Name

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VACTOAIR

Purpose

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Convert vacuum wavelengths to air wavelengths

Explanation

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Corrects for the index of refraction of air under standard conditions.
Wavelength values below 2000 A will not be altered. Accurate to
about 10 m/s.

Calling Sequence

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VACTOAIR, WAVE_VAC, [WAVE_AIR]

Input/output

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WAVE_VAC - Vacuum Wavelength in Angstroms, scalar or vector
If the second parameter is not supplied, then this will be
              updated on output to contain double precision air wavelengths.

Optional Output

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        WAVE_AIR - Air wavelength in Angstroms, same number of elements as
                WAVE_VAC, double precision

Example

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If the vacuum wavelength is W = 2000, then
IDL> VACTOAIR, W
yields an air wavelength of W = 1999.353 Angstroms

Method

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Formula from Ciddor 1996 Applied Optics , 35, 1566

Revision History

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Written, D. Lindler 1982
Documentation W. Landsman Feb. 1989
      Use Ciddor (1996) formula for better accuracy in the infrared
          Added optional output vector, W Landsman Mar 2011