Name

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      AIRTOVAC

Purpose

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      Convert air wavelengths to vacuum wavelengths

Explanation

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      Wavelengths are corrected for the index of refraction of air under
      standard conditions. Wavelength values below 2000 A will not be
      altered. Uses relation of Ciddor (1996).

Calling Sequence

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      AIRTOVAC, WAVE_AIR, [ WAVE_VAC]

Input/output

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      WAVE_AIR - Wavelength in Angstroms, scalar or vector
              If this is the only parameter supplied, it will be updated on
              output to contain double precision vacuum wavelength(s).

Optional Output

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

Example

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      If the air wavelength is W = 6056.125 (a Krypton line), then
      AIRTOVAC, W yields an vacuum wavelength of W = 6057.8019

Method

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Formula from Ciddor 1996, Applied Optics 62, 958

Notes

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      Take care within 1 A of 2000 A. Wavelengths below 2000 A *in air* are
      not altered.

Revision History

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      Written W. Landsman November 1991
      Use Ciddor (1996) formula for better accuracy in the infrared
          Added optional output vector, W Landsman Mar 2011
      Iterate for better precision W.L./D. Schlegel Mar 2011