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| Deletions are marked like this. | Additions are marked like this. |
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| For the vacuum to air conversion we used the formula from Donald Morton () for the refraction index which is also the IAU standard: | For the vacuum to air conversion we used the formula from Donald Morton (2000, ApJ. Suppl., 130, 403) for the refraction index which is also the IAU standard: |
| Line 17: | Line 17: |
| n = 1 + 0.0000834254 + 0.02406147 / (130 - s^2^) + 0.00015998 / (38.9 - s^2^), where s = 10^4^ / lambda,,vac,, and lambda,,vac,, is in Angströms | n = 1 + 0.0000834254 + 0.02406147 / (130 - s^2^) + 0.00015998 / (38.9 - s^2^), where s = 10^4^ / λ,,vac,, and λ,,vac,, is in Ångströms The conversion is than: λ,,air,, = λ,,vac,, / n. This formula comes from Birch and Downs (1994, Metrologia, 31, 315) and applies to dry air at 1 atm pressure and 15ºC with 0.045% CO,,2,, by volume. The corrections to Edlén (1953, J. Opt. Soc. Am., 43, 339) are less than 0.0001 Å at 2000 Å and less than 0.001 Å at 30000 Å. |
VALD3 stores vacuum wavelengths of all the transitions. This allows uniform handling of extraction across the whole spectral range. On the other hand the selection tools in VALD3 include options for returning the air wavelengths. Furthermore, some of the original lines list include wavelengths measured in the air. This calls for conversion tools. Such tools must be uniformly accurate and reversible across the whole spectral range.
For the vacuum to air conversion we used the formula from Donald Morton (2000, ApJ. Suppl., 130, 403) for the refraction index which is also the IAU standard:
n = 1 + 0.0000834254 + 0.02406147 / (130 - s2) + 0.00015998 / (38.9 - s2), where s = 104 / λvac and λvac is in Ångströms
The conversion is than: λair = λvac / n.
This formula comes from Birch and Downs (1994, Metrologia, 31, 315) and applies to dry air at 1 atm pressure and 15ºC with 0.045% CO2 by volume. The corrections to Edlén (1953, J. Opt. Soc. Am., 43, 339) are less than 0.0001 Å at 2000 Å and less than 0.001 Å at 30000 Å.