In astronomy, a photometric system is a set of well-defined passbands (or optical filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided.
A commonly adopted standardized photometric system is the Johnson-Morgan or UBV photometric system (1953). At present, there are more than 200 photometric systems.[1]
Photometric systems are usually characterized according to the widths of their passbands:
broadband (passbands wider than 30 nm, of which the most widely used is Johnson-Morgan UBV system)
intermediate band (passbands between 10 and 30 nm wide)
narrow band (passbands less than 10 nm wide)
Photometric letters
Each letter designates a section of light of the electromagnetic spectrum; these cover well the consecutive major groups, near-ultraviolet (NUV), visible light (centered on the V band), near-infrared (NIR) and part of mid-infrared (MIR).[a] The letters are not standards, but are recognized by common agreement among astronomers and astrophysicists.
The use of U,B,V,R,I bands dates from the 1950s, being single-letter abbreviations.[b]
With the advent of infrared detectors in the next decade, the J to N bands were labelled following on from near-infrared's closest-to-red band, I.
Later the H band was inserted, then Z in the 1990s and finally Y, without changing earlier definitions. Hence, H is out of alphabetical order from its neighbours, while Z,Y are reversed from the alphabetical – higher-wavelength – sub-series which dominates current photometric bands.
Filter Letter
Effective Wavelength Midpoint λeff for Standard Filter[3]
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).[7]
Combinations of these letters are frequently used; for example the combination JHK has been used more or less as a synonym of "near-infrared", and appears in the title of many papers.[8]
Filters used
The filters currently being used by other telescopes or organizations.
^Tonry, J. L.; Stubbs, C. W.; Lykke, K. R.; Doherty, P.; Shivvers, I. S.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Morgan, J. S.; Price, P. A.; Wainscoat, R. J. (2012). "THE Pan-STARRS1 PHOTOMETRIC SYSTEM". The Astrophysical Journal. 750 (2): 99. arXiv:1203.0297. Bibcode:2012ApJ...750...99T. doi:10.1088/0004-637X/750/2/99. S2CID119266289.
Johnson, H. L.; Morgan, W. W. (1953), Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas, The Astrophysical Journal, vol. 117, pp. 313–352 [2]