Spectral energy distribution

A spectral energy distribution (SED) is a plot of brightness or flux density versus frequency or wavelength of light. It is used in many branches of astronomy to characterize astronomical sources. For example, in radio astronomy, an SED with a negative spectral index around −0.7 would indicate a synchrotron radiation source. In infrared astronomy, SEDs can be used to classify young stellar objects.

Detector for spectral energy distribution

The count rates observed from a given astronomical radiation source have no simple relationship to the flux from that source, such as might be incident at the top of the Earth’s atmosphere.^[1] This lack of a simple relationship is due in no small part to the complex properties of radiation detectors.^[1]

These detector properties can be divided into

• those that merely attenuate the beam, including
  1. residual atmosphere between source and detector,
  2. absorption in the detector window when present,
  3. quantum efficiency of the detecting medium,^[1]
• those that redistribute the beam in detected energy, such as

1. fluorescent photon escape phenomena,
2. inherent energy resolution of the detector.^[1]

See also

• Astronomical radio source
• Astronomical X-ray sources
• Background radiation
• Bremsstrahlung
• Cyclotron radiation
• Electromagnetic radiation
• Synchrotron radiation
• Wavelength dispersive X-ray spectroscopy

References

1. Dolan JF (Aug 1972). "The Direct Reduction of Astronomical X-Ray Spectra". Astrophys. Space Sci. 17 (2): 472–81. Bibcode:1972Ap&SS..17..472D. doi:10.1007/BF00642917.

Further reading

• Eberhard Haug & Werner Nakel (2004). The elementary process of Bremsstrahlung. River Edge NJ: World Scientific. p. Scientific lecture notes in physics, vol. 73. ISBN 981-238-578-9.
• Jakob Walcher; Brent Groves; Tamás Budavári; Daniel Dale. "Fitting the spectral energy distributions of galaxies".

External links

• The High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA
• The Science of Spectroscopy