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| '''K correction''' is a correction to an [[Astronomy|astronomical]] object's [[Magnitude (astronomy)|magnitude]] (or equivalently, its [[flux]]) that allows a measurement of a quantity of light from an object at a [[redshift]] ''z'' to be converted to an equivalent measurement in the [[rest frame]] of the object. If one could measure all the light from an object at all [[wavelength]]s (a bolometric flux), a K correction would not be required. If one measures the light emitted in an [[emission line]], a K-correction is not required. The need for a K-correction arises because an astronomical measurement through a single [[filter (optics)|filter]] or a single bandpass only sees a fraction of the total [[spectrum]], redshifted into the frame of the observer. So if the observer wants to compare the measurements through a red filter of objects at different redshifts, the observer will have to apply estimates of the K corrections to these measurements to make a comparison.
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| One claim for the origin of the term "K correction" is [[Edwin Hubble]], who supposedly arbitrarily chose <math>K</math> to represent the reduction factor in magnitude due to this effect.<ref>{{cite journal | title=Effects of Red Shifts on the Distribution of Nebulae | authorlink=Edwin Hubble | first=Edwin | last=Hubble | year=1936 | journal=[[Astrophysical Journal]] | volume=84 | pages=517–554 | doi=10.1086/143782 | bibcode=1936ApJ....84..517H}}</ref> Yet Kinney et al., in footnote 7 on page 48 of their article,<ref>{{cite journal | title=Template ultraviolet spectra to near-infrared spectra of star-forming galaxies and their application to K-corrections | first=A.C. | last=Kinney et al. | year=1996 | journal=[[Astrophysical Journal]] | volume=467 | pages=38–60 | doi=10.1086/177583 | last2=Calzetti | first2=Daniela | last3=Bohlin | first3=Ralph C. | last4=McQuade | first4=Kerry | last5=Storchi-Bergmann | first5=Thaisa | last6=Schmitt | first6=Henrique R. | bibcode=1996ApJ...467...38K}}</ref> note an earlier origin from [[Carl Wilhelm Wirtz]] (1918),<ref>{{cite journal | doi=10.1002/asna.19182061302 | first=V.C. | last=Wirtz | title=Über die Bewegungen der Nebelflecke | year=1918 | journal=[[Astronomische Nachrichten]] | volume=206 | issue=13 | pages=109}}</ref> who referred to the correction as a ''Konstante'' (German for "constant"), hence K-correction.
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| The exact nature of the calculation that needs to be applied in order to perform a K correction depends upon the type of filter used to make the observation and the shape of the object's spectrum. If multi-color [[Photometry (astronomy)|photometric]] measurements are available for a given object thus defining its spectral energy distribution ([[Spectral Energy Distribution|SED]]), K corrections then can be computed by [[Curve fitting|fitting]] it against a theoretical or empirical [[Spectral Energy Distribution|SED]] template.<ref>[http://arxiv.org/abs/astro-ph/0606170 K-corrections and filter transformations in the ultraviolet, optical, and near infrared]</ref> It has been shown that K corrections in many frequently used broad-band filters for low-redshift [[Galaxy|galaxies]] can be precisely approximated using two-dimensional [[polynomial]]s as functions of a [[redshift]] and one observed [[Color index|color]].<ref>[http://arxiv.org/abs/1002.2360 Analytical approximations of K-corrections in optical and near-infrared bands]</ref> This approach is implemented in the K corrections calculator web-service.<ref>[http://kcor.sai.msu.ru K-corrections calculator]</ref>
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| ==References==
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| <references/>
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| ==External links==
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| * [http://www.ucolick.org/~cnaw/kcorr/kplot.html K Correction plots]
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| * [http://xxx.lanl.gov/abs/astro-ph/0210394 The K correction]
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| {{DEFAULTSORT:K Correction}}
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| [[Category:Astrophysics]]
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| [[Category:Doppler effects]]
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| {{astronomy-stub}}
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Latest revision as of 08:03, 12 November 2014
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