idlastro / Astronomical Utilities: AIRTOVAC

[Source code]

NAME
AIRTOVAC
PURPOSE
Convert air wavelengths to vacuum wavelengths 
EXPLANATION
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
AIRTOVAC, WAVE_AIR, [ WAVE_VAC]
INPUT/OUTPUT
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
WAVE_VAC - Vacuum wavelength in Angstroms, same number of elements as
         WAVE_AIR, double precision
EXAMPLE
If the air wavelength is  W = 6056.125 (a Krypton line), then 
AIRTOVAC, W yields an vacuum wavelength of W = 6057.8019
METHOD
Formula from Ciddor 1996, Applied Optics 62, 958
NOTES
Take care within 1 A of 2000 A.   Wavelengths below 2000 A *in air* are
not altered.       
REVISION HISTORY
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