, as well as the pointing calibration reference sensor.[9] The MIC is attached to the cryostat and it is intended to keep the science instruments cold, including IRAC, but also functions to keep out stray light.[9] The MIC is mounted to the helium chamber inside the cryostat vacuum shell, not only to efficiently keep the instruments cold but to seal out any stray light.[9] Its warm electronics assembly is housed in the spacecraft bus.[6] The IRAC instrument was built by the Goddard Space Flight Center and the detectors were built by Raytheon. Its operational and scientific management is handled by the Smithsonian Astrophysical Observatory.[6]

Bands summary

IRAC is capable of observing in the wavelengths of 3.6, 4.5, 5.8, and 8.0 microns. When its coolant ran out, only the two shorter wavelengths remained usable.[1][3]

See also

References
  1. "The Infrared Array Camera (IRAC)". Spitzer Space Telescope. NASA / JPL / Caltech. Retrieved 13 January 2017.
  2. Szondy, David (28 August 2016). "Spitzer goes "Beyond" for final mission". New Atlas. Retrieved 13 January 2017.
  3. Fazio, G. G.; Hora, J. L.; Allen, L. E.; Ashby, M. L. N.; Barmby, P.; et al. (September 2004). "The Infrared Array Camera (IRAC) for the Spitzer Space Telescope". The Astrophysical Journal Supplement Series. 154 (1): 10–17. arXiv:astro-ph/0405616. Bibcode:2004ApJS..154...10F. doi:10.1086/422843.
  4. "Infrared Detector Developments". Spitzer Space Telescope. NASA / JPL / Caltech. Retrieved 13 January 2017.
  5. "IRAC Instrument Handbook: Appendix E. Acronyms". NASA/IPAC Infrared Science Archive. Spitzer Documentation and Tools. NASA / JPL / Caltech. Retrieved 13 January 2017.
  6. Gehrz, R. D.; Roellig, T. L.; Werner, M. W.; Fazio, G. G.; Houck, J. R.; et al. (January 2007). "The NASA Spitzer Space Telescope" (PDF). Review of Scientific Instruments. 78 (1). 011302. Bibcode:2007RScI...78a1302G. doi:10.1063/1.2431313. PMID 17503900.
  7. "Warm IRAC Image Characteristics". NASA/IPAC Infrared Science Archive. Spitzer Documentation and Tools. NASA / JPL / Caltech. Retrieved 13 January 2017.
  8. Hora, Joseph L.; Marengo, Massimo; Park, Rebecca; Wood, Denise; Hoffmann, William F.; et al. (September 2012). "The IRAC point response function in the warm Spitzer mission" (PDF). Proceedings of the SPIE. Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave. Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave. 8442. 844239. Bibcode:2012SPIE.8442E..39H. doi:10.1117/12.926894.
  9. "The Multiple Instrument Chamber". Spitzer Space Telescope. NASA / JPL / Caltech. Retrieved 13 January 2017.

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