Vacuum Wavelengths
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Conversion between vacuum and air wavelengths
Because the SDSS observes many quasars at rest frame ultraviolet
wavelengths, the data are stored in vacuum wavelengths. However,
most optical astronomers know the wavelengths of transitions as measured
at S.T.P., which is how the CRC lists them for any transitions redward of
2000 Angstroms.
The IAU standard for conversion from air to vacuum wavelengths
is given in Morton (1991, ApJS, 77, 119). For vacuum wavelengths (VAC) in
Angstroms, convert to air wavelength (AIR) via:
AIR = VAC / (1.0 + 2.735182E-4 + 131.4182 / VAC^2 + 2.76249E8 / VAC^4)
These are the air and vacuum wavelength of some common transitions:
Line
|
Air
|
Vacuum
|
H-beta
|
4861.363
|
4862.721
|
[O III]
|
4958.911
|
4960.295
|
[O III]
|
5006.843
|
5008.239
|
[N II]
|
6548.05
|
6549.86
|
H-alpha
|
6562.801
|
6564.614
|
[N II]
|
6583.45
|
6585.27
|
[S II]
|
6716.44
|
6718.29
|
[S II]
|
6730.82
|
6732.68
|
There is an IRAF tool to convert air to vacuum wavelengths in Pat Hall's IRAF tools for SDSS spectra.
Last modified: Thu Apr 3 16:28:03 CST 2003
|