air_to_vac¶
- specutils.utils.wcs_utils.air_to_vac(wavelength, scheme='inversion', method='Morton2000', co2=None, precision=1e-12, maxiter=30)[source]¶
Converts air to vacuum wavelengths using different methods.
- Parameters:
- wavelength
Quantity
object (number or sequence) Air wavelengths with an astropy.unit.
- schemestr, optional
How to convert from vacuum to air wavelengths. Options are:
‘inversion’ (default) - result is simply the inversion (1 / n) of the refraction index of air. Griesen et al. (2006) report that the error in naively inverting is less than 10^-9.
‘Piskunov’ - uses an analytical solution derived by Nikolai Piskunov and used by the Vienna Atomic Line Database (VALD).
‘iteration’ - uses an iterative scheme to invert the index of refraction.
- methodstr, optional
Only used if scheme is ‘inversion’ or ‘iteration’. One of the methods in
refraction_index
, default is ‘Morton2000’- co2number, optional
Atmospheric CO2 concentration in ppm. Only used if scheme=’inversion’ and method=’Ciddor1996’. If not given, a default concentration of 450 ppm is used.
- precisionfloat
Maximum fractional value in refraction conversion beyond at which iteration will be stopped. Only used if scheme=’iteration’.
- maxiterinteger
Maximum number of iterations to run. Only used if scheme=’iteration’.
- wavelength
- Returns:
- vac_wavelength
Quantity
object (number or sequence) Vacuum wavelengths with the same unit as wavelength.
- vac_wavelength